Fish Seed Production for National Development in Kenya: Current Status, Challenges, Quality Control and Innovative Strategies for Commercialization

Abstract

From only two fish hatcheries at independence to the current number of more than 50, Kenya has achieved a milestone in aquaculture production and development. Investments in sustainable exploitation of Blue economy for national economic growth provide further impetus for seed production. Cage culture of tilapia in Lake Victoria requires use of all-male seed, whose achievement is still a challenge, and demands more innovative strategies. Therefore, production of adequate and high quality fish seed in Kenya is vital as it provides livelihood and incomes to farmers, reduces exploitation pressure on natural fisheries, and facilitates expansion and commercialization of aquaculture for food and nutrition security. This chapter reviews current seed production strategies and systems in Kenya, including quality control measures and some of the strategies that could help improve production, availability and quality of fish seed for the main cultured species in Kenya for commercialization of aquaculture. Improved practices at hatcheries, strict control of importation of live fish in to the country as well as better husbandry practices at fry nurseries and farms could help improve the quality and quantity of fish seed for expanded aquaculture in Kenya.

1. Introduction

It is well recognized that aquaculture, the fastest growing animal food producing sector globally, is poised to make an important contribution to fish food supply in the world. This is because fish supply from major fisheries in the world are either over-exploited, dwindling or collapsed. Global farmed tilapia production averaged 6 million metric tons in 2019 [1], while total farmed catfishes was 5,518,878 metric tons in 2017 [2]. Tilapias and catfishes are often the main freshwater farmed species in many African countries. A total of 1,356,370 metric tons of farmed tilapias was produced on the continent in 2019 [1]. Of this total, Egypt produced almost 80%, with 1,081,202 metric tons [1]. In 2017, 1,324,530 metric tons of Clariid catfishes were produced on the continent [2]. In 2022, total aquaculture production in Kenya was 27,939 metric tons [3], comprising of fish production from ponds, cages (in Lake Victoria) and mariculture [3]. This total was valued at US$ 57,718 [3]. Farmed sea weed production along the Kenyan coast produced 106 metric tons, valued at US$ 17,601. In the same year, the country produced a total of 136,247 metric tons of fish from inland fisheries valued at US$ 254,054,054, while 37,494 metric tons were landed from marine fishery, valued at US$ 69,716 [3]. Depending on the inland fishery, the main landed fish species is tilapia, while clariid catfishes, the African lungfish, Protopterus aethiopicus, Labeo and Haplochromine cichlids are landed. The Nile perch, Lates niloticus and silver cyprinid, Rastrineobola argentae dominate Lake Victoria. Tilapias constitute 70% of freshwater farmed finfishes, the rest being mainly Clarias gariepinus [3]. The vibrant cage culture industry in Lake Victoria is entirely for tilapias (Oreochromis niloticus), with average landings of 14,000 metric tons in 2022 [3].

However, for aquaculture to continue making a significant contribution to fish supply, especially in the tropical areas, critical improvements are required in the areas of impediment. One area that is critically important to successful expansion of aquaculture is fish seed production. Fish seed production ensures availability of stocking material for new aquaculture farmers and businesses, supports augmentation of depleted or declining fisheries to boost the fortunes of fishermen, and for the hatchery operators, it is an important source of income and livelihood. Despite this importance, fish seed production remains a challenge to farmers, both in terms of quantity and quality. This challenge seems to affect many parts of the world [4], including Asia [5], but is especially serious in sub-Saharan Africa [6]. In many of these regions, there is an overall trend of intensification of aquaculture due to high demand for fish, therefore availability of high-quality fish seed is essential, to support this growth in fish production.

In Kenya, for instance, growth in aquaculture has been boosted over the years by several factors. Between 2009 and 2012, the Government implemented the National Fish Farming Enterprise Productivity Program (NFFEPP) under the Economic stimulus program, in which farmers were supported to venture in to fish farming in a total of 140 constituencies country wide. This created an interest in fish farming nationally, and spurred farmed tilapia production to 14,738 metric tons in 2015 from about 3000 metric tons in 2008 [7]. Following the promulgation of the new constitution of Kenya 2010, implementation of the new order was initiated as from 2014, in which new devolved units of governance, county governments, took over the management of aquaculture in the country. This was previously a function of the national government.

A number of county governments have since invested substantial resources in revamping aquaculture in their jurisdictions, to boost fish production for their people. In this regard, such county governments have recruited more staff for extension services, bought vehicles and motor bikes to support staff mobility for extension service, and a few have invested in establishing new hatcheries, as well as fish feed formulation and manufacturing. For instance, Machakos, Uasin Gishu and Vihiga counties have invested in new hatcheries (Table 1), an effort that is paying off substantially by increasing availability of quality fish seed for farmers at a fair price. For sustainability, such hatcheries need to adopt innovative strategies for producing high quality seed while safeguarding the environment.

