Fishery and Biology of deep-sea chondrichthyans off the Southwest coast of India

Akhilesh, K V (2014) Fishery and Biology of deep-sea chondrichthyans off the Southwest coast of India. ["eprint_fieldopt_thesis_type_phd" not defined] thesis, Central Marine Fisheries Research Institute.

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Abstract

Class Chondrichthyes is one of the oldest groups of vertebrates, which survived for more than 400 million years since Devonian period, and the second largest class of fishes after Osteichthyes. Chondrichthyes can be differentiated from Osteichthyes (bony fishes) based on the presence of placoid scales, which has been replaced by scales in fishes and possessing simple internal skeletons formed of calcified cartilage and no true bones (Last and Stevens, 2009). The body forms of Chondrichthyes shares many similar characteristics, but is highly varied between orders, reflecting adaptations to lifestyle, habitat and environment (Compagno, 1999). Class Chondrichthyes is a monophyletic group and is divided into two subclasses, the Holocephali (holo=whole, cephalic =head) containing Chimaeras and the Elasmobranchii (elasmo =plate, branchii =gills) containing sharks, skates and rays. Elasmobranchii can be differentiated from chimaeras in having multiple paired gill openings (5-7), where as the latter have only single gill opening (Fowler et al., 2005).

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