Endrin: effects on the entire life cycle of a saltwater fish, Cyprinodon variegatus.
The sheepshead minnow (Cyprinodon variegatus) was continuously exposed for 23 wk to the organochlorine insecticide endrin, from the embryonic state through hatching until adulthood and spawing. The resultant progeny were monitored to determine the effects of the toxicant on their survival, growth, and reproduction. Average measured exposure concentrations were O (control), 0.027, 0.077, 0.12, 0.31, and 0.72 microgram/liter. Embryos exposed to 0.31 and 0.72 microgram/liter hatched early; all fry exposed to 0.72 microgram/liter died by day 9 of exposure. At 0.31 microgram/liter, fry were initially stunted and some died. Survivors seemed unaffected until maturity, when some females died during spawning; fewer eggs were fertile and survival of exposed progeny decreased. No significant effects were observed th roughout this fish's life cycle at an exposure concentration of 0.12 microgram/liter. Four-week-old juvenile fish accumulated 2,500 times the concentration of endrin in the exposure water; adults, 6,400 times; and their eggs, 5,700 times. The specific application factor (calculated by dividing the limits on the maximum acceptable toxicant concentration, greater than 0.12 and less than 0.31 microgram/liter, by the concentration lethal to 50% of the juvenile fish in 96 hr, 0.34 microgram/liter) ranged from 0.35 to 0.91. To our knowledge this is the first toxicity test carried out through the entire life cycle of an oviporous esturarine fish. Data from this experiment and from experiments with another estuarine fish and four freshwater fish all demonstrate that there is little difference between endrin concentrations that produce acute effects and concentrations that do not affect the fish in chronic exposures lasting four or more weeks.