County	Name of Hatchery	Year Started	Fish species	Annual Production
Nairobi	Kiamumbi Fish Farm	2016	Tilapia	480,000
			Catfish	360,000
	Paradise Fish Farm	2005	Tilapia	6, 000,000
			Catfish	6, 000,000
	Quarry Lane Fish Farm	2012	Tilapia	180,000
			Catfish	180,000
Kakamega	Labed Cash Marine Enterprises	2012	Tilapia	840,000
			Catfish	120,000
	Jafi Fish Farm	2010	Tilapia	480,000
Vihiga	Tigoi Fish Farm	2011	Tilapia	600,000
	Mwitoko Fish farm	2020	Tilapia	500,000
Bungoma	Chwele Fish Farm	1991	Tilapia	480,000
Busia	Wakhungu Fish Farm	2020	Tilapia	1,500,000
Kisumu	Apondo Fish Hatchery	2015	Tilapia	500,000
	Vicnaqua Hatchery	2018	Tilapia	300,000
	KEMFRI Sangoro station	1982	Tilapia	8,400,000
			Catfish	6,000,000
Homa Bay	Victory Farms	2016	Tilapia	72,000,000
	Jewlett Enterprises	2007	Tilapia	9, 600, 000
	George Muga	2013	Tilapia	500, 000
			Catfish	200, 000
	Kiba Fish Hatcheries	2017	Tilapia	1, 200,000
	Lake View Fisheries	2014	Tilapia	3, 600,000
	Homa Bay Multipurpose Farm	2010	Tilapia	500,000
	Phillip Agwanda Fish Farm	2018	Tilapia	200,000
Kisii	County Fish Multiplication and Training Centre	1987	Tilapia	500,000
	KEMFRI Kegati station	1985	Tilapia	1, 200,000
Machakos	Kamuthanga Fish farm	2011	Tilapia	3,000,000
			Catfish	960,000
	ATC	2014	Tilapia	100,000
Meru	Vision Hatchery	2010	Tilapia	1, 200,000
			Catfish	720,000
	Nchiru Children’s Home Hatchery	2012	Catfish	240,000
	Muthuri Hatchery	2014	Catfish	225,000
	Kithima Hatchery	1991	Tilapia	60,000
Kiambu	Pegi Fish Farm	2013	Tilapia	1, 200,000
			Catfish	1, 200,000
	Samaki Tu Farm	2010	Tilapia	1, 200,000
			Catfish	600,000
	Bariki Fish Farm	2014	Tilapia	360,000
			Catfish	600,000
Murang’a	Makindi Fish Farm	2016	Tilapia	1, 200,000
Nyeri	Kiganjo Trout Hatchery	1948	Trout	60,000
Kirinyaga	Mwea AquaFish Farm	2009	Tilapia	1, 500,000
			Catfish	1,000,000
	Green Algae Highlands Farm	1998	Tilapia	1, 200,000
			Catfish	1,000,000
	Emmick Farm	2011	Tilapia	1, 500,000
			Catfish	1, 500,000
	National Aquaculture Research and Training Center Sagana	1948	Tilapia	1, 560,000
			Catfish	180, 000
Nyandarua	Geta Trout Hatchery	2009	Trout	120,000
	Malewa Gorge Trout Hatchery (North Kinangop)	2013	Trout	1, 200,000
	Avil Fish Farm	2011	Tilapia	360,000
			Catfish	360,000
	Kenya Agriculture and Livestock Research Organization (Kalro)-Ol Jororok	2011	Tilapia	360,000
	Kentalo Farm	2012	Tilapia	360,000
Nakuru	Lake Naivasha Hatchery	2011	Tilapia	1, 200,000
			Catfish	250,000
	Egerton University Hatchery	2015	Tilapia	100,000
			Catfish	50,000
Uasin Gishu	University of Eldoret	2017	Tilapia	3, 600,000
			Catfish	600,000
LBDA Farms	Kibos Fish Farm (Kisumu)	1984	Tilapia	700,000
			Catfish	100,000
	Yala Fish Farm (Siaya)	1989	Tilapia	600,000
			Catfish	240,000

Table 1.

Fish hatcheries in different counties of Kenya, including number of fingerlings produced annually and year of establishment of the hatcheries. Figures for catfish seed production represent capacity, as this seeds for this species are produced on order.

1.1 Historical development of fish hatcheries in Kenya

The first hatcheries in Kenya were established during the colonial era in 1948, with Sagana Fish Culture Farm for warm water fish species and Kiganjo Trout hatchery for the cold water fish species. These were designed to provide seeds and mature fish, to boost aquaculture which had been started in the 1920s. In the 1970s, mariculture was initiated, and with it came the establishment of the Ngomeni Mariculture Prawn Farm. These hatcheries did not perform well in post-independence Kenya, mostly due to limited expertise and budgetary support by Government. In 1993, however, Sagana fish Culture farm was renovated, and the hatchery revamped, through the technical support of the Royal government of Belgium. In 1994, the Aquaculture research project Collaborative Research Support Programme/Pond Dynamics Aquaculture (CRSP/PDA) funded by the United States Agency for International Development (USAID) was relocated from Rwanda because of ethnic strife, to Sagana Fish farm. This boosted the farm’s activities and capacity to produce fish seeds and mature fish through scientific research. Since this project involved collaboration between The Kenya Fisheries Department, Moi University and Auburn University, USA, it enabled the training of graduate students of Aquaculture from Moi University, both locally and at Auburn. Similarly, the project supported the training of Fisheries Officers and other cadres of the Kenya Department of Fisheries on a variety of topics, as a way of building capacity for the Department. By the year 2000, Moi University, which had started the Department of Fisheries in 1990 constructed a fish farm and a small fabricated hatchery, which became operational in 2002, under the support of the World Bank/GEF funded Lake Victoria Environmental Management Programme (LVEMP). This facility also boosted production and supply of fish seed to farmers in the region [8, 9].

Between the late 1980s and early 1990s, when the Department of Fisheries was housed by the Ministry of Regional Development, several fish farms were set up in the country, supported by the Rural Development Fund. These included Murang’a Fish farm, Kisii Multipurpose Fish Multiplication center, and the Kithima Fish Hatchery in Meru (Table 1). At around the same time, the Norwegian Agency for International Development (NORAD) helped establish Chwele Fish Farm in Bungoma. With the establishment of the Lake Basin Development Authority (LBDA) in the 1980s, the Authority established several fish farms and hatcheries around the Lake Victoria basin, and these have been actively involved in fish seed multiplication and distribution over the years. However, many of these farms and hatcheries rely on financial support from the Exchequer, which is often unreliable and inadequate. Therefore, their activities often fluctuate, based on financial flows, and so, at times they have very low activity. Also, most of these farms have inadequate staff strength with limited technical know-how in modern fish seed production technology.

With the onset of the National Fish Farming Enterprise Productivity Program under the Economic Stimulus Program of 2009, several hatcheries were established, because of the impetus created by the Government support nation-wide. Many serious farmers were motivated and took up the opportunity, many have since established their own hatcheries (Table 1), in different parts of the country, and doing fairly well. However, and especially for the western Kenya region, many hatcheries have been established over the last seven or so years, to take advantage of the cage culture of tilapia in Lake Victoria, an industry that requires a large and steady supply of all-male tilapia fish seed. Those hatcheries established slightly earlier than this time were also motivated by the demand for catfish fry for use as bait fish to catch Nile perch, Lates niloticus in Lake Victoria using long lines. This is heavily driven by the impact of the water hyacinth in the lake, which renders the use of traditional filament nets ineffective.

