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<br />t <br /> <br />1 <br />I <br />Fish Chalet Pond. Goede and Gates (1979) said the following about the <br />effect of H2S on fish: <br />Hydrogen sulfide is described by toxicologists as a sec- <br />ondary irritant. ...It acts directly upon the nervous <br />system resulting in paralysis of the respiratory center <br />and has a paralyzing effect on the olfactory system. The <br />irritant action contributes to death by asphyxiation... <br />Wood (1960) states that hydrogen sulfide causes edema <br />under the epithelium of gill lamellae thus inducing thick- <br />ening or swelling of lamellae to a non-functioning <br />state ...It has been suggested that fish would avoid local <br />i concentrations of hydrogen sulfide but facts contradict <br />this suggestion. The paralysis of the olfactory response <br />as indicated in the literature would preclude this possi- <br />bility. If this mechanism works in fish as it does in <br />mammals they would not detect H2S after initial exposure <br />and thus would not move out of contaminated areas. <br />Given that fish predation and cestode parasitism were apparently not <br />responsible for the complete elimination of Fish Chalet squawfish, mortal- <br />ity there might be attributed to (1) invasion by bacterial or fungal <br />parasites due to poor health (or perhaps outright starvation) resulting <br />from inadequate forage, (2) dissolved oxygen occassionally slipping below <br />critical levels, (3) asphyxiation during late winter or early spring from <br />elevated concentrations of hydrogen sulfide, or (4) an undetected disease. <br />j The complete elimination of groups of stocked squawfish from Fish Chalet <br /> <br />1 20