The thiamin deficiency signs and requirement of rainbow trout (Salmo gairdneri, Richardson)

Abstract

Four growth studies were conducted to determine the signs, biochemical indices and histopathology of a thiamin deficiency and the thiamin requirement of young rainbow trout reared at 15°C on a semi-purified test diet. The major overt signs of a thiamin deficiency in rainbow trout are predominantly neurological: irritability and instability. Other signs include convulsions, feed refusal, dark pigmentation and finally mortalities. Growth reduction in the thiamin deficient trout appear to result from anorexia or feed refusal and not specifically to a thiamin deficiency. Although there were prominant neurological signs in the thiamin deficient trout, there were no histopathological signs in any tissues of the trout, including the brain and central nervous system, examined by light microscopic techniques. The tissue transketolase activity would appear to be a sensitive and specific indicator of the thiamin status in the trout. In addition, the levels of plasma lactate and serum pyruvate are also elevated in thiamin deficient trout. On the basis of the growth parameters, absence of deficiency signs and kidney and liver transketolase activity, the thiamin requirement of rainbow trout reared at 15°C on a semi-purified test diet is 1 mg/kg feed.