The effects of pulse-exposed cadmium and zinc on embryo hatchability, larval development, and survival of Australian crimson spotted rainbow fish (Melanotaenia fluviatilis)

Effects of 2 h pulse-exposure of cadmium or zinc on early life stages of Australian crimson spotted rainbow fish (Melanotaenia fluviatilis) were investigated. Ages of embryos used in experiments were 3, 46, and 92 h old. Measured end points included percentage hatch, day of hatch, larval survival time, and spinal deformities. There was a significant concentration-response of both metals on percentage hatch and spinal deformities. The 3-h-old embryos had highest percentage of deformities with 27% for embryos pulse-exposed to both 3.3 mg/L of cadmium and 33.3 mg/L of zinc. Cadmium 2 h peLC50 (SE) values (n=4) for <24-h-, 3–4-day-, and 9–10-day-old larval rainbow fish were 0.13 (0.01), 0.11 (0.01), and 0.56 (0.11) mg/L, respectively. Zinc 2 h peLC50 (SE) values for the same aged rainbow fish larvae were 0.51 (0.03), 0.56 (0.04), and 1.57 (0.22) mg/L, respectively. For both metals, 9–10-day-old larvae were significantly more tolerant than younger ages. Within each of the age groups, larvae were significantly more sensitive to cadmium than zinc. Continuous exposure LC50 (SE) values (n=4) using 9–10-day-old larvae were 0.01 (0.00) and 0.27 (0.01) mg/L for cadmium and zinc, respectively. Results show that pulse-exposed metals at moderate concentrations can significantly affect the early life stages of M. fluviatilis through decreasing percentage hatch of embryos, inducing spinal deformities, and having toxic effects on larvae at relatively low concentrations. Thus, the sensitive early life stages of M. fluviatilis are a suitable model for toxicity testing of metals on Australian species of fish.