Development of
the digestive system and metamorphosis relating hormones in spotted halibut
larvae and early juveniles
Y. Hotta, H. Aritaki, K. Ohta, M. Tagawa, M.
Tanaka-2001
Nippon Suisan Gakkaishi,
67 (1) : 40-48 (from Current
Contents)
Abstract :
In 1997 and 1998, spotted halibut Verasper variegatus
were experimentally reared from eggs through early juveniles at the Miyako
Station of Japan Sea-Farming Association in Iwate Prefecture. The primitive
digestive system of V. variegatus differentiated at the C stage at which
eyes pigmented and the mouth opened. The gastric gland and pyloric caeca
first appeared at the E stage, initiation phase of metamorphosis. The number
of gastric glands and the volume of stomach lumen increased markedly as
metamorphosis proceeded. Intestinal epithelial cell height increased from
the C stage to the F stage, early stage of metamorphosis. Tissue
concentrations of cortisol in larvae increased markedly to a peak of 48.7
ng/g BW just before initiation of metamorphosis, then decreased during
metamorphosis. Thyroxine (T-4) levels increased gradually during the early
metamorphic stage, reaching peak levels at metamorphic climax, then declined
by approximately 50%, Triiodothyronine (T-3) remained at low levels
throughout metamorphosis. Although these hormone patterns in V. variegatus
were similar to those in Japanese flounder Paralichthys olivaceus, the
adult-like digestive system of S. variegatus developed earlier than that of
Japanese flounder. This precocity seems to relate to some ecological
characteristics, such as settling behavior, in V. variegatus.
(Kyoto Univ; Grad Sch Agr; Kyoto 6068502; Japan,
e-mail: