The effects of Sumithion, an organophosphate insecticide, on the behaviour of juvenile coho salmon, Oncorhynchus kisutch Walbaum
Date
1971
Authors
Bull, Christopher John
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Abstract
Bioassays based on the measurement of unconditioned behaviours reflect the energy status and general well being of the test organism. Therefore, they offer a more objective basis for establishing acceptable limits of environmental contamination than do standard, lethal concentration, bioassays. This study explores the effects of sublethal concentrations of Sumithion on a variety of unconditioned behaviours of underyearling coho salmon, mostly included in the general categories of feeding, agonistic, and comfort behaviours. The major habitat features of the test fish were duplicated in the stream aquarium in which behaviours were observed. Test concentrations of Sumithion corresponded to zero, 10, 25, 50, and 80% of the 96 hour median tolerance limit (TLm₉₆) which is 1.30 mg/liter. In concentrations ranging up to 25 to 50% TLm96, feeding and agonistic behaviours declined exponentially whereas comfort movements increased in frequency. In this phase, termed the motivational impairment phase, the changing patterns of behaviour appeared to be a direct response to irritation rather than to serious physiological impairment. In the next phase (concentrations up to 80% TLm₉₆), all behaviours except coughing declined in frequency. In addition, changes in spatial distribution occurred so that many fish were swept downstream and pinned against the aquarium screens. The overall pattern of behavioural changes indicates that Sumithion concentrations greater than 25 to 50% TLm₉₆ cause serious physiological impairment. Below this level feeding is substantially reduced and social behaviours, which are an integral part of territory maintenance, are altered. Clearly prolonged exposure at such concentrations would seriously impair growth and ultimately survival. Short term exposure to such concentrations might be acceptable depending on how rapidly body levels of Sumithion, which accumulate to concentrations well above those of the surrounding water, can be eliminated. An acceptable level for prolonged exposure would be less than 10¼ TLm₉₆. Additional work would be required to define this level more precisely.