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Table 4.2. Fish behaviors associated with insecticide <br />poisoning (modified from South Carolina Depart- <br />ment of Health and Environmental Control 1979). <br />Organochlorine Organophosphorus <br />pesticides pesticides <br />Central nervous system Lethargy <br />disorders <br />Increased ventilation Loss of equilibrium <br />rate <br />Rapid, jerky movements Dark, often reddish, <br />of body and fins <br />Erratic, uncoordinated <br />swimming movements <br />with spasms, convul- <br />sions, and racing <br />Increased sensitivity to <br />external stimuli <br />discoloration; hemor- <br />rhaging in muscles and <br />beneath dorsal fin <br />Hypersensitivity- <br />startled fish involun- <br />tarily swim rapidly in <br />circles <br />Tremors, convulsions, <br />and coughing <br />High excitability Involuntary extension of <br /> pectoral fins and oper- <br /> cula to most forward <br /> position possible <br />Loss of equilibrium with Spinal abnormalities <br />successively longer <br />periods of quiescence <br />until respiratory move- <br />ment ceases <br />Chemical Changes Related <br />to Toxic Substances <br />The toxicity of a substance refers to its potential <br />for having a harmful effect on a living organism. <br />Toxicity is a function of concentration and the dura- <br />tion of exposure. Acute effects occur rapidly as a <br />result of a short-term exposure to a relatively high <br />concentration of a toxicant. Generally, acute effects <br />are severe and usually include mortality (Rand and <br />Petrocelli 1985). However, fish kills may also be in- <br />duced by the entry of sublethal levels of toxicants <br />through the food chain. Such kills are usually not <br />acute and do not occur at a particular time of year <br />or affect a particular life stage. <br />Frequently, the introduction of a toxic substance <br />causes no change in the water chemistry, but may <br />leave residues in the water, sediment, or animal <br /> <br />tl? <br /> <br />Top photo. Cladocerans such as Bosmina longirostris are <br />highly sensitive to toxic substances. Their presence out- <br />side the affected area but absence in the kill zone is a <br />valuable clue to the possible cause. Bottom photo. Plank- <br />ton nets are used for collecting zooplankton to check for <br />toxic effects. <br />tissues. These materials should be checked because <br />the results may yield significant information and <br />may provide the first firm evidence that a toxic <br />substance is involved. Preliminary analyses may pro- <br />vide the following information: <br />Water <br />• Water chemistry is normal for the current season <br />and local area <br />• Some water constituents are abnormal and in a <br />range known to be toxic <br />• A suspect toxicant has been detected in quantities <br />known to be toxic <br />TOXIC SUBSTANCES 21 <br /> <br /> <br />I