This respiratory structure implies selection pressures for the development of a purely respiratory organ and a purely hydrostatic organ. The respiratory section can be identified by its extensive mucosal folding and vascularization, as well as widespread capillaries throughout the epithelium. Specifically, the esophagus of a blackfish can be subdivided into a non-respiratory and a respiratory section. The Alaska blackfish is famous for its ability to breathe atmospheric oxygen through a modified esophagus. Males can be distinguished from females by the presence of a reddish fringe along the dorsal, caudal, and anal fins also, the tips of the ventral fins extend beyond the anal fin in males, whereas in females they do not. The color is dark green to brown on the dorsal side, pale below, with light-colored blotches appearing laterally. The head is broad and flat, with the trunk being long and slender. They have an easily distinguishable morphology (a branch of biology dealing with the study of the form and structure of organisms and their specific structural features), with relatively large, posterior dorsal fin and anal fins, large, lobed pectoral fins located just posterior to the operculum, a diphycercal caudal fin, and small, pointy pelvic fins. It inhabits Arctic regions of Alaska as well as Siberia and the Bering Sea islands.Īlaska blackfish are small, with an average length of 108 mm (4.3 in), but have been known to reach 330 mm (13 in). The Alaska blackfish ( Dallia pectoralis) is a species of freshwater fish in the esocid family ( Esocidae) of order Esociformes.
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