Plasma steroids in mature common dentex (Dentex dentex) stimulated with a gonadotropin-releasing hormone agonist.

The aim of this study was to identify the major C21 steroids produced in vivo during artificially induced final oocyte maturation and spawning in female common dentex (Dentex dentex). During the spawning season, mature females were treated with a gonadotropin-releasing hormone agonist (GnRHa)-loaded delivery system, with or without pimozide (given as a single dose at the beginning of the experiment). Blood samples were collected at various intervals during the experiment and were assayed for GnRHa, 17,20beta-dihydroxy-4-pregnen-3-one (17,20beta-P), and 17,20beta,21-trihydroxy-4-pregnen-3-one (17,20beta,21-P). A higher percentage of ovulated females was observed in GnRHa-implanted fish, which produced over 10 times more eggs than controls. Relative fecundity was highest in the GnRHa + pimozide group and lowest in controls. The viability of naturally released eggs was low (2 to 15%) in all groups. Plasma concentrations of 17,20beta-P in GnRHa-implanted fish did not increase, but those in control fish decreased, such that there was a significant difference between control and treated fish between 2 and 10 days after treatment. In another experiment, ovulating common dentex were injected intramuscularly with a single dose of 50 microg kg(-1) of GnRHa in saline and were sampled for blood at 0, 3, 6, 12, and 24 h postinjection. A single water sample was taken from the tanks at 9 h postinjection, the tanks having been emptied and refilled at 6 h. Measurements were made of plasma and water concentrations of free and conjugated 17,20beta-P, 17,20beta,21-P, 17beta-oestradiol (E2), and GnRHa (plasma only). The GnRHa injection increased plasma levels of all steroids, with free 17,20beta-P reaching maximal levels within 3 h. GnRHa treatment also increased the amounts of free and conjugated steroids released into the water between 6 and 9 h.

Effect of chronic irradiation on the humoral immune response of a marine fish, the eelpout (Zoarces viviparus L.).

Eelpout (Zoarces viviparus), a marine fish, were exposed to gamma-radiation at a dose-rate of 2.0 mGy h-1. They were injected with the antigen trinitrophenyl-keyhole limpet haemocyanin (TNP-KLH) and their specific humoral immune response to the TNP hapten measured. There were no differences in the primary antibody response between unirradiated controls and treated fish. However, the response to a second injection of antigen was significantly increased in irradiated fish. There were no significant radiation effects on total serum protein or serum lysozyme. Radiation effects on testis were also examined and there was a significant radiation-induced reduction in relative weight (gonadosomatic index). These results are discussed with reference to environmental radiation levels in areas of authorized radioactive waste disposal.