As envisaged in the National Oceans and Fisheries policy of 2008, government has established a hatchery for marine fisheries under the National Mariculture Centre/Hatchery in Shimoni, Kwale county, through the National Infrastructure support Programme. The hatchery is set to start operations in the multiplication and distribution of affordable, adequate and high quality seed for marine fish species. This will support investments in aquaculture by providing relevant infrastructure for production, demonstration and research activities for development of ocean resources, and sustainable exploitation of the Blue economy [10].

2. Spawning of fish

In the natural environment, the breeding behavior of tilapias begins with sexually mature males putting on bright colors, such as blueish, red, and yellow on different parts of the body. Such males constitute the ready to spawn males, and as such, they construct nests (leks) [11, 12], which is basically a “home”, where breeding will take place. The construction of the lek is called lekking, and once complete, the brightly colored male stays in the lek, guarding it against any intruding males (territoriality), while simultaneously attracting ready to spawn female tilapias. A ready to spawn female (abdomen swollen with eggs) is attracted to the lek, enters and after acquaintance with the male, the pair performs a courtship dance. The breeding pair is in an elevated energy level, and the female spawns her eggs, while the male sheds millions of milt (sperms) over the eggs simultaneously, completely covering the batch of eggs in milt to increase the chance of most of the eggs getting fertilized. It is important to note that optimal environmental temperature is necessary for this process, and so spawning by tilapias occurs on a sunny afternoon. On a cloudy afternoon therefore, the ready to spawn female will have eggs in the ovary being resorbed in to the body, and so will not spawn until the next ovulation cycle. The female picks all the fertilized eggs in to her buccal cavity [12] (Figure 1), leaves the lek, and moves to a quiet area in the water, to begin incubation of the eggs (Figure 1). Another ready to spawn female enters the lek, and the spawning process is repeated. Meanwhile, a female that is incubating the eggs frequently churns the eggs, i.e. opens the mouth a bit, to allow entry of fresh water (and oxygen), which are necessary for incubation, and also allows the eggs to change position, so that each egg is uniformly exposed to water, air and warmth, for successful development of the zygote and therefore hatching.

Figure 1.

A mouth brooding female tilapia with eggs in her buccal cavity. Eggs are harvested periodical from such mouth brooding females and taken to the hatchery for incubation at optimal temperature and aeration conditions to fasten the egg hatching process. A breeding pair is normal introduced in to a net hapa, where spawning occurs naturally under optimal sunshine conditions.

The African catfish, Clarias gariepinus, the main farmed species, breeds in the natural environment at the onset of rains, usually in inundated conditions. Therefore, catfishes move to the flood plains, either from the lake, or from upstream the river. Since the floodplains are usually flooded in the rainy seasons, there is an abundant supply of food materials that come with the waters. The food materials are exploited by catfishes with active feeding, and subsequently get energized in the inundated conditions. The sexually mature males and females pair up, perform a courtship dance around the inundated marginal areas, and the females spawn the eggs. Males release millions of milt simultaneously over the eggs, and fertilization occurs. Fertilized eggs attach on inundated marginal vegetation, where they undergo incubation. The incubation period is dependent on the ambient temperature, and hatchlings are released in to the environment, where they learn how to survive on their own.

2.1 Artificial production of tilapias

Whether in the natural waters (lakes, rivers), or in ponds at fish farms, tilapias construct leks in the shallow areas and pond dykes of the lake and ponds respectively. Hatchery operators therefore try to simulate the process of natural spawning, by pairing up ready to spawn male and female fish in net hapas in ponds or tanks, where after spawning, the female similarly picks eggs in to her buccal cavity (Figure 1). Eggs are therefore harvested from the mouth of the female the following morning after pairing up the fish in net hapas the previous afternoon. The harvested eggs are taken for incubation in McDonald’s jars (Figure 2) in the hatchery (often a greenhouse that creates higher temperatures naturally, or a hatchery where incubation units are fitted with thermostats to regulate temperature to the desired optimum). Due to lower temperatures in the natural environment, eggs hatch in about 14 days. However, incubating the eggs at optimal temperatures (25–28°C) in the hatchery substantially reduces the incubation period to about 5 days, enabling the farmer to do more cycles of egg incubation in unit time. Artificial incubation of eggs at the hatchery also releases the females earlier, so that they can begin the recovery process in readiness for the next spawning.

Figure 2.

McDonald jars used to incubate tilapia eggs at the hatchery for hatching. Water supply to the jars is from the bottom, so that the pressure of the water causes the eggs to be in constant motion upwards. This ensures the eggs do not stick on the bottom of the jar (fertilized eggs become sticky), but remain in constant motion, so that they are exposed to uniform aeration and heat, which are necessary for the development of the zygote.

2.2 Artificial production of African catfish, Clarias gariepinus

In culture facilities, C. gariepinus does not breed freely, and has therefore to be induced or artificially propagated. Artificial propagation of catfishes is a well perfected procedure, and is routinely practiced at most hatcheries in Africa [13]. The process involves injection of a sexually mature female with a hormone (from the pituitary extract of fish or a synthetic hormone), which induces maturation of eggs in the ovary [14]. The process involves the following steps:

1. A ready to spawn pair that is good looking is selected for the exercise. Ready to spawn female will have a swollen abdomen (because of eggs), while a male of suitable size will generally be able to breed. Both brooders should be good looking: uniform in body shape, not deformed, free from parasites, or injuries.

2. The brood pair is taken to the hatchery, and the female injected with a pituitary extract (containing a gonadotropic hormone) from another catfish or any other fish species like carps, to induce maturation of eggs in the ovary. This is done in the evenings (around 16.00–17.00 hours), and left overnight in separate holding tanks. The female is injected in the abdomen, with about 1 ml of pituitary extract at a dosage of 3 mg/kg of female [14]. The pituitary is taken from the head of a catfish that has been sacrificed, and stored in a saline solution.

