Valutazioni comparative sull’impiego di alcune diete inerti nello svezzamento del branzino (Dicentrarchus labrax L.)

Four types of weaning diets for marine fish were compared: 2 diets widely used (CH and AL) and 2 (SE and TE) newly formulated. With this aim, seabass larvae, weighing on average 250 mg, were allotted to 4 concrete tanks (10 m3) and stocked at 3.5/1, that is 35,000/tank. Diet composition was determined, with special attention to amino acid and fatty acid fractions, while floating sedimentation speed ad food acceptance of the single diets were evaluated at sight. During the whole trial (20 d), larvae where uninterruptly fed, 24 h a day, supplying food at the rate of 6-12 of live weight. At the beginning and every 5 d, weight and length were measured on 100 fish samples. Death rate was evaluated, by recording the daily number of dead larvae in each trial tank. Feed AL had a dramatically poor level of tryptophan. Quantitatively, lipid fraction is higher in feed CH, compared with the other three, which appear similar in this aspect, with the exception of the fatty acid C20:4n6, almost exclusively present in the diet TE. The saturated and polyunsaturated fatty acid composition is remarckably different in the compared diets. The sum of C20:5n3 and C22:6n3 percentage always exceeds 4% of the total fatty acids, which is the minimum level necessary for the survival of marine fish larvae (23). Diet SE showed a strong attraction power; diet TE, followed by CH, gave good results, while feed AL was scarsely attractive. Diet Al showed the maximum sedimentation speed (table 4). Total death rate has been acceptable in all thesis (from 8.5% to 12%), with a Constant and gradual decrease from the beginning to the end of the trial. Very similar final sizes were found in all thesis. In relation to weight, significant differences (P<0.001) between fish fed diets CH and SE and diets AL and TE were observed as from 5th d. Final data stressed marked analogies between feed AL and SE, group TE fishes being the heaviest.