Growth and morphological development of laboratory-reared yellowfin tuna Thunnus albacares larvae and early juveniles, with special emphasis on the digestive system

Yellowfin tuna Thunnus albacares larvae were reared from hatching beyond metamorphosis in May and June 1996. The larval size was 2.65 mm SL at just after hatching and 27.68 mm SL on Day 37, Transformation to juveniles occurred around 30 days after hatching at about 13 mm SL. The larvae initially fed on rotifers since Day 4, on fish larvae and Artemia nauplii since Day 16, and then on frozen fish and minced fish meat. The primitive digestive system differentiated on Day 4. The gastric gland and pyloric caeca first appeared on Day 14 and 16, respectively. The pharyngeal and jaw teeth became fully functional synchronized with gastric gland differentiation. The number of gastric glands and pyloric caeca and volume of the gastric blind sac increased markedly toward the juvenile stage. Although external morphological development of yellowfin tuna resembled to that of other marine fishes hatched from pelagic eggs, the digestive system developed precociously. The rapid development of the digestive system allows the early appearance of piscivory which can support the high growth potential as shown in other scombrid fishes.