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Genetic, environmental, and physiological factors involved in the precocious sexual maturation of chinook salmon (Oncorhynchus tshawytscha) Heath, Daniel D.

Abstract

Male chinook salmon (Oncorhynchus tshawytscha), that mature sexually one year prior to females and after at least one summer in sea water, are known as jacks. A breeding experiment to test for genetic and environmental (temperature at early rearing) effects on the incidence of jacking in chinook salmon showed significant sire, dam, and environmental effects, as well as genotype-by-environment interactions. Heritability estimates for incidence of jacking based on sire-offspring regressions within dams were0.48 (± 0.24) and 0.32 (± 0.14) for the accelerated and non-accelerated groups respectively. DNA fingerprinting was used to detect differences in allele distribution between precocious males and randomly selected fish, such differences indicate genetic involvement. Two oligonucleotide DNA fingerprinting probes were developed, however the resulting banding patterns were judged unsuitable for this application. A novel extension of Random Amplification of Polymorphic DNA (RAPD) allowed the isolation of a single-locus DNA probe for chinook salmon. This probe and another developed for Atlantic salmon, were hybridized with DNA from 74 jacks and 94 females from farmed Chinook salmon (Robertson Creek stock; RC), and with DNA from 45 precociously mature and 56 non-mature chinook salmon parr from the Nicola River (NR). The allele distributions of the jack and female RC adults differed significantly, however, there was no difference between the precocious and non-maturing NR parr due, in part, to the relatively low genetic variability of that stock. The weight-frequency distributions for three year classes of chinook salmon became significantly bimodal in the May prior to maturation due to faster growth of the jacks, relative to the non-maturing fish, from April to June. Plasma cortisol, T3, and testosterone concentrations were measured for one of those year classes during the spring and summer. No significant difference between the jacks and non-maturing fish were found for cortisol; however, T3 levels were higher in the jacks in March, and testosterone levels were higher in the jacks throughout the spring and summer. Only T3 levels were correlated (negatively) with growth in the jacks. A correlation analysis using the full- and half-sib families in the breeding experiment showed that growth-related variables did not predict jacking rates, although resting plasma glucose concentration, dam weight, and weight difference between the jacks and non-mature fish at the final sample were significantly correlated with jacking rate. The implications of these finding are discussed with respect to evolutionary theory, aquaculture, and chinook salmon physiology.

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