Nurse shark

Elasmobranch fish in the family Ginglymostomatidae

The nurse shark (Ginglymostoma cirratum) is an elasmobranch fish in the family Ginglymostomatidae. The conservation status of the nurse shark is globally assessed as Vulnerable in the IUCN List of Threatened Species. They are robust and able to tolerate capture, handling, and tagging extremely well. As inoffensive as nurse sharks may appear, they are ranked fourth in documented shark bites on humans, likely due to incautious behavior by divers on account of the nurse shark's calm, sedentary nature.

The nurse shark genus Ginglymostoma is derived from Greek language meaning hinged mouth, whereas the species cirratum is derived from Latin meaning having curled ringlets. Based on morphological similarities, Ginglymostoma is believed to be the sister genus of Nebrius, with both being placed in a clade that also include species Pseudoginglymostoma brevicaudatum, Rhincodon typus, and Stegostoma fasciatum.

The nurse shark has two rounded dorsal fins, rounded pectoral fins, an elongated caudal fin, and a broad head. Maximum adult length is currently documented as , whereas past reports of and corresponding weights of up to are likely to have been exaggerated. In the Eastern Atlantic it ranges from Cape Verde to Gabon (accidental north to France). and in the East Pacific from Baja California to Peru. Nurse sharks are also subject to piebaldism, a genetic condition that results in a partial lack of body pigmentation and results in a speckled body.

Nurse sharks are opportunistic predators that feed primarily on small fish (e. g. stingrays) and some invertebrates (e. g. crustaceans, molluscs, tunicates). Although their small mouths may limit the size of prey, they can exhibit a suck and spit behavior and/or shake their head violently to reduce the size of food items. Nurse sharks are exceptionally sedentary unlike most other shark species. Nurse sharks show strong site fidelity (typical of reef sharks), and it is one of the few shark species known to exhibit mating site fidelity, as they will return to the same breeding grounds time and time again. American alligators (Alligator mississippiensis) and American crocodiles may occasionally prey on nurse sharks in some coastal habitats. Photographic evidence and historical accounts suggest that encounters between species are commonplace in their shared habitats.

Nurse sharks are ovoviviparous, with fertilized eggs hatching inside the female. The mating cycle of nurse sharks is biennial, with females taking up to 18 months to produce a new batch of eggs. The mating season runs from late June to the end of July, with a gestation period of six months and a typical litter of 21–29 pups.