The oesophagus of eels (Anguilla) is an exception to this general pattern. It is relatively long, narrow, and serves during seawater residence to dilute ingested seawater before it reaches the stomach. A possible conflict between the osmoregulatory and digestive roles of the gut in marine fish in general will be discussed later (Section 3.5).
The particular advantage of any configuration seems to rest primarily with the stomach having a shape convenient for containing food in the shape in which it is ingested. Fish which eat mud or other small particles more or less continuously have need for only a small stomach, if any at all. The Y-shaped stomach, at the other extreme, seems particularly suited for holding large prey and can readily stretch posteriorly as needed with little disturbance to the attachments of mesenteries or other organs. Regardless of configuration, all stomachs probably function similarly by producing hydrochloric acid and the enzyme, pepsin.