The Structure and Function of the Gas Bladder in Argentina situs

Abstract

ABSTRACT Anatomical and histological observations were made on the gas bladder of the soft-rayed marine salmonoid fish Argentina silus, which usually lives at depths of about 200 m. The gas bladder is completely closed but rather unlike other known types of closed gas bladders. It is composed of three tissue layers, which may conveniently be called mucosa, submucosa, and tunica externa. The latter contains a large amount of guanine. The tunica externa is penetrated by numerous blood-vessels, which form a widely distributed rete mirabile of a peculiar ‘bi-dimensional’ type in the submucosa. All vessels reaching the mucosa seem to come from this rete system, and no special ‘resorbent mucosa’ such as occurs in euphysoclistae could be identified. The mucosa is folded, forming an alveolar-like structure of unknown function. The gas gland layer is separated from the lumen of the bladder by smooth muscles and an inner epithelium. The close anatomical association of the gas gland tissue with smooth muscles probably is of importance for gas secretion. Analyses of gases from specimens taken from a depth of about 80 m showed a mean oxygen value of almost 80%, which indicates a similar gas secretory mechanism to that in euphysoclistae. Certain aspects of the physiology of the gas bladder in relation to life in deep water are shortly discussed, and the need for a thorough histological examination of the gas bladder in deep-water salmonids is emphasized.