Digestion and digestive-transport surfaces in cestodes and their fish hosts

The structural and functional organization of digestive-transport surfaces in some lower cestodes and their fish hosts was studied. It has been shown that the ultrastructure of cestode microtriches and fish enterocyte microvilli being the basis of membrane-linked digestion is quite similar. These organelles increase the digestive-transport surfaces both in helminths and fishes. However, the hydrolytic enzyme activity in helminths is usually 2–4 times lower than that of the fishes. Desorption (adsorption) characteristics of various hydrolases in helminths and fishes are also different. In helminths the easily desorbed fraction of each enzyme is always more abundant than in fishes. In contrast, the intensity of transport processes in helminths is higher when compared with fishes. The adaptation of digestive-transport surfaces and enzyme systems to feeding conditions is discussed.