Effects of turbidity on survival of larval ayu and red sea bream exposed to predation by jack mackerel and moon jellyfish

We conducted laboratory experiments to examine the effects of turbidity on the survival of red sea bream Pagrus major and ayu Plecoglossus altivelis altivelis larvae when exposed to either visual (jack mackerel juveniles) or tactile (moon jellyfish) predators. The experiments were conducted in 30-l tanks with three different levels of turbidity obtained by dissolving 0, 50, or 300 ppm kaolin. Predators were introduced to the experimental tanks followed by larvae of either red sea bream (mean ± standard deviation 6.1 ± 0.3 to 11.4 ± 2.1 mm standard length) or ayu (6.6 ± 0.3 and 24.4 ± 1.8 mm). When exposed to jack mackerel, the mean survival rate of larvae was significantly higher in 300 ppm treatments compared with the other turbidity levels. When exposed to moon jellyfish, however, there was a less marked difference in the survival rates among different turbidity treatments. Survival rates of ayu larvae exposed to moon jellyfish were generally lower than those of red sea bream. Our study indicates that anthropogenic increases of turbidity may increase the relative impact of jellyfish predation on fish larvae.     

Spleen-Specific Development of Germinal Centers in Rats Treated with Antithyroid Drugs

The antithyroid drugs (ATDs) methimazole (MMI) and propylthiouracil (PTU) have been used for treatment of hyperthyroidism for more than several decades, despite the fact that they are associated with adverse drug reactions that are thought to be autoimmune mediated. We therefore examined histopathologic responses in the immune system in male and female rats given MMI (2, 20 and 200 mg/kg/day, p.o., in experiment 1; 200 mg/kg/day, p.o., in experiment 3) or PTU (25 and 250 mg/kg/day, p.o., in experiment 2; 200 mg/kg/day, p.o., in experiment 3) for two weeks. In experiments 1 and 2, highest doses of MMI and PTU induced histopathologic changes in the spleen consistent with those in experiment 3 without any changes in the other peripheral lymphoid organs and tissues. In experiment 3, histopathological evaluation of the spleen along with hematological and bone marrow examinations were performed. In both male and female rats, MMI or PTU induced histopathological changes in the spleen characterized by development of germinal centers and an increase in the number of IgG-positive plasma cells in the red pulp; these changes were most prevalent in the MMI-treated female rats. Total red and white blood cell counts were decreased in the MMI-treated male and female rats; lymphocytes and monocytes were lower in male and female rats, respectively. Bone marrow nucleated cells were significantly lower in the MMI-treated males. This is the first study to demonstrate that ATDs induce spleen specific B-cell reactions in rats