Laboratory experiments were conducted to determine the acute and chronic effects of endrin to estuarine fishes. Short-term bioassays in flowing seawater determined 24-hour LC50's for spot (Leiostomus xanthurus), mullet (Mugil cephalus), menhaden (Brevoortia patronus), longnose killifish (Fundulus similis), and sheepshead minnows (Cyprinodon variegatus). A population of spot was exposed continuously for eight months to a sublethal concentration (0.05 ppb.). No pathology was found in the spot after seven months of exposure, but, a three-week exposure to a near-lethal concentration (approximately 0.075 ppb.) produced pathology characterized by systemic lesions involving the brain and spinal cord, liver, kidneys and stomach. Residue analyses (gas chromatography) of spot exposed to 0.05 ppb. endrin for five months revealed an accumulation of 78 ppb. (micrograms/kilogram). No endrin could be detected in these fish after a 13-day holding period in uncontaminated water. Chronic exposure of spot to endrin did not affect their tolerance to sudden changes of salinity. Endrin-exposed fish were also able to endure extended periods of starvation. Sublethal concentrations of endrin do not appear to affect the general physical condition of spot. The threshold of toxicity is extremely critical and the importance of time must not be underestimated in determination of a sublethal concentration of endrin for fish.
