Genetic variation of body size, condition and pyloric caeca number in juvenile brown trout, Salmo trutta L.

Parental and individual variance components of body length, weight, condition (estimated as the second principal component of the length–weight relationship) and pyloric caeca number were investigated in 6-month-old brown trout (Salmo trutta L.) by the mean of two sib analyses, which provided consistent results. The average heritabilities (±SE) were 0.12 (±0.08) for length, 0.16 (±0.08) for weight, 0.47 (±0.14) for condition and 0.38 (±0.12) for pyloric caeca number. Maternal effects were also observed, although short of significance, in length, weight and caeca number. Correlations between caeca number and body size averaged +0.10 among individuals within lots, but genetic correlations were negative, i.e. about −0.9 for length and −0.7 for weight. There was no significant correlation between caeca number and condition. These results lead to question the role that pyloric caeca may play in growth, as well as their usefulness in fish breeding.