The importance of carotenoids in signaling during aggressive interactions between male firemouth cichlids (Cichlasoma meeki)

Abstract

Male firemouth cichlids, Cichlasoma meeki, have red pigmentation covering large areas of their ventral surface, which is displayed during aggressive interactions. We manipulated the levels of red pigmentation by assigning the fish to one of two diets, which were as similar as possible except that one was high in carotenoids while the other was low in carotenoids. During diadic trials under white light, fish kept on the high carotenoid diet won a higher proportion of contests than fish kept on the low carotenoid diet. Under green light, where differences in redness cannot be discriminated, there was no effect of diet on the outcome of contests. These experiments demonstrate that it is the effect of the diet on red pigmentation that is important rather than some confounding variable such as differential growth rates. The weight of the two fish was also important; there was a tendency for the heavier fish to win more contests. The mass effect was subordinate to color under white light but was the dominant factor under green light. The nature of the contests under the different light conditions also varied; the display in which the red pigmentation is most obvious was not used under green light, but was common under white light. This suggests that the display strategies are flexible and can be altered according to which displays are most effective in a given environment. Previous studies of other species of fish and birds have shown that the degree of redness influences mate choice and is affected by parasite infestations. We propose that carotenoid pigmentation is likely to reflect a general quality, influenced by several factors, rather than a context-specific quality such as fighting ability.