Fishes: A Guide to Their Diversity. Philip A. Hastings
Читать онлайн книгу.
Mouth Positions
In addition to the size of the gape and the size and type of teeth, the position of a fish’s mouth provides clues to its feeding habits. These include the following:
TERMINAL Mouth located at the tip of the snout.
SUBTERMINAL Mouth located below the tip of the snout.
INFERIOR Mouth opens ventrally, well posterior to the snout.
SUPERIOR Mouth opens dorsally.
Oral and Pharyngeal Jaw Diversity
In the chondrichthyan fishes, the upper jaw is formed by the palatoquadrate cartilage, while in the ray-finned fishes, it is formed by two bones, the maxilla and the premaxilla. In early lineages, both of these bones bear teeth and are included in the gape, while in more derived ray-finned fishes, only the premaxilla bears teeth and the toothless maxilla is excluded from the gape. In addition to these “oral jaws,” ray-finned fishes have a second set of jaws, the “pharyngeal jaws,” located anterior to the esophagus, comprising bones associated with the upper and lower gill arches. In many of these fishes, the oral jaws function to grasp and/ or ingest prey, while the pharyngeal jaws are often specialized for processing prey.
Standard Meaurements
Several standard measurements are used to document the size and shape of fishes (Hubbs and Lagler, 1958; Strauss and Bond, 1990). These include the following:
TOTAL LENGTH (TL) Horizontal distance from the most anterior point on the head to the tip of the longest lobe of the caudal fin. The most anterior point is often the tip of the snout, but may be the tip of the lower jaw in some species.
FORK LENGTH (FL) Horizontal distance from the most anterior point on the head to the end of the central caudal-fin rays.
STANDARD LENGTH (SL) Horizontal distance from the tip of the snout to the central base of the caudal fin (i.e., the end of the hypural plate). The latter can often be located as a crease formed when the caudal fin is slightly bent.
HEAD LENGTH Horizontal distance from the tip of the snout to the posterior margin of the operculum.
SNOUT LENGTH Horizontal distance from the tip of the snout to the anterior margin of the orbit.
BODY DEPTH Maximum vertical distance between the dorsal and ventral outlines of the body.
SNOUT-VENT LENGTH Distance from the tip of the snout to the anterior margin of the vent.
DISK WIDTH In batoid fishes (rays), the maximum distance between the lateral margins of the left and right pectoral fins.
Sensory Systems
Fishes have the full array of sensory systems common to all vertebrates (olfaction, taste, vision, and hearing), as well as some unusual ones such as the lateral line and electroreception. Details of these systems are often useful in diagnosing various lineages of fishes. Numerous reviews of the sensory biology of fishes are available, including several chapters in volume 1 of the Encyclopedia of Fish Physiology, edited by Farrell (2011).
OLFACTION Fishes have left and right olfactory organs (paired in most fishes, unpaired in agnathans) that are chemoreceptive. Each side includes incurrent and excurrent nostrils (or nares) that may have a divided single opening or paired openings.
TASTE Fishes have chemoreceptive taste buds located inside the mouth, and in many groups also on the gill arches, barbels, fin rays, and the skin.
VISION The eyes of fishes come in a variety of sizes and forms and frequently are reflective of a species’ habitat and habits. Eyes are often large in nocturnal species, upwardly directed in mesopelagic fishes, and small or sometimes absent in fishes from dark habitats including the deep sea and cave environments.
HEARING AND BALANCE Fishes have an inner ear with one (hagfishes), two (lampreys), or three (all other fishes) semicircular canals that function in maintaining balance and orientation. The main organs of hearing are the paired otolith organs, each of which consists of a sensory epithelium with an overlying calcium carbonate otolith (bony fishes) or otoconia (cartilaginous fishes). Sound waves are propagated from the water, through the tissues of the head, to the otoliths or otoconia, whose vibrations are detected by the sensory epithelium. A variety of so-called “otophysic connections” between the inner ear and the gas bladder serve to amplify sound reception in some fishes. These include anterior projections of the gas bladder that extend close to or, in some cases, into the otic capsule, and the Weberian apparatus, a mechanical linkage formed from modified anterior vertebrae, stretching between the gas bladder and inner ear of otophysans (Braun and Grande, 2008).
LATERAL LINE The mechanosensory lateral-line system of fishes detects water flow and vibrations made by movements of other organisms. Its sensory organs, called neuromasts, are located in pored lateral-line canals on the head (cephalic lateral line) and body (trunk lateral line), as well as on the skin (superficial neuromasts). Their expression in fishes varies greatly, but their configuration provides clues to the habits of many species (Webb, 1989, 2013).
ELECTRORECEPTION Receptors that detect weak electrical fields produced by other organisms are present in lampreys, all cartilaginous fishes, and some bony fishes (Kramer, 1996). In the cartilaginous fishes they are called ampullae of Lorenzeni, and involve sensory cells located at the base of canals filled with conductive jelly and open to the surface. They are especially common on the ventral side of the head, where they facilitate detection and capture of prey items. In teleosts the electroreceptive sense detects electrical fields in the environment, including those generated by conspecifics, as well as potential prey.
Skeletal Anatomy
The skeletal structure of fishes has been studied extensively for clues to both phylogeny and function. The skeletal structure of cartilaginous fishes was recently reviewed by Claeson and Dean (2011). Several excellent guides to the osteology of ray-finned fishes are available, including the classic text by Gregory (1933) and a recent overview by Hilton (2011). For ray-finned fishes, several superficial bones of the head are especially useful in identifying various groups of fishes (illustrated below). The major components of the caudal fin and posterior vertebral column are also illustrated below.
THE FISHES
VERTEBRATA—VERTEBRATES
The Vertebrata is one of the most successful lineages of animals, dominating both aquatic and terrestrial habitats around the globe. This diverse group, with well over 60,000 species, is characterized by the presence of ossifications surrounding and often occluding the notochord (in most living species), a well-developed brain, a notochord that is restricted posterior to the brain, a chambered heart, and a host of other features (Forey, 1995; Nelson, 2006). Aquatic representatives number well over 30,000 species and include the jawless fishes (Agnatha), cartilaginous fishes (Chondrichthyes), and ray-finned fishes (Actinopterygii). Terrestrial habitats are largely the domain of the Tetrapoda, the dominant clade of the Sarcopterygii, which also includes a handful of aquatic lung fishes and the coelacanths.