Abstract
The early life history of freshwater drum, Aplodinotus grunniens, was studied in 1965–67 to determine factors influencing year-class strength in a main stem Missouri River reservoir. Fish spawning occurred over a period of 6–7 weeks in June and July when water temperatures reached 18 C. Fecundity of fish 307 to 386 mm long and 6–9 years old ranged from 34,000 to 66,500 ova. Ova reared in the laboratory at a water temperature of 23 C hatched in 27 hr and the prolarvae averaged 3.2 mm long. The prolarval stage was complete 45 hr after hatching and postlarvae averaged 4.4 mm long. Adult characters developed at an approximate length of 15 mm. Diet of fish 6–15 mm long was Daphnia and Cyclops. Bottom fauna became important in the diet of fish longer than 20 mm. Fish movement between channel and floodplain was related to changes in diet. Growth, year-class strength, and mortality varied among years. Strong year classes were associated with warm summer (June-August) water temperatures in the spawning and nursery area and weak year classes with cold temperatures. Size of year class was determined before fish attained a length of 25 mm.
Published Version
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