Robust Silverside

The hardyhead silverside (Atherinomorus lacunosus), also referred to by various names including broad-banded hardyhead, robust silverside, and wide-banded hardyhead silverside, is a marine species belonging to the family Atherinidae. This species is prevalent near the surface in the Indo-Pacific region and has been introduced into the Mediterranean Sea via the Suez Canal (🇪🇬 Egypt) as a result of Lessepsian migration.

Characterized by its robust and broad-headed morphology, the hardyhead silverside is a small species distinguished by its unique anatomical features. Notably, it exhibits a very low and wide lateral process of the premaxilla, and its lower jaw is nearly flat at the distal end, lacking a distinct tubercle posteriorly. The posterior extremity of the jaw aligns with the vertical through the anterior margin of the pupil. The species lacks prominent ridges on the palate despite having small teeth present. Anatomically, the anus is positioned posterior yet close to the tip of the pelvic fin. It possesses 18-24 lower gill rakers and a midlateral scale count between 40 and 44. The midlateral band spans up to the third and fourth scale rows, aligning with the anal fin's origin. The dorsal fin comprises 5-8 spines and 9-10 soft rays, while the anal fin features 1 spine and 12-17 soft rays, and overall, they have around 43-44 vertebrae. Typically, these fish reach lengths of 10–12 cm, although they can grow up to 14 cm. Fresh specimens display a predominantly silvery coloration with a greenish dorsal tint and a distinct bright blue strip along the flank, complemented by dusky fins and a translucent appearance in live settings.

The hardyhead silverside's geographical distribution encompasses the eastern African coastline through to 🇹🇴 Tonga, extending north to southern 🇯🇵 Japan and south to northern 🇦🇺 Australia, while notably absent in the Andaman Sea and replaced by Atherinomorus insularum in Hawaii. It was first documented in the Mediterranean in 1902 by Tillier, marking it as the second 🌊 Red Sea species identified there post the Suez Canal (🇪🇬 Egypt)'s opening in 1869.

Predominantly forming large schools, this species is frequently encountered along sandy shores and reef margins, often displaying nocturnal schooling behavior ranging from several hundred individuals to extensive aggregations spanning over 100 meters in length and 20 meters in width. Their diet primarily consists of plankton and small benthic invertebrates, with most feeding activity occurring at night. They also inhabit estuarine environments.

In terms of reproduction, hardyhead silversides in 🇳🇨 New Caledonia (🇫🇷 Overseas France) reach sexual maturity just under a year, with spawning occurring between late August and December. The species exhibits relatively low fecundity, and its extended spawning season suggests multiple spawning events per female. Typically, they exhibit a short lifespan, with most dying after a single spawning season, although some survive into a second year. In contrast, the 🇸🇨 Seychelles experience two spawning periods in April–June and September–December, coinciding with warmer waters between monsoons, while in the 🇲🇭 Marshall Islands, spawning takes place year-round. In 🇿🇦 South Africa, spawning occurs near estuaries from October to January, with eggs utilizing fine filaments for substrate attachment.

The hardyhead silverside serves as a crucial forage fish, supporting larger predatory species such as sharks, tunas, needlefish, and amberjacks, alongside avian predators like terns, boobies, gulls, egrets, and herons. It also hosts parasites, including the cymothoid isopod Livoneca and trematodes Overstreetia cribbi and O. sodwanaensis.

Commercially, hardyhead silversides are marketed fresh or as salted and dried products in Asia, and in some English-speaking regions where they are found, they are referred to as whitebait.