|Malabar grouper, Epinephelus malabaricus|
Not all serranids are called groupers; the family also includes the sea basses. The common name grouper is usually given to fish in one of two large genera: Epinephelus and Mycteroperca. In addition, the species classified in the small genera Anyperidon, Cromileptes, Dermatolepis, Gracila, Saloptia, and Triso are also called groupers. Fish in the genus Plectropomus are referred to as coralgroupers. These genera are all classified in the subfamily Epiphelinae. However, some of the hamlets (genus Alphestes), the hinds (genus Cephalopholis), the lyretails (genus Variola) and some other small genera (Gonioplectrus, Niphon, Paranthias) are also in this subfamily, and occasional species in other serranid genera have common names involving the word "grouper". Nonetheless, the word "grouper" on its own is usually taken as meaning the subfamily Epinephelinae.
In Australia, "groper" is used instead of "grouper" for several species, such as the Queensland grouper (Epinephelus lanceolatus). In the Philippines, it is named lapu-lapu in Luzon, while in the Visayas and Mindanao it goes by the name pugapo. In New Zealand, "groper" refers to a type of wreckfish, Polyprion oxygeneios, which goes by the Māori name hāpuku. In the Middle East, the fish is known as hammour, and is widely eaten, especially in the Persian Gulf region.
Groupers are teleosts, typically having a stout body and a large mouth. They are not built for long-distance, fast swimming. They can be quite large, and lengths over a meter and weights up to 100 kg are not uncommon, though obviously in such a large group, species vary considerably. They swallow prey rather than biting pieces off it. They do not have many teeth on the edges of their jaws, but they have heavy crushing tooth plates inside the pharynx. They habitually eat fish, octopuses, and crustaceans. Some species prefer to ambush their prey, while other species are active predators. Reports of fatal attacks on humans by the largest species, the giant grouper (Epinephelus lanceolatus) are unconfirmed.
Their mouths and gills form a powerful sucking system that sucks their prey in from a distance. They also use their mouths to dig into sand to form their shelters under big rocks, jetting it out through their gills. Their gill muscles are so powerful, it is nearly impossible to pull them out of a cave if they feel attacked and extend those muscles to lock themselves in.
Groupers are mostly monandric protogynous hermaphrodites, i.e. they mature only as females and have the ability to change sex after sexual maturity. Some species of groupers grow about a kilogram per year and are generally adolescent until they reach three kilograms, when they become female. The largest males often control harems containing three to 15 females. Groupers often pair spawn, which enables large males to competitively exclude smaller males from reproducing. As such, if a small female grouper were to change sex before it could control a harem as a male, its fitness would decrease. If no male is available, the largest female that can increase fitness by changing sex will do so.
However, some groupers are gonochoristic. Gonochorism, or a reproductive strategy with two distinct sexes, has evolved independently in groupers at least five times. The evolution of gonochorism is linked to group spawning high amounts of habitat cover. Both group spawning and habitat cover increase the likelihood of a smaller male to reproduce in the presence of large males. Fitness of male groupers in environments where competitive exclusion of smaller males is not possible is correlated with sperm production and thus testicle size. Gonochoristic groupers have larger testes than protogynous groupers (10% of body mass compared to 1% of body mass), indicating the evolution of gonochorism increased male grouper fitness in environments where large males were unable to competitively exclude small males from reproducing.
As other fish, groupers harbour parasites, including digeneans, nematodes, cestodes, monogeneans, isopods, and copepods. A study conducted in New Caledonia has shown that coral reef-associated groupers have about 10 species of parasites per fish species.
Many groupers are important food fish, and some of them are now farmed. Unlike most other fish species which are chilled or frozen, groupers are usually sold live in markets. Many species are popular fish for sea-angling. Some species are small enough to be kept in aquaria, though even the small species are inclined to grow rapidly.
Groupers are commonly reported as a source of Ciguatera fish poisoning. DNA barcoding of grouper species might help in controlling Ciguatera fish poisoning since fish are easily identified, even from meal remnants, with molecular tools.
The Malaysian newspaper, the Star reported a 180-kg grouper being caught off the waters near Pulau Sembilan in the Straits of Malacca in January 2008. Shenzhen News in China reported that a 1.8-m grouper swallowed a 1.0-m whitetip reef shark at the Fuzhou Sea World aquarium.
In September 2010, a Costa Rican newspaper reported a 2.3-m (7.5-ft) grouper in Cieneguita, Limón. The weight of the fish was 250 kg (550 lb) and it was lured using one kilogram of bait. In November 2013, a 310-kg (686-lbs.) grouper had been caught and sold to a hotel in Dongyuan, China.
- The grouper is depicted on the reverse side of the 100-Brazilian reais banknote. In Aruba, the 500-Aruban guilder banknote also features a grouper in one of its faces.
- KRI Kerapu is an Indonesian Navy ship. Kerapu is Indonesian word for grouper.
- The USS Grouper was the name of a United States Navy submarine.
- In the spoken Arabic of the GCC states, the word for the most prized type of grouper, or hamour, is also used to signify a merchant of vast wealth and influence.
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- Diario La Extra 2010, Marvin Carvajal. "Cayó el más mero en el Caribe".
- "Photos: Fishermen catch wildly huge 686-pound fish, sell it to hotel".