FishFish belong to the phylum Chordata (animals with dorsal cord – notochord) and subphylum Vertebrata (animals with cartilaginous or bony skull; with vertebrae or vertebral arches). There are two different classes of fish: Osteichthyes (Fig. 1) or bony fish (for instance, sea bream and sea bass) and Chondrichthyes (Fig. 2) or cartilaginous fish (sharks, rays and ratfish). Cartilaginous fish, which fishermen commonly refer to as “peixes-couro” (leather fish), have as key features: a skin with placoid scales and five to seven pairs of branchiae in separate chambers. Bony fish have a skin with ganoid, cycloid or ctenoid scales and four branchiae pairs inside a common cavity.
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Fig. 1. External anatomy of a bony fish
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Fig. 2. External anatomy of a cartilaginous fish |
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