Comparative morpho-functional study of the intestine of the Antarctic fish Notothenia coriiceps and Trematomus newnesi (Nototheniidae): Histology and ultrastructure

Abstract

Seasonal variation in the photoperiod and light intensity in the Antarctic region influences the biomass and primary productivity in the Antarctic Ocean. This results in specialized adaptations for obtaining food, associated with morphological and physiological changes in the digestive tract of fish. The aim of the present study is the morpho-functional study of the intestine of two Antarctic Nototheniidae : Notothenia coriiceps, a benthic fish that shows relatively low levels of activity, and Trematomus newnesi, a semi-pelagic fish. Both show a proportionally big stomach and a short intestine. Those are the main characteristics of carnivorous fish. The intestinal mucosa is lined by a simple columnar epithelium with enterocytes, goblet cells, lymphocytes and rodlet cells. Goblet cells produce neutral and acid mucosubstances along the whole of the intestine, in both species. Enterocytes at the pyloric ceca and the proximal portion of the medium intestine in N. coriiceps, as well as the medium intestine of T. newnesi, show ultrastructural characteristics of lipid absorption cells. Enterocytes with characteristics of protein absorbing cells were observed along the posterior intestine of both species. In addition, N. coriiceps shows deep folds at the posterior intestine and a high concentration of blood capillaries, suggesting that in this region there is active transport of macromolecules by pinocytosis. Osmoregulation seems to occur mainly in the medial and distal portions of the medium intestine in N. coriiceps, while in T. newnesi it occurs along the entire medium intestine. These differences in intestinal functional morphology in both species can be related to their feeding habits and their energetic metabolism, resulting from different utilization of food nutrients, as N. coriiceps is a generalist, while T. newnesi ingests a narrow spectrum of food items.