   In the absence of the pituitary hormone from fish, a synthetic hormone is used: an example is deoxy-corticosterone acetate (DOCA, 50 mg/kg of female), or human chorionic gonadotropin (HCG, 2500 IU/kg of female) which are purchased from authorized commercial dealers.

3. In the morning (about 8 hours), the ready to spawn female is stripped of the eggs, by gently pressing on the abdomen (Figure 3), so that the eggs ooze out through the genital papilla, into a clean bowl.

4. A male catfish is sacrificed immediately, and the testes (Figure 4) slit open, so that the milt pours over the eggs in the bowl. Note: The stucture and location of the testes cannot allow the milt to be removed by pressing the abdomen of the male fish, so each time artificial propagation is done, a male has to be sacrificed, to provide the milt.

5. A clean feather is used to mix the eggs and the sperms (milt) gently, to ensure complete mixing, so that as many eggs as possible are fertilized.

6. Fertilized eggs are then transferred on to an egg tray (Figure 5) (fish eggs become adhesive immediately they are fertilized). They therefore attach on to the mesh of the egg tray or any other suitable substrate or kakaban material.

7. The egg tray is transferred in to the aquarium or the incubation tank (Figure 5), and the incubation process started. The incubation tank should be supplied with clean fresh water continuously for the 24 or so hours over which eggs will hatch, as well as ample supply of oxygen (aeration of the water), and optimal temperature (25–28°C). This temperature will be obtained by use of a thermostat fixed in to the tank.

8. Complete hatching of the eggs will be accomplished in 12–24 h, depending on the temperature of the water. It is important to note that catfish hatchlings drop down into the tank bottom from the egg shells, and eggs that do not hatch turn white, either because they were not fertilized, or they are infested with bacteria and fungi.

Figure 3.

A gravid female Catfish being stripped of her eggs in to a bowl, in readiness for fertilization by milt from a sacrificed male.

Figure 4.

A pair of gonads (testes) from a male catfish. These are cut open and the resultant milt mixed with eggs in the bowl, for fertilization of eggs.

Figure 5.

Glass tank (Aquarium) for incubating Clarias eggs during artificial propagation at the hatchery. Fertilized eggs are spread on the egg tray (see the board in the tank stretching from top right to bottom left corner of the tank, with brownish stuff), and immersed in the water in the tank. Any newly hatched fry drops to the bottom of the tank, and can be sucked out of the tank. Water supply to the tank is from up the tank (see the yellow-black stripped horse pipe), and the thermostat for temperature regulation is inserted in to the tank. Aeration of the eggs in water is via the white tubes in the tank, connected to the blower.

Therefore, during this process of artificial propagation, it is critical to ensure complete mixing of eggs and milt for complete fertilization. Also, incubation process must be done under very clean or hygienic conditions, to avoid contamination of eggs with fungi and bacteria that will prevent hatching, even if the eggs are fertilized.

In the absence of egg trays, diverse materials can be used as kakabans, substrates on which fertilized eggs attach for incubation. Such simple substrates include sisal threads from sacks or gunny bags, and in the Lake Victoria basin where water hyacinth is abundant, roots of the hyacinth are also used as kakabans [14, 15]. Eggs attach on to the roots, and the plants introduced in to incubation tanks where leaves float on the water, while the roots are inside the water to allow ample incubation of eggs.

2.3 Nursery of tilapia and catfish seed

After full absorption of yolk sac, fry should be transferred to nursery units (Figure 6) for good management. At this stage, fry require optimal temperature and feeding, because this is also the stage of fast development and growth. For species like C. gariepinus that have high mortality at the fry stage, optimal rearing temperature and feeding regimes of fry are critical. Ideally, it is desirable to develop a fish nursery under a green house, for ease of achieving the requisite high temperatures cost effectively. Also, in the green house, it is easier to maintain a higher standard of hygiene, to reduce on fry mortality due to parasites and pathogens, as well as control of predators, and unnecessary human traffic around fish holding facilities that cause stress to fry. However, because of the high cost of green house facilities and related installations, only resource endowed hatchery operators are able to acquire these facilities and develop the fish nursery unit in a green house. Farmers who must establish fry nursery units outside the green house need to devise ways to address the need for optimal rearing temperature.

Figure 6.

Tanks for rearing fry at the nursery unit. Each tank is supplied with aerator and water supply, in a green house, where high temperatures prevail naturally, to support fast growth.

2.4 Feeding of tilapia and catfish fry in the nursery unit

In the nursery, fry are fed on live feeds because the digestive system is not yet well formed, and so fry survival increases by application of live feeds that are easy to digest and absorb. Main live feeds are zooplankton and phytoplankton that are easily harvested from an enriched pond on the farm or at the hatchery. This means that the farmer or hatchery operator has to invest in fertilization of a pond with organic manure, to make it green, or boost primary productivity in the pond. Alternatively, the brine shrimp, Artemia may be acquired and used as a live feed by periodical hatching of Artemia cysts.

The feeding frequency for the fry should be high, depending on the species, to ensure satiation always that helps to reduce cannibalism and hampered growth of the fry. For instance, catfish may be fed 6 times daily, while tilapia fry should be fed 3 or 4 times daily and gold fish 4 times per day.

After a period of about 1 month, when the digestive system of the fry is fully developed, the fry should be introduced to dry feeds, i.e. formulated or commercial diets. Such diets should be of high quality, i.e. be of the required crude protein content. Diets of about 45% crude protein would be ideal for fry. An appropriate feeding frequency should be maintained on this diet, depending on the species. The feeding ration should be adequate, of about 3% body weight daily, to ensure satiation of the fry. Higher feeding ration should be avoided, as it leads to wastage of feed, causes a deterioration of water quality leading to fish mortality, and unnecessarily increases production costs while reducing profitability of the enterprise. Also, fry should be fed at certain times of the day, without delayed or earlier application of the feed, to get the fish accustomed to the schedule, which increases the response of the fish to feeds, and maximizes feed utilization. The particle size of the feed should be the right for the fry, so that it is ingested with ease.

