2001 Volume 67 Issue 1 Pages 40-48
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 48.7ng/g BW just before initiation of metamorphosis, then decreased during metamorphosis. Thyroxine (T4) levels increased gradually during the early metamorphic stage, reaching peak levels at metamorphic climax, then declined by approximately 50%. Triiodothyronine (T3) 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 V. variegatus developed earlier than that of Japanese flounder. This precocity seems to relate to some ecological characteristics, such as settling behavior, in V. variegatus.