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 ap plied via two feed types, on production characteristics and physiologi cal 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, 1 0, or 20% ascorbyl palmitate (AP) and yielding 530, 1200 and 1600 mu g AA g(-1) DW Artemia, respectively; the other three treatments were fe d the same Artemia diets which were partially substituted by an artifi cial diet containing no vitamin C (ratio 20:80), No differences in sur vival could be observed; however, from day 6 onwards the 20%-AP group showed significantly better growth compared to the 0%- and 10%-AP trea tments, For the cofeeding series, the same positive, but not significa nt, influence of vitamin C on dry weight was found. Moreover, the anim als receiving the highest vitamin C supplementation displayed a consid erably lower stress sensitivity than those of the 0%- and the 10%-AP g roups, for both the 100%- and the 20%-Artemia series. These difference s had occurred by day 2, which might be indicative of the importance o f AA in early development. A second trial, which was a repetition of t he first one, revealed the same tendencies; however, growth difference s 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 or ganelles in the 20%-AP group of the Artemia series compared to the con trol are indicative of a more active metabolism, The slow growth in th e cofeeding series was documented by the poor condition of the hepatoc ytes. 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 incorpo ration and not of the concomitant palmitic acid (PA). which was set fr ee after hydrolysis of AP in the Artemia nauplii, and which could poss ibly be used as a supplemental energy source. The three treatments wer e fed Artemia nauplii enriched with 0% AP, 12% PA and 20% AP, respecti vely. Growth and stress resistance of the latter group were significan tly higher compared to the control and the PA-supplemented fish. To ou r knowledge this is the first evidence for the positive role of high d ietary vitamin C levels (more than 1500 mu g AA g(-1) DW) on larval de velopment of an aquaculture species, and more specifically of C. garie pinus. (C) 1997 Elsevier Science B.V.