CHANGES IN CHEMICAL CONTENTS AND ENZYME-ACTIVITIES DURING EMBRYONIC-DEVELOPMENT OF BLUEFIN TUNA

Naturally fertilized bluefin tuna Thunnus thynnus eggs which were obta ined from 7-year-old broodstock in a net cage were incubated until hat ching at 27 degrees C. No conspicuous changes were found in egg moistu re and amounts of total nitrogen and phospholipid during the embryonic development. Egg protein gradually increased, but free amino acid dec reased with the development. Triacylglycerole (TG), a main egg constit uent of 420 mg/g dry egg at the stage of early cleavage, rapidly decre ased after the stage of late gastrula and reached 140 mg/g dry egg jus t before hatching. Activities of aspartate aminotransferase, alanine a minotransferase, creatine kinase, and lactate dehydrogenase fell betwe en the stages of early cleavage and Kupffer's vesicle and rose thereaf ter. Activities of alkaline phosphatase remained high until embryo for mation but fell rapidly thereafter. These results indicate that TG pla ys an important role as a main energy fuel, and that the differentiati on and formation of organs are prompted immediately before or after th e stage of Kupffer's vesicle during the embryonic development of bluef in tuna.