Genetic analysis of female reproduction traits of farmed coho salmon (Oncorhyncus kisutch)

Abstract

Based on 8 years of data on 891 daughters from 190 sires and 398 dams, females produced an average (standard deviation) of 4251 (957) green eggs with a total weight of about 680 (191) g; the females produced 3226 (1255) eyed eggs, average egg weight was 180 (27) mg, and the average day of spawning was 137.5 (9.8) days measured from December 31. Average body weight was 3247 (879) g at harvest, 3702 (876) g at spawning and 3022 (730) g post-spawning. Estimated heritability of weight of green eggs spawned was 0.39, while that for number of green eggs was 0.42, that for heritability for average egg weight (egg size) and number of eyed eggs were slightly lower at 0.32 and 0.33, respectively, while the estimate for spawn day was low (0.24). Number of green eggs was highly, and positively, correlated with weight of eggs spawned (0.79), number of eyed eggs (0.82) and number of eyed eggs with weight of eggs spawned (0.53) and spawn day (0.52). The genetic correlations between number of eggs and average egg weight were negative (−0.63 for green eggs and −0.44 for eyed eggs). None of the estimated genetic correlations between spawn day and the four measures of fish size differed from zero, suggesting genetic independence of spawning date and body size, within spawning season; however, this may have been due to the inclusion of only early spawning females in the study. Estimates of genetic correlations between the various measures of fish size were all positive and ranged from 0.60 to 0.70 for spawning weight and spawning length, spawning length and post-spawning weight and harvest weight and post-spawning length of females. Spawning weight was highly correlated with weight of eggs spawned (0.69) and moderately related genetically to number of green eggs (0.34) and average weight of ova (0.37). Estimates of genetic correlation between spawning weight and number of eyed eggs did not differ from zero. The corresponding phenotypic correlations all were low or near zero. Harvest weight and post-spawning weight were not correlated with number of green or eyed eggs, but were associated with egg weight and weight of eggs spawned; both genetic correlations were 0.46 for harvest weight, while the correlations with post-spawning weight were 0.37 for egg weight and 0.56 for weight of eggs spawned. The results indicate that the coho population under study contains a high level of additive genetic variation for all traits related to female reproduction and estimates of genetic correlations suggest that correlated changes that may accompany selection for larger body size at market will be favourable in most instances.