268 Organic waste recycling: technology and management
Figure 6.2 Examples of herbivores, carnivores and omnivores
6.2.3 Omnivorous fish
Carnivorous fish have alimentary systems, which are more or less intermediate
between those of the extreme herbivores and carnivores, but there is a range of
types between the extremes. The alimentary canal is much longer, relative to
body length. Most fish belonging to these groups, that consume both animal and
plants, for example, the Chinese common carp (Cyprinus carpio) and Tilapia
(Oreochromis niloticus) (Figure 6.2d & e), have a wide range of diet.
The terms herbivores and carnivores have relative meaning. Usually they just
indicate the type of food predominantly consumed by the fish (actually most
fish are highly adaptable in their feeding habits and utilize the most readily
available foods (Lagler et al. 1962)). Relatively few kinds are being strict
herbivores or carnivores, and perhaps none of all feed solely on one organism.
Food habits may change as fish grow, accompanied by marked change in the
morphology of alimentary system in early life. Fish such as Bermuda angelfish
(Holacanthus bermudensis) may even change their diet with season. It may be
quite herbivorous in winter and spring and become predominantly carnivorous
in the summer and early fall.