A possible cause of sunburn in fish

A LESION DESCRIBED AS A GRAY ΡATCH GENERALLY LOCATED ΑΝΤΕRIOR TO THE DORSAL FIN has been associated with high mortality of fish on numerous occasions in production hatcheries throughout the United States. This lesion has been called "sunburn" or "backpeel." No bacteria or other pathogens have been found in fish with these symptoms. For example, at a Montana hatchery in April 1956, mortality of 10 to 15 percent occurred daily and this lesion was the only syndrome found.  On occasion, shade has prevented this condition and even restored affected fish to an apparent normal condition; thus there has seemed to be a correlation between sunshine and the condition in fish. To our knowledge, this has been the only therapy attempted.