Recent Developments in Fish Nutrition and Culture Technologies in Kenya

Abstract

Kenya has immense potential for aquaculture growth and development due to recent decline of capture fisheries production from Lake Victoria, which accounts for over 80% of the national production. However, lack of subsidies and slow adoption of aquaculture nutrition and culture technologies have slowed aquaculture growth and development nationally. There is need to explore innovative aquaculture production technologies and alternative protein sources that can replace fish meal to yield optimal returns in the foreseeable future. The study reviews the use of re-circulatory aquaculture system in tilapia hatchery to conserve limited water supplies and guarantee 95% success in mono-sex production of all male tilapia fingerlings. In Kenya, Freshwater shrimps, Caridina niloticus is the most common fish meal in aquafeed formulations. Although readily affordable, plant-based protein sources contain low crude protein levels and lack essential micronutrients. More sustainable animal protein sources such as black solder fly (BSF) Hermetia illucens pre-pupae and Redworms Eisenia foetida have shown the potential to yield optimal returns in a commercial scale, and can solve environmental problems associated with aquaculture. This study further recommends the use of recirculatory aquaculture in water scarce areas and those faced with intermittent interruptions due to prolonged droughts and pollution of surface waters.

1. Introduction

The dwindling nature of capture fisheries production in Lake Victoria and other inland lakes, accounting for ~ over 80% of the total national catch has been attributed to many anthropogenic interventions [1, 2]. This has contributed to lower national catch. For instance, the country’s annual fish production declined from ~150,000 tons in 2013 to 102,000 tons in 2020 [3]. Whereas this decline contributes to an annual per capita fish consumption of 4.5 kg, which is comparatively lower than the global average per capita of 20 kg [4], aquaculture has still the great potential of bridging the deficit in affordable animal protein supply among developing countries [5]. While some fish mongers have taken an entrepreneurial advantage to import frozen tilapia from China, there have been inconclusive discussions among various stakeholders as to whether the current fish importation can sustainably bridge the existing demand-supply gap [3]. Currently, the Kenyan aquaculture sector is facing many critical challenges. These could be attributed to lack of bilateral and multilateral subsidies as well as weak adoption of the existing aquaculture technologies. For instance, during the 2009–2012, Kenya reported significant aquaculture growth due to marginal subsidies injected into the subsector by the inter-sectorial economic stimulus program (ESP) [3, 6]. Nevertheless, aquaculture subsector has continued to grow steadily with a high potential to improve food and nutrition in Kenya. The period 2016–2023 was characterized by the radical shift from extensive to semi-intensive pond management and culture systems, which constitute of 90% of fish farming systems in Kenya. Despite these milestones, there has been low adoption of sustainable aquaculture technologies. This can be attributed to such factors as low levels of education, high cost of inputs, limited awareness on the available technologies, limited appropriate financing mechanisms and limited extension services.

The most pertinent challenges include lack of accessibility to affordable and high-quality fingerlings and fish feed [7]. These challenges have been compounded by inadequate sharing of information, extension services, training and capacity building on best aquaculture production and management practices [8]. With the projected growth in fish supply gap to about 350,000 tons annually, it is highly expected that aquaculture growth will create hundreds of job and business opportunities for many actors within the expanded value chain and contribute to improved food and nutrition security in Kenya [7, 9]. Furthermore, Kenya has many unexploited small water bodies (SWBs), which can be utilized to promote aquaculture growth and development. Due to the foregoing developments, there is need to review the recent developments in fish feeding and culture technologies to assess development needs for future sustainability [8, 10].

2. Development of aquaculture technologies

Various studies have posited that Kenya has an immense potential for aquaculture growth and development. However, the country is yet to report significant global aquaculture contribution because of slow adoption of the recent aquaculture technologies [11]. According to Munguti et al. [7], there is need to explore various technological interventions that have been employed to boost aquaculture growth and development in many parts of the world. Recent aquaculture technologies include biofloc technology, genetic engineering, selection and breeding and hybridization [11, 12]. These aquaculture technologies seek to increase protein utilization for improved growth performance and reduce the cost of production and shortening the time taken by cultured fish to attain consumer demand driven sizes. For instance, biofloc technology aims to maximize on-farm utilization of available protein sources and reduce discharge of effluents to surrounding water sources [13]. The main fish species cultured include Nile tilapia and the African catfish (Figure 1).

Figure 1.

Two major cultured aquaculture species in Kenya: A—Nile tilapia, Oreochromis niloticus and B—The African catfish, Clarias gariepinus.

