Evaluation of different feeding protocols for larvae of Atlantic bluefin tuna (Thunnus thynnus L.)

Mass mortality is still one of the main constraints in larval rearing of Atlantic bluefin tuna (Thunnus thynnus L.; ABT). Early data related to the feeding sequence of ABT larvae suggested that mortality observed during the first stages of life could be partly due to nutritional deficiencies. Previous studies demonstrated that copepods ap- peared to be a superior live prey compared to rotifers during the first 2 weeks of life. Our overarching aim was to evaluate different feeding strategies during first feeding of ABT larvae from a performance, compositional and molecular perspective. In order to do so, two groups of ABT larvae were fed with either copepod (Acartia tonsa; C) nauplii or rotifers (Brachionus rotundiformis; R) enriched with Algamac 3050® from mouth opening to 13 days after hatching (dah). After this, the group C-larvae was fed either Artemia enriched with Algamac 3050® (CA), Acartia nauplii and copepodites (CC) or sea bream (Sparus aurata) yolk-sac larvae (CY), while the R group were fed on Artemia enriched with Algamac 3050® (RA) up to 18 dah. At 13 dah, larvae fed copepods (C) had grown better than those fed enriched rotifers (R) although there were no significant differences in survival. ABT larvae fed R accumulated highest eicosapentaenoate (EPA) but lowest docosahexaenoate (DHA) and total n-3 long- chain polyunsaturated fatty acids (LC-PUFA) than C-fed larvae, reflecting the dietary contents. There was no activation in the expression of the enzymes involved in EPA and DHA biosynthesis. However, the different live prey showed regulation of transcription factor, digestive enzyme, lipid metabolism and oxidative stress genes. At 18 dah, larvae fed CY and CA treatments were largest in size, with larvae fed RA displaying the lowest growth, with no significant differences in survival among the dietary treatments. The highest DHA contents were found in ABT larvae fed CC and CY, whereas the lowest contents were found in RA-fed larvae. Indeed, larvae fed RA showed the highest level of the intermediate product n-3 docosapentaenoate, which could reflect increased activity of the biosynthetic pathway although this was not supported by gene expression data.

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