Effects of formalin and chloramine-T treatments on oxygen consumption of juvenile salmonids

The effects of formalin and chloramine-T on oxygen consumption of juvenile brook trout (Salvelinus fontinalis) at low water temperature (2 degrees C) were studied with a flow-through respirometer. No changes were found in the oxygen consumption of these fish after exposure to formalin at 200 and 400 micro l/litre or to chloramine-T at 10 micro l/litre during 1-h flow-through treatments. Additionally, there was no evidence of chemical oxygen demand exerted by formalin at dose levels up to 1600 micro l/litre or by chloramine-T at 10 micro l/litre. When juvenile rainbow trout (Oncorhynchus mykiss) were treated with formalin at 200 micro l/litre for 1 h in an aerated tank simulating a static bath treatment, sham-treated control tanks had a significantly greater maximum decline in dissolved oxygen than formalin-treated tanks. It is suggested that posttreatment mortalities that occur after low-temperature bath treatments with these chemicals are not directly related to oxygen consumption..