The fish exterior generally contains either 1) scales (originating from the dermal layer and comprised of a type of bone) that are covered by the epidermis (eg, koi, goldfish, cichlids, tetras, and loaches-that have very fine scales) ; 2) no scales (eg, channel catfish) ; or 3) bony plates (eg, Corydoras sp. catfish, Plecostomus catfish [Hypostomus and related genera], seahorses [Hippocampus spp.]).