Research on Captive Broodstock Technology for Pacific Salmon, 1995 Annual Report.

Abstract

Studies encompassed several categories of research, including fish husbandry, reproductive physiology, immunology, pathology, nutrition, and genetics. Captive broodstock programs are being developed and implemented to aid recovery of endangered Pacific salmon stocks. Like salmon hatchery programs, however, captive broodstock programs are not without problems and risks to natural salmon populations. Captive broodstock programs can sustain high mortality, which may increase a population's risk of extinction if the captive component is a substantial fraction of this population. Rearing systems must be designed and operated to minimize the risk of loss due to disease, poor reproductive performance of adult fish, and poor offspring viability. Additional risks include genetic change imposed on a population by a captive broodstock program, genetic interaction between captive and natural fish in the wild, and ecological impacts of releases of captive fish on natural populations. The research projects described in this report were developed in part based on our literature review, Assessment of the Status of Captive Broodstock Technology for PaciJic Salmon. This assessment elucidated the need for standard, efficient hatchery rearing practices to yield maximal numbers of high-quality offspring (i.e., those that are as similar to the founder stock as possible), as well as the need to determine the genetic consequences of captive broodstock programs for natural salmon populations. Part I: Fish Husbandry: Effects of Rearing Environment on Survival and Reproduction of Sockeye Salmon An experiment was performed to compare growth, survival, and reproduction of sockeye salmon broodstock reared in three different environments: 1) tanks containing freshwater, 2) tanks containing filtered and UV-treated seawater, and 3) seawater net pens. For this experiment, 1990-brood Lake Wenatchee sockeye salmon were reared in either freshwater or seawater until 1 month prior to spawning, when fish reared in seawater were transferred to freshwater. During 28 months of rearing, survival averaged about 32% for replicates held in freshwater tanks, 35% for replicates in tanks supplied with pumped, filtered, and sterilized seawater; and 26% for replicates held in conventional seawater net-pens. Survival of fish in net-pens was significantly lower than that of fish reared in tanks. In fall 1993, about 15% of the fish reared in fresh water matured at age-3, but no fish from either the seawater tank or seawater net-pen treatments matured. In fall 1994, 79% of fish in the freshwater treatment and 70% of those reared in the seawater tank treatment matured as 4year-old fish. In contrast, only 8% of 1990-brood fish reared in the net-pen treatment spawned at this time. Growth differences between treatments were also noted, with average prespawning sizes of 2.26 kg in replicates from freshwater tanks, 1.57 kg in those from seawater tanks, and 1.49 kg in replicates from the seawater net-pen. There were significant differences between average weights of fish in ...