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mackerels, tunas and bonitos
Rafinesque [C. S.]
Body elongate and fusiform, moderately compressed in some genera. Snout pointed, premaxillae beak-like, free from nasal bones which are separated by the ethmoid bone; mouth rather large; teeth in jaws strong, moderate, or weak; no true canines; palate and tongue may bear teeth. First dorsal fin usually short and separated from second dorsal fin, depressible into a groove; finlets behind second dorsal and anal fins; pelvic fins moderate or small; caudal fin deeply forked with supporting caudal rays completely covering hypural plate. At least 2 small keels on each side of caudal fin base, a larger keel in between on caudal peduncle in more advanced species. Lateral line simple. Vertebrae 31-66. Body covered with small to moderate scales or a scaly corselet developed (area behind head and around pectoral fins covered with large thick scales) and rest of body naked or covered with tiny scales. Scombrids are swift, epipelagic predators; some species occur in coastal waters, others far from shore. Mackerels (<b><i>Scomber </i></b> and <b><i>Rastrelliger </i></b> ) filter plankton out of the water with their long gillrakers. Spanish mackerels, bonitos, and tunas feed on larger prey, including small fishes, crustaceans, and squids. The main predators of smaller scombrids are other predacious fishes, particularly large tunas and billfishes. Scombrids are dioecious (separate sexes) and most display little or no sexual dimorphism in structure or color pattern. Females of many species attain larger sizes than males. Batch spawning of most species takes place in tropical and subtropical waters, frequently inshore. The eggs are pelagic and hatch into planktonic larvae. Mackerels and tunas support very important commercial and recreational fisheries as well as substantial artisanal fisheries throughout the tropical and temperate waters of the world. Catches in cold and warm temperate waters predominate over tropical catches, with more than half of the world catch being taken in the northwestern Pacific, the northeastern Atlantic and the southeastern Pacific. Many species of tunas and mackerels are the target of long-distance fisheries. The principal fishing methods used for fish schooling near the surface include purse seining, driftnetting, hook and line/bait boat fishing, and trolling; standard and deep longlining are used for (usually bigger) fish occurring at least temporarily in deeper water. Recreational fishing methods involve mostly surface trolling and pole-and-line fishing, while numerous artisanal fisheries deploy a great variety of gear including bag nets, cast nets, lift nets, gill (drift) nets, beach seines, hook-and-line, handlines, harpoons, specialized traps, and fish corrals. The Scombridae contains 15 genera and 51 species (Collette et al. 2001 [ref. 25629]). The family is divisable into two subfamilies: Gasterochismatinae, which contains only the peculiar Southern Ocean <b><i>Gasterochisma melampus</i></b>, and Scombrinae. Some of their major morphological features were discussed by Collette 1979 [ref. 26991]. On the basis of internal osteological characters, Collette & Chao 1975 [ref. 5573] and Collette & Russo 1979 [ref. 26994] divided the Scombrinae into two groups of tribes. The more primitive mackerels (Scombrini) and Spanish mackerels (Scomberomorini) are characterized by: (i) a distinct notch in the hypural plate that supports the caudal fin rays, (ii) absence of a bony support for the median fleshy keel (when present), and (iii) preural vertebrae centra not greatly shortened as compared to those of the other vertebrae. Bonitos (tribe Sardini) are a group of 4 genera and 7 species that are intermediate between Spanish mackerels (tribe Scomberomorini) and higher tunas (tribe Thunnini). They lack any trace of a specialized subcutaneous vascular system or dorsally projecting cartilaginous ridges on the tongue, and the bony structure underlying their median fleshy caudal peduncle keel is incompletely developed; they also lack the prominent paired frontoparietal fenestra on the dorsal surface of the skull characteristic of most Thunnini. The Thunnini contains 5 genera, 4 of which (all except <b><i>Allothunnus </i></b> ) are unique among bony fishes in having counter-current heat exchanger systems that allow them to retain metabolic heat so that the fish is warmer than the surrounding water. Three genera of this tribe (<b><i>Auxis</i></b>, <b><i>Euthynnus </i></b> and <b><i>Katsuwonus </i></b> ) and the yellowfin group of <b><i>Thunnus </i></b> have central and lateral heat exchangers, while the specialized bluefin group of <b><i>Thunnus </i></b> have lost the central heat exchanger and evolved very well-developed lateral heat exchangers (Graham & Dickson 2001 [ref. 26992]). [ref. 19476], [ref. 5375], [ref. 7208], [ref. 13640], [ref. 27065]</i></b>
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