The logistic function y=(A+Be2x)/(l+Ce2j), which earlier has proved to fit the course of growth in broiler chickens and young bulls very accurately, was also found to describe the course of growth in rainbow trout during the period from 168 days of age to spawning very closely. Thus, the ratio between the sum of squares of deviations from the regression curve, based on the body weight means, and the total sum of squares was less than 2xl0'5. All the parameter estimates A, B, C, X were significantly different from zero in each of the two sexes and three strains, one control (C) and two selection strains (Y and E). Selection for body weight at 364 days of age in strain Y caused a change in the growth pattern of the fish without giving any positive response in body weight at 364 days and earlier ages. This situation occurred because the positively correlated selection effects on A, C and X were counteracted by the negatively correlated selection effect on B.

G. Su, Liljedahl L E, G. Gall

Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume 19. Selection and quantitative genetics; growth; reproduction; lactation; fish; fiber; meat., , 391–394, 1994
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