Nonanadromous Life History Diversity of Rainbow Trout (Oncorhynchus Mykiss)
Nonanadromous Life History Diversity of Rainbow Trout (Oncorhynchus Mykiss)

Author: Martin C. Arostegui

Publisher:

Published: 2019

Total Pages: 189

ISBN-13:

DOWNLOAD EBOOK

Rainbow trout (Oncorhynchus mykiss) is a salmonid species, native to Pacific Ocean drainages in North America and eastern Russia, which exhibits fluvial (stream-resident), adfluvial (lake-migrant), and anadromous (ocean-migrant) ecotypes. The differentiation of fluvial and anadromous individuals in sympatry is well-studied, whereas comparatively little research has focused on the adfluvial form and its distinction from fluvial individuals in sympatry. Thus, the purpose of this dissertation was to investigate the ecological, genetic, and phenotypic diversity of nonanadromous rainbow trout in a natural stream-lake system to better understand the differentiation of fluvial and adfluvial individuals in sympatry, the basis of residency versus migration in this species, and the role of lakes in salmonid diversification. Rainbow trout were sampled in the lake (thus, by definition, adfluvial) and in several tributary streams (where adfluvial and fluvial individuals may co-occur), and were examined for a variety of features to develop a holistic understanding of the behavior, ecology, and evolution of these life history pathways. Stomach contents and stable isotopes revealed disparate trophic ecology among rainbow trout in connected stream and lake habitats, suggesting both an ontogenetic shift in the diet of adfluvial fish as well as divergence in diet between adfluvial and fluvial ecotypes. Rainbow trout in streams fed primarily on aquatic insects, while those in the lake largely consumed snails and amphipods; however, partial trophic convergence among trout in these two habitats occurred when they incorporated the marine nutrient subsidy of spawning sockeye salmon eggs. Stable isotope data suggested that the minimum size of migration from stream to lake habitat by adfluvial fish was ~150 mm fork length, suggesting a juvenile stream-rearing period of a year or more prior to lake entry. Dietary niche comparisons with sympatric Salvelinus species suggested a greater degree of dietary overlap between rainbow trout and Dolly Varden (S. malma) in streams than between rainbow trout and Arctic char (S. alpinus) in the lake, which may increase the relative fitness benefits of migration over residency for rainbow trout. Restriction site-associated DNA sequencing revealed an association between habitat type (stream or lake) and a chromosomal inversion in the rainbow trout genome as well as numerous single nucleotide polymorphisms, supporting the genetic divergence of adfluvial and fluvial ecotypes in sympatry. Rainbow trout in streams were nearly fixed for the rearranged haplotype of the Omy05 inversion, whereas trout in the lake exhibited a markedly higher frequency of the ancestral, anadromy-associated haplotype. The functions of outlier genes with nonsynonymous mutations among stream- and lake-caught trout paralleled those documented in studies of fluvial and anadromous O. mykiss, highlighting the migratory nature of the adfluvial ecotype even though it is nonanadromous. Structure was present at both non-outlier and outlier loci among and within streams supporting populations nearly fixed for the rearranged Omy05 haplotype (i.e., with a genetic predisposition for stream-residency), highlighting the roles of local adaptation and genetic drift via spatial isolation in population divergence. Assessment of lateral coloration patterns and multivariate analyses of body shape of rainbow trout from stream and lake habitats over a range of body sizes revealed ontogenetic and ecotypic variation in coloration and morphology. Color differences among trout of different size classes and habitats indicated ecotype-specific pathways resulting in different terminal coloration patterns; banded parr in streams transitioned to either a silver coloration suited to pelagic waters in the lake (when adfluvial) or bronze coloration suited to confined cover in streams (when fluvial). The morphology of lake-caught rainbow trout was distinct from that of stream-caught trout, and their morphological differentiation exhibited many shared but some unique patterns compared to sympatric Dolly Varden in streams and Arctic char in the lake. Patterns of morphological variation in rainbow trout among and within habitats suggested the presence of partial migration, in which both fluvial and adfluvial individuals are produced from the same population. A review of the spawning behaviors, rearing strategies, and trophic polymorphisms in lakes among 16 species of salmonids from the genera Oncorhynchus, Salmo, and Salvelinus identified a negative association between the extent of reliance on lakes and the degree of anadromy. Oncorhynchus exhibits the least lake reliance, Salmo an intermediate level, and Salvelinus the greatest; opposite of the anadromy spectrum identified in previous studies. Lakes support life history forms, reproductive ecotypes, and trophic morphs unique to lacustrine habitat, and also support anadromous and fluvial salmonids by providing spawning, rearing, overwintering, and/or summer refuge habitat. Adfluvial and anadromous salmonids exhibit similar migration-associated traits and behaviors including the parr-smolt transformation, sex-biased partial migration, and the presence of precocious 'jack' males.

