The symptoms of acute fluoride intoxication in carp and rainbow trout include lethargy, violent and erratic movement, and death where there is partial or complete muscle contraction. Excessive mucus production associated with an increase in mucous cells in the epithelium of the head region and the gills also occurs. Changes in the electrophoretic pattern of the serum proteins in carp blood are evident. There is an increase in the fluoride concentration of the bones and a hypertrophy of the ultimobranchial gland. Rainbow trout embryos display initial symptoms similar to adult fish, including lethargy, violent movement, and tetany. Rupturing of the chorion by the embryo is attributed to violent movement during the onset of intoxication. Lethal doses and the sensitivities of fish to the toxin are dependent on several variables including size of fish, temperature of medium, and calcium and chloride concentration of the medium. It was demonstrated that there is an uptake of fluoride in muscle tissue, cancellous bone, and skeletal bone, and that uptake was increased when there was a rise in the fluoride concentration of the medium. The uptake of fluoride by the bone was via a second‐order reaction and is assumed to be an enzymatic process. Proliferation of mucous cells in the epithelium of the gills and the head region is postulated to be instrumental in the excretion of fluoride from the body, and is considered an effective defense mechanism against fluoride intoxication. Hypertrophy of the ultimobranchial gland is thought to result from a deficiency in calcium induced by the effects of fluorides. The uptake of fluoride by the bone is a defense mechanism against fluoride intoxication and is postulated to occur with the elimination of fluoride from body circulation. This fluoride forms a stable mineral complex.