Centropomus undecimalis
Common snook
(Also: Pike; Seargent fish; Sergeant fish; Snook; Thin snook)

Common snook, Centropomus undecimalis, range from the coastal mid-Atlantic regions of the United States through the Gulf of Mexico and Caribbean to parts of Central and South America. Common snook have been documented as far north as Pamlico Sound, North Carolina and as far south as Rio de Janeiro, Brazil. They are particularly abundant around coastal Florida. ("Encyclopedia of Life", 2001; "Texas Parks and Wildlife Department", 2009; Froese and Pauly, 2010; Hill, 2005; Press, 2010)

Common snook are amphidromous fish, moving between fresh and salt water during their life, but not for the purpose of breeding. They can be found in freshwater, brackish, or marine environments at depths up to 22 m. They commonly associate with underwater structures such as pilings, reefs, or sea grass beds, but they most often prefer mangrove-fringed estuarine habitats. As adults, common snook are generally non-migratory, but often assemble in high salinity regions in order to spawn. Most live in waters of temperatures between 25 and 31°C. ("Encyclopedia of Life", 2001; "Texas Parks and Wildlife Department", 2009; Froese and Pauly, 2010; Hill, 2005; Press, 2010)

Common snook are easily recognized by their elongate body, distinct sloping forehead, concave snout, and protruding lower jaw. They are further characterized by their prominent black lateral line, which is formed by 67 to 72 pored scales, that extends into the caudal fin. Common snook range from 0.14 to 140 cm in length (average 50 cm) and can weigh as much as 23.3 kg. Females are generally larger than males.

Coloration ranges from dark brown to dull gray with a yellow to green tint on the dorsal surface. The lateral surface tends to be silvery, and the ventral surface is generally white. The pectoral fins, pelvic fins, second dorsal fin, and the dorsal lobe of the caudal fin are all bright yellow in color, however, some specimens are considerably darker.

Unlike in other species within the genus Centropomus, the tips of their pelvic fins do not overlap or reach the anus. Common snook have 2 dorsal fins that are well-separated, each with 8 to 9 dorsal spines and 10 dorsal soft rays. The anal fin has 3 spines and 6 soft rays, and the second anal spine does not reach vertical from the caudal base. The pectoral fins have 15 to 16 rays and do not reach vertical from the tip of the pelvic fins. ("Encyclopedia of Life", 2001; "Texas Parks and Wildlife Department", 2009; Froese and Pauly, 2010; Hill, 2005; Press, 2010)

The oocytes in follicles of common snook mature in a manner typical of most teleost fishes. The yolk averages 91% of egg mass. Eggs average 0.6 – 0.8 mm in diameter (0.27 mm^3 volume).

Hatchlings measure 1.4 to 1.5 mm in length. Common snook grow slowly in the first month following hatching, but growth rates nearly triple thereafter until the end of the first year. Juveniles can grow as much as 1 mm per day, but this rate slows to about 0.15 mm per day once they reach 2.4 mm in length. Juvenile common snook typically have absorbed their yolk sac by the time they reach 2.2 mm in length (in about 4 days). At 4.0 mm in length, melanophores become visible, and, by 7.0 mm in length, adult pigmentation becomes apparent. Bone ossification begins when juveniles reach roughly 5.0 mm in length, and by 8.6 mm the jaws are completely ossified and lined with teeth. (Hill, 2005)

Although common snook can occupy both freshwater and marine environments, they must spawn in saltwater, as sperm can only become active in saline conditions. Common snook are often observed congregating at the mouths of rivers, inlets, and canals during times of spawning. Several males often follow a single female during these mass spawning congregations. Common snook spawn in the evening over a period of several days. In Florida, two reproductive peaks are often observed, the first from June to July and the second from August to October. Reproductive peaks often occur during times of increased rainfall, which may be the result of increased phytoplanktonic primary production during rainy periods. If so, spawning activity may related to food availability. (Hill, 2005; Press, 2010)

Common snook are protandric hermaphrodites, meaning they change from male to female after maturation. The gonads of common snook contain both male and female sex cells. Female gonads mature directly from mature male gonads shortly after a male has concluded spawning. This transition takes place between the ages of 1 and 7 years. As a result of this process, the majority of small common snook are male and the majority of large individuals are female. In Florida, the ratio of males to females between the ages of 0 and 2 years differs significantly between the east and west coasts of the state. This variation is attributed to protrandry and differences in growth and mortality rates.

