Copper Sulfate Toxicity to Channel Catfish Fry: Yolk Sac versus Swim-Up Fry

Abstract

Yolk sac and swim-up fry from five separate spawns of channel catfish Ictalurus punctatus were exposed to dissolved copper sulfate (CuSO₄) in a series of static toxicity bioassays to observe age sensitivity at 24 and 48 h in waters with two different chemistries at a temperature of 23.1 ± 0.47°C (mean ± SD). The two waters were (1) well water with a total alkalinity (as CaCO₃) of 217 mg/L and a total hardness of 126 mg/L and (2) a 1:1 mixture of well water and deionized (WDI) water with a total alkalinity of 112 mg/L and a total hardness of 66 mg/L. Probit median lethal concentration (LC50) values were estimated with PoloPlus using the nominal CuSO₄ concentrations. The mean 24-h LC50 values for the yolk sac fry were 62.8 ± 37.1 mg of CuSO₄/L in the well water and 10.2 ± 3.4 mg/L in the WDI water; the 24-h LC50 values for the swim-up fry were 13.5 ± 11.5 mg/L in well water and 4.3 ± 4.4 mg/L in WDI water. The mean 48-h LC50 values for the yolk sac fry were 14.9 ± 5.0 mg/L in well water and 3.9 ± 1.6 mg/L in WDI water; the 48-h LC50 values for the swim-up fry were 3.5 ± 1.8 mg/L in well water and 1.5 ± 0.3 mg/L in WDI water. The yolk sac fry were about 4.6 times more tolerant of CuSO₄ than the swim-up fry at 24 h and 4.3 times more tolerant at 48 h. Fry were about 4.7 times (at 24 h) and 3.3 times (at 48 h) more sensitive to CuSO₄ in water with low alkalinity and hardness (WDI water) than in water with high alkalinity and hardness (well water). The differences in LC50 values between the different spawns of each fry type and time within a water type are attributed to natural variation and channel catfish strain.