Toxicity of intraperitoneally injected formalin in Atlantic salmon, Salmo salar L.

Abstract. Atlantic salmon, Salmo salar L., parr were injected intraperitoneally with different quantities of formalin (37% formaldehyde) following anaesthetization with either benzocaine (ethyl-p-aminobenzoate) or chlorbutol (1,1,1,-trichloro 2-methyl-2-propanol) The LD₅₀ for injected formaldehyde was found to be approximately 50mg kg⁻¹ body weight. The type and concentration of the anaesthetic used did not influence mortality rates. Formalin is commonly used to inactivate microorganisms in vaccines. Doses of formalin which were shown to be toxic in this study are close to those which may be injected into fish as a component of various vaccines against bacterial fish diseases. Hence, the formalin content in fish vaccines may well cause mortality under certain conditions.