Genetic, maternal, and environmental variance components for body weight and length of Atlantic cod at 2 points in life1

Abstract

Variance components were estimated for 2 body size traits of Atlantic cod at 2 time points. Wild-caught founders from 3 regions off eastern North America were spawned and their progeny were reared at 2 locations in 2 consecutive years. Full-sib families (n = 148) were kept separate until individuals achieved a size large enough to be tagged. At that time (220 d of age), BW and length of 47,637 offspring from 90 sires and 89 dams were recorded. The juveniles were then transferred to sea cages at 3 sites, where they grew further for more than a year. A second set of measurements was collected on 11,839 fish (634 d of age). Dispersion parameters were estimated using REML in bivariate analyses. Models included fixed degree-days (covariate), year × location subclasses, and genetic groups composed of connected families within region of origin. Random factors were animal (additive genetic effects), considering known relationships among the fish; dam (maternal effects); and family (effects common to full-sibs). At tagging, heritability estimates were small to moderate (0.15 and 0.24 for BW and length, respectively; SE = 0.14), similar to or somewhat larger than the proportions of variation ascribed to dams and families (11 to 16%). Later, heritability estimates were greater (0.27 ± 0.08 and 0.31 ± 0.09 for BW and length, respectively), whereas dam and family variance proportions were very small (3 to 4%). Omitting maternal or family components substantially increased the values obtained for heritability at both time points. At the later point, failure to account for maternal effects inflated heritability estimates by about 24% for both traits; ignoring family effects had double the impact. These effects persisted even though endogenous feeding lasts only a couple of weeks in this species and the fish had been pooled since tagging. Discarding data from parents that were completely confounded with their mates decreased heritability estimates slightly (by 0.04, for both traits) at the second point, with no loss of precision despite 15% fewer records and 34% fewer parents; the improved design seemed to have more fully disentangled the additive genetic effects. Estimates of genetic correlations between traits and between time points were very large (>0.89). The results imply that genetic variation exists for body size of cod at both stages. Poor data structure and inadequate models can potentially lead to overstatement of heritability, and thus also of the predicted selection response.

Morphometric traits as selection criteria for carcass yield and body weight in Nile tilapia (Oreochromis niloticus L.) at five ages

“…Despite neither study evaluating the importance of including c 2 , both did show a trend towards its decreasing importance as the fish become older, similar to our results. A trend of decreasing importance of family effect when increasing the age has been observed in other fish as well(Tosh et al, 2010).…”

Using purposeful inbreeding to reduce outbreeding depression caused by escaped farmed Atlantic cod

“…However, most mortality occurs over the period we measured. One study showed that, in relation to maternal effects on larval body size of cod, variation seen in juveniles was still apparent in offspring nearing 2 yr old (Tosh et al 2010). Another study used otolith backcalculations to determine that fast-growing larvae had better chances of survival in the long term (Campana 1996).…”

Rapid assessment of genotype-by-environment interactions and heritability for growth rate in aquaculture species using in vitro fertilisation and DNA tagging

“…However in other experimental designs where c 2 is present genetic variances tend to be overestimated when c 2 has been unaccounted in statistical models (Tosh et al, 2010). Dupont-Nivet et al (2009) went to the extent of creating maternal clones for genetic variance component assessment to minimise maternal effects.…”

“…In some fish species the maternal common environmental effect (c 2 ) for growth can be as high as 0.21 Khaw et al (2009) but are generally below 0.10 ( Dupont-Nivet et al, 2010;Doupe, 2004;Gall and Huang, 1988). Even with estimates below 0.10, omitting maternal or family components can substantially inflate heritability estimates (Tosh et al, 2010;Winkelman and Peterson, 1994). The confounding of common environmental effects with additive genetic effects is a particular problem when only one generation of performance measurements is available.…”