Phenotypic plasticity of muscle fiber type in the pectoral fins of Polypterus senegalus reared in a terrestrial environment

Abstract

Muscle fiber types in the pectoral fins of fishes have rarely been examined, despite their morphological and functional diversity. Here we describe the distribution of fast and slow muscle fibers in the pectoral fins of Polypterus senegalus, an amphibious, basal actinopterygian. Each of the four muscle groups examined using mATPase staining show distinct fiber type regionalization. Comparison between fish raised in aquatic and terrestrial environments reveals terrestrially-reared fish possess 28% more fast muscle compared to aquatically-reared fish. The pattern of proximal-distal variation in the abductors differs, with a relative decrease in fast muscle fibers near the pectoral girdle in aquatic fish compared to an increase in terrestrial fish. Terrestrially-reared fish also possess a greater proportion of very small diameter fibers, suggesting that they undergo more growth via hyperplasia. These observations may be a further example of adaptive plasticity in Polypterus, allowing for greater bursts of power during terrestrial locomotion.