Groupers are generally solitary predators. Like other predatory fish such as barracuda, they are most active at dawn and dusk. Some prefer deep waters. Others are found in warm, shallow coastal waters, often in coral reefs and sometimes in estuaries. Groupers have been described as patient hunters because they like to lurk in caves or crevices and wait for a crustacean or slow-moving fish to pass their way and then lunge, open their large mouth and suck in the prey. Coral groupers catch fish with the suction created when it opens its huge mouth.
Groupers are members of the Serranidae family of ray-finned fishes. They live for a long time and reproduce for short periods. Some species gather in large groups to spawn. Groupers tend to be fond of spiny lobster and also frequently eat crabs, small fish and juvenile sea turtle. When they are young they are fed on by other predators but if they manage to make it to adulthood the only real threat they face comes from humans.
Groupers feed on a wide variety of fish, octopus, crustaceans, shrimp and lobsters, They are considered monandric protogynous hermaphrodites. This means that juveniles contain immature sex organs of both genders and mature as either male or female.
They are among the top predators in reef community food webs and may control some aspects of community balance in reef systems.
There are several species of grouper. The giant grouper, which lives in the Indian Ocean and the western and central Pacific, is one of the largest species and is known to occasionally feed on small sharks. Other large species include the goliath grouper. Many kinds of groupers can change their color to match their surrounding. Some species register victory or defeat by changing color. Some species such as the gag grouper and the red grouper are caught for food and are valued as a major fishery resource.
Websites and Resources: Animal Diversity Web (ADW) animaldiversity.org; National Oceanic and Atmospheric Administration (NOAA) noaa.gov; Fishbase fishbase.se ; Encyclopedia of Life eol.org ; Smithsonian Oceans Portal ocean.si.edu/ocean-life-ecosystems ; Woods Hole Oceanographic Institute whoi.edu ; Cousteau Society cousteau.org ; Monterey Bay Aquarium montereybayaquarium.org ; MarineBio marinebio.org/oceans/creatures
Groupers and Humans
Groupers sometimes are tame enough to be fed by hand. But don't go diving near such groupers unless you have a free hand out. Diver who have done this have discovered that groupers can also feed "on" hand. Groupers the size of refrigerators have been known to follow divers around like dogs. In spear hunting competitions divers have said large groupers were often ideal target because they were slow and incurably friendly..[Source: David Doubilet, National Geographic, November 1987]
Groupers have beeen dangerously overfished in some places. They are all but extinct in many parts of the Caribbean. Because they attain a large size there are generally few of them in a reef. Because they take so long to grow and reach that size once they have been fished it takes a very long are for them to return.
Because some species of grouper spawn at same place and time every year, they are an easy target for fishermen. On the full moon of December, January and February, thousands of Nassau groupers once gathered at a reef near Isla Guanaja in the Gulf of Honduras to spawn. Divers who discovered the site in 1988 were astonished by water turned white with eggs and milt from these 15-pound fish. The divers tried to keep the location of the reef a secret, but fisherman eventually found it and after a year bountiful "fishing moon" catches the population of fish plummeted to 500.
Jewfish are what Atlantic goliath groupers used be called. The word is not used so much anymore. Giant sea bass are also known as black jewfish and Pacific Jewfish.
For decades the Maryland-based American Fisheries Society received complaints about the name. In 2001, it t announced that the name was deemed “culturally insensitive” and was changed to goliath grouper – not for the biblical Philistine Goliath who was slain by David, but because of the fish’s ability to grow so large.
According to the Jewish Telegraphic Agency: There are several theories for how the jewfish (Promicrops itaiara), an Atlantic saltwater grouper with fins and scales, got its name. It may derive from the Italian “giupesce,” which means “bottom fish,” or may have originally been named “jawfish” for its large mouth. A less flattering theory is that in the 1800s, jewfish were declared inferior and only fit for Jews.
Groupers Use Sign Language When Hunting with Moray Eels
According to a study published in 2013, the coral grouper uses sign language to advise fellow hunters of hiding prey. AFP reported: It is the first time that a fish has been known to make “referential gestures,” or specific signs that alert a partner to an object of mutual interest, it said.
Reporting in the journal Nature Communications, a trio of biologists at Switzerland’s University of Neuchatel and Cambridge University in England studied how the coralgrouper works with two hunting pals. Previous research has shed light on the unusual relationship between the coralgrouper (Plectropomus pessuliferus marisrubri), the giant moray eel (Gymnothorax javanicus) and the Napoleon wrasse (Chelinus undulatus). By cooperating, the three species maximise their chances of getting dinner. [Source: AFP, April 25, 2013]
“The grouper has “burst speed” to capture prey in open water, while the eel can slide into crevices where small fish lurk and the wrasse has powerful extendable jaws that can suck out prey from a hole or smash the reef around it. The grouper has two signals it uses in these hunts, according to the paper. The first is a “high frequency shimmy,” or a kind of body shake, that it performs in front of the moray as a general invitation to join it in a chase. The second is specific, or “referential.” It is a headstand, which the grouper performs vertically and head-down, indicating to the moray or the wrasse where a prey is hiding or where it was last seen.
