A Lactobacillus sp. from diseased female rainbow trout, Salmo gairdneri Richardson, in Newfoundland, Canada

Abstract. Post-spawning mortalities of 2- to 3-year old female rainbow trout, Salmo gairdneri Richardson, at a Newfoundland hatchery were studied. The fish were found to have a mixed bacterial infection involving primarily a Lactobacillus sp. (a Gram-positive, chain-forming coccobacillus) and to a lesser degree Enterobacteriaceae, Aeromonas hydrophila and Pseudomonas fluorescens. The bacteria were isolated from the visceral organs, kidney, and ascitic fluid present in the coelomic cavity. The fish had extensive degeneration and necrosis of the liver, spleen and kidney, and sloughing of intestinal epithelium, but whether these were caused directly by the bacterial infection was not established because the fish appeared to have received substantial stress from the mechanical stripping and from the retention of dead, unshed eggs in the coelomic cavity. Tissue sections suggested that substantial growth of the Lactobacillus sp. was occurring within these unshed eggs. The present study describes this unusual observation and compares the Lactobacillus sp. to two other Lactobacillus isolates from cultured trout.