Genetic Variation for Disease Resistance in Rainbow Trout (Oncorhynchus Mykiss).
Genetic Variation for Disease Resistance in Rainbow Trout (Oncorhynchus Mykiss).

Author: Gareth Melgalvis Butterfield

Publisher:

Published: 2008

Total Pages:

ISBN-13:

DOWNLOAD EBOOK

Proliferative Kidney Disease (PKD) caused by the Malacosporean parasite Tetracapsuloides bryosalmonae, is presently the most economically damaging disease of British rainbow trout farming, costing the industry in excess of £2.5 million per annum in the UK alone. With no vaccine or prophylactic treatment available, and only management techniques currently adopted to minimise the stress and mortality associated with the disease, alternative approaches must now be considered. This document investigates if selective breeding for PKD resistance is possible by assessing the level of additive genetic variation, and calculating the subsequent estimates of heritability, for commercial strains of rainbow trout. During a PKD outbreak on a commercial farm, 1500 communally reared juvenile rainbow trout from two strains (Houghton Spring and Isle of Man) were sampled on a single day, their body weight and fork length measured, and severity of kidney swelling scored according to the scale of Clifton-Hadley et al. (1987). Fish were assigned to individual families using microsatellite parentage assignment. Significant additive genetic variation was observed in the population, and families were ranked according to estimated breeding values. A combined estimate of heritability (h2 = 0.19 ± 0.08) for kidney score suggests the population will respond well to selective breeding for kidney score, which may be deemed a measure of resistance, whilst the favourable genetic correlations between kidney score and the production traits measured suggest simultaneous selection for kidney score and growth traits should also be effective. In order to support the findings of the initial research, controlled challenge experiments were conducted. Using the family EBV information on kidney score from the IoM strain (due to its certification as a disease-free site), four females, two with high and two with low response to PKD, were each crossed with a randomly selected neomale to produce twenty two families for PKD challenge experiments. The PKD experimental challenges showed evidence of additive genetic variation to kidney score over an eleven week period, supporting initial findings. A low score was deemed as evidence of greater resistance to the parasite in this study. Although female EBV was taken into consideration in the statistical model, there was found to be no significant difference in resistance according to family. Immunohistochemistry stained kidney sections from each individual involved in the challenges proved kidney score correlated significantly to the number of parasites in the kidney, suggesting that the scale of Clifton-Hadley et al. (1987) is a sufficient and accurate basis on which to describe the severity of PKD, and infection level in rainbow trout. Having discovered evidence that furunculosis, causative agent Aeromonas salmonicida, plays a major role in the mortality of fish suffering from PKD in the field, the bacterial disease was investigated to assess the resistance of the same families used in the PKD challenges. Twenty one of the families were used to discover that additive genetic variation for resistance to furunculosis is apparent when assessed as both a binary and longitudinal trait, suggesting significant genetic improvement can be made to increase resistance to furunculosis in the IoM stock. No significant correlation was observed between kidney score, EBV, and resistance to this bacterium, but there was a positive phenotypic correlation found between furunculosis resistance and size, suggesting simultaneous selection for performance and resistance is possible within this population.