Susceptibility of coho salmon, Oncorhynchus kisutch (Walbaum), to different toxins of Clostridium botulinum

Coho salmon Oncorhynchus kisutch (Walbaum), held at 15 °C were tested for their susceptibility to toxins of proteolytic and nonproteolytic Clostridium botulinum types A, B, C1, C2, D, E, F, and G administered by the oral and intraperitoneal (i.p.) routes. By the oral route, the fish were most susceptibile to type E neurotoxin, which was lethal at a dose equivalent to 90 mouse intraperitoneal minimum lethal doses (MLDs). The oral lethal dose increased to 2000 MLD for nonproteolytic and proteolytic type F neurotoxins, but the toxin types A, B, and C1 were not lethal to fish at 2000 MLD and type D was not lethal at 20 000 MLD (highest titre tested). The fish were not susceptible to 200 MLD (the highest titres tested) of type G neurotoxin or C2 cytotoxin. By the i.p. route, all of the toxins except type G were lethal to coho salmon. Type E neurotoxin was the most toxic at a level of one-half the mouse MLD. Coho salmon held at temperatures ranging from 1 to 20 °C were sensitive to type E neurotoxin by both the oral and i.p. routes. As the temperature decreased the fish became more resistant to type E neurotoxin by the oral route, but the i.p. dose remained one-half the mouse MLD at all temperatures.