2.1 Re-circulatory aquaculture system

A re-circulatory aquaculture system comprises of a water filtration system to prevent algal growth and a water recycling system (Figure 2). The system uniformly distributes fish feed and other ecological parameters, allowing accessibility by all fry hence guarantees greater success of sex reversal. In this water re-use system, optimum water quality is maintained through bio-filtration, removal of ammonia, Carbon (iv) oxide and suspended solids and re-oxygenation of water [14]. The water is re-used continuously as it is being recycled with approximately 10–15% replacement biweekly, to cater for system loses due to evaporation and cleaning of biofilters. Although the system is highly suitable for water deficient regions, it can be also used in areas which experience high levels of pollution from urban and municipal wastes as well as untreated sewage discharge into freshwater sources [15]. This makes it virtually impossible to attain 95% all male fingerlings during sex reversal conducted in nursery ponds. Availability of planktons or live feed in the nursery ponds causes a shift in preference of fry feeding from consuming hormone impregnated feeds to planktons [16]. Nevertheless, the design should take into consideration the local needs to ensure long-term sustainability in efficiency and operational costs [16].

Figure 2.

Proposed sketch design plan of a recirculatory aquaculture system at the County Fish Multiplication and training Center (CFM &TC) in Kisii County, Kenya.

2.2 Design of the re-circulatory aquaculture system

2.2.1 Egg incubation system

This system includes a table stand with several MacDonald jars, made from transparent plastic material, hatching trays, and a UV sterilizer. Water is drawn from the header tank into the jars through a vertical tube causing upwelling to keep the eggs suspended. Each jar overflows in a plastic hatching tray, where swim-up larvae are trapped until stocking in the larvae system. For instance, the jars have a height of 46 cm and a diameter of 16 cm with 8-liter capacity for can be used to incubate up to 20,000 eggs [17].

2.2.2 Larval rearing system

This system consists of 20 nestable tanks fitted with a center drain that pulls all the wastes into a common drain pipe to the collecting basin at the drum filter. The drum filter that is backwashed periodically is used as the mechanical filter. The system bio-filter consists of a sump that contains bio media containing nitrifying bacteria (Nitrobacter) that breaks down toxic un-ionized ammonia (NH₃), which is highly toxic to fish and known to depress the appetite of tilapia at concentrations more higher than 0.2 mg, by converting it into less toxic nitrites [18]. The concentration of un-ionized ammonia in aquaculture systems can be controlled by maintaining a pH of 7.0–max. 8.75. It also contains a booster pump with an inlet and outlet that moves the water from the sump into the header tank. It is also fitted with a regenerative blower replenishes dissolved oxygen in the header tank and in the sump [19].

Water is pumped from spawning and rearing systems to cylindrical header tanks for bio-filtration and waste removal to maintain water quality by the main pump, placed after the bio-filter. In addition to bio-filters, drum filter tanks remove suspended solids and those that can settle. The drum rotates so the screen can be backwashed using high pressure water sprays to prevent clogging while the wastewater and solids are removed from the system enter the main drain. Another inlet pipe from the reservoir tank connects to the header tank to replenish the systems water [20].

To produce large quantities of fish seed, large amounts of dissolved oxygen is required for developing eggs and fry. Aeration is provided to the biofilter sump and header tank using an air pump connected to an air grid and submerged air stones respectively. The flow of air bubbles increases contact with air and thus oxygen exchange between the air and water [21]. This type of aeration also strips carbon dioxide from the water. Two regenerative air blowers are used in the system. There is one spare air blower which should be stored in a clean, cool area, together with the spare parts. From the manifold, air stones in the header tanks are connected through air hoses. Air stones used are disc stones with a diameter of 5 cm and 20 cm [22].

