Читать книгу Clinical Guide to Fish Medicine - Группа авторов - Страница 74

These are the lobe‐finned fish. Coelacanths (Latimeria spp.) are rarely seen and were considered extinct until a specimen was discovered in the 1930s. Lungfish (Dipnoi) species come from Australia, Africa, and South America. In all species, the pectoral and pelvic fins are on fleshy stalks extending from the body from a type of humerus or femur similar to the teleost model of multiple bones. Lungfish have electrosensory ampullae over the head and trunk. They have tooth‐plates and teeth that are on the interior jaw bones rather than the margins. There is a spiral valve distal to the duodenum, except in Australian species where the valve starts at the esophagus. The atrium and ventricle are partly divided by a partition which more closely resembles the tetrapod four‐chambered heart than typical fish hearts (Jorgensen and Joss 2016).

Australian lungfish (Neoceratodus forsteri) are the largest, with well‐developed tooth‐plates. Scales are cycloid, large, and thick. Four gill arches are present. They are facultative air‐breathers. There is a single lung. Sexual maturation occurs at 15–20 years and longevity is 65–70 years, with some living beyond this time frame.

African lungfish (Protopterus spp.) have pectoral and pelvic fins that are thinner and more filamentous. Their scales are small. The gilled lungfish (Protopterus amphibius) are most easily identified as they retain three large external gills on the sides of the head; otherwise only larvae have external gills. Six gill arches are present. They are obligate air‐breathers with paired lungs (Figure A1.14). They are known for their ability to estivate in dry habitats for remarkable periods of time (seven to eight months, up to four years experimentally). Aestivation involves constructing a burrow which is filled with mucus that dries to form a cocoon. When estivating, the animal breathes air, its heart rate drops, and body proteins are metabolized.

South American lungfish (Lepidosiren paradoxa) have small scales and thin, filamentous fins. They have five gill arches, with external gills as larvae. They are obligate air‐breathers with paired lungs as adults. Estivation occurs in burrows but is poorly documented (Helfman et al. 2009; Jorgensen and Joss 2016; Nelson et al. 2016)