Life-Cycle Toxicity of Bis(Tributyltin) Oxide to the Sheepshead Minnow (Cyprinodon variegatus)

Abstract.

The effects of tributyltin (TBT) to the life cycle of the estuarine fish Cyprinodon variegatus were examined in a 180-day flow-through exposure. The study was initiated with embryos less than 24 h postfertilization and monitored through hatch, maturation, growth, and reproduction under continuous exposure to mean measured TBT concentrations of 5.4, 3.2, 1.3, 0.66, and 0.41 μg TBT/L. Progeny isolated at the onset of reproduction by the parental generation (F₀) were monitored for survival as embryos, survival as fry/juveniles, and growth 30 days postisolation. TBT, at a concentration of 5.4 μg/L, significantly reduced embryo survival of the F₀ generation sheepshead minnows. By day 145 of the exposure, significant effects to the survival of this generation increased and included all test concentrations ≥0.66 μg/L. Survival of 0.66 μg/L was reduced 59% relative to control survival by termination of the F₀ generation. Growth of F₀ generation organisms as measured by standard length was significantly reduced only on day 90 at 3.2 μg/L, however no significant reductions of wet or dry weight related to treatment concentration were detected. Due to complete mortality of organisms exposed to 5.4 μg/L by study day 7, effects to fecundity and progeny were monitored at measured concentrations of 3.2, 1.3, 0.66, and 0.41 μg TBT/L. Fecundity, as measured by the production of viable eggs produced per female per day, was unaffected by any of the test treatments. All F₁ generation embryos isolated from treatment chambers into 3.2 μg/L died. Survival, standard length, wet and dry weight of the F₁ generation at the remaining treatment concentrations were unaffected. The results of this study indicate that exposure to TBT reduced survival of the F₀ generation sheepshead minnow and establishes the lowest observed effect concentration (LOEC) as 0.66 μg TBT/L, and the no observed effect concentration (NOEC) as 0.41 μg TBT/L for this species.