The Effects of Long-Term Exposure to Low Concentrations of Hydrogen Sulfide on Brown Trout, Salmo trutta.

Abstract

The effects of long term exposure to low concentrations of hydrogen sulfide on fry of the brown trout, Salmo trutta, were studied. Fifty percent mortality was obtained within 96 h at the two higher experimental concentrations (0.007 and 0.013 mg/1. hydrogen sulfide). The mean 84 and 96-h median tolerance limits (TLm) were 0. 010 ± 1.89 x 10-8 mg/l. and .007 ± 1.88 x 10-8 mg/l. hydrogen sulfide respectively. Exposures to the three lower experimental concentrations ( 0.002, O.OO3 and 0. 005 mg/l. hydrogen sulfide) extended to 8 days in the first bioassay and 22 days in the second . Brown trout fry subjected to these chronic, or sub-lethal, concentrations had survival rates equal to or greater than the controls. The greatest increase in total length occurred at the highest of the chronic concentrations (0.005 mg/l. hydrogen sulfide) and the least increase in total length occurred at the lowest chronic concentration (0.002 mg/l.). Observations of fry held at 0.002 to 0.005 mg/l. hydrogen sulfide also revealed increased respiratory movements, reduced swimming activity and significant gill pathology as compared with control fry. Although chronic concentrations of hydrogen sulfide had a beneficial effect on survival and growth of brown trout fry, concomitant changes in respiration, activity and gill structure suggest the presence of chronic local stress. This stress could reduce the adaptability of the fry and consequently, reduce the success of the species in its rigorous natural environment.