A study of bacteria present within unfertilized salmon eggs at the time of spawning and their possible relation to early lifestage disease

Abstract

The eggs of 30 female chinook salmon, Oncorhynchus tshawytscha (Walbaum), were collected at spawning. Some eggs from each fish were collected for bacteriologic study. Two salmon produced eggs judged to be of poor quality which were not used. The remaining 28 of the 30 groups of eggs were fertilized from a single sperm pool and the eggs incubated in separate groups. Mortality data on the developing salmon were recorded regularly through the twelfth week on feed. Unfertihzed eggs from each group were surface-disinfected with an iodine solution, then crushed and subjected to a culture procedure designed to permit growth of as many bacterial types as possible. Bacteria were cultured and identified, and a comparison made of the types of organisms present in eggs from groups which later incurred high or low mortalities. Bacteria were recovered from both groups of salmon eggs. Although no single organism could be identified as a cause of increased mortality, the more frequent occurrence in the eggs of the 'high mortality' group of species of Vibrio, Listeria, Corynebacterium and Staphylococcus suggests that these bacteria may play a role. It is suggested that the cause of so-called early Ufestage disease of salmon is muUifactorial.

Flavobacterium psychrophilum in Baltic salmon Salmo salar brood fish and their offspring

“…Previously, E psychrophilum has been isolated in milt from mature chinook and coho salmon (Holt 1987). In contrast, neither Sauter et al (1987), studying mature coho salmon, nor Rangdale et al (1996), studying rainbow trout, detected F. psychrophilum in milt. The presence of E psychrophilum in the milt indicates the possibility that male fish may transfer the bacteria to the egg at the time of fertilisation.…”

In vitro evidence for the antibacterial role of lysozyme in salmonid eggs

“…The latter may thus be rendered so permeable as to result in the loss of cell viability without lysis. Sauter et al (1987) reported the occurrence of a wide range of bacteria in the eggs of chinook salmon Oncorhynchus tshawytscha from a population of highly stressed iisn. T'neir findings are, however, at odds with the results of others who report that the yolk of salmonid eggs and alevins, unlike the egg and alevin surfaces (Bell et al 1969, Yoshimizu et al 1980, Barker et al 1989, are generally bacteria-free (Yoshimizu et al 1980, Evelyn et al 1984a, b, Barker et al 1989, 1991, Lee & Evelyn 1989.…”

“…Cells of the bacterium can apparently enter the egg prior to ovulation (Lee & Evelyn 1989) or through the rnicropyle after ovulation, while the egg is in contact with infected coelomic fluid (Evelyn et al 1984a). Other Gram-positive and Gram-negative bacteria that are small enough to pass through the micropylar canal, including the fish pathogens Aeromonas hydrophila, A. salmonicida, and Carnobacterium piscicola (Collins et al 1990) (formerly Lactobacillus piscicola; Hiu et al 1984), also occur in the coelomic fluid of spawning fish (Cone 1982, Evelyn et al 1984a, b, Sauter et al 1987, Barker et al 1989. These bacteria are thus in a position to enter the eggs yet, unlike R. salmoninarum, they appear not to be vertically transmitted.…”

Characterization of Bacteria Isolated from Landlocked Fall Chinook Salmon Eggs from Lake Oahe, South Dakota

“…Although this mortality is probably due to a number of factors, bacteria isolated during egg incubation have been implicated in these deaths in several studies (Barnes et al 1997(Barnes et al , 2005Stephenson et al 2003). Other researchers have also suggested that bacteria may negatively impact egg survival (Sauter et al 1987;Barker et al 1989;Holcomb et al 2005), although this relationship is far from certain (Barker et al 1990;Omnes et al 1993). Soft egg disease, possibly caused by bacteria (Wood 1979;Erdahl 1993), has also been observed in Lake Oahe Chinook Salmon .…”