This experiment was conducted to study the effect of altering the linoleic acid (LA) and linolenic acid (LNA) levels and ratios in the diet of Nile tilapia (Oreochromis niloticus) on fry performance. Twelve diets were formulated to be isonitrogenous, isocaloric, and differed only in their main lipid source. An oil rich in n-3 fatty acids [linseed oil (L)] and two oils rich in n-6 fatty acids [soybean oil (S) and corn oil (C)] were added at 6% of the basal diet either separately or in equal combinations (L1:S1 or L1:C1 or S1:C1) or at ratio 2:1 (L2:S1 or L2:C1 or C2:L1 or C2:S1 or S2:L1 or S2:C1). The fish were fed twice daily (09 and 16 h) to apparent satiation throughout the duration of the trial (16 weeks). Survival rates increased in a linear pattern with increasing the LA level in the diets (R 2 = 0.764). Final body weight was significantly higher in fish fed S, S2:L1, and L2:C1 diets, being 14.29, 14.14, and 14.09 g/fish, respectively. However, tilapia fed C, S1:C1, and C2:S1 diets exhibited low final body weight (11.41, 11.60, and 11.76 g/fish, respectively). The final body weight was negatively affected by increasing the LA/LNA ratios (R 2 = 0.647). Either LA or arachidonic acid (%) in the whole body of fish increased in a linear patterns (R 2 = 0.641 and 0.746, respectively) with increasing dietary LA. Besides, LNA, eicosapentaenoic, acid and docosahexaenoic acid (%) in the whole body increased in a linear pattern (R 2 = 0.777, 0.501, and 0.8148, respectively) the increasing dietary LNA level. The present study indicated that LA/LNA ratio less than 13 is recommended for nutrition of tilapia fry.

World aquaculture production in 2002 reached 39.8 million metric tons (Mt). However, despite a general understanding that the advancement of aquaculture is very important for food security and poverty alleviation, aquaculture in Africa is insignificant compared to the rest of the world. African aquaculture contributed only 1.2% (463 × 10 3 Mt) of world aquaculture production. Moreover, our calculation based on FAO statistics revealed that the average per capita consumption of fish in Africa decreased from 9 kg in 1990 to 7.8 kg in 2001. This decrease in the per capita consumption of fish appears to be a threatening sign for food security in Africa. There are many political, economic and technical issues that are obstructing the development and promotion of aquaculture in Africa. Egypt, the desert but rice producing country, has a long history of aquaculture and is the leading producer, especially of freshwater aquaculture in Africa. Total aquaculture production in Egypt in 2002 was 376 × 10 3 Mt, which supplied 81% of that in Africa. In the present review, based on the case of Egypt, we propose measures and research areas to develop and promote rice-fish culture and desert aquaculture. Rice-fish culture is a model of aquaculture styles for wet and pluvial regions, and desert aquaculture is also a model for arid and semi-arid regions not only in Egypt but also for other African countries. Poor knowledge on fish feeds and feeding technology is one of the major constraints in the expansion of aquaculture. In order to improve and increase the productivity of aquaculture in Africa, we propose measures and research subjects for developing supplementary and complete feeds using regional ingredients.

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Journal of Aquaculture Research & Development