Fingerling Size Research Articles

Toxicity of intermittent chlorination to freshwater fish: Influence of temperature and chlorine form

Fingerling size Salmo gairdneri, Oncorhynchus kisutch, Notemigonus crysoleucas, Cyprinus carpio, and Ictalurus punctatus were exposed in the laboratory three times daily for up to seven days to pulses of either free chlorine or monochloramine. This regime simulated conditions often encountered in the outfall of steam electric generating plants which chlorinate intermittently. LC50's, LT50's and response isopleths giving various percentage mortalities, were computed from the bioassays. S. gairdneri, O. kisutch, and I. punctatus were the most sensitive to both types of chlorine. C. carpio were most resistant and the N. crysoleucas were intermediate in sensitivity. Temperature had relatively little effect on the toxicity of intermittent chlorine to the species tested. In this type of test regime, free chlorine was three to fourteen-fold more toxic (depending on the species) than monochloramine. Water quality criteria for the protection of fish should, in the future, take this differential toxicity into consideration.

Overwinter Survival of Wild Fingerling Brook Trout in Lawrence Creek, Wisconsin

Overwinter survival of brook trout (Salvelinus fontinalis) from the 9-month-old fingerling stage to the 16-month-old yearling stage varied from 35 to 73% during 11 successive winters (1954–65). Mean survival through these first winters of life was 54%.Survival appeared to be independent of fingerling density most winters, and especially when September densities were less than 2200/km, as they were during 7 of 11 years. Overwinter survival tended to increase with an increase in mean length of fingerling stocks (r = 0.83++) and with an increase in winter water temperatures. Intraspecific predation did not appear to be a critical mortality factor. The survival advantage of increased fingerling size was probably related to increased physiological resistance to temperature-associated stresses rather than reduced vulnerability to predation.