Abstract
Long-term growth of hatchery-reared and released Paddlefish of the Yellowstone-Sakakawea population was compared with wild fish of the same cohort tagged and recaptured up to 19-years later. Hatchery-reared fish from the 1995-cohort tagged with coded-wire tags were released into Lake Sakakawea, North Dakota, USA and recovered as mature fish in harvest fisheries in North Dakota and Montana. Length and weight at age were compared with wild fish of the same cohort over this 19-year period. Wild Paddlefish, both males and females, were larger at age than hatchery-reared fish. Differences in weight at age were more pronounced for females, for which wild fish were highly significantly greater in weight at age than hatchery-reared fish in every year captured. The Gonadosomatic Index (GSI) of hatchery-reared fish was numerically higher than for wild fish every year from age 15 through 19, and highly significantly higher (p < 0.01) for two of the years. In contrast, the ovarian adiposity were both highly significantly (p < 0.01) lower for the hatchery-reared fish than for wild fish for every year for fish ages 15 - 19. Relaxed selection for rapid growth in the hatchery may have allowed substantial numbers of larger hatchery fish released to survive, grow, and mature along with wild fish but grow more slowly and have less ovarian oviposity than wild fish. Results have implications for hatchery releases of Paddlefish and potentially sturgeons, gars, and many other species that exhibit high early growth rates during their first 1 - 2 years of life.