Adaptive ontogenetic shape change in flyingfish Parexocoetus mento mento

Abstract

Body shape transformation of flyingfish Parexocoetus mento mento was examined to relate its functional importance in flight evolution and ecology using morphometrics. With growth, snout elongation and head depth decreased relative to other anterior body proportions. Associated with the decrease in head depth were a decrease in eye diameter and shortening of postorbital length, resulting in a small head. The lengths of the trunk and caudal regions increased disproportionately relative to their depth, resulting in an overall elongated body shape. The distance from the last dorsal fin ray to the base of the first upper caudal fin ray increased at a greater rate than the distance from the last anal fin ray to the base of the first lower caudal fin ray, resulting in a ventrally inclined caudal fin. Ontogenetic changes in the shape of the head and body are considered to improve streamlining, while the downward inclination of the tail acts to maximize the extended hypocaudal tail lobe, which remains in the water or close to the water's surface during those times when the body is out of the water.