Specialized locomotion - Fishes

Specialized locomotion

Among the more interesting variations on locomotory type are fishes that have abandoned swimming for other meansof getting around. A number of species walk along the bottom of the sea or leave the water and move about on land; these fishes have bodies that depart from a streamlined shape. Sea robins (Triglidae) move lightly across sand bottoms using modified pectoral rays that extend out from the fin webs. They give the appearance of someone tiptoeing on many moving fingers; dactylopterid flying gurnards similarly tiptoe but use modified pelvic rays instead. Antennarioid frogfishes and batfishes pull themselves along the bottom by moving their modified pectoral and pelvic fins; their forward motion is aided by jet propulsion of water out their backward-facing, constricted opercles(Pietsch & Grobecker 1987). Australian hand fishes(Brachionichthyidae), which get their common name because their pectoral fins are modified into an armlikeappendage with an elbow and fingers, also use pectoral and pelvic fins to walk (Bruce et al. 1998).

Fishes are not restricted to spending all their time in water, and some actually move about on land (Sayer 2005).Terrestrial locomotion is accomplished in a variety of ways. Climbing perches use paired fins and spiny gill covers to ratchet themselves along, whereas snakeheads row with their pectoral fins. So-called “walking catfishes” move across land by lateral body flexion combined with pivoting on their stout, erect pectoral spines. Mudskippers swing their pectoral fins forward while supporting their body on the pelvic fins. They then push forward with their pectoral fins, like a person on crutches. Rapid leaps of 30–40 cmare accomplished by coordinated pushing of the tail and pectoral fins. Their unique pectoral fins are roughly convergent with the forelimbs of tetrapod’s, including an upper arm consisting of a rigid plate like region and a fanlikeforearm and plantar surface (Gray 1968). Some species with anguilliform movement (moray and anguillid eels) are able to move across wet land employing their normal locomotion, which is analogous to the “serpentiform” terrestrial and aquatic movements of most snakes (Chave &Randall 1971; Lindsey 1978; Ellerby et al. 2001).

Aerial locomotion grades from occasional jumping to gliding to actual flapping flight. Many fishes jump to catch airborne prey (trout, Largemouth Bass); meter-long arawanas(Osteoglossidae) can leap more than a body length upward and pluck insects and larger prey, including bats, from overhanging vegetation. Other fishes take advantage of the greater speeds achievable in air: needlefishes, mackerels, and tunas leave the water in a flat trajectory when chasing prey, and salmon leap clear of the water when moving through rapids or up waterfalls. Hooked fish jump and simultaneously shake their heads from side to side inan attempt to throw the hook; such oscillation is less constrained by drag in air than in water and therefore allows more rapid and forceful to-and-fro movement. Prey suchas minnows, halfbeaks, silversides, mullets, and Bluefishjump when being chased.

Fishes capable of flight include gliders such as the exocoetid flying fishes and pantodontid butterflyfishes, as wellas gasteropelicid hatchet fishes, which purportedly vibrate their pectoral wings to generate additional lift (Davenport1994;  Evading pursuit). The anatomy of the marine flying fishes is highly modified for flying. The body is almost rectangular in cross-section, the fl attenedventral side of the rectangle providing a planning surface that may aid during take-off. The ventral lobe of the caudal fin is 10–15% larger in surface area than the dorsal lobe and is the only part of the body in contact with the water during taxiing. The pectoral fins are supported by enlarged pectoral girdles and musculature. The pectoral fins differ from normal teleost fins in the shape of and connections between the lepidotrichia, and the pectoral fin rays are thickened and stiffened, giving the leading, trailing, dorsal, and ventral surfaces more of a wing like than a finlike construction. In some flying fishes, pelvic fins also contribute lift and are appropriately modified.

Some other atheriniform fishes such as needlefishes and half beaks also propel themselves above the water’s surface by rapidly vibrating their tail, the lower lobe of which is the only part still in the water. Some halfbeaks have relatively large pectoral fins and engage in gliding flight. Gradations of pectoral fin length and lower caudal lobe strengthening and lengthening among atheriniforms provide a good example of apparent steps in the evolution of a specialized trait, namely flying (Lindsey 1978; Davenport 1994).