Warm water aquaculture is widely practiced in Kenya and is dominated by the culture of Nile tilapia (Oreochromis niloticus) (75% of total production) followed by African catfish (Clarias gariepinus) at 18%. Aquaculture started in Kenya in 1920's and has been on upward trend until 2014 when it peaked at 24,096 MT. However, production reduced drastically in the past 3 years, with 14,952 metric tonnes (MT) reported in 2016. Most farmers practice earthen pond based semi-intensive culture system. Commercial intensive culture of Nile tilapia (O. niloticus) in cages in Lake Victoria has grown significantly in the last five years with a production of 12 million kg of fish every cycle (about 8 months). Recirculation aquaculture system (RAS) is also gaining popularity mainly in intensive hatcheries. The freshwater cages have been marred by increasing frequencies of fish kills with obvious financial and environmental implications. Although limited information exists on fish disease outbreaks across the country, certain well known diseases in farmed fish have been reported. These include; fungal, mainly saprolegniasis, bacterial, mainly hemorrhagic disease and pop-eye diseases. Parasites have also been documented in farmed O. niloticus and C. gariepinus. Although prophylactic treatments are used in some hatcheries in order to prevent infections, limited biosecurity measures are in place to prevent diseases in farmed fish. This is because of inadequate knowledge of the economics of fish diseases, poor infrastructure and inadequate human resource specialized in fish diseases. This review describes the aquaculture production and health mangement practices of farmed fish in Kenya in order to document actions required for effective monitoring and regulation of future fish health problems across the country.

Insects have been proposed as potential alternative animal protein sources to replace fishmeal (FM), which is expensive and has limited availability for fish feed formulation. However, studies on the effects of replacing FM with black soldier fly (Hermetia illucens) larvae (BSF‐L) on growth performance of Nile tilapia (Oreochromis niloticus) fry, water quality and economic benefits are currently limited. This study determined the effects of replacing 100% FM, 75% FM, 50% FM, 25% FM and 0% FM with cheap BSF‐L meal, hereafter referred to as BSF‐L0, BSF‐L25, BSF‐L50, BSF‐L75 and BSF‐L100 diets, respectively for rearing all‐male Nile tilapia fry produced by YY technology. The study further determined the optimum percentage of BSF‐L meal for maximum growth of Nile tilapia fry. A total of 2400 visually healthy Nile tilapia fry weighing 0.001 g were randomly stocked into 20 plastic tanks (120 fry per tank, four replicates per treatment) and fed the BSF‐L diets for 12 weeks. The BSF‐L75 diet increased significantly specific growth rate, total weight gain, Zihler's index of fry and nitrate in the culture water but reduced feed conversion ratio of diet and total suspended solids in the culture water (p < 0.05). Feeding the Nile tilapia fry with BSF‐L50 diet increased significantly hepatosomatic index (p < 0.05). The diets with BSF‐L75 and BSF‐L100 reduced significantly the incidence cost by 31.97% and 28.77% (p < 0.05), and increased profit index by 3.97 and 3.44%, respectively. The optimum percentage of BSF‐L inclusion required for maximum growth performance of Nile tilapia fry was estimated as 81% to 84% based on polynomial analysis. Taken together, feeding Nile tilapia fry with diets containing 81% to 84% BSF‐L meal improved growth performance. The BSF‐L75 diet enhanced feed efficiency and had no deleterious effect on the liver and intestines. Meanwhile, it improved nitrate concentration for increased natural productivity. Incorporating 75% BSF‐L meal in diets for Nile tilapia fry reduced 30% of feed cost leading to 4% higher economic returns.

Poor culture conditions in low input ponds make fish highly susceptible to infectious pathogens which lead to diseases and mortalities yet the effects of probiotics on immunity, gut microbiota and microbiological quality of fish in low input ponds are unknown. Nile tilapia, Oreochromis niloticus fingerlings (40 g) were randomly stocked at 50 fish m⁻³ in 1.25 m³ cages in low input ponds. The fish were fed on diets supplemented with either Saccharomyces cerevisiae (1 × 10¹⁰ CFU g⁻¹) or Bacillus subtilis (1 × 10⁹ CFU g⁻¹) at six levels: Diet 0 (No probiotic); S. cerevisiae at 2 g kg⁻¹ (Diet 1); 4 g kg⁻¹ (Diet 2) and 6 g kg⁻¹ (Diet 3) and B. subtilis at 5 g kg⁻¹ (Diet 4); 10 g kg⁻¹ (Diet 5) and 15 g kg⁻¹ (Diet 6) for 180 days. Results indicate that hemato-immunological parameters (hemoglobin (Hb), red blood cells (RBC), white blood cells (WBC) serum protein, albumin, globulin and lysozyme activity) were significantly higher in fish fed on probiotic treated diets compared to the control (P < 0.05). On the contrary, fish fed on Diet 6 presented significantly similar Hb and globulin values compared to the control (P > 0.05). Additionally, fish fed on probiotic treated diets retained the probiotics in their guts and lower microbial load was realized in their muscle (P < 0.05). In conclusion, B. subtilis and S. cerevisiae supplementation in diets of Nile tilapia reared in low input ponds improves immunity, manipulates gut microbiota and enhances fish flesh quality.

Aquaculture plays a major role in curbing malnutrition and food insecurity. Nonetheless, aquaculture sustainability is threatened by expensive fish feeds due to the overreliance on fish meal (FM) as the main source of protein. Fish meal is not only expensive but also scarce due to declining capture fisheries and competition from other animal feed producers. This has prompted research on potential FM replacers, amongst them the black soldier fly (BSF) larvae (Hermetia illucens). The BSF larvae can effectively convert organic wastes into a potential valuable feed source, and its high nutritional content (crude protein of up to 64% dry matter) is vital for fish feed formulation. Nevertheless, there are no documented studies on the complete replacement of FM in the diets of fish using BSF larvae. Therefore, the current study reviewed 107 research publications related to BSF larvae vis-a-visfish feeds production to build capacity for existing theories, identify gaps, and suggest new and further research directions, based on the previous studies available in the area of larvae production and utilization in aquaculture nutrition. The study results are expected to help farmers make an informed decision on how to reduce the cost of fish production, increase yields, thus promoting food security, livelihoods, and ecological balance.