No abstract

ABSTRACT. Clothianidin (CTD) is a neonicotinoid developed in the 1990s as an insecticide having selective toxicity, but it was later found to cause reproductive abnormalities in rats through oxidative stress. There is an attempt to preserve endangered animals, including the Japanese crested ibis, in Japan. However, there is a concern that neonicotinoid affects the reproduction of this bird, since it is used in its habitat. CTD toxicity in the birds is poorly understood, so we investigated whether or not the daily oral administration of CTD has any deleterious effects on the reproductive functions of mature male quails as experimental animals. The animals were randomly divided into four groups of 6 or 7 quails each, treated orally with 0, 0.02, 1 or 50 mg CTD/kg body weight (Control, CTD0.02, CTD1 and CTD50). After that the males bred with untreated females to estimate the egg weights, and rates of fertilization and normal development, the testes, liver and spleen were examined histologically. Vacuolization and the number of germ cells having fragmented DNA in seminiferous tubules, and the number and size of vacuoles in hepatocytes increased dose-dependently. There were no significant differences in egg weights and fertilization rates between the groups, but some eggs of the CTD1 and CTD50 groups failed to develop, and embryonic length decreased dose-dependently. Thus, it was found that CTD affected the reproduction of the male quail through the fragmentation of germ cells and the inhibition or delay of embryonic development.

For bioremediation of organically enriched sediment deposited below fish farms, the extremely high potential for population growth of a deposit-feeding polychaete, Capitella sp. I, in the organically enriched sediment, and the effect on decomposition of organic matter in the sediment, were examined. A mass-culturing technique was conducted for this species. Bioremediation experiments were conducted on the organically enriched sediment in a fish farm in Kusuura Bay, Japan in 2003-2006. Approximately 1.7 million individuals of the worms were placed on the sediment below one net pen in December 2003, 9.3 million individuals in November 2004, and 2.2 million individuals in November 2005. After the worms were spread on the sediment, they rapidly increased in number and reached the highest densities of approximately 134 000 inds/m 2 in February 2004, 527 000 inds/m 2 in March 2005 and 103 000 inds/m 2 in January 2006.In the process of rapid population growth, the decomposition of the organic matter of the sediment was enhanced markedly. Our results demonstrate that the promotion of population growth by spreading cultured colonies of Capitella can enhance the decomposition rate of organic matter markedly in organically enriched sediment below fish farms. This method is promising for minimization of the negative effects of fish farms.

Fish farming using net pens has become very widespread in the coastal areas of various countries in the sediment and to prevent further progress of the organic enrichment of the sediment below the fish farm.

Bacterial abundance, electron transport system activity (ETSA) and organic matter content (total organic carbon [TOC], total nitrogen [TN] and chl a) on the burrow wall of the mud shrimp Upogebia major were determined and compared with those in surrounding non-burrow sediments and on the tidal-flat surface. The values of each parameter in burrow sediment tended to decrease outwardly from the wall, while bacteria abundance was highest in the subsurface of the burrow wall. In summer, the abundance of bacteria on the burrow wall was double that in the non-burrow sediments. In winter, both bacterial abundance and ETSA were at the same level as those in nonburrow sediments. The levels of TOC and TN on the burrow wall were more than 3 times higher than those in non-burrow sediments, regardless of the season. However, there was no significant difference in chl a content between burrow wall and non-burrow sediments. These results suggest that fresh organic matter in the burrow wall is supplied from the tidal-flat surface, making the burrow environment a suitable niche for microbial populations in the sediment. The mud shrimp burrow functions as a trap for organic matter and thus, helps prevent the outflow of carbon and nitrogen from the tidal flat.