Phenotypic plasticity and predator effects on morphology and physiology of crucian carp in nature and in the laboratory

Abstract

Crucian carp Carassius carassius show great phenotypic plasticity in individual morphology and physiology, and strong variation in population density in different fish communities. Small fish with shallow bodies and large heads are typical in overcrowded monospecific fish communities in small ponds, whereas deep-bodied, large fish are found in larger, multispecies lakes. Crucian carp are especially vulnerable to predation by piscivorous fish and their greater relative body depth in multispecies fish communities has been proposed to be an induced defence against size-limited predation, and hence to be an adaptive feature. Data are presented here on the two divergent body forms in field populations in eastern Finland, together with results of laboratory experiments on predator effects on morphology and physiology (growth, respiration, heart rate). The deep body can be achieved in a few months by introducing a low population density of shallow-bodied fish into a food-rich environment with no piscivores. In the laboratory, both the presence of piscivores (chemical cues) and enhanced food availability increased the relative depth of crucian carp, but only to a modest extent when compared to natural variation. It is concluded that the deep-body form of crucian carp in the low density populations of multispecies fish communities is the normal condition. Reproduction in monospecific ponds results in high intraspecific competition, low growth rate and a stunted morphology. According to pilot tests, the mechanism behind the predator effect in the laboratory might be a behavioural reaction to chemical cues (alarm substances/predator odour) causing changes in energy allocation: predator-exposed crucian carp adopt a ' hiding ' mode with decreased activity (less swimming, lower respiration and heart rate) and with higher overall growth. Whether, and to what extent, this predator-induced mechanism works in nature is unclear.1997 The Fisheries Society of the British Isles

Challenging fear: chemical alarm signals are not causing morphology changes in crucian carp (Carassius carassius)

“…Firstly, the classical alarm pheromones triggering behavioural responses are not the ones possessing the primer pheromone effect (e.g., Karlson and Lüscher 1959;Wilson and Bossert 1963), meaning that they are not the causative agents for inducing morphological changes in crucian carp. Secondly, permanent presence of alarm signals do not result in increased body depth through indirect behavioural means, causing decreased activity, energy allocation and an higher overall growth, as suggested by some authors (e.g., Holopainen et al 1997a;Vøllestad et al 2004;Andersson et al 2006;Johansson and Andersson 2009). Our results may, on the other hand, explain the lack of morphological responses from the "scratching with a knife" injury method by Brönmark and Pettersson (1994), because non-soluble tissue may not have been released with that method.…”

“…3), when the fish were released into ponds at low densities with abundant natural food, BDI and CF showed a linear relationship. However, in neither case any signs of increased growth resulting from presence of alarm signals were noted, as proposed by Holopainen et al (1997a). On the contrary, in both the environments we found that crucian carp exposed to chemical alarm signals grew less when compared to control fish.…”

Costly plastic morphological responses to predator specific odour cues in three-spined sticklebacks (Gasterosteus aculeatus)

“…The larger size of roach water fish might thus be a response to a perceived amount of competition. In crucian carp for example both predation risk and intraspecific competition has been shown to influence morphology (Holopainen et al 1997). A similar pattern has been described in wood frog tadpoles (Rana sylvatica) which developed larger bodies and smaller tails, both in the presence of conspecific and heterospecific competitors (Relyea 2002a).…”

“…4 Differentiation of the three treatment groups of adult sticklebacks along the first two CV axes. Deformation grid with displacement vectors for CV1 (a) and CV2 (b) demonstrated in other animal species (e.g., Brönmark and Miner 1992;Holopainen et al 1997;Lass and Spaak 2003;Hettyey et al 2010). Body shape, spine length, condition factor and standard length of juveniles and adults were quantified after rearing full-sibs Eight principal components comprising most explanatory power ([2%) were tested Significant differences (P \ 0.05) are given in bold under regular perch water (predator-treatment), roach water (non-predator-treatment, fish control) and tap water treatment (treatment control).…”

“…Group size did not differ significantly between treatment groups (mean ± SD, perch: 12.8 ± 6.5, roach: 13.2 ± 5.5, tap water: 10.0 ± 8.4; F 2,6 = 1.48, P = 0.3). Nevertheless, as also shown in many other fish species (e.g., Holopainen et al 1997), group size significantly influenced body length (P \ 0.01) and was therefore included in all final models to control for this source of residual variance. We applied mixed-effect linear models using the lme function of the nlme library (Pinheiro and Bates 2000).…”