Two consecutive experiments were conducted to study the e¡ects of stocking density on growth, food utilization, production and farming pro¢tability of Nile tilapia (Oreochromis niloticus) ¢ngerlings (initial mean weight:16.2 AE 0.2 g) fed Azolla, as a main component in diet. In experiment 1, ¢sh were hand-fed twice daily with three isonitrogenous (28.5% crude protein) and isocaloric (14.5 kJ g À1 ) diets A30, A35 and A40 containing 30%, 35% and 40% Azolla, respectively, for 90 days. Diets were formulated by mixing Azolla with locally available by-products. No signi¢cant di¡erences were found in growth parameters and production (P40.05). Total investment cost was signi¢cantly higher with A30 (Po0.05), but same pro¢tability values were obtained with all diets (P40.05). In experiment 2, three stocking densities, 1, 3 and 5 m À 2 , were assigned to three treatments T 1 , T 2 and T 3 respectively. Fish were hand-fed twice daily with diet A40. The ¢nal mean weight (89.53^115.12 g), the mean weight gain (0.811.10 g day À1 ), the speci¢c growth rate (1.90^2.20% day À1 ) and the apparent food conversion ratio (1.29^1.58) were a¡ected by stocking density, with signi¢cant di¡erence (Po0.05) at 5 m À 2 , compared with the other densities. Stocking density did not affect survival rate (P40.05).Yield and annual production increased with increasing stocking density, ranging from 7.10 AE 0.90 to 25.01 AE 1.84 kg are À1 and 28.79 AE 3.66 to 101.42 AE 7.48 kg are À1 year À1 , respectively, with signi¢cant di¡erences between all densities (Po0.05). Higher stocking density resulted in higher gross return and lower cost of ¢sh production, with signi¢cant variations (Po0.05). The net return increased with increasing stocking density (Po0.05). However, both densities of 3 and 5 m À 2 produced the same pro¢tability values. On the basis of growth values and economic return, it was concluded that Nile tilapia could be raised at a density of 3 ¢sh m À 2 with A40 to improve production and generate pro¢t for nutritional security and poverty alleviation in rural areas.

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Two 90-day experiments were conducted in the same period in tanks and in earthen ponds to study the effects of culture systems on growth and fatty acid (FA) of Nile tilapia (Oreochromis niloticus L.) fingerlings (mean weight: 16.3 g) fed Azolla, as partial replacement for fish meal (FM). Diets were isonitrogenous (29.2% CP) and isoenergetic (16.9 kJ•g −1) containing 0% (A 0), 10% (A 10), 20% (A 20), 30% (A 30), 40% (A 40) and 50% (A 50) of Azolla meal (AM) respectively. Diet A 0 , without AM, acted as a control. In both experiments, fish growth decreased as AM level increased in diets (P < 0.05), and values were significantly higher (P < 0.001) in ponds than in tanks (ranges: 88.8-135.9 g vs. 51.0-88.3 g). Some dissimilarity was noticed in fish FA composition. FA profiles in fish fed in tanks was influenced by diet, except for the high content in arachidonic acid (20:4n-6) in fish fed high AMdiets. On the contrary, FA profile in fish fed in ponds was different from that in fish fed in tanks, and from diets. The lower resemblance of fish composition was more pronounced in fish fed high AM (A 30-A 50). Interestingly, those fish were rich in eicosapentaenoic acid (EPA, 20:5n-3) and docosahexaenoic acid (DHA, 22:6n-3). Consequently, the n-3/n-6 values decreased in tanks, whereas an increasing trend was found in ponds, and values were significantly higher in ponds than in tanks (0.35-0.53 vs. 0.08-0.17). The results suggest raising Nile tilapia with Azolladiets in ponds to improve growth and produce fish with a better FA composition, for the wellbeing of consumers.