Crucian carp are able to change their body shape and swimming performance in response to the presence of predatory fishes in their habitat, according to a study published in the most recent issue of the journal Proceedings of the Royal Socety B: Biological Sciences.
The study by Paolo Domenici, Hkan Turesson, Jakob Brodersen and Christer Brnmark studied crucian carp (Carassius carassius) in ponds with and without piscivorous pike (Esox lucius) in southern Sweden.
It has been known from previous research that the crucian carp respond to chemical cues from piscivorous fishes by becoming deeper-bodied.
It is believed that the deeper body in the carp decreases predation risk by gape-limited piscivores such as pike.
The researchers examined the escape locomotor performance of both shallow-bodied crucian carp (from ponds without pike) and deep-bodied crucian carp (from ponds with pike) by filming the escape response of the fish with a high-speed camera in an arena.
They found that the presence of a predator induces an increase in escape swimming performance, and that this increase is accompanied by morphological changes such as a deeper body and higher percentage of muscle mass.
According to the authors, ...a large body depth and a relatively high muscle mass:body mass ratio enhance acceleration performance, owing to the high thrust produced by a large area, and high muscle power. Besides having superior acceleration, the predator-induced deep-bodied individuals had a higher turning rate than the shallow-bodied ones. This implies that deep-bodied crucian carp can achieve any given turn away from danger in a shorter time than shallow-bodied individuals. A high proportion of muscle mass, and hence muscle power, may increase turning rate...
The phenotypic plasticity of crucian carp may be related to the variable environment in which they live. In Scandinavian lakes and ponds, pike and crucian carp often coexist...Predation pressure on crucian carp can vary greatly within one prey generation due to hypoxic events which may kill pike and other predators, but not crucian carp, since they are extremely resistant to hypoxia...Phenotypic plasticity allows crucian carp to take advantage of a shallow body form for high cruising ability in the absence of predators, while the deep-bodied morph shows a high escape swimming performance, together with a defence mechanism in the presence of gape-limited predators...
For more information, see the paper: Domenici, P, H Turesson, J Brodersen and C Brnmark (2008) Predator-induced morphology enhances escape locomotion in crucian carp. Proceedings of the Royal Society B: Biological Sciences 275, pp. 195"201.