LARVAL REARING OF AN AFRICAN CATFISH HETEROBRANCHUS-LONGIFILIS (TELEOSTEI, CLARIIDAE) - EFFECT OF DIETARY LIPIDS ON GROWTH, SURVIVAL AND FATTY-ACID COMPOSITION OF FRY

With the aim of improving dry diets for first feeding of Heterobranchu s longifilis larvae, the effect of dietary lipid sources on growth rat e, survival rate and fatty acid composition of fry from 2 days up to 1 7 days of age was evaluated. Six feeding regimes were tested: Artemia nauplii which served as a reference, and 5 experimental dry diets diff ering only by the lipid source. The different oils used for the differ ent experimental diets were the following: cod liver oil, palm oil, co pra oil, peanut oil and cotton seed oil. Each diet was tested on dupli cate groups of 400 larvae placed in the 40 l tanks of a recirculating system (27-29 degrees C) and fed to excess six times per day every 4 h ours. Separation and identification of the fatty acids of diets; eggs and fry were carried out by gas-liquid chromatography. After 15 days o f feeding, survival rates were high for all treatments (71-87%) and di d not differ significantly. By contrast, growth rates were largely inf luenced by the feeding regime. Fry fed with Artemia were significantly bigger (289 mg) than those fed artificial dry diets (79-115 mg). Howe ver, it was found that the specific growth rate of fry fed Artemia was superior to that of fry receiving dry diets only for fish of less tha n 50 mg body weight, indicating that Artemia presents a nutritional ad vantage only for fry at their youngest stages of development (first 6 days of feeding). Among the artificial dry diets, the best results wer e obtained with diets containing palm or copra oil, the lowest growth rate being observed with the cod Liver oil diet. Peanut and cotton see d oil diets led to intermediate results. The fatty acid composition of the whole fry reflected that of the experimental diets. All together, the results indicated the existence of an optimal ratio between n-3 a nd n-6 fatty acids for covering essential fatty acids requirement of t he fry. Growth rates tended to be reduced by an excess of n-3 fatty ac ids (cod Liver oil) or by an excess in n-6 fatty acids (cotton seed oi l) as well. Evidence of the occurrence of HUFA (20:4n-6 and 22:6n-3) b iosynthesis are given.