Chronic toxicity of waterborne thiocyanate to the fathead minnow (pimephales promelas): A partial life‐cycle study

Juvenile fathead minnows (Pimephales promelas) were exposed to thiocyanate (SCN − ) concentrations of 0, 1.1, 7.3, 16.6, or 32.6 mg/L for 124 d while monitoring growth, physiological, reproductive, and histological parameters. The NOEC for decreased egg production, increased time to first spawn, and development of overt goiter was 1.1 mg/L, whereas the LOEC for these parameters was 7.3 mg/L. Histological changes in thyroidal tissue were the most sensitive parameter observed, with an LOEC of 1.1 mg/L. Fish exposed to 16.6 or 32.6 mg SCN − /L neither completed development of secondary sexual characteristics nor spawned. The LOEC for decreased growth and hematocrit was 32.6 mg/L. SCN − accumulated in the plasma of fish exposed to 16.6 and 32.6 mg/L, with BCFs of 2.7 and 13.8, respectively. Development and mortality of embryos and larvae to 3 d post‐hatch were also monitored in eggs spawned by adults exposed to 0 or 1.1 mg SCN −1 /L and subsequently incubated and hatched at 0, 1.1, 7.3, 16.6, or 32.6 mg/L. Eggs spawned by adults exposed to 1.1 mg SCN −1 /L exhibited increased percentage of eyeup and hatch, while decreasing time to hatch and mortality. There were no effects of SCN − concentration during incubation on egg viability. After the 124‐d exposure, adults were transferred to SCN − ‐free water for 30 d. Insufficient numbers of adults were available from groups exposed to 32.6 mg/L to be included in the recovery study. Eggs were spawned by all groups during the recovery period, regardless of the SCN − preexposure level, although time to first spawn increased with preexposure concentration.