Oblong Mojarra

The slender silver-biddy, also known as the Oblong Mojarra (Gerres oblongus), is a species commonly found in marine and brackish waters along the coastal regions of the Indo-Pacific, ranging from the 🌊 Red Sea and East Africa to 🇼🇸 Samoa and 🇹🇴 Tonga, extending north to the Ryukyu Islands (🇯🇵 Japan) and south to 🇳🇨 New Caledonia (🇫🇷 Overseas France).

This species inhabits estuaries, coastal waters, and lagoons at depths ranging from 1 to 10 meters (3 to 33 feet). The slender silver-biddy can grow up to 30 cm (12 inches) in length, with an average size of approximately 15 cm (5.9 inches).

The distinguishing characteristics of this species include a dusky caudal fin, occasionally exhibiting a dark distal margin, with the lower edge of the lower caudal fin presenting as hyaline. Dusky stripes above the lateral line are generally absent or indistinct, though specimens smaller than 10 cm SL may exhibit 4 to 9 slightly oblique dusky bands. Below the lateral line, 4 to 9 slightly oblique dusky bands or columns of ovoid dark spots may be observed, becoming more prominent in preserved or stressed live specimens. The adult body is primarily silver, with the possibility of faint dusky bars in juveniles. The body is elongated, with a maximum depth of 2.8-3.3 in SL. Notably, the preopercle's lower flange is scaleless, the caudal fin is deeply forked with long lobes, and the pectoral fins do not extend beyond the level of the anus.

The slender silver-biddy prefers coralline areas and exhibits migratory behavior, traveling to specific sandy areas near the outer reef edge to spawn during late afternoons under a full moon. Its diet consists mainly of small benthic organisms residing on sandy bottoms. In Palau, this species similarly migrates to designated sandy locations near the outer reef edge for spawning purposes. The slender silver-biddy is known to form schools and primarily feeds on small invertebrates found in the sand.

The genus name Gerres derives from the Latin term for a type of anchovy, as cited by Pliny. This species holds significant importance for local commercial fisheries in many tropical countries.