2.5 Challenges in fish seed production

Quality of fish seed, the ability of the seed to serve its purpose, by ensuring fast growth rates, high survival and high fecundity of fish being grown by the farmer, is dependent on genetic characteristics of brood stock, and husbandry practices under which the brood stock are kept. Fish seed are generally obtained from two sources: hatcheries owned by individual farmers or institutions and the natural habits (what is commonly called the wild). In each of these two sources, fish can and do lose their genetic quality (the vigor or strength to grow, survive and reproduce at a fast rate or in sufficient quantity), and therefore, when such fish are collected for use as brood stock or as seed in aquaculture enterprises, the fish exhibit stunted growth. The growth rate, survival and fecundity of fish is generally low, leading to small sizes of individual fish at harvest after a reasonable grow-out period, occasioning loses to the farmer.

The problem of stunted growth in cultured fish results from genetic drift, the change in the frequency of alleles or genes of the fish due to random processes [16, 17]. This way an allele, for instance responsible for growth rate or survival or fecundity can be lost from the population of the fish, in which case the allele becomes rarer in members of the population, and individual fishes lose the ability to grow, survive or reproduce in desirable quantities in aquaculture. On the other hand, an allele for any of these traits can increase in frequency in the population, and become fixed in members of the population, so that many individual fishes of the population harbor the allele. However, whether an allele is being fixed in the population (fixation) or is lost from the population (loss), the overall effect of genetic drift in fish is always negative [18], in so far as it reduces genetic variability at a locus for the desirable trait of the cultured fish. Similarly, since genetic drift occurs mostly in small populations, or a fish population with fewer members, it is invariably accompanied by inbreeding [18], another process that exacerbates loss of quality in fish. In small populations, the actual number of fish individuals that breed to form the next generation is small. Therefore, the possibility of repeated use of same breeders to create the next generation is higher. This increases the chances of using related parental stock to create the next generation, a practice that indirectly favors fixation of some alleles in the population, as well as loss of other valuable alleles from the population. If fish suffering these effects is reared in a poor environment or under poor husbandry, stunting is exacerbated, and performance in culture declines substantially.

In natural fish populations, loss of genetic quality occurs through several processes. For instance, natural aquatic habits can undergo fragmentation through damming, which disconnects the fish upstream from those downstream. This structures the fish population, interferes with the biology of the fish species, which eventually reduces the size of the population and reduces its genetic variation. Introduction of exotic fish species to aquatic habitats seriously affects native fish populations, either through predation [19], hybridization [20, 21], competition for feeding, breeding and nursery grounds [22] or through introduction of parasites and or disease pathogens for the native fish species. The overall effect of these factors is the reduction of population sizes of native fish species, which reduces the genetic variation of the species and consequently, loss of genetic quality or vigor to grow, survive and reproduce. Therefore, farmers collecting native fish species from such habitats for use as brood stock, or directly as fish seed for stocking in ponds invariably end up with stunted fish and poor harvests [20]. For instance, the native tilapias of Lake Victoria, Oreochromis esculentus and O. variabilis declined under the effects of predation from the exotic Nile perch [23, 24], as well as hybridization [25, 26] and competition [26] by the exotic Nile tilapias, O. niloticus and Oreochromis leucostictus. If the populations of the native tilapias ever recover and begin to appear in fishermen’s landings, they will be suffering from low genetic variation due to population bottleneck induced by predation, hybridization and competition.

While hybridization may lead to genetic drift in a fish population by creating genotypes whose fitness in the wild is low, prejudicing recruitment of the fishery, it also creates fish individuals of impure genetic make-up. Therefore, what farmers collect from natural sources for use as brood stock at the hatchery is not pure stock, whose performance at the hatchery and in ponds declines [20]. Hybridization has been reported in sympatric O. esculentus and O. niloticus of Lake Kanyaboli [27], as well as other satellite lakes of East Africa [28, 29]. Hybridization is also reported between O. niloticus and O. leucostictus of Lake Baringo [30], and, together with changes in genetic diversity in O. niloticus [31], as well as water quality variability, is thought to have affected the growth of O. niloticus in the lake. Other examples include hybridization of O. niloticus and O. urolepis in the Great Ruaha-Rufiji rivers system [32], as well as between O. niloticus and O. mossambicus in South Africa [33], and O. niloticus and the native O. macrochir and O. andersonii of Kafue River [21]. Hybridization between farmed O. niloticus and O. mossambicus in Asia, with both species established from imported stocks suffering from founder effects, caused widespread stunting and poor growth of O. niloticus [20], occasioning the need for developing improved strains to boost farmed production of the species [34].

For small water bodies such as satellite lakes, genetic drift in natural fish populations could result from overfishing, which creates a population bottleneck due to fishing mortality. Examples include tilapias of Lake Kanyaboli, and other satellite lakes where the size of native tilapas O. esculentus has since dropped from a maximum size of 50 cm to about 17–20 cm length per piece of fish [35, 36], and also the numbers have gone down in the lake. This invariably reduces genetic variation of the fish, which makes the fish unsuitable for use as brood stock for aquaculture enterprises. Coupled with this is periodical desiccation of small lakes and reservoirs due to recurrent drought in arid and semi- arid areas, leading to massive mortality of fish species. When the lakes fill up again during the rainy season, the fish populations increase through natural recruitment, but suffer population bottlenecks which reduce genetic diversity of the fish. Examples of such lakes include Kamnarok in the Elgeyo Marakwet county and Kenyatta in Lamu county, Kenya, which are also isolated, and so suffer high levels of genetic drift. Furthermore, fish stocks of these lakes have been boosted by re-stocking or fishery augmentation by conservationists, using germplasm from the Lake Victoria region. This augmentation with fish from different drainage basins merely exacerbates the loss of quality by respective fish species, because of mixture of different genotypes. Fish populations in such lakes are unsuitable for use as brood stock for aquaculture enterprises.

Farmed fish also undergo genetic drift and inbreeding [16, 37], leading to loss of quality, and therefore poor performance in ponds expressed as poor growth, survival and low fecundity of the fish. This is mainly because aquaculture enterprises naturally start with a small number of brooders. Therefore, even before the start of aquaculture activities, the fish is already suffering from founder effects, where population bottleneck induces genetic drift. This is compounded by selection of good-looking brooders from the pool of brood stock available on the farm, since not all the brooders available on the farm can be used for propagation to generate seed. Because of selection of brooders and the smaller numbers of brood stock on the farm, aquaculture practices therefore commonly involve fish of imbalanced sex ratios. Also, the actual number of breeders that give rise to the next generation is low, and the fish used to create the next generation have different reproductive success, i.e. the fish give different number of eggs or fry during spawning [37]. Differences in reproductive success among brooders arise from differences in fecundity, fertility, viability or longevity [37], so that different brooders will contribute different numbers of fry to the next generation.

