Читать книгу Clinical Guide to Fish Medicine - Группа авторов - Страница 67

Known as the “bony tongues”, they have well‐developed teeth on the tongue and roof of the mouth that provide a shearing bite. The intestine curls around to the left of the esophagus and stomach; in most fish, it passes to the right (Nelson et al. 2016). They possess one or two pyloric ceca.

Arapaima (Arapaima spp.) are some of the largest freshwater fish in the world and have large, corrugated scales which complicate venipuncture and injections. They are obligate air‐breathers.

Freshwater butterflyfish (Pantodon buchholzi) have greatly enlarged pectoral fins just dorsal to their large pelvic fins. They have a swim bladder and are obligate air‐breathers. They are not related to marine butterflyfish.

Elephantfish (Mormyridae) have a proboscine snout. Many generate weak electric fields to locate objects and for communication (up to 10 V at low frequency) (Roberts 2011). The electric organ is derived from muscle and located in the peduncle. Their cerebellum is large and they show excellent learning skills. They have an otic gas‐bladder that is separate from the swim bladder. Eyes are small and show adaptations to low light, including small reflective cups on the retina. There is only a left gonad. Uniquely, the sperm have no flagellum (Hopkins et al. 2007).

The African and Asian knifefish (Notopteridae) lack many fins (anal, caudal, and pelvic) but have one long dorsal fin. They also generate weak electric fields. They have small eyes and poor eyesight (Nelson et al. 2016). They are not related to the South American or neotropical knifefish (Gymnotiformes).