Portuguese Shark aka Portuguese Dogfsish
The body of the Portuguese dogfish is thick and cylindrical except for the flattened belly. The two dorsal fins are small and of similar size and shape, each bearing a tiny grooved spine in front. The first dorsal fin originates well behind the pectoral fins, while the second dorsal originates over the middle of the pelvic fin bases. The pectoral fins are medium-sized with a rounded margin. There is no anal fin. The caudal fin has a short but well-developed lower lobe and a prominent ventral notch near the tip of the upper lobe. The very large dermal denticles change in shape with age: in juveniles, they are widely spaced and heart-shaped with an incomplete midline ridge and three posterior points, while in adults they are overlapping, roughly circular, smooth, and flattened with a round central concavity, superficially resembling the scales of bony fishes. Young sharks are a uniform blue-black in color, while adults are brown-black; there are no prominent fin markings.
Living almost exclusively in the aphotic zone where little to no sunlight penetrates, the Portuguese shark is relatively common and the dominant shark species in deeper waters. The large, squaline-rich liver of this shark allows it to maintain neutral buoyancy and hover with minimal effort; males contain more squalene in their livers than females. A tracking study in the Porcupine Seabight has found that the Portuguese dogfish has an average swimming speed of 0.072 m/s (0.24 ft/s), and does not remain in any particular area for long. This species may be preyed upon by larger fishes and sharks. An active predator of mobile, relatively large organisms, the Portuguese shark feeds mainly on cephalopods and bony fishes. It has also been known to take other sharks and invertebrates, as well as scavenging from whale carcasses.
Aplacental viviparous, with the female retaining eggs internally until they hatch. The embryos are sustained by yolk, and possibly also by uterine fluid secreted by the mother.
Appearance
Biology
Reproduction
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