THE EFFECT OF LOW HUFA-ENRICHED AND HIGH HUFA-ENRICHED ARTEMIA, FED AT DIFFERENT FEEDING LEVELS, ON GROWTH, SURVIVAL, TISSUE FATTY-ACIDS AND LIVER HISTOLOGY OF CLARIAS-GARIEPINUS LARVAE

The present study investigated the effect of two diets containing different levels of HUFA, given at three different feeding levels on the growth performance, fatty acid composition and liver structure of African catfish, Clarias gariepinus (Burchell), larvae. The larvae were raised at 27.5 degrees C until a final weight of 50 mg. The fish were fed Artemia which was enriched with an emulsion low in n-3 HUFA (coconut-oil) or high in n-3 HUFA (SELCO). Both feed types had similar protein and ash levels, but differed mainly in their fatty acid composition. The level of the n-3 HUFA in SELCO-enriched Artemia was three times higher (14.5 mg/g dry weight) than in the coconut-oil-enriched Artemia (5 mg/g dry weight). Feed type did not affect growth or survival. Dietary HUFA levels affected the fatty acid composition of the fish but this feed type effect was statistically not significant. The specific growth rate ranged, depending upon the feeding level, from 17 to 52% body weight.day(-1) and survival rate varied between 79 and 89%. The total amount of food given to the fish did affect significantly the dry matter content, tissue fatty acid composition and the liver lipid content in the fish. At the start of exogenous feeding, docosahexaenoic acid (22:6n-3) was the most abundant fatty acid in the fish (17.1 mg/g dry weight or 28.2% of total fatty acids), but its level decreased to 2-4 mg/g dry weight at the end of the experiment. Fatty acid retention percentages revealed the capacity to synthesize HUFA. Feeding the larvae at optimal feeding level or higher resulted in accumulation of lipid in the liver (>40% of the hepatocyte volume consisted of lipid). Overall, feeding level had a more pronounced effect than feed type.