Pyloric caecal morphology of brook charr,Salvelinus fontinalis,in relation to diet

Synopsis Brook charr, Salvelinus fontinalis, shifts its diet from zoobenthos to pelagic prey when living sympatrically with white sucker, Catostomus commersoni, in lakes of the Laurentian Shield. We tested the hypothesis that this diet difference would have a significant impact on their pyloric caecal morphology in 5 lakes containing allopatric brook charr populations and 6 other lakes containing both brook charr and white sucker. We observed that the mean length of the most posterior caecum of charr was significantly greater in sympatry than in allopatry (X ± 1 SD: 9.91 ± 1.12 mm versus 8.44 ± 0.67 mm). This is equivalent to an increase of 18% of total pyloric caecal mass (dry weight) in sympatric brook charr. These results indicate that this response to differences in diet, well known in birds, also occurs in fish.