Development of Growth Hormone Cells of Laboratory Reared Yellowfin Tuna Thunnus albacares Larvae and Early Juveniles

Abstract

Development of the pituitary and growth hormone (GH) cells of laboratory reared yellowfin tuna Thunnus albacares larvae and early juveniles were examined by histological and immunohistochemical procedures. The pituitary first appeared in the ventral edge of diencephalon of the brain on Day 2, and suspended from the brain on Day 16. The growth hormone (GH) immunoreactive cells were first detected on the day of first feeding, Day 4. Percent GH, defined as ratio of GH cell-mass volume to pituitary volume, was very high during the first three days after initiation of feeding. Percent GH rapidly decreased, and remained at the lowest level throughout the flexion phase. The ratio began to increase from the postflexion phase to the early juvenile stage. The %GH of yellowfin tuna was relatively higher than those of other marine fish species previously examined. These features suggest that the yellowfin tuna has a relatively high growth potential during the early life stages.