Читать книгу Clinical Guide to Fish Medicine - Группа авторов - Страница 26

The stomach varies in size depending on food items. Some species are agastric, e.g. goldfish (Carassius auratus), common carp and koi (Cyprinus carpio), and zebrafish (Danio rerio). The stomach becomes a grinding organ in sturgeons (Acipenseridae), gizzard shads (Dorosoma spp.), and mullets (Mugilidae) (Helfman et al. 2009). Histologically, the cardia consists of striated muscle and transitions to smooth muscle in the pyloric stomach. The mucosa has numerous mucus glands (Roberts and Ellis 2012). Pyloric caeca are diverticula off the stomach that are present in salmonids and many other teleosts. They increase the absorptive surface area. These organs are dissimilar to the ceca of birds and mammals as they are not fermentative (Buddington and Diamond 2016).

The intestines are variable in length and shape but fairly simple. The colon is minimal or not distinguishable (Roberts and Ellis 2012). In the lungfish (Dipnoi) and sturgeon (Acipenseridae), the intestine is spiral‐shaped, similar to the elasmobranchs (Figure A1.11). A rectum is present (Roberts and Ellis 2012). Gastrointestinal emptying times are highly variable and both temperature‐ and volume‐dependent; more details can be found in Chapter A4.

Pufferfish are unique in being able to inflate their bodies with water or air. Mouthfuls are pumped into the stomach which then expands. The pectoral girdle and head have modifications that function as a pump and the skin is very distensible; ribs are absent to accommodate inflation (Wainwright and Turingan 1997). In some species the skin has spines which stand erect on inflation.

External intestinal and urogenital openings differ among species. In most, there is a separate anus and reproductive opening or urogenital pore (Yanong 2003). In some bony fish, there is a cloaca: a common area where the intestinal, urinary, and gonadal ducts empty, e.g. lungfish and coelacanths (Latimeria spp.).