Sciaenidae

Sciaenidae
Atlantic croaker, Micropogonias undulatus
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Order:	Perciformes
Suborder:	Percoidei
Family:	Sciaenidae
Genera
See text.

Sciaenidae is the family of fish commonly called drums or croakers in reference to the repetitive throbbing or drumming sounds they make. The family includes the weakfish, and consists of about 275 species in about 70 genera; it belongs to the order Perciformes.

Characteristics

A sciaenid has a long dorsal fin reaching nearly to the tail, and a notch between the rays and spines of the dorsal, although the two parts are actually separate. Drums are somberly colored, usually in shades of brown, with a lateral line on each side that extends to the tip of the caudal fin. The anal fin usually has two spines, while the dorsal fins are deeply notched or separate. Most species have a rounded or pointed caudal fin. The mouth is set low and is usually inferior. Their croaking mechanism involves the beating of abdominal muscles against the swim bladder.

Sciaenids are found worldwide, in both fresh and salt water, and are typically benthic carnivores, feeding on invertebrates and smaller fish. They are small to medium-sized, bottom-dwelling fishes living primarily in estuaries, bays, and muddy river banks. Most of these fishes avoid clear waters, such as coral reefs and oceanic islands, with a few notable exceptions (i.e., reef croaker, high-hat, and spotted drum). They live in warm-temperate and tropical waters and are best represented in major rivers in Southeast Asia, northeast South America, the Gulf of Mexico, and the Gulf of California.

Fisheries

They are excellent food and sport fish, and are commonly caught by surf and pier fishers. Some of them are important commercial fishery species, notably small yellow croaker with reported landings of 218,00–407,000 tonnes in 2000–2009; based on the FAO fishery statistics from 2009, it was the 25th most important fishery species worldwide. However, a large proportion of catches is not reported at species level; in the FAO fishery statistics, the category "Croakers, drums, not elsewhere included", is the largest one within sciaenids, with annual landings of 431,000–780,000 tonnes in 2000–2009, most of which were reported from the western Indian Ocean (FAO fishing area 51) and northwest Pacific (FAO fishing area 61).

Croaking Mechanism

A notable trait of sciaenids is the ability to produce a "croaking" sound. However the pitch and use of croaking varies species to species. The croaking ability is a distinguishing characteristic of sciaenids. The croaking mechanism is used by males as a mating call in some species.

To produce the croaking sound, special muscles vibrate against the swim bladder. These muscles are called sonic muscle fibers, and run horizontally along the fish's body on both sides around the swim bladder and are connected to a central tendon which surrounds the swim bladder ventrally. These sonic muscle fibers are contracted against the swim bladder to produce the croaking sound that gives drum and croaker their common name. The swim bladder of species in sciaenids, is used as a resonating chamber. The large swim bladder is more expansive and branched than species outside of sciaenids, which aids in croaking. In some species the sonic muscle fibers are only present in males. These muscles strengthen during mating season and are allowed to atrophy when not in the mating season., causing the croaking mechanism to be inactive. In other species, most notably the Atlantic Croaker, the croaking mechanism is present in both genders and remains active year round. These species are theorized to use croaking for communication purposes such as announcing hazards and location when in turbid water.

Croaking in communication

In some species croaking is used for communication aside from attracting mates. For those species that have year round croaking ability it is theorized that the croaks serve as a low-aggression warning during group feeding as well as to communicate location in turbid waters. In those species that lack the ability to croak year round, croaking is usually restricted to males for attracting mates. A disadvantage to the croaking ability is that it allows Bottlenose dolphin to easily locate large groups of croaker and drum as they broadcast their position, indicating large amounts of food for the dolphins.

Genera and selected species

File:7080 aquaimages.jpg

Juvenile spotted drumfish, Bonaire, Netherlands Antilles

File:3726 aquaimages.jpg

Adult and juvenile spotted drumfish, St. Kitts

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Timeline of genera

Further reading

• Froese, Rainer, and Daniel Pauly, eds. (2006). "Sciaenidae" in FishBase. May 2006 version.