Effect of 17beta-estradiol on gamete quality and maturation in two salmonid species

In the present study the effect of environmentally relevant concentrations of 17beta-estradiol on gamete quality and gamete maturation in rainbow trout (Oncorhynchus mykiss) and grayling (Thymallus thymallus) was investigated. Male rainbow trout were exposed to 0.5-2.5ngl(-1) 17beta-estradiol for 35days during the spawning season. At concentrations of > or =1ngl(-1) the semen volume obtained per male was significantly reduced, and after 50days also the sperm density and the sperm fertility. When male grayling were exposed to 1.0ngl(-1) 17beta-estradiol for 50days during the prespawning season a similar number of males gave semen as in the control. However, the volume of semen produced per male was decreased. The percentage of motile spermatozoa and their sperm swimming velocity were decreased while the percentage of locally motile spermatozoa was increased. In rainbow trout and grayling also the sperm motility pattern was affected by 17beta-estradiol exposure. When female rainbow trout were exposed to 0.5-2.5ngl(-1) 17beta-estradiol and egg portions were stripped in 1 week intervals the egg viability changed in a similar way as in the control indicating that egg overripening processes were not influenced by 17beta-estradiol. When female grayling were exposed to 1.0ngl(-1) 17beta-estradiol during the prespawning time ovulation occurred earlier than in the control group (group exposed to 17beta-estradiol: 35days after the onset of the experiment, control group 35-50days after the onset of the experiment).