a significant correlation between body shape and diet and suggested
that the intermediate phenotype of hybrids may play a role in their
feeding abilities, i.e. hybrids use a broader trophic spectrum than parental species, which is in line with the high ecological success of hybrids in
Ireland. However, Corse et al. (2009) showed that there was no correlation between body shape (or mouth deformation) and diet analyzed
using stable isotopes, i.e. they observed a wide overlap of isotope signature and fish body and mouth shapes between C. nasus, P. toxostoma and
their hybrids in sympatric zones. Even though we did not perform stable
isotope analyses, our analyses revealed the clear intermediate character
of hybrid intestine size when compared to both parental species.
Concerning the general status of diet, both species may be considered
omnivorous on the basis of their diet spectra. However, the natural
diet of common carp living in ponds and artificial reservoirs is composed mainly of zooplankton and zoobentos (Baruš and Oliva, 1995).
In addition, common carp reared in ponds for commercial purposes
are fed with supplementary feed. The long intestine typical of gibel
carp suggests its ability to also utilize vegetable food (Baruš and Oliva,
1995), which may represent an advantage when competing with common
carp for food. The intermediate size of the intestine in gibel carp × common
carp hybrids may suggest that hybrids are able, at least partially, to
utilize vegetable food. However, supplementary analyses of diet
composition in gibel carp × common carp hybrids are needed and
only experimental studies can resolve the question of whether hybrids are able to exploit the energy obtained from vegetable food
for their growth and survival.