Chemical foraging stimulation in the omnivorous species crucian carp, Carassius carassius (Linnaeus 1758)

In fish aquaculture, great efforts are made to develop feed that excludes marine fish proteins and oils, or at least to decrease these parts to a minimum but the fish might not be attracted to or might not eat the alternative feed. Molecules detected by the olfactory sense can induce arousal and search behavior that attract the fish and induce foraging. In the present study, we have examined whether mussel extracts can induce foraging behavior in crucian carp, Carassius carassius. Free amino acids are present in high concentrations in mussels and they are detected at low concentrations by olfaction and induce food search behavior in several fish species. We studied the behavior responses to water extracts of mussel powder compared to extracts of a plant-based commercial carp feed. Extracts of different concentrations were administered in glass aquaria with individual fish. The tests began with 5 min with only tap water and this was followed by 5 min with extracts or amino acid solutions. The behavior was recorded with a video camera. The initial control period was compared to the following period with odors. No significant foraging response was observed with extracts of mussels, but the commercial carp feed extract induced increased bottom snapping. Synthetic mixtures of five nutritional amino acids present at high concentrations in both extracts did not give any significant foraging response. Our results show that mussels are not suitable as a protein source in feed to crucian carp.