A comparison of the effect of silicone coated ascorbic acid and ascorbyl phosphate on the course of ichthyophthiriosis in rainbow trout, <i>Oncorhynchus mykiss</i> (Walbaum)

Abstract

Abstract. The aim of the present study was to compare the effect of high and low doses of different vitamin C formulations on the course of ichthyophthiriosis ( Ichthyophthirius multifiliis infection) in rainbow trout. After a depletion period, trout fingerlings were fed diets deficient in vitamin C(AA 0), or containing different levels of silicone coated ascorbic acid (AA; 50/200 mg kg feed −1 ) or ascorbyl phosphate (AP; 50/2000 mg AA equivalent kg feed −1 ). Fish infected with I. multifiliis demonstrated a significant reduction in mortality when fed high levels of AA or AP. A correlation between the parasite burden and the vitamin C content in the diet was not found. Specific immunity—measured as immobilization litre of sera—was not influenced by the level or the formulation of vitamin C in the diet. The most probable mechanism of high level doses of vitamin C is an increase of the general health status expressed as an improved nonspecific resistance and ability to cope with different stressors. In rainbow trout infected with I. multifiliis , the beneficial effect of ascorbyl phosphate is equal to that of silicone coated ascorbic acid, and therefore, the more stable AP may be a valuable alternative for use in fish diets.