Sensitivity of the metamorphic events and morphogenesis of Japanese flounder Paralichthys olivaceus during larval development to thyroxine
J.H. Yoo, T. Takeuchi, T. Seikai-2000
Fisheries Science, 66 (5) : 846-850
(from Current Contents)
Abstract :
An experiment was conducted to determine the impact
of exogenous thyroid hormone on metamorphic events and morphogenesis of
larval Japanese flounder Paralichthys olivaceus. Six groups of 600 larvae
each were immersed in 10 nmol thyroxine-sodium salt (T-4) during different
developmental stages: A and B, C and D, E and F, C to F, and A to F. T-4
treatment during stages E and F resulted in premature metamorphosis
including not only advanced settlement but also advanced eye migration of
the juvenile fish. T-4 treatments also resulted in rapid absorption of the
dorsal fin rays during stages C to F. As a result, metamorphosis to the
bottom juvenile was induced by 10 nmol T-4. It was also found that the rate
of metamorphosis was proportional to the T-4 immersion period. These results
confirm that T-4 plays a major role in metamorphic events and morphogenesis
during the early life stages of flounder. Thus, this study suggests that
sensitivity to T-4 depends on the larval organ and the larval developmental
stage.
(Tokyo Univ Fisheries, Dept Aquat Biosci, Tokyo
1088477, Japan, e-mail: take@tokyo-u-fish.ac.jp)