Wastewater management and disposal in aquaculture is becoming increasingly important due to stringent water regulations regarding waste discharges into natural water systems. Recirculation ...aquaculture is one of the technologies designed to reduce waste discharge through the nitrification process. However, nitrification results in nitrate accumulation which is normally reduced by dilution through water exchange. Water exchange is only possible with sufficient water. Although nitrification is a conventional process, it has limitations because the autotrophic bacteria require long start-up and multiplication periods. The nitrifiers require high levels of oxygen with relatively higher aeration costs. Moreover, the bacteria are sensitive to rapid changes in pH, temperature, and flow rate. Denitrification can be a solution to the limitations of nitrification since denitrifiers are most abundant in the natural environment and have higher growth rates than nitrifiers. In addition, the process reduces energy costs since there is no need for aeration, water consumption is also reduced drastically since water exchange is minimized. Organic loading can be reduced when fish waste is utilized as a carbon source. An alternative process to manage aquaculture wastes is through anaerobic ammonium oxidation (anammox), where ammonia and nitrite are converted into nitrogen gas. Anammox can efficiently reduce ammonia and nitrites from culture water, but it has not received wide application in aquaculture. Aquaculture wastewater contains nutrients which are essential for plant growth. The plants maintain good water quality by absorbing the dissolved nutrients. Denitrification, anammox, and nutrient uptake by plants are feasible strategies to reduce wastes from aquaculture effluents.
Use of fish meal in aquaculture is gradually becoming unsustainable due to competition, cost and ecological challenges hence the need to expand the alternative protein sources. The earthworm, Eisenia ...fetida is among the non‐conventional protein sources, which have been tested with relatively promising results, thanks to its high protein levels, proper amino acid profile, high reproduction rate, low mortalities, fast growth and ease of production. The feasibility of using E. fetida for commercial fish feed production depends on the fundamental knowledge of its growth and reproductive biology, as well as the production methods. On the other hand, the nutritional suitability of E. fetida is determined by its amino acid composition and meal processing methods. Therefore, this study reviews the biological, biochemical composition as well as production and processing methods, as critical aspects for sustainable production and utilization of the earthworm in commercial fish feed production. Further, the study provides some recommendations and options to provide nutritionally complete and economically viable fish feed for efficient and sustainable aquaculture production systems.
In aquaponic systems, plants absorb dissolved nutrients from aquaculture wastewater for their growth. The removal of nutrients allows reuse of water and minimises wastewater discharge to the ...surrounding environment. This study evaluated the relative nutrient removal efficiencies of three plant species and the performance of Nile tilapia (
Oreochromis niloticus
) in a small-scale aquaponic system. Three aquaponic systems were assigned as treatments PU (pumpkin), SW (sweet wormwood) and AM (amaranth). Physical-chemical water quality parameters were measured in the fish tanks as well as hydroponic inlets and outlets. Fish sampling was done every 2 weeks for 60 days. Results showed significantly (
p
< 0.05) lower nutrient concentrations in the hydroponic outlets than the inlets. There was no significant difference in nutrient removal efficiency of the plants (
p
> 0.05) for all the tested nutrients except for phosphorus. Phosphorus removal was substantially high in PU (75.5 ± 16.8%) than SW (47.36 ± 14.5%) and AM (40.72 ± 13.2%). In addition, the SW system had better (
p
< 0.05) relative growth rate (0.06 ± 0.00) than that of PU (0.05 ± 0.00) and AM (0.05 ± 0.00). Nitrogen and phosphorus content in plant tissues was significantly high (
p
< 0.05) in SW and PU plants respectively. Water quality parameters had a significant influence on the growth of fish (
p
< 0.05). The growth of fish was not different (
p
> 0.05) in the three treatments. The findings indicate that the tested plants can reduce nutrients in aquaculture discharge water.
