THE ACUTE TOXICITY OF PULSE-DOSED THIOCYANATE (AS KSCN AND NASCN) TO RAINBOW-TROUT (ONCORHYNCHUS-MYKISS) EGGS BEFORE AND AFTER WATER HARDENING

The effects of a 3-h pulse exposure of rainbow trout (Oncorhynchus mykiss) eggs to thiocyanate (KSCN and NaSCN) were evaluated. Observations on fertilization success, mortality, incidence of deformaties and embryonic heartrate were recorded for 5 wk at 13.5-degrees-C. The eggs were exposed either immediately after fertilization (before water hardening) or 3 h later after water hardening had begun. Pulse exposure adversely affected the survival and development of the eggs, both before and after water hardening. Significant egg mortality occurred at SCN- concentrations greater-than-or-equal-to 2,700 and 1,290 mg l-1 in the before and after treatments respectively. Alevins that hatched from treated eggs exhibited abnormalities of the tail and spine after exposure to KSCN and NaSCN. Deformities occurred at significantly higher frequencies, relative to controls, at SCN- concentrations greater-than-or-equal-to 85 and 2,700 mg l-1 before and after water hardening respectively. Embryonic heart-rates were not significantly affected by NaSCN.