Incorporation of dietary carotenoids into the fins of yellow- and red-finned Eurasian perch Perca fluviatilis

The colour of the ventral, anal and caudal fins of Eurasian perch can range from pale yellow to intense red. Within spatially separated populations, however, individuals are usually very uniform in colour. We fed astaxanthin- and canthaxanthin-enriched dry feed to juvenile perch from a yellow-finned and a red-finned population to compare the influence of dietary carotenoids on fin colour between these two populations. In this way we wanted to test whether fin colour in perch is predominantly a phenotypically plastic trait or whether differently coloured individuals represent colour morphs. The ventral fins of perch from the red-finned population always exhibited significantly more intense redness when their feed was supplemented with either one or both carotenoid additives. Perch from both populations deposited more canthaxanthin in their ventral fins than astaxanthin, red-finned perch in particular. Yellow-finned perch probably converted canthaxanthin into β-carotene, which was the dominant carotenoid in their ventral fins, whereas the fins of red-finned perch contained only trace amounts of β-carotene. We conclude that these two populations represent colour morphs that differ fundamentally in their ability to metabolise and deposit dietary carotenoids into their ventral fins. Considering the multiple physiological functions of carotenoids, these fundamental differences in carotenoid metabolism between perch colour morphs may have far-reaching consequences for the performance of different populations, for example in their response to parasite infections.