Effects of Copper Sulfate on Ion Balance and Growth in Tilapia Larvae (Oreochromis mossambicus)

Abstract

Newly hatched tilapia larvae were exposed to sublethal concentrations of Cu²⁺ (0, 30, 50, and 100 μg/L) and lethal concentrations of Cu²⁺ (200 and 400 μg/L) for 24–96 h. The interaction of the exposure dose and time was related to the Cu²⁺ accumulation rate, which showed a higher accumulation rate with sublethal concentrations of Cu²⁺ within 24 h compared to the other treatments. Furthermore, Cu²⁺ contents in the whole body of larvae significantly increased following Cu²⁺ exposure times up to 96 h. Cu²⁺ in the medium produced a dose-response effect on Na⁺ and K⁺ contents in larvae after 96 h of exposure time. Changes in Ca²⁺ contents statistically significantly decreased and were shown to be dose-responsive for larval exposure times exceeding 72 h. Changes of Ca²⁺ contents were more sensitive than those of Na⁺ and K⁺ with Cu²⁺ treatment of early larvae. Notably Na⁺ and K⁺ contents showed significant increases of 17–23% in larvae exposed to low concentrations of Cu²⁺ (30–50 μg/L) for 24–72 h as compared to control larvae. Cu²⁺ caused no significant effect on body Cl⁻ content or osmolality except at 100 μg/L Cu²⁺ for 24 h in tilapia larvae as compared to the control. However, there was a restoration phenomenon in larvae exposed to 100 μg/L Cu²⁺ for longer than 72 h. The water content of larvae exposed to Cu²⁺ for 96 h significantly decreased. The yolk absorption rate of tilapia larvae was significantly suppressed when they were exposed to Cu²⁺ medium containing 30, 50, 100, 200, or 400 Cu²⁺ μg/L from 72 h post transfer. These results obviously show that larvae are sensitive to Cu²⁺ during early development.