The effect of supplemental ascorbic acid in enriched live food for Clarias gariepinus larvae at startfeeding

The effect of three dietary ascorbic acid (AA) concentrations, each applied via two feed types, on production characteristics and physiological condition of African catfish (Clarias gariepinus) larvae has been assessed in two 10-day culture trials. Three treatments received only Artemia nauplii enriched with an experimental emulsion containing 0, 10, or 20% ascorbyl palmitate (AP) and yielding 530, 1200 and 1600 mu g AA g(-1) DW Artemia, respectively; the other three treatments were fed the same Artemia diets which were partially substituted by an artificial diet containing no vitamin C (ratio 20:80), No differences in survival could be observed; however, from day 6 onwards the 20%-AP group showed significantly better growth compared to the 0%- and 10%-AP treatments, For the cofeeding series, the same positive, but not significant, influence of vitamin C on dry weight was found. Moreover, the animals receiving the highest vitamin C supplementation displayed a considerably lower stress sensitivity than those of the 0%- and the 10%-AP groups, for both the 100%- and the 20%-Artemia series. These differences had occurred by day 2, which might be indicative of the importance of AA in early development. A second trial, which was a repetition of the first one, revealed the same tendencies; however, growth differences were smaller, probably due to the higher incorporation levels of AA obtained in the live diet (530, 1700 and 2300 mu g AA g(-1) DW) and in the catfish larvae. Growth results of both experiments were supported with data from the ultrastructural evaluation of the hepatocytes; i.e. a more organized cell compartmentation and better-structured cell organelles in the 20%-AP group of the Artemia series compared to the control are indicative of a more active metabolism, The slow growth in the cofeeding series was documented by the poor condition of the hepatocytes. In a third experiment it was verified that the growth effect of the 20%-AP boosted Artemia diet was the result of the extra AA incorporation and not of the concomitant palmitic acid (PA). which was set free after hydrolysis of AP in the Artemia nauplii, and which could possibly be used as a supplemental energy source. The three treatments were fed Artemia nauplii enriched with 0% AP, 12% PA and 20% AP, respectively. Growth and stress resistance of the latter group were significantly higher compared to the control and the PA-supplemented fish. To our knowledge this is the first evidence for the positive role of high dietary vitamin C levels (more than 1500 mu g AA g(-1) DW) on larval development of an aquaculture species, and more specifically of C. gariepinus. (C) 1997 Elsevier Science B.V