Morphology of the digestive system of Antarctic nototheniid fishes

Although Antarctic nototheniid fishes are ecologically diverse, this survey of aspects of the anatomy and histology of the digestive system of 25 species showed little interspecific variation in the structure of this system. The gastrointestinal tract is illustrated and all but two species shared a similar pattern of intestinal coiling. The average number of pyloric ceca in most nototheniids was 6 7, with means ranging from 3.0 to 7.6. Reduction in the number of ceca was evident in both phyletically basal and derived species. Intraspecific variation in cecal number was nonexistent in sonic species, but in others ranged between 2 and 4 ceca. Numerous hepatic ducts, contained within the liver parenchyma, converged on the neck of the gall bladder. The bile duct penetrated the gut wall near the origins of the most dorsally located ceca. The terminal portion of the pancreatic duct paralleled, but did not join, the bile duct. The exocrine pancreas was diffuse and present in intercecal and splenic mesenteries, in the wall of the gall bladder and in tissue near the willis of the bile and pancreatic ducts. Unlike many other teleosts, the liver of nototheniids usually lacked pancreatic exocrine tissue. Nototheniids had a principal pancreatic islet (Brockmann body) and 2-3 accessory islets. Peritoneal melanism was a convergent feature of species living in the water column and probably served to screen the bioluminescence from gut contents.