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Juvenile landlocked fall Chinook Salmon Oncorhynchus tshawytscha were coded‐wire‐tagged and reared in 1.8‐m‐diameter circular tanks at a low or high density for up to 52 d prior to stocking in Lake Oahe, South Dakota, during late May of 1999, 2003, and 2004. Final hatchery rearing densities ranged from 7.29 to 11.72 kg/m3 for the low‐density tanks and from 15.02 to 25.22 kg/m3 for the high‐density tanks, with the higher densities being at least double the lower densities in each year. Flows were adjusted to maintain similar loadings (kg·L−1·min−1) between the treatments each year. The fish used in this study came from spawns collected during the October prior to stocking; TL at the end of hatchery rearing ranged from 103 mm in 1999 to 124 mm in 2004. In each year‐class, the percentage of fish that were harvested by anglers or that returned to spawn was significantly greater for the lower‐density treatment than for the higher‐density treatment. Angler harvest primarily consisted of age‐3 fish, with a small number of age‐4 fish harvested as well. Feed conversion ratios were significantly improved in the lower‐density tanks relative to the higher‐density tanks in 1999 and 2003, and fish from the lower‐density tanks were also significantly longer just prior to stocking in 1999 and heavier prior to stocking in 2003. To maximize poststocking survival for landlocked fall Chinook Salmon, lower rearing densities are recommended.

Soft‐egg disease was observed in the spawn from 5 of 15 landlocked fall chinook salmon Oncorhynchus tshawytscha from Lake Oahe, South Dakota, with the percentage of prematurely hatching fry per spawn ranging up to 42.0%. Soft‐egg disease was only identified in eggs collected from presumed 4‐year‐old salmon, and its occurrence is hypothesized to be at least partially caused by maternal dietary stress during egg development. Egg mortality after the appearance of soft‐egg symptoms was significantly less in the incubation trays receiving daily hydrogen peroxide treatments at 1,000 or 2,000 mg/L for 15 min and trays receiving either daily or twice‐daily formalin treatments at 1,667 mg/L for 15 min, compared with the trays that received either iodophor treatments or no therapeutic treatment at all.

Selected reproductive characteristics obtained during the spawning of landlocked fall chinook salmon Oncorhynchus tshawytscha from Lake Oahe, South Dakota, were evaluated for their use as predictors of embryo survival to the eyed egg stage. Spawn was categorized according to the presence or absence of observable overripe eggs. No significant differences in female length, female weight, the number of eggs per female, egg size, the amount of ovarian fluid released during spawning, and ovarian fluid specific gravity, pH, and conductivity were observed between spawn containing overripe eggs and spawn without overripe eggs. Conductivity was significantly positively correlated to embryo survival only in spawn without overripe eggs, while the total number of eggs per female was only positively correlated to embryo survival in spawn with overripe eggs. Spawning female weight, the number of eggs per female, and egg size were significantly different in spawn containing overripe eggs where no embryo survival was observed compared with spawn containing overripe eggs with at least some embryo survival to the eyed egg stage. Although no definitive predictors of subsequent embryo survival were detected, spawning personnel are probably justified in discarding landlocked fall chinook salmon spawn if more than 10% of the eggs are overripe and the female releasing the eggs is smaller than normal with relatively fewer, smaller eggs.