Research Product

The toxicity of total residual chlorination (TRC) to early life stages of the striped bass, Morone saxatilis, was determined using percent embryo hatchability, incipient LC50 bioassays, histopathology, and avoidance responses. Beginning 8 to 9 hours after fertilization, developing embryos were exposed continuously to TRC in flowing water at 1.0-3.0 ppt salinity and 18 ± 1 C. Fifty-six percent of the control group (no TRC exposure) hatched. None of the embryos exposed to a measured TRC concentration of 0.21 mg/l hatched. Only 3.5 percent of the embryos exposed to 0.07 mg/l TRC and 23 percent of those exposed to 0.01 mg/l TRC hatched. Incipient LC50 bioassays were used to determine the sensitivity of 2-, 12- and 30-day-old striped bass to concentrations of TRC in flowing water (1.0-3.0 ppt salinity at 18 ± 1 C). The estimated incipient LC50 was 0.04 mg/l TRC for 2-day-old prolarvae, 0.07 mg/l for 12-day-old larvae and 0.04 mg/l for 30-day-old juveniles. Histological examination of 30-day-old juveniles which survived exposure in the incipient LC50 bioassay indicated gill and pseudobranch damage for fish exposed to 0.21 to 2.36 mg/l TRC. Statistical analysis of avoidance tests conducted at 1.0-3.0 ppt salinity and 18 ± 1 C with 24-day-old larvae showed significant (X2, p < 0.05) and reproducible avoidance responses to measured TRC concentrations of 0.79-0.82 mg/l and 0.29-0.32 mg/l. No avoidance was indicated at TRC concentrations of 0.16-0.18 mg/l.