Evaluation of chronic gas supersaturation on growth, morbidity, and mortality of fingerling rainbow trout infected with Myxobolus cerebralis

The effect of environmental stressors on trout infected with Myxobolus cerebralis, the causative agent of whirling disease, is of great interest because the parasite has spread to most areas of the United States that support wild trout populations. Gas supersaturation is an environmental stressor found in at least two rivers in Colorado where M. cerebralis exists, and year-class losses of rainbow trout Oncorhynchus mykiss have occurred. Both of these stress factors may also occur in fish culture operations. A controlled laboratory experiment was conducted to test the hypothesis that chronic low levels of gas supersaturation affect growth, morbidity, and mortality of fingerling rainbow trout infected with M. cerebralis. Fingerling rainbow trout, exposed and unexposed to M. cerebralis, were held in gas saturations of 110, 107.5, 105, and 100-102.5% for 22 weeks. Significant effects on growth, morbidity, and survival were found due to M. cerebralis infection. Gas saturation levels tested did not significantly affect growth, morbidity, or survival of fish in this experiment.