Common snook
(Centropomus undecimalis)

The common snook (Centropomus undecimalis) is a species of marine fish in the family Centropomidae of the order Perciformes. The common snook is also known as the sergeant fish or robalo.

One of the largest snooks, C. undecimalis grows to a maximum overall length of 140 cm (4.6 ft), but common length is 50 cm (1.6 ft). The IGFA world record is 24.32 kg (53 lb 10 oz) caught in Parismina Ranch, Costa Rica, by Rafael Montalvo.

Of typical centropomid form, it possesses drab coloration except for a distinctive black lateral line. It can also have bright yellow pelvic and caudal fins, especially during spawn.

The common snook is an estuarine and freshwater-dependent fish species. Within estuaries, juvenile common snook are most often found inhabiting areas such as coastal wetland ponds, island networks, and creeks. Despite being a euryhaline species of fish, the common snook does show a tendency to gravitate towards lower-salinity conditions in the early stages of its life. By being able to adapt and thrive in both high- and low-salinity conditions through osmoregulation, common snook display a high level of habitat plasticity.

Common snook are opportunistic predators whose feeding habits indicate a positive relationship between their size and the size of their prey, meaning that as the snook grows, it feeds on larger and larger prey. Common snook have been found to occasionally engage in cannibalism. This usually occurs during the winter when adult and juvenile common snook are in close proximity to one another within their estuarine habitats. This form of cannibalism where the juveniles are fed on by the adults is referred to as intercohort cannibalism. The adult common snook that do cannibalize juveniles most likely target them because the juveniles may be the largest of the available prey, so are nutritionally efficient to prey upon.

Physiological ecology
Common snook, like many species of fish, are very in tune with their environments; even a slight change in their surroundings can have a significant impact on their behavior. For example, common snook are able to determine when to start and stop spawning based on the temperature and salinity of the water they inhabit, the amount of rainfall in the area, and whether or not the moon is full. However, in some cases, disturbances in their environment can have very negative effects on the snook population. One example is the devastating results of a cold snap. Snook are very susceptible to cold temperatures, with the effects ranging from the complete halt of all feeding at a water temperature of 14.2 °C (57.6 °F), to the loss of equilibrium at 12.7 °C (54.9 °F), to death at a temperature of 12.5 °C (54.5 °F).[16] Recently, a cold snap in January 2010 resulted in a 41.88% decline in nominal abundance of the common snook population in southwest Florida from the previous year and a 96-97% decrease in apparent survival estimates.[17]

Distribution and habitat
C. undecimalis is widespread throughout the tropical waters of the western Atlantic Ocean from the coast of the North Carolina to Brazil including the Gulf of Mexico and the Caribbean Sea.

Snook likely originated in Central America, and changes in the earths climate brought the snook to Florida. During a great warming trend after the Ice Age, snook moved northward along the Mexico shoreline. They followed the perimeter of the Gulf of Mexico, along the west and east coasts of Florida. Massive snook are found in Central America, although they seem to look a little different because of the weather and water quality, but they are the same. No restrictions exist in most of Central America on the size or quantity of snook one can keep, consequently many locals have been keeping and killing these large snook for quite a while. Occurring in shallow coastal waters (up to 20 m (66 ft) in depth), estuaries and lagoons, the fish often enter fresh water. They are carnivorous, with a diet dominated by smaller fishes, and crustaceans such as shrimp, and occasionally crabs.