DIFFERENTIATION AND DEVELOPMENT OF THE SWIMBLADDER IN LARVAE OF THE JAPANESE SEA BASS LATEOLABRAX-JAPONICUS

Development of the culture of marine fishes is dependent on detailed i nformation on their early life stages. This paper describes the timing of differentiation, initial inflation and development of the swimblad der in Japanese sea bass larvae. Developmental changes in yolk and oil globule volumes and specific gravities were also observed. The mouth opened when the yolk mass was greater than the oil globule volume. Fir st feeding was observed when the oil globule volume became greater tha n that of the yolk. Specific gravity of larvae increased rapidly durin g the first day after hatching then became relatively constant around the neutral bouyancy level. A rudimentary swimbladder, protruding from the dorso-posterior wall of the primordial stomach, was first observe d 2 days after hatching. Initial inflation of the swimbladder occurred 8 days after hatching and was complete in most larvae by 16 days afte r hatching, when the oil globule was completely absorbed. A few larvae were observed with uninflated swimbladders in which epithelial cells exhibited hypertrophy. Uninflated swimbladders were atrophic about 30 days after hatching. These results indicate that the development and d egeneration of the swimbladder of the Japanese sea bass is similar to that of other physoclistous species.