Читать книгу Clinical Guide to Fish Medicine - Группа авторов - Страница 71

This group lacks scales but some have bony plates or tubercles. They can produce abundant mucus which is used for cutaneous respiration (Bruton 1996). They have small eyes and up to four pairs of barbels that are chemosensory and tactile (Helfman et al. 2009). In some catfish, the spine‐like rays at the front of the dorsal and pectoral fins have glandular cells that secrete a toxin with variable levels of potency. The pancreas is visible as white nodules (Brockmann bodies). They are physostomous with a bilobed swim bladder, but they are generally negatively buoyant due to the small swim bladder and heavy skull. Males in some families have an anal fin modified into an intromittent organ (Melo et al. 2011). Electric catfish (Malapteruridae) have bilateral electric organs in the skin that can emit up to 300 V at high frequency (Johnels 1956; Helfman et al. 2009).