ANATOMY OF THE SWIMBLADDERS OF SEVEN FAMILIES OF TRANSVAAL FRESHWATER FISHES

SUMMARY

IN the genera Barbus and Labeo of the family Cyprinidae there is a typical twolobed, cylindrical swimbladder: a shorter anterior and a longer posterior lobe, connected by an isthmus. The pneumatic duct passes from the anteroventral end of the posterior lobe to the oesophagus. In the genus Labeo two spiral bands encircle the posterior lobe twice. No rete mirabile, nor any indication of a gas gland, was observed.

The species Hydrocynus vittutus of the family Characidae has a very similarly shaped swimbladder to that of the Cyprinidea. Inside the anterior lobe, however, there is a peculiar structure, which is evidently the gas glad, although a rete mirabile was not observed.

In the families of the Siluriformes, studied, with the exception of the Clariidae, a single lobed, heartshaped swimbladder is present. It is divided by a longitudinal and a transverse. septum into three chambers: an anterior, a right and a left posterior chamber. The pneumatic duct originates from the medial posteroventral part of the anterior chamber. In Clarias gariepinus the two-lobed, right and left lobed, swimbladder lies in a bony capsule, which is attached transversely to the posteroventral part of the skull. In all the Siluriformes, studied, no trace of a gas gland, nor of a rete mirabile was found.

The Cichlid swimbladder has no pneumatic duct, nor any other exit, hence it is physoclistic. In the Cichlids the retroperitoneal position of the swimbladder is accentuated, as the peritoneum and the outer tectum of the swimbladder have united to form a thick, tough membrane, which divides the body cavity into a distinct ventral, or visceral cavity, and a dorsal, or swimbladder cavity. The swimbladder cavity acts as an outer swimbladder. It contains an inner, smaller bladder whose internal ventro-anterior surface is covered with arborescently arranged patches of gas glands.

The attachment of the swimbladder to the tripus and also to the ossa suspensoris is discussed.