Abstract
BackgroundGrowth in fishes is regulated via many environmental and physiological factors and is shaped by the genetic background of each individual. Previous microarray studies of salmonid growth have examined fish experiencing either muscle wastage or accelerated growth patterns following refeeding, or the influence of growth hormone and transgenesis. This study determines the gene expression profiles of genetically unmanipulated large and small fish from a domesticated salmonid strain reared on a typical feeding regime. Gene expression profiles of white muscle and liver from rainbow trout (Oncorhynchus mykiss) from two seasonal spawning groups (September and December lots) within a single strain were examined when the fish were 15 months of age to assess the influence of season (late fall vs. onset of spring) and body size (large vs. small).ResultsAlthough IGFBP1 gene expression was up-regulated in the livers of small fish in both seasonal lots, few expression differences were detected in the liver overall. Faster growing Dec. fish showed a greater number of differences in white muscle expression compared to Sept. fish. Significant differences in the GO Generic Level 3 categories ‘response to external stimulus’, ‘establishment of localization’, and ‘response to stress’ were detected in white muscle tissue between large and small fish. Larger fish showed up-regulation of cytoskeletal component genes while many genes related to myofibril components of muscle tissue were up-regulated in small fish. Most of the genes up-regulated in large fish within the ‘response to stress’ category are involved in immunity while in small fish most of these gene functions are related to apoptosis.ConclusionsA higher proportion of genes in white muscle compared to liver showed similar patterns of up- or down-regulation within the same size class across seasons supporting their utility as biomarkers for growth in rainbow trout. Differences between large and small Sept. fish in the ‘response to stress’ and ‘response to external stimulus’ categories for white muscle tissue, suggests that smaller fish have a greater inability to handle stress compared to the large fish. Sampling season had a significant impact on the expression of genes related to the growth process in rainbow trout.
Highlights
Growth in fishes is regulated via many environmental and physiological factors and is shaped by the genetic background of each individual
When the full-sib families within each of the Sept. and Dec. half-sib families were examined for parental effects on weight, significant dam effects were found in the Dec. fish (Figure 2)
thermal growth co-efficient (TGC) can be taken as an estimate of growth efficiencies in the fish during a given growth interval
Summary
Growth in fishes is regulated via many environmental and physiological factors and is shaped by the genetic background of each individual. Other factors are more complex and relate to interactions between extrinsic and intrinsic factors that regulate growth, such as individual responses to stress and disease [12], population density [13], social status [14], and feeding regime [15]. 15 of the 29 linkage groups in rainbow trout (Oncorhynchus mykiss) have QTL for body weight and/or condition factor with genome-wide effects, with an additional 8 linkage groups housing QTL with chromosome-wide effects [20] This indicates that perhaps three quarters of rainbow trout linkage groups contain genomic regions with major influences on growth. Microarray studies have examined fish experiencing muscle wastage [6,7,8] with the premise that genes down-regulated during muscle wastage will be up-regulated during muscle growth and vice versa. Myosin genes showed down-regulation during muscle wastage [7] and during GH-stimulated growth [21] in rainbow trout
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