Furthermore, viability of the fry is quite critical. In Clarias gariepinus for instance, poor survival of fry is a key challenge in seed supply for aquaculture. Therefore, genetic drift is likely to seriously affect the stocks available for the enterprise. Different environmental conditions on the spawning grounds or presence of predators on nursery grounds, as well as contamination of egg incubation facilities with parasites and pathogens may affect reproductive success of individual fishes [37]. Brooders with lower viability will have a higher number of their fry die early, before they reach sexual maturity and reproduce, and so their overall contribution to the pool of the next generation decreases. This means that the fish in this generation that will grow to sexual maturity and reproduce will be from only a few parents, a factor that increases inbreeding in subsequent generations, and poor performance of the fish.

Sex ratio of the breeding pairs is another crucial factor that influences inbreeding and genetic drift, and therefore loss of genetic variation in farmed fish [37]. While in the propagation of catfishes at the hatchery milt from a single male is used to fertilize eggs from a single female, sex ratio of the breeding pairs in tilapias is often skewed towards more females per male. Some studies recommend a sex ratio of 1 male to 2 females [38], while [39] recommends 1 male to 3 females. Ideally, the correct stocking ratio for tilapia breeding pairs in net hapas should be 1:1, to reduce chances of inbreeding and therefore increase the genetic vigor of the resultant fry to grow, survive and reproduce. Furthermore, using imbalanced sex ratios of breeding pairs of tilapias in net hapas increases fight for mates, which injure the brooders in the net hapas and affect spawning.

3. Measures for producing high quality fish seed

3.1 Genetic approaches of producing high quality fish seed

Fish hatcheries keen on producing high quality fish seed need to focus on both genetic and managerial practices in their operations. To start with, however, there is need to ensure genetic principles are applied in the brood stock acquired and maintained at the hatchery, as well as the breeding techniques and designs used to generate the next cohort of fingerlings. This should be followed by appropriate fish husbandry practices, to ensure that the farm reaps from the investment made from the application of genetic principles. This is because some of the measures will require substantial investment in facilities and expertise. In this regard, therefore, the most important factor in fish seed quality is to ensure the starting stock has a very high genetic variation [9, 40]). This means minimizing on factors that reduce genetic diversity in populations of fish, or factors that increase genetic drift and inbreeding in fish.

In the development of the Genetically Improved Farmed Tilapia (GIFT) strain, for instance, genetic variation of the base population of GIFT was boosted by a complete diallele cross of the 8 founding strains (4 natural and 4 farmed) [34]. Due to this, the GIFT strain had a very high growth rate, helping tilapia farmers in the Philippines increase their farmed tilapia production by 186% between 1990 and 2007 [41]. Similarly, the use of GIFT strain helped farmers increase availability of quality tilapia seed in the Philippines [41], as well as China and Thailand. Since its development in 1997 and subsequent distribution to farmers in Asia and lately to most parts of the world for culture, the GIFT strain still performs very well in culture, as long as it is reared under good management practices.

Therefore, the first step in ensuring high genetic variation of the brood stock at the hatchery is to source the fish from natural habitats that are large. While large aquatic habitats do not automatically imply the extant fish population is large, there is high possibility that a large water mass will host a large population of a given fish species. For instance, sourcing fish brood stock from Lake Kanyaboli may be less desirable than Lake Victoria, since Lake Kanyaboli, a satellite and therefore a fragment of the main Lake Victoria, is much smaller, and its fish populations are likely to have been affected further by higher fishing pressure. Therefore, it will comparatively have less genetic variation and less vigor to grow and survive in culture facilities. Related to the size of the fish population is the fact that in a large population, the fish will also have random mating, with less severe competition for mates, since the pool of mates will be larger. Therefore, as many fish individuals as possible will be able to contribute their genes to create the next generation. Brood stock obtained from such an ecosystem will have a high genetic variation. However, even if the aquatic ecosystem is large, habitats whose fish are known to have undergone interspecific hybridization, or have received additional fish from different drainage basins should be avoided, since the stock will be impure, or homogenized, and so negatively impact growth and survival of the seed.

Furthermore, after identifying a habitat that meets these criteria on genetic variation, a large number of brooders should be collected [18], in order to avoid founder effects in the fish that the hatchery will use to start the aquaculture enterprise. Many hatcheries naturally collect a small number of brood stock from the wild during expeditions to collect fish brooders from the wild, in order to minimize costs [42]. This is because of limited facilities at the hatchery to hold a large number of brooders, limited finances to support collection of more fish during the expedition, and limited capacity to transport a large number of live fish at once, especially if the natural habitat is far away from the hatchery. Also feeding cost of a large number of brooders would be high. However, it is always desirable that hatcheries collect and maintain a high number of brood stock at the hatchery for their aquaculture enterprises [42], in order to benefit from the higher genetic diversity and vigor of the fish to grow and survive. Most of the tilapia brood stock imported in to Asia in the 1980s were composed of few founders, with some as few as 30 or much less [43, 44], and because of founder effects, most were highly inbred and introgressed [45], and therefore had stunted growth in ponds [34].

For farmers collecting fish seed from other hatcheries, care is still needed, so that the fish is purchased only from reputable hatcheries, i.e. those with a good name from their good practices on fish breeding, rearing and fish brood stock management. Good hatcheries are those that practice good husbandry for their brood stock, and understand the genetic principles of fish hatchery operations. Such hatcheries should also have been certified by professionals, and so use best management practices in their operations. Many hatcheries in Kenya may not be managing their brood stock well, and so the quality of their fingerlings is probably poor. The poor quality of seed is often manifested in poor survival. For tilapia, poor survival of seed is especially noted in cages in Lake Victoria. Poor quality seed therefore occasions losses to farmers and hampers expansion of commercial aquaculture in the country.

