High concentrations of TBT (2.5 to 52.5 times those in muscle) were detected in the blood of three cultured fish species (Japanese flounder, red sea bream, and yellowtail), and in a wild flatfish. The results of gel filtration, performed on serum from the Japanese flounder, showed that TBT was bound to a protein (mol. wt. ca. 50,000). In controlled experiments, Japanese medaka (Oryzias latipes) were fed daily diets containing TBT, polychlorinated biphenyls (PCB), or a combination of TBT+PCB. All contaminant doses were 1 mg/kg body weight per day for three weeks. In the combined TBT+PCB treatment there were significant reductions in spawning frequency relative to toxin-free controls. There also were decreased numbers of both total and fertilized eggs. Exposure to TBT alone significantly reduced the survival of larval fish, which hatched from eggs that contained up to 170 ng TBT/g.

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The Seto Inland Sea is the largest inland sea in Japan and characterized by highly enclosed topography. The quality of aquatic environment such as water quality and sediment quality had deteriorated especially since late 60's due to the industrial development and urbanization along the coast. Historical changes of the environment and countermeasures employed were reviewed. Present status of the water and sedimet quality was depicted. Effects of aquaculture and collection of sea sand as material for construction on coastal environment and on coastal ecosytem were pointed out. Since the environmental policy on the management of the Seto Inland Sea is expected to be changed in near future, perspective is given and the new idea of comprehensive approach for the environmental management is proposed. Research plan on the sustainable biological production of the Seto Inland Sea was also proposed.

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Why is the fish catch per unit area so high in the Seto Inland Sea, Japan, compared to other semi-enclosed seas, such as Chesapeake Bay, USA, and the Baltic Sea? To answer this question, it is necessary to understand the production process in the lower trophic levels of the food chain on which fish production depends. A cooperative research was conducted once per season in 1993 and 1994 to investigate the biological production in the lower trophic levels in the Seto Inland Sea, and revealed that the sea is characterized by high production rates of phyto- and zooplankton and high efficiency of energy transfer between trophic levels of the food chain. It is our responsibility to preserve the health of this productive and efficient ecosystem in order to sustain fishery production in the future.

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Rare metals such as vanadium and cobalt are dissolved in sea water at very low levels. Ascidians are known to accumulate high levels of vanadium, a rare metal, selectively. The concentration of vanadium reaches 350 mM corresponding to 10⁷ times the vanadium concentration in sea water. Recently, we have isolated vanadium-associated proteins, 12.5 kDa and 15 kDa, that are thought as the key to the solution of the mechanism, from ascidian blood cells and cloned cDNA encoding the proteins. We are carrying forward a scheme to elucidate the accumulation mechanisms of vanadium by ascidians and to apply the mechanism to leaching out rare metals from sea water.

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The behavior of marine algae (Dunaliella salina, Chattonella antiqua, Heterosigma akashiwo, Skeletonema costatum, Chaetoceros debile and Thalassiosira weissflogii) against arsenate, arsenite and dimethylarsinic acid (DMAA) in a medium and the effects of glutathion that influenced the redox condition on arsenic accumulation of D. salina were studied. It was found that the order of growth inhibition of marine algae by arsenic species was As (III)>As (V)>DMAA. The order of arsenic accumulation by D. salina was As (V)≥As (III)>DMAA at a concentration of 100 mg/L. A small part of the arsenic accumulated by D. salina was methylated in vivo. The arsenic content increased with an increase of surrounding arsenic and iron. However arsenic content decreased at a phosphorus and selenium. Glutathion treatment increased arsenic accumulation by D. salinaat a concentration of 10-100 mgGSH/L.

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The authors have to estimate the role of bacteria in the larvae culture of bay scallops, Pecten albicans, and investigate the growth and survival of the larvae cultured by two different sea water methods, i.e, a still water system and a flowing water system. In the flowing water system, sea water in the 500 L larval tank flowed out continuously in the amount of 500 L per day. The growth and survival of the larvae in the still water system were found to be higher than those in the flowing water system. The amount of bacteria was almost equal in the two water systems, but genus compositions of bacteria in the flowing water system fluctuated more sharply than those in the still water system. Thus, it is inferred that the growth and survival of the larvae are more affected by the fluctuation of genus composition of bacteria in culture water than by the amount of bacteria. In conclusion, it is necessary to good growth and survival of the larvae that all the genera be stable.

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The effects of rapid changes in salinity and temperature on the elemental composition of sagittal otoliths taken from the juvenile Japanese flounder, Paralichthys olivaceus, were studied using a particle induced X-ray emission (PIXE) technique. Four elements were detected in the otoliths; Ca, Mn, Zn and Sr. Seven days' exposure to low salinity (transfer from 100% to 50% sea water) caused an increase in Sr and a decrease in Zn of the otoliths, while no significant changes were found in Ca and Mn. Thirty and 60 days' exposure to 50% sea water caused a decrease in Sr and a slight increase in Zn and Mn. A rapid drop in culture temperature (transfer from 20°C to 15°C) caused a remarkable increase in Sr concentration in the otoliths on day 7. Zinc concentration also decreased significantly. Thirty and 60 days after the exposure, Sr was slightly higher than that of the control. No significant differences were found in the concentrations of Zn and Mn between the control and the low temperature groups, while Zn decreased slightly 30 and 60 days after the exposure. A similar relationship was also found in each element to the Ca ratio of the otoliths. It was thought that the ratios of Sr and Zn concentrations to Ca in fish otoliths were effective indices (information sources) for predicting the history of environmental conditions experienced by a fish in the past. However, these results also suggest that the physiological fluctuations triggered by radical changes in environmental conditions seriously affect not only the reabsorption rate but also the incorporation rate of various elements into the otoliths in direct or indirect ways. Therefore, effects of the changes in various environmental factors on physiological conditions of fish must be carefully considered for the interpretation of otolith element data.

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Experiments were conducted to asses the application of steelmaking slag for improving the waters and bot-tom sediment, as well as the fish bank in coastal sea areas. We carried out experiments using steelmaking slag in January 1997 when circulation occurs and again in August 1997 when there is stagnation. We measured the water quality, including pH, magnesium, calcium, ammonium nitrogen, nitrite nitrogen and nitrate nitrogen, and observed periphyton on the surface of the slag.
In the area with small steelmaking slag (under 30 mm), we observed that the pH of the sea water close to the slag and the pH of slag interstitial water rose at the time the slag was set. Then the pH of the sea water close to the slag decreased to a level equal to that of the other sea water for several hours after the slag was set. Several hundred hours after the setting, the steelmaking slag did not have any impact on the pH. We observed deposits of hydroxide and carbonate from magnesium in the sea water and we detected elution calcium in the slag, which was thought to be caused by the high pH. Therefore, we observed a decrease in both the ammonium and phosphate content in the slag interstitial water and in the sea water close to the slag.
Growth of diatoms, green algae, neverids worm, barnacles and tunicate were observed on the surface of the slag, and the habitation of gobies, conger eels and crabs were observed in the gaps between the large steelmaking slag (150 mm-70 mm).
From these results, it can be seen that steelmaking slag is applicable to the improvement of water and bottom sediment as well as fish banks.

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