Читать книгу Clinical Guide to Fish Medicine - Группа авторов - Страница 38

Elasmobranchs produce placoid scales, also known as dermal denticles. These give the sandpaper feel to shark skin as well as focal areas in the skin of batoids. These denticles are formed like teeth with a calcified layer, dentin, and enamel (Moss 1977). This skin represents an abrasion risk to human handlers and exposed skin should be protected. In silky sharks (Carcharhinus falciformis), the denticles are minute which makes the skin softer compared to other sharks (Camhi et al. 2008). In blue sharks (Prionace glauca), females have a significantly thicker skin to withstand mating trauma (Camhi et al. 2008). Many rays have few to no scales e.g. whiptail rays (Dasyatidae), eagle rays (Myliobatidae), mantas and mobulas (Mobulidae). These species tend to have a significant mucus layer which can affect water quality during prolonged restraint. Porcupine rays (Urogymnus asperrimus) and some other rays have “armor” on their dorsum complicating ultrasounds from the dorsal aspect. In many batoids and some sharks, sharp spines can develop. A venomous spine or barb is present in most rays, with the exception of mantas, mobulas, and porcupine rays (Meyer and Seegers 2012). The barbs are covered by integument which includes cells where venom is created. Several barbs can be present. Chimaeras (Holocephali) are scaleless (except in juvenile stages) and are very sensitive to skin trauma (Didier 2004).

Elasmobranch skin has visible, symmetrical epithelial pores known as pit organs and ampullae of Lorenzini (Figure A1.16) (Hueter et al. 2004). Pit organs are free neuromasts which use sensory hair cells to detect water motion. Ampullae are gel‐filled tubular structures that allow elasmobranchs to detect electric fields for navigation, prey and predator detection, and mating (Meyer and Seegers 2012). Clinicians should note that electric fields can exist in aquarium systems, especially where equipment is worn or corroded, and these impact elasmobranchs.