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OAHN Arctic Char Case Study

Arctic char (Salvelinus alpinus) at Ontario Aquaculture Research Centre (OARC) were observed to have increased total suspended solids in outdoor production tanks. Increased concerns with total suspended solids (TTS) were noted starting in September 2023 and were initially chalked up to maintenance issues. Despite daily cleaning, TTS continued to be a challenge. During health monitoring observations, it was noted that the fish appeared to have diarrhea, where the feces were being expelled as fines rather than as a solid string. Unlike normal feces, the fines do not settle to the bottom of the tank where they can be discharged down the drain. Because the fecal fines are not removed from the tank, they are often resuspended  in the water column when the fish are active (e.g. feeding). While initially dietary changes were suspected, Arctic char from the same originating population but held indoors for future broodstock remained clinically unaffected and therefore, a parasite was suspected.