“The team carried out 187 hours of observations of groupers in the wild, in reefs off Australia or Egypt. They recorded 34 occurrences of the headstand. In 31 of the cases, either a moray or a wrasse rushed to inspect the location to which the grouper pointed. In five cases, the outcome was capture of the prey. “In the animal world, postures or referential gestures have until now only been seen among great apes and ravens,” said Neuchatel researcher Redouan Bshary.
Large Cods (Groupers) in Australia
Groupers are known as cod in Australia. Among the largest fish found in the Great Barrier Reef, they are large, slow, plodding reef dwellers characterised by their stout bodies and large mouths. Bigger ones can reach 2.7 meters (9 feet) and weigh over 180 kilograms (400 pounds). Divers like them as they are harmless and docile and let people approach them and sometimes even seek them out. They are usually speckled grey and brown in color and in places where fishing is restricted they can be quite numerous. [Source: Great Barrier Reef.com]
The Potato rockcod (Scientific name: Epinephelus tukula) is among the largest grouper species. They can grow over two meters in length and weigh over 110 kilograms (240 pounds). According to the Australia Museum: In some areas it was common for divers to feed these large fish and this practice has resulted in some individuals boldly approaching divers underwater.
Also call the potato grouper, potato group and potato bass, the Potato rockcod is found on coral reefs throughout Indian Ocean and western Pacific Ocean. It is grey-brown with large dark brown spots on the body. It has small spots on the head and lines from the back of the eye. In Australia it is known from off north-western Western Australia and the Great Barrier Reef. It's recorded as far south as Moreton Bay, Queensland.
Potato rockcod adults are found at depths between 10 to 150 metres (33 to 492 feet). They are solitary and usually remain within their home range. Ambush predators which prey on small rays, crabs, fish, squid, octopuses and spiny lobsters, they hide from their prey using the coral as cover and lunge when the prey is in range, swallowing the prey item whole. They aggressively defend their territory but they have a relatively small home range. They reach sexual maturity at 90 to 99 centimetres (35 to 39 inches) and a weight of 16 to 18 kilograms (35 to 40 pounds), at approximately 12 years of age.
Barramundi Cod (Scientific name: Cromileptes altivelis) is also known as the humpback grouper, panther grouper, plum pudding cod and polka dot. It is widely associated with with Australia and generally found in the waters off the Northern Australian coast and as far as Western Australia but has also been observed in the Western Pacific, from Southern Japan to Palau and in the Eastern Indian Ocean, from the Nicobars of India to Broome, Australia. [Source: Diana Zepeda, Animal Diversity Web (ADW) /=]
Barramundi Cod are usually found in reefs, most frequently in dead or silty reef areas to a depth of 40 meters. They inhabit lagoons and seaward reefs and are sometimes seen even in tide pools. The younger fish live in shallow water and are occasionally seen in rock pools at low tide. They are known for eating nekton, organisms that can swim against currents, and primarily feed on finfishes, squid, cuttle fish, and bony fish.Barramundi Cod are not threatened or endangered. It is not on the International Union for Conservation of Nature (IUCN) Red List. One threat they face is that they are among the most prized and highly priced of all groupers in Chinese restaurants.
According to Animal Diversity Web: The Barramundi Cod is a very distinctive looking fish. The profile of its head is and it has scattered black spots on its body and fins. The Barramundi Cod can grow up to 70 centimeters in length. It is usually either fawn, reddish-brown, or terra-cotta colored. Its most notable feature is that its body is completely covered with round black spots. The largest spots are found on the fish's back and are usually smaller than the eye. On the younger fish the spots are larger but less numerous.
The Barramundi cod has a curious personality. It fears what is not familiar to it. When something unfamiliar approaches them, they usually swim away but do not swim very far. They swim very differently from other fishes; they move very slowly with many odd turns and sometimes it seems as if they are trying to swim upside down,
Barramundi cod sense using touch and chemicals usually detected with smell. They reproduce by means of protogyny, which means there is sequential hermaphroditism in which an individual transforms from female to male. The eggs are scattered in open water and are fertilized externally. Once the eggs are fertilized they are left unguarded.
