A survey of the bacteria in the ovarian fluid of landlocked fall Chinook salmon Oncorhynchus tshawytscha from Lake Oahe, South Dakota, was conducted to investigate possible effects on egg mortality. Bacteria were isolated from the ovarian fluid of 15 out of 19 spawning females. A number of bacteria, including known and potentially pathogenic species, were identified: Acinetobacter spp., Aeromonas hydrophila, Aeromonas veronii, Arthrobacter spp., Pseudomonas spp. (including P. putida), Moraxella spp., and Microbacterium spp. With the exception of Aeromonas hydrophila, none of these bacteria had previously been isolated from Chinook salmon ovarian fluid. There was no observable association between the aeromonads or pseudomonads and egg survival. However, there was a weak but significant positive correlation between bacterial density (colony-forming units/mL of ovarian fluid) and egg survival; the significance of this correlation is uncertain.

Abstract:This study evaluated the use of ovarian fluid turbidity as a potential indicator of landlocked fall Chinook Salmon Oncorhynchus tshawytscha egg survival. A total of 21 females were spawned, with nine of the spawns containing between one and ten broken eggs per spawn. Ovarian fluid turbidity ranged from 55.1 to 159 nephelometric turbidity units (NTU), and egg survival to the eyed-stage of egg development ranged from 0 to 68%. There was no significant correlation between ovarian fluid turbidity and egg survival. Mean survival of eggs from the spawns containing broken eggs was 12.3%, which was significantly lower than the 32.9% mean survival from spawns without broken eggs. These results indicate ovarian fluid turbidity cannot be used to predict egg survival in spawns of landlocked fall Chinook Salmon, but the presence of even a small number of broken eggs may be indicative of poor survival to the eyed-egg stage of development.

Egg disinfection is an important practice that prevents potential disease transfer, but currently allowable disinfection regimes do not completely eliminate external egg membrane microbes. In this experiment, newly fertilized and water‐hardened landlocked fall Chinook Salmon Oncorhynchus tshawytscha eggs were submersed for 10 min in povidone‐iodine solutions containing 0, 100, 200, and 400 mg/L active iodine. External egg bacterial numbers (CFUs) were quantified after each disinfection treatment, and egg survival (%) was calculated at the eyed stage. All of the disinfection treatments significantly reduced CFUs compared with untreated controls. However, eggs from the 400‐mg/L iodine treatment had significantly lower CFUs (2.20 ± 0.59 [mean ± SE]) than the 100‐mg/L (10.43 ± 8.01) and 200‐mg/L (8.10 ± 1.51) treatments. Percent survival was not significantly different among any of the treatments; survival was 18.86 ± 5.17%, 19.17 ± 4.76%, and 20.16 ± 5.27% in the eggs subjected to 100 mg/L, 200 mg/L, and 400 mg/L iodine, respectively. These results indicate that 10‐min treatments of 400 mg/L active iodine on landlocked fall Chinook Salmon eggs provide the most microbial reduction with no effect on subsequent egg survival.

Although an important part of the natural environment of fish, overhead cover is usually absent during hatchery rearing. To evaluate the possible influence of overhead cover on juvenile brown trout Salmo trutta hatchery rearing performance, this study compared three different cover treatments: near-full (98%) cover, partial (65%) cover, and no cover (completely open). After 12 weeks of rearing in 1.8 m-diameter circular tanks, total tank weight gain was significantly greater and feed conversion ratios were significantly less in tanks of brown trout that were either partially or near-totally covered, in comparison to those tanks that were completely open. The viscerosomatic index, hepatosomatic index, and splenosomatic index values were not significantly different among any of the treatments. Fin condition indices were also not significantly different. The use of either partial or full covers is recommended to maximize brown trout rearing efficiencies, with full covers providing the additional benefit of preventing fish from jumping out of the tanks.

Abstract:This study compared the survival of landlocked fall Chinook salmon Oncorhynchus tshawytscha eggs incubated in either upwelling jars, either with or without daily formalin treatments, or vertically-stacked trays treated daily with formalin in a production hatchery. In the first year of the study, survival to the eyed-egg stage was significantly greater in eggs incubated in jars without formalin compared to trays, but there was no significant difference in survival to hatch between the treatments. In the second year, there were no significant differences in eggs incubated in trays, in jars without formalin treatments, and in jars with formalin treatments. In the final year, there was no significant difference in eyed-egg survival between eggs incubated in trays and jars without formalin, but survival to hatch was significantly greater in the eggs incubated in jars. Jar incubation is recommended to maximize the survival of landlocked fall Chinook salmon eggs.