Lack of suitable diets for semi‐intensive production of Oreochromis niloticus in Kenya has necessitated use of expensive diets designed for intensive production. To address this problem, two isonitrogenous (24% protein) diets were formulated and evaluated for production of O. niloticus in fertilized ponds. One diet contained vitamins and minerals premix (CV) while the other had no premix (CW). Growth of fish fed on the formulated feeds was compared with groups of fish fed on commercial pig pellets (PP) and wheat bran (WB). There were significant differences in mean weights, growth rates and feed conversion ratios between the formulated and the other diets. No significant differences in these parameters were observed between CV and CW and also between PP and WB. Fish that fed on the formulated feeds produced significantly lower number of juveniles than those fed on PP and WB. Fish fed on WB gave the best economic returns while those on PP had the least returns. Present results suggest that vitamins and minerals premix may not be necessary in diets for semi‐intensive production of O. niloticus. Present results showed that the formulated feeds produced higher yields than PP and WB, but WB had the best economic returns among the test diets.

Despite the well‐documented herbivorous food habits, commercial feeds for production of Oreochromis niloticus usually contain between 7% and 15% animal protein. However, animal protein feedstuffs are expensive, hence the need to search for cost‐effective alternatives in plant‐protein sources. Such alternatives are probably more effective in semi‐intensive systems where natural pond food forms part of the diet. This study evaluated the performance of O. niloticus after feeding diets in which fresh shrimp meal (SM) was gradually replaced by a mixture of plant‐protein sources in fertilized ponds. Three isonitronegenous (24% crude protein) diets containing 12 (control), 6% and 0% SM were fed to three groups of O. niloticus in four replicates per group for 250 days. Fish were fed daily at 2% body weight and sampled monthly to monitor growth and make feed adjustments. Growth, yields, survival and feed conversion ratio were not significantly different (P>0.05) among treatments. Growth of males was double that of females, while the sex ratio was skewed towards females. Although complete substitution of SM by plant protein did not affect the growth of tilapia, production cost was reduced by 36%. In conclusion, animal protein is not required in diets for production of O. niloticus in fertilized ponds.

Nile tilapia (Oreochromis niloticus L.) was fed rice bran (RB), wheat bran (WB) and maize bran (MB) at 1.5% body weight. Fingerlings averaging 14 g were stocked at 19 462 fish ha−1 in three treatments with six replicates per treatment. Clarias gariepinus was stocked at 250 fish ha−1 to reduce the density of tilapia fry. Growth and economic performance were compared for 250 days in 0.08 ha fertilized ponds. Fish growth was highest (P < 0.05) in MB and least in RB treatment. Growth in WB treatment was intermediate. Feed conversion ratio in MB and WB treatments was similar (P > 0.05), but significantly higher (P < 0.05) than in RB treatment. Water quality parameters were similar (P > 0.05) among treatments. At retail price of US$ 1.28 kg−1 fish, returns above both variable and total costs from MB and WB treatments were positive, while those from RB were negative. However, at US$ 1.79 kg−1 fish, all test‐feeds had positive returns above variable and total costs. In conclusion, MB treatment produced the highest growth, but the highest profitability was obtained in the WB treatment. Under present study conditions, RB was not cost‐effective in the production of O. niloticus. A selling price of US$ 1.79 kg−1 fish is recommended.

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.

The e¡ects of open-water and caged ¢sh density on growth, feed utilization, water quality and pro¢tability were investigated to assess the feasibility of a small-scale rotational system for production of Oreochromis niloticus (L.) in fertilized ponds. Hand-sexed male ¢ngerlings averaging 18.6 and 29.9 g were stocked in open water and cages, respectively in four treatments with open-pond:caged tilapia ratios of 300:0 (control), 150:150 (L), 300:150 (H1) and 300:300 (H2). The ponds in L and H1 contained one cage, two cages in H2, and the control ponds had no cages. Each cage contained 150 ¢sh, which were fed daily at 1.5% body weight for 125 days. All ¢sh in the open water except the control ¢sh were not fed. Growth of open water tilapia was signi¢cantly (Po0.05) higher in L than in control. Feed utilization, dawn DO and economic returns were signi¢cantly better (Po0.05) in caged than control ponds. Growth of tilapia in L was signi¢cantly lower (Po0.05) in cages than in open water. Fingerling production was signi¢cantly lower (Po0.05) in L than in other treatments. In conclusion, cage-cum-open-pond integrated treatment (L) was optimal for O. niloticus production in fertilized ponds. However, the system could not rotate and needed further ¢ne-tuning to rotate.