Giant Sea Bass
Giant sea bass (Scientific name: Stereolepis gigas) are also known as black jewfish, California black sea bass and Pacific Jewfish. They are the largest coastal bony fish in the Northeastern Pacific. They can grow up to 2.7 meters (nine feet) long and weigh up to 315 kilograms (700 pounds). They among the oldest known fish, with an age estimated to be over 75 years old and may live for over 100 years.[Source: Zack Helke and Antone Lahr, Animal Diversity Web (ADW) /=]
Giant sea bass are native to North America and the Pacific Ocean. They inhabit coastal waters of California, from Humboldt Bay to the tip of Baja California, Mexico in temperate, saltwater and marine environments in coastal areas and on or near the sea bottom at depths of six to 80 meters (19.7 to 262.5 feet) at an average depth of 40 meters (131 feet). Juvenile giant sea bass are found at depths of six to 10 meters, over mud flats and in coastal lagoons of southern California and the Baja California peninsula. Older juveniles and adults are found in 10 to 40 meters of water over sandy bottoms, kelp beds and rocky reefs, as well as within deep ridges at depths of 70 to 80 meters. Adult sea bass venture offshore of these coastal areas at various times in the year to prey on groups of spawning squid. /=\
Giant sea bass are listed by the Red List as Critically Endangered and US Federal List as Endangered; They have no special status according to the Convention on the International Trade in Endangered Species (CITES). Giant sea bass were one of the most economically important species of fish in the Gulf of California and were fished heavily in the 1930s and 40s for as food. The fish have have been protected in California since 1982, when the California State Legislature recognized the great decline in populations and banned recreational and commercial fishing of them. The species can still be fished in Mexico, where there are more of them.
Giant sea bass are sit-and-wait ambush predators that capture their prey by rapidly opening their mouth, creating a vacuum and sucking their prey into their throats. They mainly consume benthic invertebrates (living on or near the bottom of the sea) including rock crab and California spiny lobster. They also prey on fishes such as round stingrays, California barracuda, kelp bass, ocean whitefish, and barred sand bass. Giant sea bass are apex carnivores that prey on many kelp forest species. They are most likely to be preyed upon while they are in larval or juvenile stages, by a wide variety of marine creatures. Due to their large size, only large sharks and humans have the ability to prey on adults. Their main known predators are great white sharks.
Giant Sea Bass Characteristics and Behavior
Giant sea bass range reach the weight of 255.6 kilograms (563.00 pounds) and the length of 2.5 meters (8.20 feet). Both sexes are roughly equal in size and look similar. According to Animal Diversity Web: Juvenile giant sea bass are a brilliant shade of orange, with distinctive large black spots. As a fish matures, its spots deminish and its colorful exterior gradually darkens and acquires a bronzy purple hue. At full maturity, it begins to develop a white underside while the rest of its body turns black or even gray. Features characteristic of giant sea bass are dorsal spines that fit into grooves in the back and a large mouth specialized for ambush predation. Perhaps the most well-known feature of this species is its large size, with individuals historically exceeding two meters in length. [Source: Zack Helke and Antone Lahr, Animal Diversity Web (ADW) /=]
Giant sea bass are diurnal (active mainly during the daytime), motile (move around as opposed to being stationary), sedentary (remain in the same area) and solitary. They move among kelp beds and rocky reefs to wait for and ambush their prey. Their large mouth opens quickly, creating a vacuum that sucks the prey into the mouth. Due to its rarity in the wild, other behaviors have not been observed in this species, but it is assumed that giant sea bass might display similar behaviors to other species of a similar size, such as groupers. Individuals have been repeatedly observed in the same locations, indicating that these fish reside within particular areas. However, there are no published estimates of the size of these home ranges. /=\
Giant sea bass communicate with vision and sense using vision, touch, sound, vibrations and chemicals usually detected with smelling or smelling-like senses. They have the ability to rapidly and dramatically change color, producing black spots and white mottling over the body. It is believed that these color changes serve as stress signals and a means of communication between conspecifics. In addition to the use of visual cues, giant sea bass are able to perceive their environment through the use of their lateral line system, which detects pressure changed and movement in surrounding waters. They can also detect dissolved chemical substances via their nares, which are analogous to nostrils in terrestrial animals. /=\
Giant Sea Bass Mating, Reproduction and Offspring
Giant sea bass are oviparous (young are hatched from eggs) and iteroparous (offspring are produced in groups). They engage in seasonal breeding, engage in external reproduction in which sperm from the male fertilizes the female’s egg outside her body and employ broadcast (group) spawning, the main mode of reproduction in the sea. It involves the release of both eggs and sperm into the water and contact between sperm and egg and fertilization occur externally. Females and males reach sexual or reproductive maturity at 11 to 13 years. [Source: Zack Helke and Antone Lahr, Animal Diversity Web (ADW) /=]
Giant sea bass are polygynandrous (promiscuous), with both males and females having multiple partners. The fish spawn annually, potentially engaging in multiple individual spawning events during a single spawning season. Spawning occurs once a year between July to September. The number of offspring ranges up to from 60 million. The time to hatching ranges from 24 to 36 hours. As is the case with the majority of species that broadcast spawn, there is no parental parental involvement in the raising of offspring. /=\
Spawning behavior of giant sea bass has rarely been observed in the field. One study documented groups of two to 20 fish spawning in one particular area. As is the case with other broadcast spawning species, pair bonds are not formed, and individuals may spawn multiple times with several different mates. Male giant sea bass reach sexual maturity at about 18 kilograms, while females mature at sizes of 23 to 27 kilograms.
