Strain and maturation effects on female spawning time in diallel ...

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The timing of the spawning season has major consequences on farming operations:
seasonal product availability <strong>and</strong> labour requirement, <strong>and</strong> reduced facility use. The result is
lower production efficiency with consequent profit loss. In order to optimise production, a
producer may want to move the spawning season of part of their broodstock to a different
time of year, or condense the season to a more specific time of year. Either may be
accomplished by using genetic selection methods. By determining the underlying genetic
factors influencing spawning time, the potential for selection as a method to manipulate
the spawning season in rainbow trout can be evaluated.
The genetic factors controlling spawning time have been studied somewhat less than
have those relating to other production traits. Purdom (1993) stated that different strains of
rainbow trout had varying spawning times, indicating some genetic basis for this trait. Gall
<strong>and</strong> Huang (1988b) demonstrated that spawning season was controlled by a strong genetic
component. There is anecdotal evidence that a wide range of spawning times has been
developed by selection (Purdom, 1993) <strong>and</strong> responses to spawn date selection have been
observed (Siitonen <strong>and</strong> Gall, 1989; Sadler et al., 1992). A few studies have attempted to
quantify the variance components of spawning time in salmonids. Heritability <strong>and</strong>
repeatability have been estimated by Gall et al. (1988), Siitonen <strong>and</strong> Gall (1989), Sadler
et al. (1992), Su et al. (1997, 1999), <strong>and</strong> Quinton et al. (2002).
A project is underway to develop a synthetic strain of rainbow trout for aquaculture
which would be characterised by fast growth, reduced precocious <strong>maturation</strong>, <strong>and</strong> a spring
spawning season (McMillan <strong>and</strong> McKay, 1992). Knowledge of the underlying genetics of
these traits is necessary to establish the optimum selection <strong>and</strong> breeding methods required
to develop the strain. To determine genetic factors regulating spawning time, four main
objectives for this study were set: rank three strains of rainbow trout <strong>and</strong> their hybrids
according to spawn date; determine strain interactions that affect spawn date (characterised
by heterosis <strong>and</strong> differences between reciprocal crosses); find <strong>effects</strong> of age of <strong>maturation</strong>
on spawn date; <strong>and</strong> calculate the repeatability <strong>and</strong> shift in time of spawn date from 3 to 4
years of age.
2. Materials <strong>and</strong> methods
2.1. Experimental design
C.D. Quinton et al. / Aquaculture 234 (2004) 99–110
The study was conducted at the Alma Aquaculture Research Station (AARS), University
of Guelph, Guelph, Ontario, Canada. Fertilised eggs from three farmed strains of rainbow
trout were brought to the AARS to form a base population (G0). All G0 fertilisations had
been done between March 14 <strong>and</strong> April 6, 1991. <strong>Strain</strong> OC was an Ontario commercial strain
in which females had been selected for late spawning <strong>and</strong> males had been selected for fast
growth. <strong>Strain</strong> MG was descended from the Ontario Ministry of Natural Resources’
Ganaraska River strain, <strong>and</strong> had undergone two generations of mild selection for faster
growth. <strong>Strain</strong> WC was a Washington State commercial strain. Previous studies have
compared these pure strains for early growth, survival, <strong>and</strong> <strong>maturation</strong> (McMillan <strong>and</strong>
McKay, 1992; McKay <strong>and</strong> McMillan, 1997). Evaluations of mitochondrial DNA <strong>and</strong>
allozyme variation have also been done for the Ontario strains by Ferguson et al. (1993).