Graduate Thesis Or Dissertation
 

Predator-prey interactions under the influence of ammonia

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  • Predator-prey interactions, as measured by the consumption and growth rates of a predator (Micropterus salmoides) and by the observed activities of both predator and prey (Gambusia affinis), were found to be sensitive to sublethal levels of ammonium chloride (reported as unionized ammonia NH₃). One bass and 15, 30, 60 or 120 mosquitofish were placed in each of 13 150 liter aquaria, designed with uniform cover for the prey, and allowed to interact for ten days. These prey densities were maintained by restocking every 24 hours, thus providing a wide range of food availability for the predators. Experiments were first run without adding ammonium chloride in order to establish baseline responses of both predators and prey. The system was then exposed to a range of toxicant concentrations from 0.13 mg/l to 0.86 mg/1 NH₃. Responses of predators and prey were measured and compared to the baseline data. Consumption and growth rates of the unexposed bass increased with increasing prey densities. Consumption rates ranged from one to ten percent of mean dry weight of bass per day, growth rates from a loss of two percent to a gain of three and one-half percent of mean dry weight of bass per day. Exposure to low levels of NH₃ had no observable effect on the interactions. When exposed to toxicant concentrations higher than 0.34 mg/l NH₃, substantial decreases in consumption and growth rates were found for bass in experiments with prey densities above 15. These deviations from the baseline correlated well with prey density in that the effects were greatest at high prey densities where the bass were being continuously harassed by the mosquitofish. The utility of this type of bioassay approach to aquatic pollution is discussed.
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