Common snook breed seasonally and are often observed congregating at the mouths of rivers, inlets, and canals during times of spawning. In Florida, two reproductive peaks are often observed, the first from June to July and the second from August to October. Spawning often peaks during times of increased rainfall. Common snook practice broadcast spawning. (Hill, 2005; Press, 2010)

Little information is known regarding the parental investment of common snook in their offspring. As broadcast spawners, however, members of this species are unlikely to provide parental care to hatchlings or juveniles.

It is estimated that common snook can live about 20 years. The oldest captured common snook on the Atlantic coast was an 18-year-old female, while on the Gulf coast the oldest was a 15-year-old female. (Froese and Pauly, 2010; Press, 2010)

Common snook, as amphidromous fish, often move between fresh and salt water throughout their life. Common snook congregate seasonally in saltwater near the mouths of rivers, inlets, and canals in order to spawn. Common snook are considered social in that they are often found in groups, especially during times of spawning. (Hill, 2005; Press, 2010)

Home ranges are not recorded for common snook.

Common snook, like most fish, uses their lateral line system to detect movement and vibrations in the surrounding water. This sense organ allows a fish to orient itself in the water column, avoid collisions with other fish or submerged objects, and sense the presence of other organisms such as predators or potential prey. Common snook are sight-feeders, using their sense of vision in concert with their olfaction and gustatory senses to find prey. They attempt to capture any moving particle in their mouth, where the potential food item is then either ingested or rejected depending on taste and texture. Marine fishes, including common snook, can distinguish amino acids solutions at concentrations to the order of 10^-9 M using their sense of olfaction. Common snook, with their acute senses of vision and olfaction in combination with their lateral line system, are some of the top predators in their habitat. (Borquez and Cerqueira, 1998; Hill, 2005)

Common snook are pelagic feeders. Daily feeding peaks occurrs 2 hours before sunrise and 2 to 3 hours after sunset. Their feeding behavior is affected by the tidal cycle, and feeding activity noticeably increases with an increase in water flow following a period of standing flood or ebb tides

Common snook are voracious predators and opportunistic carnivores. They primarily feed on other pelagic fish, though diet varies with habitat type. Juveniles generally inhabit freshwater habitats, and their diet primarily consists of palaemonid shrimp, microcrustaceans, copepods and mosquitofish. In saltwater environments, common snook have a similiar diet, but they may also prey upon other species of fish such as sheepshead minnows, bay anchovies, and pinfish. In saltwater environments, common snook also consume zooplankton and larger crustaceans. (Hill, 2005; Press, 2010)

Common snook are considered top predators in their habitat, and adults do not have any natural predators other than humans. Juveniles are preyed upon by dolphins (Delphinidae and Phocidae), fish-eating birds such as osprey and herons, and larger species of fish. (Hill, 2005; Press, 2010)

Adult common snook are top predators in their environment, preying on many species of pelagic fish, crustaceans, and copepods. Juveniles are preyed upon by dolphins, birds, and larger fish. In Florida, common snook are often parasitized by myxosporeans: Myxobolus centropomi, Fabespora sp., and Ceratomyxa choleospora. (Hill, 2005; Press, 2010)

While commercial fishing of common snook is illegal throughout Texas and Florida, they are prized game fish throughout their known geographic range. They are known as strong fighters when hooked. In 1986, Florida's fisheries and sport fishing enterprises of all game fish were estimated to be worth 5 to 7 billion USD annually. Common snook is prized for its culinary value. ("Texas Parks and Wildlife Department", 2009; Froese and Pauly, 2010; Hill, 2005; Press, 2010)

There are no known adverse effects of common snook on humans.

Populations of common snook have declined over the last 50 years due to commercial and recreational overfishing as well as habitat degradation and destruction. In 1957, a bill was passed in the Florida legislature which prohibited commercial fishing and the sale of common snook. Passage of this bill helped alleviate commercial fishing pressures on native populations, but habitat loss and water quality degradation may have a continued effect on populations of common snook. In January 1999, the Florida Fish and Wildlife Conservation Commission implemented a slot limit for recreational fisherman in order to protect larger breeding females. Florida fisherman can only harvest common snook between 26 and 34 in (66 to 86 cm) in length. Furthermore, there is a bag limit of 1 or 2 fish per person per day depending on the area. Fishing for common snook is closed between December 15 and January 31 statewide in Florida. (Hill, 2005; Press, 2010)