Rapid population and economic growth, increased health benefits of aquatic food, and changes in lifestyles and preferences as a result of rapid urbanization and globalization are all contributing to ...the rapid growth of aquaculture production in Kenya. Despite significant investment efforts from the national and devolved governments as well as donors and international organizations, smallholder aquaculture production is yet to result in a significant increase in incomes and improved food and nutrition security. We conducted a scoping review to investigate the roles of multilateral development organizations, international financial institutions, and public and private investments in Kenya’s aquaculture subsector. We draw on lessons learned from previous projects implemented at the national, county, and farm levels to make recommendations for sustainable aquaculture intensification in Kenya. To unlock Kenya’s aquaculture potential and improve its food and nutrition status, deliberate efforts must be made to create a conducive environment for public and private investment in the industry. First, there is a need to coordinate and clearly articulate the roles and responsibilities among devolved and national governments, donors, and financial institutions through public-private partnerships to ensure optimal allocation of financial, human, and infrastructure resources. Second, more collaborative research should be devoted to the design and construction of climate smart culture systems, developing new species to guarantee supply of high-quality products; developing and scaling low-cost and highly nutritious fish feeds based on novel ingredients; and enhancing resilient livelihoods through innovative aquaculture practices and market linkages to create employment opportunities for youth and women. Finally, the national and devolved governments should create an enabling policy environment through tax incentives and regulatory reforms to combat climate change, protect nature and biodiversity, sustain livelihoods, and mainstream food and nutrition initiatives into the design and implementation of future aquaculture projects.
The maintenance of optimal water quality for fish production is one of the major challenges in aquaculture. Aquaponic systems can improve the quality of water for fish by removing the undesirable ...wastes and in turn produce a second marketable crop. However, there is no information on the growth and nutrient removal capability of Artemisia annua in aquaponic systems. This study evaluated the effect of plant density on water quality, the growth of A. annua and Oreochromis niloticus in a small scale aquaponic system in Kenya. The aquaponic system consisted of three treatments representing different plant densities (D1: 48 plants/m2, D2: 24 plants/m2 and D3:0 plants/m2). The high plant density system contributed significantly (p < 0.05) to the removal of all nutrients. The removal efficiency of ammonia was significantly higher in D1 (64.1 ± 14.7%) than in D2 (44.5 ± 6.8%) and D3 (38.0 ± 12.1%). Nitrates and nitrites were inconsistent, whereas phosphorus increased gradually in all treatments. The productivity of plants was higher in D1 than D2. Fish growth rates were significantly higher in D1 (0.35 ± 0.03 g/d) and D2 (0.32 ± 0.02 g/d) than in D3 (0.22 ± 0.04 g/d). The results show that A. annua can be cultivated in aquaponic systems due to its nitrogen removal capabilities.
Most recirculation aquaculture systems (RAS) use aerated biofilters to maintain suitable water quality for fish production. However, application of non-aerated biofilters may provide opportunities to ...lower aeration costs, water usage and concentration of all nitrogenous wastes in the effluent water. Our study aimed at comparing the biofiltration performance characteristics of two biofilters: a conventional aerated biofilter and a non-aerated biofilter receiving the same effluent water from a small-scale RAS. The two biofilters were evaluated in triplicate and tested concurrently for seven months. Water quality parameters were monitored at the biofilter inlets and outlets and in the fish tanks. At the beginning of the experiment, the concentration of ammonia at the two biofilter outlets were not significantly different. However, the concentrations decreased with time reaching mean values of 1.33 ± 0.02 mg L
and 1.23 ± 0.21 mg L
N-NH
in the aerated and non-aerated biofilters, respectively. Whereas phosphorus and nitrate levels were significantly high in the aerated biofilter. There was no significant difference in the growth of fish between the aerated and non-aerated biofilters. The results suggest that non-aerated biofilters can be as effective as aerated biofilters in maintaining suitable water quality for
production.
The findings of this study provide useful insights into the key aspects of fish cage farming to be considered during setting and overall management of multi-purpose water resources so as to maximise ...their aquacultural potential. The study was conducted in Machakos District, Kenya, to characterise limnochemistry and algal composition of three small man-made reservoirs Ngeki, Ngei and Kavovi, used for cage culture of Nile tilapia (
Oreochromis niloticus
). In Ngeki, the open water was compared with areas in between the cages and significant differences in dissolved oxygen were found. For N, P and chlorophyll-
a
, no differences were noticed. In all the reservoirs, temporal variations were noticed for all parameters except NO
3
N and NH
4
N. Peak concentrations of nutrients occurred during the rainy season with lower values in the dry season (below detectable limits for SRP). All reservoirs were classified as hyper-eutrophic with a strong positive correlation between chlorophyll-
a
and TP. Algal abundances changed with season. Chlorophyta dominated at the start of the rainy season, while cyanobacteria prevailed at the onset of thermal stratification. Diatoms prevailed in the dry season but were notably absent in the rainy season. It was concluded that all the reservoirs are suitable for cage culture of Nile tilapia, but this should be undertaken with caution considering critical periods when anoxic conditions may occur.
