6.3 Common Carp (Cyprinus carpio)
Common carp are representative of many cyprinids, including goldfish, squawfish, minnows, dace, chubs, and tench in North America. Most of these fish, including common carp, are omnivores, similar in several respects to catfish, but also differing significantly in several respects. Carp have maxillary barbels (most cyprinids do not) and forage in mud like catfish. However, carp ingest a considerably greater amount of plants than catfish and then chew the plants using a set of interdigitating pharyngeal teeth placed just anterior to the oesophagus. Carp lack a stomach, but have a long intestine which winds extensively throughout the visceral cavity. The gall bladder rests on the dorsal surface of the anterior midgut and the bile duet opens into the intestine just anterior to the gall bladder. In addition, the liver has no specific shape, but seems to serve as packing material around the intestine. Food seems to be ingested in small particles in a relatively steady stream instead of intermittently in large units, so the storage function of a stomach probably is not missed. With the liver filling all the available visceral space, there would be no room for accommodating the stomach expansion of a large meal anyway. The remainder of the visceral organs are relatively unremarkable (Figure 1c).
a. Rainbow trout (carnivore);
b. Catfish (omnivore emphasizing animal sources food);
c. Carp (omnivore, emphasizing plant sources of food);
d. Milkfish (microphagous planktovore).