Effects of Diet and Intraspecific Scaling on the Viscera of Muraenid Fishes.

Diet has a strong influence on the morphology and physiology of vertebrates. Members of numerous fish clades have provided excellent comparative models for examining the effects of diet, primarily carnivory vs. herbivory, on organ systems. In this study, we comparatively examined the effects of carnivory, specifically independent evolutions of piscivory and durophagy, on body dimensions, organ topology, and organ proportions between nine moray species (Muraenidae). We found that organ placement via the anteroposterior organ positions differed between members in the two diet categories, although general organ topology is conserved. The stomach (31 - 55%) and intestine (68 - 76%) consistently occupied the majority of the body cavity irrespective of diet. Diet was shown to influence overall body dimensions and relative organ proportions across all moray species. Durophagous morays have shorter head lengths and body depths, and shorter heart, liver, gall bladder, and spleen lengths compared to piscivorous species. There was also greater variation in organ lengths among durophagous species than within piscivorous species. We attribute this greater variation in organ lengths to the multiple independent origins of durophagy within Muraenidae. Our single intraspecific comparison of the California moray, Gymnothorax mordax, a piscivorous species, revealed that all organs scale isometrically with body cavity length over ontogeny. The stomach grows proportionally with body cavity length and is the second longest organ in G. mordax at all ontogenetic stages, with the longest being the intestine. This suggests that morays can consume large quantities of prey or relatively large individual prey throughout their life history. In addition to scaling patterns of G. mordax, our study is the first to investigate the effects of diet and the intraspecific scaling patterns on the viscera of members of the Muraenidae, a clade of obligate carnivores that inhabit most marine ecosystems.