Nucleic Acid, Protein Content, and Growth of Larval Fish Sublethally Exposed to Various Toxicants

Larval fathead minnows (Pimephales promelas) were exposed for 96 h to several concentrations of benzophenone, ethyl acetate, hexavalent chromium, hydrogen cyanide, or p-cresol. The range of "safe" concentrations determined from 96-h macromolecular content (RNA, DNA, and protein) and growth was within or very near the range of "safe" concentrations determined by concomitant longer term exposure (28- to 32-d early life stage toxicity test). RNA, DNA, and protein content per larva and RNA/DNA ratio were sensitive to toxicant stress and followed a log-linear dose response. Larval RNA content appeared to be the 96-h measurement most responsive to toxicant exposure. A disruption of nucleic acid and protein metabolism apparently occurred within 96 h of sublethal toxicant exposure and resulted in (1) decreased rates of mitosis, (2) reduced protein synthesis, and (3) reduced growth. Measurement of growth and macromolecular content after a 96-h larval exposure provided a physiologically relevant measurement of toxicity that was predictive of longer term sublethal toxicity.