Preliminary Observations on Development of Pacific Bluefin Tuna Thunnus thynnus (Scombridae) Larvae Reared in the Laboratory, with Special Reference to the Digestive System

Abstract

Pacific bluefin tuna larvae (Thunnus thynnus) were experimentally reared from 2-day-old yolk-sac larvae through 30-day-old early juveniles in June and July 1994. The larvae initially fed on rotifers on Day 3 and Artemia nauplii, fish eggs and larvae around Day 13, and thereafter were fed Artemia larvae and an artificial diet. The larvae had transformed to the juvenile stage after 30 days. The primitive digestive system differentiated on Day 3. The gastric gland and pyloric caeca first appeared on Day 11 and 14, respectively. The pharyngeal and jaw teeth became fully functional with gastric gland differentiation. The number of gastric glands and pyloric caeca and volume of the gastric blind sac increased markedly with development to the juvenile stage. Although the external morphological development of the tuna resembles the pattern of many other marine fish larvae, the basic digestive system developed at an earlier larval stage; this precocity may relate to the early appearance of piscivory and the high growth potential of tuna larvae.