3. Development of fish nutrition

3.1 Alternative protein sources

Cultured fish have diverse nutritional requirements based on their trophic levels and feeding habits [23]. For instance, the highly omnivorous African catfish require high in protein content in their diets compared to exclusively herbivorous species such as the Nile Tilapia. This makes their feed more expensive than those of Nile tilapia. High cost of fish feed that accounts for up to 70% of the total production costs usually results from the inclusion of high-quality animal-based protein ingredients which are essential in promoting faster growth in cultured fish [24]. Their high-quality protein usually is responsible for highly palatability; digestibility and assimilation of fish feed into fish tissues to build up high quality and balanced amino acid (AA) profile. Besides being a relatively expensive ingredient, fishmeal, the common source of protein in fish feeds is geographically unavailable to most farmers and has many other competitive uses such as formulation of poultry and livestock feeds [25, 26]. The main sources of fish meal in Kenya are the freshwater shrimps, Caridina niloticus, and the discards of silver cyprinid, Rastrineobola argentea. However, the seasonal availability of C. niloticus has served to increase the overall cost of production because of competition for the use of fishmeal from other production enterprises such livestock sector, where it is mainly used as feed ingredient for poultry and other livestock [27]. Increased dependency on fish meal often leads to unsustainable exploitation of freshwater fisheries in Lake Victoria, while threatening the stability of food chains of the self-sustaining native and exotic stocks as well as diversity of Lake Victoria’s highly diverse multi-species ecosystems [1, 27]. Slow growth and development of aquaculture has been linked to availability of few reputable large-scale feed mills which continues to hamper aquaculture growth, contributing to increased cost of production, in addition to decreased availability and reliability of the quality fish feed supply [24]. Some unscrupulous sellers have resorted to incorporating of low-level crude protein in fish feeds which they sell directly to unsuspecting farmers resulting to slow growth of the cultured species [24, 28].

Most semi-intensive pond-culture systems employ pond fertilization together with supplemental feeding to increase nutrient supply for fish growth [7]. It is recommended to fertilize the ponds of Nile tilapia prior to stocking of fingerlings to promote production of live feeds (Which include larger zooplankton such as daphnia and phytoplankton). However, supplemental feeding is still required as the production tends to be insufficient to meet the nutritional requirements of early stages of growth [29].

3.2 Black soldier fly (Hermetia illucens)

The dry matter of black soldier fly (Hermetia illucens) pre-pupae contains 42% crude protein and 35% fat and several micro-nutrients such as magnesium, Copper, Iron, Molybdenum, and Zinc [30]. These dietary components have been found to promote optimal growth farm animals such as chicks, swine, rainbow trout and catfish [31, 32]. Studies have shown that black soldier fly pre-pupae has been used to replace more than 25% of the fish meal in formulating the diet of rainbow trout and channel catfish, producing a feed with over 60% crude protein level. Nevertheless, growth trials using these feeds showed no significant reduction in weight gain and feed conversion efficiency [31, 32]. In addition, culture trials of Nile tilapia and channel catfish have shown no significant differences between formulated BSF pre-puppae diets and commercial diets [33]. However, to enhance feed digestibility and protein utilization, it is necessary to remove chitin from BSF larvae if using raw insect as a feedstuff for fish feeds formulation. Furthermore, studies on food safety and bacteriological considerations have shown that BFS larval activity significantly reduced Escherichia coli and Salmonella enterica in chicken manure, which could be due to anti-microbial factors they contain [34]. However, there will be need to conduct detailed bacteriological assessments and other food safety issues to ascertain the safe use of this novel feedstuff in aquaculture. The feedstuff requires less energy for processing than fish meal, and provides better management of problematic manure to reduce negative impacts on the environment because it reduces pathogens that naturally occur in manure [34, 35].

3.3 Fishmeal and fish oil

The demand for fishmeal and fish oil has doubled over the last three decades due to increased production of farmed fish [36]. However, the annual global fishmeal and fish oil production has correspondingly stagnated implying that the aquaculture industry cannot continue relying on finite stocks of fishmeal in the foreseeable future [37]. The increased use of fishmeal has sparked global interest into finding most suitable alternative feedstuffs to replace it in aquafeed production.

Although plant-based ingredients are readily affordable, they can only replace up to 3% of fishmeal in the aquafeed for farmed tilapia [38]. It is prudent to find other protein and fish oil alternatives, which can meet the nutritional requirements to yield optimal growth and production [39]. This can cause a knock-on effect to decrease over-reliance on fish meal protein and reverse the dwindling trends in freshwater fisheries [40]. However, plant-based protein has low crude protein levels. They lack certain essential amino acids and micro-nutrients, and contain high amounts of crude fiber which lowers their palatability and digestibility [41], and anti-nutritional factors, which lower their feed conversion efficiencies [42]. In addition, some feedstuffs such as soya beans require additional processing before, they are incorporated into fish feeds, to improve their nutritional quality [43, 44]. Terrestrial plant oils have shown limited ability to fully replace fish oils in aquafeeds. With exception of some oilseeds, they low levels of Omega-3 (ω3) PUFAs and completely lack long chain Omega-3 (ω3) PUFAs, but are rich in Omega-6 (ω6) and Omega-9 (ω9) fatty acids. Feeding fish exclusively on plant protein sources will result in inevitably lower levels of docosahexaenoic acid (DHA) and eicosatetraenoic acid (EPA) in their tissues which will reduce the health and nutritional benefits derived from fish, which will be detrimental to human health after fish consumption [37]. It will also predispose fish to a high incidence of cardiovascular disorders [45]. Consequently, the plant protein sources to be considered as a most suitable substitute for FO should contain high levels of ω3 poly-unsaturated fatty acids (PUFAs) (LNA) and a high ω3/ω6 ratio. This makes plant proteins have a lower nutritional advantage over fishmeal.

