Copper sulfate toxicity to channel catfish fry: Yolk sac versus swim-up fry

Authors: Straus, David - Dave

Submitted to: North American Journal of Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/14/2007
Publication Date: 7/31/2008
Citation: Straus, D.L. 2008. Copper sulfate toxicity to channel catfish fry: Yolk sac versus swim-up fry. North American Journal of Aquaculture. 70(3):323-327.

Interpretive Summary: Copper sulfate is used for fungus control on channel catfish eggs in the hatchery. Yolk-sac fry (1 day old fry that have a yolk-sac) and swim-up fry (fry that were 7 days old that have absorbed the yolk-sac) were put in different solutions of copper sulfate to determine how much it takes to kill 50% of the fry in a container (this is called the LC50 value and it is used to compare toxicity of different chemicals). We also wanted to see if this toxicity was related to how old they were in well water and in well water diluted 50% with deionized water. Yolk-sac fry were more tolerant of copper sulfate than swim-up fry by about 4.4-fold. This study also showed that fry are more sensitive to copper sulfate in well water diluted with deionized water (softer water) by about 4-fold than in well water (harder water); this is normally what you will find in copper toxicity studies. There are few instances where copper sulfate would be administered to swim-up fry unless they are located in a hatching trough that also contains eggs being treated for fungus control; data provided in this study shows that this situation should be avoided. This information will help hatchery managers and extension personnel formulate safer and more effective application rates for copper sulfate.

Technical Abstract: Channel catfish yolk-sac fry and swim-up fry from 5 separate spawns were exposed to dissolved copper sulfate (CuSO4) in a series of static toxicity experiments to observe age sensitivity in high and moderate alkalinity waters at 24 and 48 hrs at 23.1°C. The waters had total alkalinity and total hardness of 217 and 126 mg/L (as CaCO3), in filtered well water (high alkalinity) and 112 and 66 mg/L (as CaCO3) in filtered well water diluted 50% with deionized (DI) water (moderate alkalinity), respectively. Probit LC50 values were calculated using nominal CuSO4 concentrations. The mean 24-hr median lethal concentration (LC50) values for yolk-sac fry were 62.8 and 10.2 mg/L CuSO4 in high and moderate alkalinity, and the mean LC50 values for swim-up fry were 13.5 and 4.3 mg/L CuSO4 in high and moderate alkalinity, respectively. The mean 48 hr LC50 values for yolk-sac fry were 14.9 and 3.9 mg/L CuSO4 in high and moderate alkalinity, and the mean LC50 values for swim-up fry were 3.5 and 1.5 mg/L CuSO4 in high and moderate alkalinity, respectively. Channel catfish yolk-sac fry are more tolerant of CuSO4 than channel catfish swim-up fry by about 4.6-fold at 24 hrs and by 4.3-fold at 48 hrs. This study also demonstrates that channel catfish fry are more sensitive to CuSO4 in waters with moderate alkalinity by 4.7-fold at 24 hrs and by 3.3-fold at 48 hrs than in waters with high alkalinity.