Characterization of the fatty acid composition of Pacific bluefin tuna Thunnus orientalis larvae by body part and depending on growth rate

In this study, we aimed to elucidate the characteristics of faster-growing Pacific bluefin tuna (Thunnus orientalis) larvae by focusing on the localization of long-chain polyunsaturated fatty acids in different body parts and at various days post-hatch (dph). To accomplish this, we compared low- and high-growth-rate groups of larvae under mass-rearing conditions. Multivariate analysis revealed that the first axis separated the dph and growth groups, and the high-growth-rate group tended to be distributed on the same side at 20 dph. This suggests that the faster-growing larvae had switched their diet sooner after the change in feeding regime, either from rotifers to yolk-sac larvae of the spangled emperor (Lethrinus nebulosus) or from yolk-sac larvae to a commercial diet. However, the fatty acid compositions differed significantly between the two growth groups at 10 dph, before the change in feeding regime (PERMANOVA; P < 0.001). Notably, %DHA was higher in the head (mean: 24.4 %) and eyes (29.2 %) of the high-growth group, while %DHA levels in the trunk remained similar between groups (range: 23.1 %–23.7 %). These findings suggest that early accumulation of DHA (approximately 30 %) in the eyes, in contrast to the lower requirement in trunk tissues, may be critical for sustaining rapid growth in Pacific bluefin larvae during the pre-diet-shift period.