Estimation of genetic parameters for upper thermal tolerance and growth traits in grass carp (Ctenopharyngodon idella)

As an ectothermic animal that lives in water for a lifetime, grass carp (Ctenopharyngodon idella) has a strong dependence on environmental temperature. The objective of this study was to estimate the genetic parameters for heat tolerance and growth traits in grass carp using reconstructed pedigree and molecular relatedness. The experimental population consisted of 800 offspring at 60 days old and 55 parents (♀, 32; ♂, 23) from selected line F4 and 539 at 6 months old offspring from selected line F5 with 87 parents (♀, 44; ♂, 43). Genetic genotyping of the experimental population was conducted using 10 pairs of microsatellite markers, and all 10 markers exhibited a high degree of genetic polymorphism across all 1394 grass carp (Ho = 0.751–0.981; He = 0.783–0.942; PIC = 0.759–0.938). Parentage assignment divided F4 individuals into 203 full-sib, and the Pearson correlation coefficient between reconstructed pedigree relatedness and molecular relatedness was 0.475. For the selected line F4, the heritability for each trait based on reconstructed pedigree relatedness (PR) were 0.320 ± 0.092 for body weight (BW), 0.303 ± 0.093 for standard length (SL), 0.246 ± 0.082 for body height (BH), 0.193 ± 0.074 for body thickness (BT), and 0.131 ± 0.063 for upper thermal tolerance (UTT) was 0.131 ± 0.063. Similarly, the heritability for each trait based on molecular relatedness (MR) were 0.330 ± 0.092 for body weight (BW), 0.348 ± 0.097 for standard length (SL), 0.248 ± 0.080 for body height (BH), 0.197 ± 0.073 for body thickness (BT) and the heritability for upper thermal tolerance (UTT) was 0.260 ± 0.037. For the F5 generation, the heritability of body weight (BW) and standard length (SL) estimated by molecular relatedness (MR) was 0.281 ± 0.045 and 0.283 ± 0.044. These results indicate that molecular relatedness is a viable method for estimating genetic parameters when pedigree information is inaccurate or missing. The findings of this study can provide theoretical support for the optimization of breeding programs aimed at developing productive and heat tolerant grass carp strains. •Microsatellites were used for parentage assignment and calculation of molecular relatedness.•We estimate genetic parameters by using molecular relatedness.•Heritability of heat tolerance trait was calculated in grass carp.