Abstract
Abstract The relationship between fish length and number of pyloric caeca was studied in fullsib families, with different caeca number, which were obtained through genetic selection and reared in two different hatcheries. At Lees-Athas hatchery a significant positive correlation between caeca number and size of fish of the same age was demonstrated, both within and between families. An influence of rearing conditions upon this relationship was also observed as no significant correlation was found in Donzacq hatchery with the same families. In both hatcheries, families with many caeca exhibited better food conversion ratios than families with fewer caeca, the former showing either lower feed intake for the same growth rate or greater weight gain for the same feed intake. Two non-exclusive hypotheses could account for the growth-caeca number relationship: the caeca number could be either an indicative character reflecting initial growing conditions or a causal character, acting on intestinal morphology and food utilization. In either case, caeca number seems to be an interesting criterion in trout selection.
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