Evalution of Heavy C-oil from Tanker "Nahodka" on the Early Life Stages of Marine Fish under Laboratory Condition

福井県立大学Scedule:17-18 March 2003, Vemue: Kanazawa, Japan, Kanazawa Citymonde Hotel, Project Leader : Hayakawa, Kazuichi, Symposium Secretariat: XO kamata, Naoto, Edited by:Kamata, Naoto

Ⅱ.Impact assessment for fish and wildlife

福井県立大学摂南大学Editor : Tazaki, Kazue |田崎, 和

Effect of thyroid hormones on the stage-specific pigmentation of the Japanese flounder Paralichthys olivaceus

Three experiments were carried out to clarify the effect of thyroid hormones on the pigmentation of larval Japanese flounder Paralichthys olivaceus. The first two experiments were conducted to investigate the critical concentration of thyroxine (T-4) which causes abnormal pigmentation, and the third was to determine the sensitive stage of larval development at which albinism is induced by exogenous T-4. The larvae treated with over 10 nM T-4 showed a significant increase of albinism in Experiments 1 (concentration: 0, 1, 10, 50 nM) and Experiment 2 (concentration: 0, 1, 5, 10 nM). in Experiment 3, seven groups were immersed in 10 nM T-4 at specific stages: between A and B, C and D, E and F, G and I, C and F and A and F. The groups of hormonal treatment at stages E and F (prometamorphosis) produced more than 90% albinism, indicating that differentiation of adult-type melanophores took place at this point. Another 4 groups of larvae were separately treated with levels of 10 nM T-4 at stages A and B, C and D, E and F and G to I. T-4 content of larvae increased corresponding to the developmental stage 180 ng/g-wet weight in A and B, 740 in C and D, and 1350 in E and F, but decreased to 130 in stage G to I (n=3, p<0.01). Changes in the body content of T-4 were reflected in the groups with higher incidence of albinism. The present experiment has revealed the T-4 sensitive period for the induction of albinism in Japanese flounder. The absence of normal coloration in the juveniles after T-4 treatment clearly indicates the involvement of the thyroid in pigmentation at the early stages of development

Distributional changes in branchial chloride cells during freshwater adaptation in Japanese sea bass Lateolabrax japonicus

Distributional changes in branchial chloride cells were examined in Japanese sea bass (Lateolabrax japonicus) juveniles transferred from seawater (SW) to fresh water (FW) during their migration season toward low salinity habitat in nature. Chloride cells were identified by immunocytochemistry with a specific antiserum for Na+,K+-ATPase. In fish reared in SW as controls, branchial chloride cells were localized exclusively in the filaments and absent in the lamellae. When sea bass were transferred from SW to FW, chloride cells emerged in gill lamellae, starting at the proximal part of the lamellae and thereafter spread over the lamellar epithelium. On 7th and 15th days after FW transfer, chloride cells were mostly found on the lamellae, whereas the number of filament chloride cells was decreased. These results suggest that, in Japanese sea bass juveniles, chloride cells in the gill lamellae are important in FW adaptation, and that lamellar chloride cells originated from the filaments and migrated to the lamellae during FW adaptation