Mat Couchman’s honours project for his degree from the University of Plymouth was an investigation into the feeding interactions among crucian and common carp species within a small reservoir within the university grounds.
The full manuscript (10,000 words) is available from Mat by e-mail request.
The food choice of crucian carp (Carassius carassius) in Drakes reservoir and the influences upon on this by the aquatic environment were investigated.
Thirty-five fish stomachs were observed and it was found that the feeding preference of the crucians revolved around chironomid larvae (Chironomus), small bodied pelagic cladocera (C. ovalis), benthic cladocera (A. affinis) and one species of ostracoda (Cypridopsis). The chironomid larvae and benthic cladocera became more important as the fish increased in length. Rotifers and phytoplankton were not an important part of the diet; Arcella were utilised, but in unknown proportions.
It is suggested that heavy macrophyte growth was the main organism responsible for many interactions and influences upon the fishes’ diet and species diversity in the reservoir.
This population of crucian carp is omnivorous, relying upon more benthic organisms as they increase in length. Stunted growth suggests that intraspecific competition is prevalent in the reservoir. Interspecific competition with common carp (Cyprinus carpio) is suggested. It is believed the crucian carp have reverted to a more cladoceran-based diet to combat this competition with the common carp; this indicates a predominately benthic niche overlap between species.