3.2 Fish breeding designs that reduce genetic drift and inbreeding

An important technique of increasing genetic variation by reducing inbreeding and genetic drift among brooders is to increase the spawning stock. Here, several suitable mating pairs are chosen, allowed to breed and an equal number of hatchlings from each mating pair or family is chosen and pooled, to form the next breeding stock at the hatchery. If the breeding pairs are taken from families, it is often desirable to use half-sib rather than full-sib families. Full-sib family is one in which the offspring have the same parents (mother and father, dam and sire), while Half-sib family is one in which the offspring have the same one parent but not both [18]. Fish seed from half-sib family have a higher genetic variation, and increasing the spawning stock similarly increases genetic variation of the breeders, which give high quality fingerlings.

Genetic quality of fish seed is also attained at the hatchery by operators practicing pedigree mating rather than random mating schemes for breeders. In pedigree mating scheme, each breeding pair of known productivity or performance in culture contributes an equal number of offspring to the next generation. A farmer is able to know the productivity of the fish on his farm or hatchery by accurate record keeping, and tagging of individual fishes. Only high performing fish (high growth rates, survival and fecundity) are allowed to breed, and the population of the spawning stock is increased by allowing the chosen breeders to contribute an equal number of fry to the next generation.

Hatchery operators should also avoid overlapping generations in their fish culture enterprises, or even in the rearing of fry or brood stock. Overlapping generations involve mixing of different generations of fish, which, by extension, will be of different ages and sizes. During fish harvests at grow-out, farmers should harvest all the fish in ponds or tanks for sale or consumption. Partial harvest of the fish should be avoided, so that at the time of restocking ponds with a new crop of seeds, the younger generation should not mix with older generation of fish. This reduces the chances of breeding of related fish, which will increase inbreeding and genetic drift in the stock. This is especially critical for quality of tilapias, which mature precociously [46] and breed with ease in culture facilities [47, 48], so that at the end of the grow out period, the farmer has many but small sized fish of low market value.

The sex ratio of the breeding pairs should as much as possible be kept equal, at 1:1, and the frequency of re-use of any given brooder minimized as much as possible. This ensures that the offspring are generated from diverse fish individuals, and so minimizes inbreeding and genetic drift in the seeds.

3.3 Fish husbandry practices for maintaining quality in fish seed

These are husbandry practices at the hatchery that ensure the number of brood stock kept does not reduce and create a bottleneck that would induce genetic drift and inbreeding in the fish. Also, they ensure the fish are in a good health and nutritional state as to be able to grow, survive and reproduce adequately in culture facilities, to give the desired quality and quantity of the end product. Healthy- and good-looking fish of uniform shape are often appealing to sight, and can attract steady market and value.

One of the most important husbandry practices for maintaining the quality of brooders so that they produce high quality fingerlings is feeding. Fish should be fed on a high-quality diet, often measured as crude protein content (CP%). Brood stock should be fed on diets of crude protein content of 20–30%, which should preferably be formulated on the farm. This assures the quality of the feed. Similarly, the fish should be fed daily on recommended feeding ration (3% body weight). This ration is administered in several portions, the feeding frequency. The feeding frequency will vary according to fish species, but the brooders should be fed at least twice daily. At each of these intervals, the feed should be applied when it is sunny (morning and afternoon), and at each feeding exercise, the feed should be applied until the fish is satiated.

In order to reduce mortality from parasites and diseases, the hatchery environment should always be kept clean, with a good flow of waste water so that it does not accumulate on the floor, but drain out smoothly. All facilities at the hatchery should be cleaned, disinfected and kept at the right places. In particular, the egg incubation and larval rearing facilities should be thoroughly cleaned, before egg incubation and new batch of fry are introduced. This ensures that eggs do not get contaminated with bacteria and fungi, which limit fertilization of eggs and interfere with the hatching process [49]. In the fry nursery unit, these pathogens and parasites attack the fry leading to mortalities and deformities [50]. Mortality of brooders reduces the total number of brooders, which lowers the effective number of breeders, and consequently reduces genetic variation. This should be accompanied by cleaning and slashing around the ponds, hatchery and larval rearing units, including draining pools of water that may be stagnant around these facilities that may harbor predators, parasites and other pathogens.

The control of predators at the farm or brood stock ponds is very critical in maintaining a high number of brooders. Common predators include birds such as the king fisher and cormorants, snakes, and otters, as well as theft by humans. All these reduce the number of fish, and so should be controlled effectively.

Similarly, water quality monitoring should be undertaken regularly. This ensures that sudden declines in water quality do not occur in the ponds or the hatchery, which would otherwise suddenly kill the fish. Such mortalities will reduce the number of brood stock at the hatchery and lead to genetic drift, inbreeding and lose of genetic variation.

In order to preserve the quality and quantity of brood stock for production of quality seed, it is important that all inlets for water supply to the brood stock ponds and the hatchery are screened with fine mesh. This prevents entry of feral fish to the ponds and hatchery facilities. Feral fish are fish of unknown origin, identity and therefore quality, which enter aquaculture facilities with the water supply, especially if the source is a river or stream. Entry of feral fish into brood stock ponds and hatchery facilities creates competition for space, feeds and mates with the brooders, affecting the growth rates of the brooders as well as breeding to produce hybrids or fry of inferior quality, or creating an impure stock. Similarly, feral fish could introduce parasites and disease-causing pathogens to the brood stock and eggs in the hatchery and fry in the nursery units, leading to stress and mortality of the fish. Additionally, some of the feral fish could be cannibalistic, and therefore predate on the brood stock, eggs or fry, which will reduce the numbers, leading to genetic drift and inbreeding.

