Changes in brain dopamine levels, oocyte growth and spermatogenesis in rainbow trout, Oncorhynchus mykiss, following sublethal cyanide exposure.

Whole brain dopamine (DA) and norepinephrine (NE) levels were measured in sexually maturing (2 years +) male and female rainbow trout, Oncorhynchus mykiss, following exposure to 0.01 mg/L hydrogen cyanide (HCN). Following a 12 day exposure period in July and August 1988, whole brain DA levels of HCN exposed fish were significantly higher (p less than 0.05), relative to control fish, as measured by high performance liquid chromatography (HPLC). Brain NE levels were unaffected by HCN exposure. Whole brain DA and NE levels showed a strong correlation in control fish (r = +0.81), but not in HCN exposed fish (r = +0.28), likely due to altered DA levels in the latter group. No significant differences were found in brain DA and NE levels between males and females. Mean diameters of oocyte from ovaries of the vitellogenic females were significantly (p less than 0.01) reduced from 226 to 183 microns in control and HCN exposed fish respectively. Testes from males revealed significantly (p less than 0.001) higher numbers of spermatogonial cysts in HCN exposed fish. Evidence is given that chronic exposure to sublethal levels of HCN significantly alters brain DA levels in both sexes of rainbow trout, reduces growth in vitellogenic oocytes of the ovary in females and interferes with the passage of spermatogonia to the spermatocyte stage in sexually maturing males. Collectively, these results suggest that sublethal HCN affects the reproductive mechanisms via the hypophyseal-gonad axis in sexually maturing rainbow trout.