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) "\ ~ .0 ,)0 .~N , ., .:. :.' I,.' .' (D ,) ,.c:,. 1 ., ") '. " .-~, ',', . , .,-, lchthyophthirius ("leh") was nol detected during main river fish health surveys, but Ich posilive samples from backwater areas were examined. Rainbow and brown trout were occasionally sampled and cranial tissue was taken for plankIon centrifuge method of analysis for Myxobolus cerebralis, the causative agent for whirling disease. Even though Ihis area is not suitable for salmonid populations, the cold spring water runoffs allowed for a few trout to be present. A sample of the seasonal trout population was taken, but no M cerebra/is spores were detected. Viruses: All viral assays from San Juan River fish were negative from samples taken from May 1994 to May 1999. Histopathology imdings: Lesion samples were collected and shipped to Dr. Vicki Blazer, National Fish Health Laboratory, Kearneysville, West Virginia, for histological analysis. Dr. Blazer presented three potential explanations for Ihe lesions: "I) some mineral deposit, possibly with sharp projections, gelS into the dermis of bottom dwelling fish and causes the reaction; 2) A metabolic disorder, possibly in response to some contaminant, which causes the body to produce the malerial or deposit it, abnormally in the dermis, which lead to a reaction to it; and 3) Some interaclion of a contammant with Ultra Violet radiation which leads to skin damage."(Blazer 1996, personal communication). Dr. Blazer's opinion on the presence of "masses of bacteria" in the eroded epidermis and associated necrotic muscle is that they are secondary invaders, which concurs with Ihe analysis. DISCUSSION: Flannelmouth suckers as an indicator species: C. latipinnis remained the best choice as an indicator species for environmental problems on the San Juan River throughout the study. This species has the highest proportion of abnormalities (in excess of 80 percent) than any other fish species sampled, but was only about 60 percent of all fish sampled. This is consistent with the abnormalilies and fish species observed by Gaufin, Smith, and Dotson (1960) in the Green River. Cause of lesions and other abnormalities: We hypothesize that bacteria isolated from fish lesions are secondary invaders-they are opportunistic organisms that cause lesions after initial trauma due to contaminants, unsuccessful bird or fish predation, elc. The National Fish Health Laboratory concurs Ihat the bacteria are secondary. Dr. Blazer also proposes (in two of her three explanations for the cause of lesions) that a conlaminant was present which initiates the epidermal necrosis. Walker (1992) in a prcliminary investigation on lesions from suckers in the Animas River, a tributary to the San Juan River, thought that the cause was a type of Aeromonas salmonicida baclerium. Gaufin, Smilh, and Dotson (1960) noted that most of the t1annelmouth suckers with lesions were just downstream of Green River, Wyoming, where municipal sewage and oil discharge was taking place. Histological samples consistently have shown an unlmown material in micro quantities to be present in lesion sections. Herman and Lemm (1990) found this possible putative auloimmune reaction in striped bass. Until a micro-probe is available to analyze this material, the probable cause of these fish lesions will remain unlmown. From all the fish health samples taken during Ihis investigalion, we can eliminate viral, baclerial, or parasitic agents as the primary cause oflesions in San Juan River fish. 7