3.4 Chemical analysis of fish feed components

While several studies have evaluated and compared the proximate composition of locally available proteins sources such as red-worms Eisenia foetida, Black solder fly and bioflocs, finding an alternative protein source that can adequately substitute fishmeal in formulated fish feeds is still a high global interest [46]. Some previous studies have reported that E. foetida is a viable alternative to fish meal because of its high composition of protein, essential amino acids, fats and minerals which are comparable to the composition of fishmeal [47, 48]. For instance, Akidiva et al. [49], compared the proximate composition of dried red worms, E. foetida and fishmeal (Figure 3).

Figure 3.

Comparative chemical analysis of different components of fish feeds used in aquaculture trials. Data obtained from Akidiva et al. [49] and Zablon et al. [13].

Nevertheless, although its proximate composition indicates it is a viable alternative for replacement of fishmeal; little information has been documented on its use in feed formulation.

3.5 Access to quality feeds

Access to quality feeds is one of the challenges faced by most aquaculture farmers who lack adequate resources to purchase the high-quality feeds [35]. To reduce the cost of feeds, previous studies have recommended a paradigm shift from overdependence of fishmeal and fish oil towards the use of cheap and readily available alternative protein sources. Most of farmers however, lack adequate knowledge to formulate homemade feeds from locally available feedstuffs such as corn meal, wheat bran, and rice bran and cassava meal. UNGA FEEDS and Sigma Feeds are some of the major private commercial fish feed millers with extensive network of distributors in many parts of the country [24, 46]. These companies produce micro-extruded tilapia and catfish pellets that offer better pellet stability and reduced nutrient leaching into the culture water. The pellet sizes range from 0.1 mm to 5.0 mm, targeting the fish stage with specific gape size to economize consumption, while the specific protein level included in the feed target specific requirements to support optimum growth and development and reduce production cost [50].

It is prudent to note that both fry and fingerling stages require crude protein levels of >40% and >30% respectively, for muscle tissue formation which may have an important impact on later growth and maturation [51]. Therefore, the fish feeds should be formulated in such a way that they provide balanced nutrition, their protein content is sufficient to support growth and muscle development, so that the fish can attain the consumer demand driven sizes during the production cycle, and the required fatty acids and available amino acids in line with the requirements for the export market [51, 52].

4. Conclusions and recommendation

In many successful trials, BSF Hermetia illucens and the red worms have been extensively studied as potential feedstuffs for replacement of fish meal in aquaculture production and feed production for other livestock. In almost all cases, culture trials have shown greater success. Commercialization of BSF prepupae and red worms’ production and adoption of biofloc technology can solve many agricultural and environmental problems associated with conventional aquaculture. There is need to assess whether the production and utilization of Hermetia illucens prepupae and redworms in commercial scale to replace fish meal would have significant positive economic and environmental impact. This study further recommends the use of recirculatory aquaculture in water scarce areas and those faced with intermittent interruptions due to prolonged droughts and pollution of surface waters.

Acknowledgments

The manuscript benefitted from technical contributions by G. Gicheru and Wilfred O. Zablon of the County Directorate of Fisheries, Kisii County Government. This however does not imply endorsement by the County Government.

Author contributions

Job Omweno conceived and conceptualized the study, wrote and supervised the writing of the manuscript with Argwings Omondi. Argwings Omondi edited, provide additional literature content, and proofread the manuscript. Authors have read and approved the final manuscript.

Funding information

This review received no funding from any institution or funding agency.

Competing interests

The authors declare that they have no known competing academic, professional and financial interests or personal relationships that could appear to influence the outcome of this paper after publication.

Availability of additional information

All sources analyzed during this review are included in the references. For supplementary material and information, all correspondences and requests should be addressed to Job Omweno.