Читать книгу Clinical Guide to Fish Medicine - Группа авторов - Страница 47

There are usually five gill arches in elasmobranchs, although there may be up to seven. They consist of a hemibranch cranially (with one row of filaments) and holobranchs for the remaining arches (with two rows of filaments). The interbranchial septum extends to form gill slits on the external surface of the animals. The cranial‐most gill slit is modified into a spiracle in some species (Figure A1.18). These are well‐developed on the dorsal surface of skates and rays and they are present in some slow‐moving sharks (Butler 1999). The spiracle is absent in the more pelagic sharks.

Damage to the gills can affect gas exchange as well as other physiological needs. In saltwater species, gills play an important role in acid–base balance and in freshwater species, gills are important in salt regulation. Gills are also critical for urea retention, particularly in some species like the spiny dogfish (Squalus acanthias) (Ballantyne and Robinson 2010).

The oral cavity is divided into orobranchial and parabranchial cavities. In species that show buccopharyngeal pumping, these areas have a double pumping action which delivers oxygenated water through the mouth or the spiracles to the gills. In ram‐ventilating species, where water continually flows over the gills, the mandibular muscles control the opening of the mouth to manage the water flow (Shuttleworth 2012).