After fertilization, the eggs absorb water and swell up, measuring up to 1.6 millimeters in diameter (much larger than the eggs of other bass species). Eggs are positively buoyant and float to the surface. After hatching, larvae drift and feed on plankton for about a month until they sink and start their juvenile phase.
Giant Sea Bass Are Critically Endangered in the U.S. But Thriving in Mexican Waters
Arturo Ramírez-Valdez wrote in The Conversation: “Giant sea bass live in both Mexican and U.S. waters. I have found that large differences in regulation and research effort between the two countries has led to a significant misunderstanding of giant sea bass population health. In California, commercial fishing for the species began in the late 1880s. Large fish used to be very abundant across the entire range, but the fishery collapsed in the early 1970s. As a response, in 1981 the U.S. banned both commercial and recreational fishing for giant sea bass, and there are many ongoing research and population recovery efforts today. The collapse and subsequent protection and flurry of research in the U.S. stand in stark contrast to Mexico. In Mexico, there are minimal regulations on fishing for the species, and there is almost a complete lack of data and research on it — there are only three studies on giant sea bass with any data from Mexico. [Source: Arturo Ramírez-Valdez, Researcher, University of California San Diego, The Conversation, January 10, 2022]
“The International Union for Conservation of Nature considers giant sea bass to be a critically endangered species due to the population being “severely fragmented, leading to a continuing decline of mature individuals.” But this decision was based on a report that had no data whatsoever from Mexico. This lack of data is concerning, considering 73 percent of the species’ range is in Mexican waters.
“In 2017, I led an effort to document the giant sea bass population in Mexico and look for clues to what it was in the past. At the beginning of the project, my colleagues and I feared that the records in Mexico would confirm the precarious situation of the fish in the U.S. But the reality turned out to be the opposite. To our surprise, we found giant sea bass everywhere in the fish markets and fishing grounds from our very first assessments. The fishmongers were never out of the fish; instead, they would ask us, “How many kilos do you need?” It was clear that for fishers in Mexico, the species is still common in the sea, and therefore, in their nets. It is still possible to find big fish up to 450 pounds 200 kilograms, and the average catch was around 26 pounds (12 kilograms).
“It was fantastic to see an abundance of these fish in markets, but I also wanted to understand the fishery trends through history and how current fishing levels compared to previous years. I looked at historical and contemporary fishing records and found that the Mexican commercial fleet has caught an average of 55 tons per year over the past 60 years, and the fishery has been relatively stable over the past 20 years, with a peak in 2015 at 112 tons.
“According to U.S. and Mexican records, the largest yearly catch ever recorded for giant sea bass in Mexico was 386 tons in 1933. Biologists consider a fishery to have collapsed when total catches, under the same effort, are less than 10 percent of the largest catches on record. So a steady trend of 55 tons per year shows that the fishery in Mexico has not collapsed. It is clear that giant sea bass populations have faced severe declines throughout their range; however, the health of the species is not as dire as thought.
“Another interesting finding from my research is that the apparent collapse of the giant sea bass fishery documented in the 1970s actually began as early as 1932. Over the first half of the 20th century, as the U.S. commercial fleet overfished U.S. waters, they began fishing in Mexican waters too — but they continued to count all catches as from the U.S. This changed in 1968 when the two governments signed the Mexico–U.S. Fisheries Agreement, limiting how much fish each country’s fleet could take from the other country’s waters. The collapse of the U.S. fishery in the 1970s was not due to a drastic reduction in fish numbers in Mexican waters, but driven by changes in fishing regulation between the U.S. and Mexico. The California fish populations had been depressed for decades, but this was hidden by fish from Mexico.
Image Sources: Wikimedia Commons; YouTube, Animal Diversity Web, NOAA
Text Sources: Animal Diversity Web (ADW) animaldiversity.org; National Oceanic and Atmospheric Administration (NOAA) noaa.gov; Wikipedia, National Geographic, Live Science, BBC, Smithsonian, New York Times, Washington Post, Los Angeles Times, The New Yorker, Reuters, Associated Press, Lonely Planet Guides and various books and other publications.
Last Updated March 2023