, Volume 264, Issue 3, pp 137-152

An in situ study of rock bass (Ambloplites rupestris) physiology: effect of season and mercury contamination

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Abstract

Selected physiological and biochemical variables were examined in rock bass, Ambloplites rupestris, which were collected on five different sampling dates from an area of chronic mercury contamination and a reference site on the South River, Virginia.

The onset of spawning represented the most significant seasonal influence in the physiological profile of the fish, with elevations in hematocrit, hemoglobin, plasma protein, and plasma glucose. Sex-related differences in plasma calcium, liver glycogen and liver ascorbic acid were also unique to the period. Female rock bass had significantly higher levels of liver glutathione than did males on all but one of the sampling dates, although the cause of this difference is not clear.

Rock bass from the mercury contaminated site had an average muscle mercury concentration of 1.37 mg Hg g−1, and an average liver mercury concentration of 2.86 mg Hg g−1. These levels were approximately an order of magnitude greater than those found in the tissues of the reference fish which averaged 0.165 and 0.101 mg Hg g−1 in muscle and liver respectively. In July 1987, mercury concentrations in the liver of both reference and contaminated fish increased significantly, possibly the result of greater uptake of the metal through increased feeding or changes in the mercury level of selected prey items. Rock bass collected from the two sites in July also had significantly different levels of liver glutathione: reference fish exhibited an elevation and contaminated fish a depression. When fish from the two sampling stations received a 96-hr exposure to 150 µg HgCl2 in the laboratory, both groups exhibited elevated liver mercury and decreased liver glutathione. Mercury levels in the gall bladders of the exposed fish were also elevated, suggesting that glutathione may have been lost through excretion with the metal in the bile.

On the whole, physiological differences between the two groups of rock bass were limited, indicating that exposure to the mercury is not having a significant impact on the rock bass from the contaminated area. This is further supported by field examination of the fish and comparison of condition indices from rock bass previously taken from the same two stations.

Those factors which significantly altered the physiology of the rock bass were unique to certain times of the year, indicating that the most appropriate sampling approach in future studies is one which examines a number of variables over a range of environmental conditions.