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28 JOSEPH B. HUNN AND ROSALIE A. SCHNICK
<br />the length of exposure is long enough. Although data
<br />obtained from 24-hour exposures are most appropri-
<br />ate for use in evaluating an acute kill situation, data
<br />from 24-, 48-, and 96-hour tests can also be used to
<br />estimate the toxicity of a substance suspected of
<br />causing the kill. The 95% confidence interval estab-
<br />lishes a range for the LC50 and is helpful in deter-
<br />mining whether the concentration of chemical found
<br />in the field was high enough to cause acute toxicity
<br />(Mayer and Ellersieck 1986).
<br />Sources of
<br />Toxicity Information
<br />One of the best sources of information on toxicity
<br />developed since 1970 is the data base AQUIRE. It
<br />includes information on acute and chronic toxicity,
<br />bioaccumulation, sublethal effects, chemical sub-
<br />stance information, details on test organisms, study
<br />protocols, experimental design details, and results.
<br />Bibliographic references to the original sources are
<br />included. AQUIRE is one of the Chemical Informa-
<br />tion System components sponsored by the Office of
<br />Toxic Substances of EPA. The data base focuses on
<br />the toxic effects of chemical substances on fresh-
<br />water and saltwater organisms, other than aquatic
<br />mammals, birds, and bacteria. As of July 1988,
<br />about 68,000 records were available on more than
<br />4,000 chemicals.
<br />The following references are sources for toxicity
<br />information: McKee and Wolf (1963); EPA (1973,
<br />1977, 1980-1989, 1983-1989, 1986); Thurston et al.
<br />(1979); Alabaster and Lloyd (1982); Rand and Petro-
<br />celli (1985); U.S. Department of the Interior (1985-
<br />1989); Mayer and Ellersiek (1986); Mance (1987);
<br />Mayer (1987); and Weed Science Society of Ameri-
<br />ca (1989).
<br />Clinical Signs of Toxicosis
<br />Few of the signs related to fish poisoning are
<br />unique to a particular compound or group of com-
<br />pounds. For example, if adequate oxygen is available
<br />in the water at the time of exposure, cyanide poison-
<br />ing results in bright red gills and blood because the
<br />available oxygen cannot be used at the tissue level.
<br />This condition might lead an investigator to assume
<br />that water conditions were normal; however, there
<br />will be hemorrhages and blood clots in the liver and
<br />viscera.
<br />Acetylcholinesterase-inhibiting compounds (e.g.,
<br />organophosphates or carbamates) reduce brain
<br />levels of cholinesterase activity, induce a forward
<br />positioning of the pectoral fins in moribund scaled
<br />fishes, and may induce spinal abnormalities.
<br />High concentrations of nitrite can induce methe-
<br />moglobinemia, a condition that is characterized by
<br />brown blood. However, hydrogen sulfide can also
<br />bind to hemoglobin to produce sulfhemoglobin,
<br />which also results in dark, chocolate-colored blood.
<br />Exposure to sulfide reduces the level of cytochrome
<br />oxidase in fish tissues and increases the levels of
<br />thiosulfate in the blood, kidney, and spleen.
<br />The clinical signs listed must be observed in
<br />freshly dead or moribund fish because they disap-
<br />pear soon after the fish die. Other signs that have
<br />been observed in relation to toxicant-caused fish kills
<br />are listed in Table 4.4. It should be noted that the
<br />listed signs and behavioral responses (Tables 4.1 and
<br />4.2) are not strictly diagnostic as to the cause of
<br />death, but they provide useful information in devel-
<br />oping evidence.
<br />Table 4.4. Clinical signs associated with toxicosis
<br />in fish (modified from U.S. Department of the
<br />Interior 1970).
<br />Sign Possible causative agent
<br />White film on gills, skin, Acids, heavy metals,
<br />and mouth trinitrophenols
<br />Sloughing of gill Copper, zinc, lead,
<br />epithelium ammonia, detergents,
<br /> quinoline
<br />Clogged gills Turbidity, ferric hydroxide
<br />Bright red gills Cyanide
<br />Dark gills Phenol naphthalene,
<br /> nitrite, hydrogen sulfide
<br /> low oxygen
<br />Hemorrhagic gills Detergents
<br />Distended opercles Phenol, cresols, ammonia,
<br /> cyanide
<br />Blue stomach Molybdenum
<br />Pectoral fins moved to Organophosphates,
<br />extreme forward carbamates
<br />position
<br />Gas bubbles (fins, eyes, Supersaturation of gases
<br />skin, etc.)
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