Hatchery operators should also routinely seine the brood stock ponds to remove any newly hatched fry, especially with tilapias that are highly prolific in culture. Such fry should then be kept in a separate pond. This ensures that offspring do not continue staying with their parents, as this will bring challenges of breeding. When the offspring reach sexual maturity in just 2–3 months of age, they will start breeding with their parents, and any other older generation in the holding pond or tank, leading to inbreeding. Also, the number of fish in the pond increases exponentially due to prolific breeding, overshooting the carrying capacity, which easily leads to stunted growth of fish. Therefore, separating fry from brood stock ponds is a good management strategy because it helps avoid inbreeding and keep the fish at suitable carrying capacity, for faster growth with reduced stress levels. It improves management of the different stages of fish, especially on feeding and management of feeding costs, since different stages of fish require feeds of different quality (crude protein content). It is also an easier way of managing seeds, for a farm that also deals in sale of fingerlings, since it will take a very short time to get the number of seeds required when a customer comes to buy seeds.

4. Perspectives on seed production for commercial aquaculture in Kenya

Countries that are global leaders in aquaculture production, such as China, Indonesia, Thailand and Egypt have invested heavily in fish seed production, for sustainable supply to farmers. For instance, Bangladesh has over 400 hatcheries that produce over 5 billion monosex male tilapia fry annually [51]. In Vietnam, up to 93 hatcheries produce 813 million fry of the striped catfish, Pangasianodon hypophthalmus annually [52], for uptake by farmers.

Kenya’s aquaculture industry is dominated by two species: O. niloticus and C. gariepinus, although many farmers are focused on producing O. niloticus. This is because the species commands a higher market. Similarly, landings of the species from inland fisheries has declined due to overfishing, habitat degradation and impacts of invasive species. As a result, cage culture of tilapias is now practiced in Lake Victoria, and offers new frontiers for intensification of farmed tilapia production. Additionally, devolution of aquaculture extension services to county governments in the new constitution of Kenya 2010 provided new impetus for investment in aquaculture ventures. As a result, new hatcheries have been constructed. County governments now support augmentation of inland fisheries by purchasing tilapia seed from existing hatcheries for stock augmentation. Although this practice is largely undocumented, initial observations show that this exercise does not substantially increase fish stock abundance and landings in the lake, even with closed seasons that should encourage growth and survival of the introduced seed.

These require special focus on the quality of the seed produced by hatcheries. In order to minimize the impact of tilapia cage culture on natural tilapias in the open waters of the lake for instance, seed stocked in cages need to be all-male tilapia. However, current methods used by hatcheries to produce all-male tilapia seed (manual sorting, heat treatment, hormonal, hybridization, and YY super male tilapia technology) are inefficient, and even technically complex. Sex reversal by hormonal steroids [53], for instance, achieves sex inversion rates of only 70–90%. Therefore, the batch of such seed that is assumed to be all-male will have some females, and so breeding will occur in cages when the stocked seed reach sexual maturity. Fry so spawned in cages escape through the mesh to the open waters, and interact with the natural tilapias in the open waters of the lake in ways that are often negative, including hybridization. Similarly, the use of hormonal substances at the hatchery is environmentally unfriendly, and unhealthy for the workers.

In view of these challenges, there is need for developing more innovative methods of producing all-male tilapia seed for commercial and intensive farmed tilapia production in Kenya. One possible method is the use of molecular markers and genomic selection [54, 55] in combination with hormonal sex reversal as well as sex inversion by heat treatment [56] to identify and map the sex determining loci in strains of O. niloticus. This will enable development of highly inbred lines whose crossing will yield 100% all-male progeny for commercial use. Developing such a strain requires large financial resources, and as well as a strong collaborative team of scientists with a clear focus on the work, similar to the efforts that produced the GIFT strain of tilapia.

Despite a proliferation of hatcheries along the beaches of Lake Victoria to supply all-male tilapia fingerlings to cage culture farmers, there is still a challenge of adequacy, as well as quality of the seed so produced. High mortality of seed in cages is currently experienced by most cage culture farmers. These deaths may be attributed to environmental impacts from the high concentration of cages especially in shallower areas [57], as well as pollution of the water from nutrient loading by feeds, parasiticides and antibiotics used in managing diseases of caged fish [58]. However, mortality of fish in cages could be also be attributed to poor quality of seed stocked in the cages, especially with regard to survival. Poor quality of seed from hatcheries could result from use of impure brood stock for spawning, inadvertent use of different tilapia species as brood stock at the hatchery, while thinking it is O. niloticus, often due to poor taxonomic skills among hatchery operators and extension personnel at counties around the lake.

Use of different tilapia species is possible and may be already happening at many of the hatcheries, through collection from the natural waters of Lake Victoria. The native tilapiine species of the lake (O. esculentus and O. variabilis) are recovering due to changed dynamics in the lake, and these could be caught by fishermen or hatchery operators for use as brood stock at the hatcheries. Similarly, it is suspected that different tilapia species are also be imported in to the country by well-endowed hatchery owners, especially due to porous borders and weak enforcement of existing laws against importation of live fish in to the country. Apart from the possibility of the imported tilapia not being O. niloticus, it could also be the improved variety, suitable for culture only under certain husbandry conditions. This mix of tilapia species potentially reduces the vigor of the seed for growth, survival and fecundity, especially in a natural ecosystem like Lake Victoria, even if the seed is caged. Similarly, if a different species is used to breed for the seed, then if the batch stocked in cages is not 100% all-male, then spawning in cages will release a different species in to the open waters of the lake, potentially creating negative impacts on the O. niloticus of the lake. This will threaten tilapia biodiversity, persistence in the environment and performance in culture, should such impacted tilapias in the natural habitats be collected for use as brood stock at hatcheries. All these threats are so far not studied, and therefore are less documented and little understood. In order to improve the quality of seed supplied by hatcheries, and conserve existing tilapia biodiversity in the Lake Victoria basin while improving sustainable utilization, these challenges need to be tested in well-structured scientific studies.

5. Conclusion

In conclusion, hatchery operators need to improve practices used in seed propagation, and inparticular incorporate genetic principles in seed production. Maintaining optimal conditions at fry nursery units is also critical to improve survival of seed. In general, government needs to strictly enforce laws against importation of live fish in to the country, and hatchery opearators and farmers need to be encouraged to source their seed from reputable hatcheries, and as much as possible, avoid harvesting of natural fish populations for use as seed or broodstock at hatcheries and fish farms. In order to improve the quality and quantity of fish seed available for aquaculture, farmers also need to improve husbandry practices at their farmes, especially feeding, as well as the control of diseases and predators.