Comparison of azinphosmethyl toxicity to juvenile red drum (Sciaenops Ocellatus) and the mummichog (Fundulus Heteroclitus)

The acute and sublethal responses of juvenile red drum (Sciaenops ocellatus) and mummichogs (Fundulus heteroclitus) were evaluated to determine the relative effects of exposure to azinphosmethyl (APM). Acute responses were based on 96-h static-renewal bioassays at salinities of 5 and 20%. Sublethal responses were based on inhibition of brain acetylcholinesterase (AChE) activity after 24-h exposures at each salinity and by measuring behavioral and stamina (swimming ability) responses of each species. The acute toxicity tests indicated that juvenile red drum were significantly more sensitive to APM than were mummichogs (mean lethal concentration [LC50] = 6.3-7.1 microgram/L versus 65-84 microgram/L). No significant differences were noted in the LC50 response of either species at reduced salinities. In contrast, mummichogs were more sensitive to APM-induced inhibition of brain AChE activity than juvenile red drum (mean effective concentration [EC50] 1.0 microgram/L in mummichogs and 5.0 microgram/L in red drum). Behavioral response tests indicated that neither species avoided pesticide-laden water, which may increase their vulnerability to APM runoff. Stamina assays indicated that juvenile red drum experienced a decreased ability to swim after a 6-h exposure to 12 microgram/L APM. Mummichogs were less sensitive with respect to the effects of APM on swimming ability at concentrations as high as 24 microgram/L APM (p 0.1)