Growth and mortality under low pH of two strains of wild brook trout (Salvelinus fontinalis)

Growth and mortality under low pH of two strains of wild brook trout (Salvelinus fontinalis)

Acid rain -- Environmental aspects

Brook trout -- Effect of water pollution on

Wesner, Jeff

2005

Martin, Thomas

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Two genetically distinct strains of brook trout Salvelinus fontinalis, northern hatchery derived (NBKD and native southern (SBKT), occur in southern Appalachia, an area susceptible to acid deposition. Two experiments were conducted to determine differences in growth under low pH between these strains. In the first experiment, 44 individuals of each strain (88 total fish) were collected from wild populations and maintained in the Aquatic Ecology laboratory at Western Carolina University. Following an acclimation period of at least 30 days in laboratory well water (pH 7.4, 13.4 C), fish were exposed to either pH 5.6 (experimental) or pH 7.4 (control) using a randomized block design with both treatments represented in each of two blocks. pH was maintained in the experimental treatment by the addition of dilute (0.6 mol) sulfuric acid (H2S04). Fish were fed live chopped earthworms at a ration of 3% body weight per day. Fish were measured for wet weight (g) and total length (mm) at the beginning of the experiment and every 14 days thereafter for 8 weeks (56 days). Growth in wet weight and instantaneous growth rates for both total length and wet weight were significantly different between the strains (p < 0.05), but not between treatments. Growth in total length, combined for both strains, was significantly different between both pH treatment and strains, but the interaction of strain and treatment was not significant for any growth measurements, indicating that treatment effect was similar for both strains. Mortality was significantly higher for southern brook trout, but was not affected by pH treatment for either strain. Slow growth and high mortality of SBKT may have been the result of stress due to laboratory conditions. Experiment 2 used only fish that showed positive growth in experiment 1. There were 18 southern strain brook trout that showed positive growth in experiment 1, and all were used in experiment 2. Two tanks containing 9 fish/strain/treatment were used, and maintained at either approximately pH 5.2 or pH 7.4. All fish were fed the same rations as described above. pH did not have a significant effect on any growth measurements. Mean weight of SBKT decreased throughout the experiment, and only 1 fish of this strain showed positive growth in wet weight. Growth was significantly different between strains. Changes in mean relative condition factor were significantly different between strains, with southern strain fish decreasing and northern strain fish maintaining steady values. Mortality was significantly higher in the low pH treatment, but was not different between strains. SBKT that showed negative growth in experiment I were held separately under neutral pH conditions and monitored for growth recovery. These fish showed negative growth in experiment I had zero mortalities and positive mean instantaneous growth rates that were significantly higher than mean growth rates for the same individuals in experiment 1.

2014-07-08

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