Atherina boyeri
The big-scale sand smelt (*Atherina boyeri*), often simply called "atherin", is a small fish with huge local ecological and economic importance in the Danube Delta and the Razim-Sinoe complex. Although individually insignificant, the atherin forms colossal schools that constitute the food base for most ichthyophagous birds (such as pelicans and cormorants) and for marine predatory fish.
It is a slender fish with an elongated and slightly laterally compressed body. The most visible feature is a wide longitudinal band of bright silvery colour extending along the flanks. The mouth is small and slightly upturned, and the eyes are relatively large. It has two dorsal fins, the anterior one equipped with thin and flexible rays. The scales are large and detach easily.
It is an extremely versatile species, found in marine, brackish and even completely fresh waters. In the Danube Delta, it massively occupies lagoons, limans and estuarine zones. It is very resistant to temperature and oxygen variations, which allows it to colonise habitats that are difficult for other fish species.
The atherin is a typically gregarious species, moving in dense schools in the upper layers of the water column. Feeding is mainly through active capture of zooplankton, small crustaceans (mysids, gammarids) and insect larvae. Schools have synchronised protection behaviour: when attacked by a predator, thousands of fish jump simultaneously above the water to create confusion.
Reproduction is prolonged, taking place from April to August. The eggs have adhesive filaments with which they attach to submerged plants or algae. Development is very rapid, with fry often reaching sexual maturity even in the first year of life. This high reproduction rate allows the species to quickly replenish its numbers after natural mortality.
Classified as Least Concern (LC), the big-scale sand smelt is one of the most resistant species in the region. However, it is sensitive to chemical pollution of coastal areas. In the Delta area, it is commercially fished with special gear (seines with small mesh) to be consumed fried, being a highly appreciated local delicacy.