Abstract

As part of a larger study to assess the health management of Atlantic salmon used for Connecticut River restoration efforts, non-lethal sampling methods were used to determine the presence of fish pathogens at the primary broodstock facility (Sunderland, MA). A water filtration method was designed and tested to detect bacterial pathogens in the effluent from tanks maintaining the adult salmon. Also, a mucus sampling procedure was used to determine bacterial prevalences.

Weekly water samples taken from tank effluents, as well as prespawning and post-spawning, mucous samples were examined for the presence of fish pathogens. Water samples routinely contained the fungal pathogen, Saprolengia, despite ongoing formalin treatments. Water samples taken in June and July of two consecutive years also contained Cytophaga columnaris (0. 01 to 1.00 cfu/ml). The salmon did not display any clinical signs of columnaris disease, and the bacterium was not subsequently isolated from mucus samples taken during the pre-spawning examinations (October) or post-spawning necropsies (January). Saprolengia was isolated from mucus throughout the study and, in some cases, fish showed clinical signs of disease after spawning.

Although the salmon did not experience an epizootic of columnaris disease, C. columnaris may predispose fish to fungal infections. To further investigate this possibility, laboratory trials have been initiated. An experimental protocol for establishing temporary colonization (3 days) of C. columnaris in salmonids has been established using bath exposure. Also, hematological parameters, lysozyme activity as well as lysis of C. columnaris cells by serum are being assessed for correlation to colonization of the mucus by C. columnaris and subsequently, experimentally induced Saprolengia infections.