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Sublethal effects of mercuric chloride on some aspects of behaviour of anadromous fish Prentice, Norman David Joseph


The effects of short term exposures to sublethal doses of mercuric chloride were studied using species of anadromous fish. Aspects of grou/th and behaviour u/ere used as indicators of physiological and psychological malfunctions due to mercurialism. The characteristic migration tendencies ( upstream or downstream ) of Lower Babine and Fulton River alevins were tested in experimental laboratory channels. The were conducted in a chamber in which a day, dawn through dusk, could be simulated. Each stock was divided into three groups and each group was assigned a level of treatment ( control, 0.5 ppm and 1.0 ppm HgCl₂ ). The performance of the fish in each group placed in the channels was scored. An analysis of data obtained from the migration experiments indicated that sublethal mercurialism had a disruptive influence on migration patterns of Sockeye salmon alevins. The lower level of intoxication produced a downstream drift in both stocks while the fish treated at the higher level of intoxication showed an upstream migrational tendency in both stocks. The effects of sublethal mercurialism on growth were studied using Sockeye, Chum, and Coho salmon fry. The fish received standard daily feedings. The fed fish for each of the species were divided into three treatment groups ( control, 0.5 ppm and 1.0 ppm mercuric chloride ) .Weight data were collected and analyzed using regression analysis and the analysis of covariance. The fed Sockeye and Chum salmon fry showed a significant weight loss (⍺= 0.05 ) in the 0.5 ppm and the 1.0 ppm treatments when compared to their respective controls. There was no significant difference in weight between treatments in the fed Coho salmon experiment. A six week starvation experiment was designed to test if there were any significant differences in weight loss between control fish and fish treated with 0.5 ppm and 1.0 ppm mercuric chloride. Regression analysis and the analysis of covariance did not reveal any statistically significant differences on the rates of weight loss. A flight responce experiment was conducted using Coho salmon prey and predators. Wild and hatchery Coho salmon prey were used with hatchery Coho predators. Three treatment levels of mercuric chloride were administered ( control, 0.5 ppm and 1.0 ppm ), Prey and predators were placed in an experimental laboratory performance channel and, after a timed exposure to each other, scores indicative of flight responce mere obtained. The data was analyzed using the Kolmogorov-Smirnov Large sample : one tailed test. No significant differences in the responces between treatments were noted for the hatchery Coho. The wild Coho prey treated with 0.5 ppm and 1.0 ppm mercuric chloride had a statistically significant differences when compared to their controls. It was noted that as the level of intoxication increased the the level of flight responce decreased. The results of the above experiments indicate that mercurialism has measurable effects on the physiology and psychology of fish at sublethal level.

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