Social and genetic determinants of size variation in tanks of Nauyuk, Norwegian, and hybrid Arctic charr, Salvelinus alpinus (L)

An experiment was performed to determine the relative importance of social and genetic factors on the development of size variation in tanks of Arctic charr, Salvelinus alpinus (L.). Growth and the development of size variation were monitored for approximately 300 days in one-year-old fish from 18 families of Nauyuk, Norwegian and hybrid charr. Initial mean weights ranged between 21 and 85 g, and initial CVs (CV = coefficient of variation = 100 x standard deviation / mean) were between 4% and 52%. The final mean fish weights and variances of weight in tanks were highly predictable in terms of initial mean weights, initial variances, and elapsed time, suggesting that the same social influences were present in test tanks, Changes in CV depended on both the initial mean weights and initial CVs. The largest increases in CV occurred in tanks of small fish with initially small CVs and the largest decreases in tanks of large fish with initially large CVs. In general, tanks tended toward CVs of 20-40%, with tanks of initially small fish tending toward the larger CVs. On the basis of the observed results, it is suggested that to optimize growth and minimize size variation, charr should be sorted to CVs between 25% and 35% and then cultured at high densities (> 40 kg m(-3)). As expected, there were significant differences in strain and family growth rates. However, the relationship between size variation and mean weight did not differ between strains, but differed slightly but significantly between families within strains. These effects were weak compared with social effects. It is concluded that social factors are the most important in determining the growth of individual charr, and may have confounded previous experiments examining the genetic basis of growth.