The Blacktip Reef Shark is a species of requiem shark, family Carcharhinidae.Timid and skittish, the blacktip reef shark is difficult to approach and seldom poses a danger to humans unless roused by food. However, people wading through shallow water are at risk of having their legs mistakenly bitten. This shark is used for its meat, fins, and liver oil, but is not considered to be a commercially significant species. The International Union for Conservation of Nature has assessed the blacktip reef shark as Near Threatened. Although the species as a whole remains widespread and relatively common, over fishing of this slow-reproducing shark has led to its decline at a number of locales.
A robustly built species with a streamlined "typical shark" form, the blacktip reef shark has a short, wide, rounded snout and moderately large, oval eyes. Each nostril has a flap of skin in front that is expanded into a nipple-shaped lobe. Not counting small symphysial (central) teeth, the tooth rows number 11–13 (usually 12) on either side of the upper jaw and 10–12 (usually 11) on either side of the lower jaw. The upper teeth are upright to angled and narrowly triangular in shape, bearing serrations that are more coarse on the bases; the lower teeth are similar, but more finely serrated. The teeth of adult males are more abruptly curved than those of females.
The pectoral fins are large and narrowly falcate (sickle-shaped), tapering to points. The sizable first dorsal fin is high with a curving "S"-shaped rear margin, and originates over the free rear tips of the pectoral fins. The second dorsal fin is relatively large with a short rear margin, and is placed opposite the anal fin. There is no ridge between the dorsal fins. This shark is a pale grayish-brown above and white below, with an obvious white band on the sides extending forward from above the anal fin. All the fins have black tips highlighted by lighter-colored borders, which are especially striking on the first dorsal fin and lower caudal fin lobe. Most blacktip reef sharks are no more than 1.6 m (5.2 ft) long, though rarely individuals may reach 1.8 m (5.9 ft) or possibly 2.0 m (6.6 ft). The maximum weight on record is 13.6 kg (30 lb).
The blacktip reef shark is found throughout nearshore waters of the tropical and subtropical Indo-Pacific. Although it has been reported from a depth of 75 m (246 ft) the blacktip reef shark is usually found in water only a few meters deep, and can often be seen swimming close to shore with its dorsal fin exposed. Younger sharks prefer shallow, sandy flats, while older sharks are most common around reef ledges and can also be found near reef drop-offs. This species has also been reported from brackish estuaries and lakes in Madagascar, and freshwater environments in Malaysia, though it is not able to tolerate low salinity to the same degree as the bull shark (C. leucas). At Aldabra in the Indian Ocean, blacktip reef sharks congregate in the channels between reef flats during low tide and travel to the mangroves when the water rises. There is equivocal evidence that sharks from the northern and southern extremes of its distribution are migratory.
As often the most abundant apex predator within its ecosystem, the blacktip reef shark plays a major role in structuring inshore ecological communities. Its diet is composed primarily of small teleost fishes, including mullet, groupers, grunters, jacks, mojarras, wrasses, surgeonfish, and smelt-whitings. Groups of blacktip reef sharks in the Indian Ocean have been observed herding schools of mullet against the shore for easier feeding. Squid, octopus, cuttlefish, shrimp, and mantis shrimp are also taken, as well as carrion and smaller sharks and rays, though this is rare.