Effects of Inbreeding and Family Origin on Variation of Size of Chinook Salmon Oncorhynchus tshawytscha Fry

We cultured separate lines of Chinook salmon fry Oncorhynchus tshawytscha of Chickamin River, Southeast Alaska ancestry in 7 common garden enclosures. A parentage analysis based on variation of microsatellite alleles showed that within these lines, 7 brother-sister matings (F = 0.25) had created 35 inbred fi sh in 7 families [bred from 6 females (dams) and 6 related males (sires)], and other matings of unrelated fi sh had created 37 outbred fi sh in 10 familes (bred from 7 females and 6 males.) There was no measurable effect of inbreeding on growth of Chinook salmon fry through 114 days post swim-up. A general linear model showing the effects of dam, sire, and the interaction of dam and sire explained a signifi cant amount of the variation of length and weight, but not of condition factor. However, analysis of a mixed model showed that only the interaction between dam and sire explained a signifi cant amount of the variation of lengths and weights. Because variation among individuals from different families can be large, effects of individuals can potentially be confounded with the effects for which a study is designed. To avoid drawing improper conclusions, studies should estimate the amount of variation that can be attributed to family origin, or be certain that many families are sampled. Authors: CARA J. RODGVELLER is a fisheries technician with the Pacific States Marine Fisheries Commission and is contracted by the National Marine Fisheries Service, Auke Bay Laboratory, 11305 Glacier Highway, Juneau, Alaska, 99801-8626. Email: [email protected]. WILLIAM W. SMOKER and ANTHONY J. GHARRETT are professors at the University of Alaska Fairbanks, Juneau School of Fisheries and Ocean Sciences, 210 Anderson Building, 11120 Glacier Highway, Juneau, Alaska, 99801. ANDREW K. GRAY (fisheries geneticist) and JOHN E. JOYCE (fisheries biologist) are with the National Marine Fisheries Service, Auke Bay Laboratory, 11305 Glacier Highway, Juneau, Alaska, 99801-8626. Acknowledgments: We acknowledge the Rasmuson Foundation for their fi nancial support, and the National Marine Fisheries Service Auke Bay Laboratory and Douglas Island Pink and Chum, Inc. for their support in kind. This research was carried out according to a protocol approved by the University of Alaska Fairbanks Institutional Animal Care and Use Committee in accordance with policy and regulations of the University of Alaska Fairbanks and the U.S. Government. This research was carried out with permission of the Commissioner of the Alaska Department of Fish and Game in accordance with policy and regulations of the State of Alaska. INTRODUCTION Inbreeding Depression Inbreeding is a concern for conservation biologists managing small populations and for hatchery managers raising salmonids for ocean ranching and supplementation of endangered stocks. If inbreeding depresses fi tness in salmon to the degree that some studies have reported in rainbow trout Oncorhynchus mykiss (e.g., Aulstad and Kittelsen 1971; Kincaid 1976a; Kincaid 1976b; Kincaid 1983), then salmon hatchery managers must become more aware of the potential hazards of inbreeding and adopt methods to minimize potential inbreeding in the hatchery. Inbreeding is the mating of individuals that share a recent common ancestor. The primary effects of inbreeding are a decrease in heterozygosity and an increased probability of the fi xation of an allele at a locus, and therefore, a loss of genetic diversity. Inbreeding depression is the reduction in the performance of a trait relative to non-inbred individuals in a population. This reduction in performance can be due to a loss of genetic variation or an increased probability of receiving deleterious alleles from parents (Falconer and Mackay 1996). Although inbreeding has been shown to depress fi tness in many species, there is little knowledge of how inbreeding is manifested in fi sh at different life stages, and very little knowledge about inbreeding in salmon populations. Several studies have demonstrated that rainbow trout show signs of depression at various levels of inbreeding. After one generation of full-sib mating (inbreeding coeffi cient, F = 0.25), rainbow trout families showed an increase in the number of crippled fry (Aulstad and Kittelsen 1971), diminished egg hatchability, feed conversion effi ciency, and fry survival (Kincaid 1976a). Juveniles and adults grew more slowly (Kincaid 1976b) and fewer fi sh stocked in a pond survived (Kincaid 1983). When inbred Chinook salmon (F = 0.25) were exposed to Myxobolus cerebralis, the parasite that causes whirling disease, the probability and severity of infection increased (Arkush et al. 2002).