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~~ ..-,' ~ ;, ,- ,..) ~ C:J ~. . (;::) ~ .. ~.. .a ~ ~ ~ .~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~. 4 4 4 ~ 4 4 4 4 4 ~ ~ ) ) ) 4 4 4. ~ ~ ~ Lesions remain the most appropriate abnormality for use as an indicator of stressful environmental conditions and resulting fish disease. The reason for this is that the years when the percentage of fish with abnormalities is high, the percentage of abnormalities that are lesions also is high. Thus, incidences of lesions in C. tat/pinnis will continue to be a useful tool as the primary indicator of fish health in the San Juan River. Any future investigations should integrate histopathological methods with the use of a micro probe (when developed) or some of the new techniques utilizing proteins as a method to detect fish stress. Conclusions: Fish pathogens are not the primary cause of the majority of lesions observed on San Juan River fish. Asian tapeworm, B. acheilognathi, was discovered within a few months of its initial introduction, and its infection of cyprinids was documented both upstream and downstream as it spread. A large number of bacterial species were present on and in San Juan River fish. Many of these taxa have the potential of secondary infections in both fish and mammals. . Reconfiguration of electro fishing equipment (cathodes) can reduce the amount of injury to fish. . Flannelmouth sucker, C. tatipinnis, remains the best species for monitoring. Future research on fish lesions should concentrate on the development of a nano probe to analyze the unknown material found in histopathological samples of lesions. EXECUTIVE SUMMARY: Fish health surveys on the San Juan River from Farmington, New Mexico to Clay Hills, Utah were initiated in October 1992 by Pinetop Health Center personnel. The goal of the survey was to determine the cause of lesions and other abnormalities observed in native and nonnative fish. This report summarizes the fish health findings from October 1992 through May 1999. The investigation focused on the t1annelmouth sucker, Catostomus tatipinnis, as it is the most common fish species sampled and had been the most susceptible species to abnormalities, including lesions. Since this section of the San Juan River was part of the recovery area of the endangered Colorado pikeminnow (squawfish), Ptychocheilus tucius, and threatened razorback sucker, Xyrauchen texanus, concern about these abnormalities was high. Fish health sampling included both field observations and laboratory investigations. Fish also were examined for electro-induced injury. As a result of the fish health survey, the introduced Asian tapeworm was discovered, a large number of bacterial species were identified, and modifications in electro fishing equipment were made to minimize damage to fish in the future. The exact cause of the lesions was not determined, but parasitic, bacterial, and viral agents have been eliminated. Future investigations should be undertaken when an appropriate nano probe is developed for the unidentified material found in histopathological examinations. 9