Anatomy of finfish and shellfish

4.1.4. Pyloric caeca
(Fishes are only vertebrates that have appendages (Caeca) at the gastro-intestinal junctions). On the intestine of most bony fishes at the pyloric end of the stomach. There may be from one to many blind sacs or pylonic caeca or intestinal caeca. A few groups such as cat fishes (Ictaluridae) topminnows (Cyprinidae) and pikes (Esocidae) lack these structures.
In such groups as flat fishes (Pleuronectiformies) the pyloric caeca are few usually not more than five (5). In others such as Mackerels (Scombridae), Salmons (Salmonidae) the number of these caeca may range to 200 or more. Generally caeca of different species vary considerably in size, state of branching and the connection with the gut. In sturgeons (Acipenseridae) the many caeca forma large mass, but only a single duct leads to the intestine. In salmon, each caecum communicates directly with the gut, the functions of pyloric caeca probably involve both digestion and absorption.