The study amalgamated earthworm and agro‐industrial wastes through vermicomposting and then evaluated the potential of the bedding (mixture of Eisenia fetida and vermicompost) to replace fishmeal in ...semi‐intensive farming of Oreochromis niloticus. The bedding was used to substitute fishmeal at inclusion rates of 100, 60, 30 and 0% (D100, D60, D30 and control D0). In triplicates, the four homogeneous diets were fed to quadruplicate groups of 30 g O. niloticus for 112 days. There was no significant difference (p > .05) in mortalities, average length gain and FCR among all tests. Nevertheless, diet D0 had significantly (p < .05) superior amino acid profile, low fibre content and fish carcass crude protein (63.2 ± 0.72% dry matter). Subsequently, D30 and D0 produced fish with significantly higher (p < .05) mean weight gain (256.03 ± 0.4 g) and biomass (369,136 g) respectively. On to the contrary, diet D100 had significantly higher (p < .05) crude lipids content (9.4 ± 0.6% dry matter), economic returns and profit index than the control diet due to the comparatively low cost of producing the earthworm bedding. This simple biotechnology can commercially be upscaled to sustainably produce cheap and nutritious fish feed capable of increasing yields and maximizing profits.
Feeds and feed management practices are key to the development of the aquaculture sector. To achieve high levels of aquaculture production, fish farmers need nutritionally adequate and cost-effective ...feeds, which are coupled with good feed management practices. Access to high quality and cost-effective feeds is one of the prerequisites to successful fish farming. This paper reviews the current status of the Kenyan fish feed industry and feed management practices. The review includes constraints and opportunities in fish feeds from a farmer's perspective. The review shows that the fish feed industry has been boosted by the development of fish feed standards, which has ensured access to high-quality fish feeds by all farmers. Feed management practices considerably impact on the economic performance in fish production. Thus, adopting appropriate feed management technologies and feeding strategies is instrumental in maximizing aquaculture productivity. Some of the major challenges faced by fish farmers in the feed sector including limited access to finance, lack of appropriate technical innovations, limited knowledge in feed formulation and processing and poor feed handling and storage are discussed. These challenges pose limitation in investment opportunities for a viable and sustainable fish feed processing and manufacturing to meet the rising demand occasioned by increased demand for fish food in Kenya. There is a huge potential to develop public-private partnerships with farmer groups to improve access to training and information dissemination on feeds availability and quality. Training fish farmers on feed formulation using locally available feed ingredients provide an opportunity to reduce feed costs, increase feeding efficiency and improve profitability. This paper reviews the current status of the Kenyan fish feed industry and feed management practices including constraints and opportunities from a farmer's perspective.
Agro-industrial wastes pose great economic and environmental hazards, while the economic success of aquaculture is threatened by the unsustainability of fishmeal use. The aims of the present study ...were to bio-convert agro-industrial wastes through vermicomposting, and then evaluate the potential of the by-products in promoting aquaculture nutrition. Coffee husks (CH), barley wastes (BW), and kitchen wastes (KW) were pre-composted and inoculated with earthworms, Eisenia fetida, and then vermicomposted for 70 days under a controlled environment. The vermicomposting by-products, i.e., earthworms and vermicast, were amalgamated in the ratio of 1:5 into bedding and then analyzed. There were neither earthworm mortalities nor significant difference (P>0.05) in cocoons produced by E. fetid in all treatments. The earthworms grown in KW attained the highest average weight gain of 27.8±0.7g, followed by CH (24.9±0.6g) and BW (24.8±0.7g). Earthworms grown in CH and BW had significantly higher (P<0.05) nutritional attributes. All experimental wastes produced vermicast with carbon and nitrogen ratios within the preferred agronomic limit of 20. The nutritional profile of the BW bedding was comparable with that of Caridina nilotica meal and was within the recommended dietary requirements of fish. The wastes can be bio-converted through vermicomposting into various forms appropriate for providing aquaculture nutrition.
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