DOI: 10.5061/dryad.kd51c5bfh
title: Finotypic plasticity: Predator-induced plasticity in fin size, darkness, and display behaviour in a teleost fish

description: Fish fins are remarkable devices of propulsion. Fin morphology is
 intimately linked to locomotor performance, and hence to behaviours that
 influence fitness, such as foraging and predator avoidance. This
 foreshadows a connection between fin morphology and variation in predation
 risk. Yet, whether prey can adjust fin morphology according to changes in
 perceived risk within their lifetime (a.k.a. predator-induced plasticity)
 remains elusive.  Here, we quantify the structural size of five
 focal fins in crucian carp (Carassius carassius) following controlled
 manipulations to perceived predation risk (presence/absence of pike Esox
 lucius). We also assess if crucian carp respond to increased predation
 risk by shifts in dorsal fin colouration, and test for differences in how
 fish actively use their dorsal fins by quantifying the area of the fin
 displayed in behavioural trials.  We find that crucian carp show
 phenotypic plasticity with regard to fin size as predator-exposed fish
 consistently have larger fins. Individuals exposed to perceived predation
 risk also increased dorsal fin darkness and actively displayed a larger
 area of the fin to potential predators.  Our result thus provides
 compelling evidence for predator-induced fin enlargement, which should
 result in enhanced escape swimming performance. Moreover, fin-size
 plasticity may evolve synergistically with fin colouration and display
 behaviour, and we suggest that the adaptive value of this synergy is to
 enhance the silhouette of deep-bodied and hard-to-capture prey to deter
 gape-limited predators prior to an attack. Together, our results provide
 new perspectives on the role of predation risk for the development and
 evolution of fins. 
description: Data of fin size, fin display and fin colouration extracted from
 digital photographs of crucian carps reared in the presence or absence of
 a natural predator. 
description: # Finotypic plasticity: Predator-induced plasticity in fin size, darkness,
 and display behaviour in a teleost fish
 [https://doi.org/10.5061/dryad.kd51c5bfh](https://doi.org/10.5061/dryad.kd51c5bfh) Data for this study consists of measurement of the structural size of five focal fins, colouration, and fin display behaviour in crucian carp (*Carassius carassius*) following controlled manipulations to perceived predation risk (presence/absence of pike *Esox lucius*). ## Description of the data and file structure Information on data column labels: Treatment: Fish held in the absence (1) or presence (2) of a pike predator Tank: The specific tank identity in which fish were held Standard length: The distance (cm) between the tip of the snout to the end of the last scale anterior to the caudal fin Lateral_depth: The vertical distance (cm) from the anterior end of the dorsal fin to the lateral line Dark_Pixels_(%): The average percentage (%) of dark pixels in a standardized rectangular area (10 mm high, extending from the anterior base to the posterior edge of the dorsal fin). Dorsal_Fin_Actual size: Dorsal fin size (cm2) as measured with the fin splayed in air. Dorsal_Fin_Expressed size: Dorsal fin size (cm2) expressed in our behavioural observation trials. n/a denotes specimens in which measures of fin size/colour was not possible.