Effects of intermittent chloramine-T exposure on growth, serum biochemistry, and fin condition of juvenile rainbow trout (Oncorhynchus mykiss)

Chloramine-T is a commonly used drug for the treating bacterial gill and skin diseases in the intensive aquaculture of salmonids; however, little is known about its effects on healthy fish. Juvenile rainbow trout were exposed weekly to 5, 10, and 20 mg/litre active chloramine-T ingredient in a tank replicate flow-through facility. Control fish were treated with tank water only. Growth parameters and haematocrits were taken twice weekly and serum biochemistry was measured on termination of the experiment. Absolute growth rates were suppressed but only statistically significantly in fish treated with 20 mg/litre chloramine-T compared with controls. Fish exposed to 10 and 20 mg/litre chloramine-T showed significant predisposition to an erosive dermatitis of the caudal fin which appeared to be caused by opportunistic pathogens of the genus Pseudomonas spp. and Flavobacterium spp. Haematocrits decreased in control and all treated fish. A significant concentration-dependent decrease in plasma sodium and chloride was observed. Plasma glucose levels did not vary and were similar to those reported for unstressed trout. It is recommended that care be taken when using chloramine-T prophylactically and that concentrations of less than 10 mg/litre be used..