Which fish species are noted as very susceptible to copper sulfate?

• A. Trout and carp
• B. Goldfish and koi
• C. Largemouth bass
• D. Catfish

Answer: (A)

Copper sulfate acts as an algaecide by releasing copper ions, which are highly toxic to fish. Different species vary in sensitivity, and trout and carp are noted as very susceptible because their gill tissues absorb copper readily, making them more vulnerable to toxicity. Water chemistry matters a lot: in softer, more acidic water, copper ions are more available and toxic, so these species can be harmed at lower concentrations than others. Labels often warn against using copper sulfate in waters containing trout or carp or connected to habitats where these fish could be exposed. Other fish like goldfish and koi, largemouth bass, and catfish can be affected as well, but they are not typically singled out as highly susceptible in the same way.