Relation of Water Temperature to Infections of Coho Salmon (Oncorhynchus kisutch), Chinook Salmon (O. tshawytscha), and Steelhead Trout (Salmo gairdneri) with Aeromonas salmonicida and A. hydrophila

Abstract

Juvenile steelhead trout (Salmo gairdneri), coho salmon (Oncorhynchus kisutch), and spring chinook salmon (O. tshawytscha) were infected by intraperitoneal or intramuscular injection with Aeromonas salmonicida or A. hydrophila at seven temperatures from 3.9 to 20.5 °C. At 3.9 and 6.7 °C, mortality in fish infected with A. salmonicida varied from 2 to 26% among the three salmonid species. At 20.5 °C 93–100% of these animals died within 2 or 3 days; at 6.7 °C or lower the fish survived for 12–23 days. Growth of A. salmonicida in vitro was influenced by temperature in a manner very similar to its influence on the in vivo infection. Comparable experiments with A. hydrophila gave results much like those with A. salmonicida, though some differences were noted. At a temperature of 20.5 °C percent mortality ranged from 64 to 100%. At 9.4 °C or below no deaths attributed to A. hydrophila occurred. Fatally infected fish died more rapidly at the higher temperatures. Key words: Aeromonas salmonicida, A. hydrophila, water temperature, furunculosis, motile aeromonas septicemia, coho salmon, chinook salmon, steelhead trout