Morphological Characteristics of the Sciaenidae
Sciaenids are a highly diverse family of predacious perciform fishes. The morphological diversity reflects their ecological diversity; members of the family occur in the open ocean as well as in freshwater systems, although the majority of species are adapted for life in estuaries (coastal areas that serve as an interface between freshwater rivers and the ocean). Sciaenids are also quite variable in size with some species, such as members of the genus Stellifer, being relatively small (~10 cm standard length, SL), whereas species in other genera such as Sciaenops, Pogonias, and some Cynoscion are quite large (well over 1 m SL).
Perhaps the most characteristic feature of the family is that most members are hearing specialists. Sciaenids have extremely large, morphologically divergent saccular otoliths, with a characteristically tadpole shaped sulcus, and large, often complexly structured swim bladders. The head has large cavernous canals and conspicuous pores on snout and lower jaw. They also have a highly developed lateral line system, that extends to the posterior tip of the caudal fin. These features may be adaptations to life as predators in turbid estuarine ecosystems.
There are several other characteristics that also serve to unite the family (based on Trewavas, 1977; Nelson 1994). The dorsal fin is long with the spinous and soft portions separated by a deep notch or rarely completely separated. The first dorsal has between 6 and 13 spines, and the second dorsal has one spine and 20 to 35 rays. The anal fin has one or two spines, as opposed to three of most other Perciformes. The post-temporal bone has a fimbriate edge. The upper bony edge of the operculum is forked. Teeth are usually absent from the vomer and palatine. Some genera have single or patch of small barbels on the chin.
Some of the distinguishing characteristics of sciaenids:
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Skull of Cynoscion analis
Notice cavernous nature of dorsal surface |
Saccular otolith of Cynoscion arenarius
Notice tadpole shaped sulcus |
References:
Nelson, J.S. 1994. Fishes of the World. John Wiley & Sons, Inc. New York. 600 pp.
Trewevas, E. 1977. The sciaenid fishes (croakers or drums) of the Indo-West-Pacific. Transactions of the Zoological Society of London 33:253-541.
