Growing up to 25 centimeters in length, Gerres longirostris features a laterally compressed, silvery body with a pale golden or olive tint on its dorsal surface, fading to a bright silver on the ventral side. Its most defining trait is the elongated, pointed snout, which gives the species its name and aids in sifting through sandy substrates to locate prey. Large, reflective eyes and a small, protractile mouth adapted for bottom feeding allow it to efficiently capture small invertebrates, such as crustaceans, worms, and mollusks, buried in the sediment. The dorsal fin is divided into two parts: a spiny anterior section and a soft-rayed posterior section, with the first few spines slightly elongated in mature individuals.

Native to estuaries, lagoons, and sheltered coastal areas, the long-snouted mojarra thrives in waters less than 20 meters deep, often near mangrove forests, seagrass beds, or rocky outcrops. It is a schooling species, forming dense aggregations that move in synchronized patterns to forage or avoid predators. During the breeding season, typically in the warmer months, adults migrate to nearshore waters to spawn, releasing pelagic eggs that develop in the water column. Juveniles seek refuge in the protected habitats of mangrove roots or tidal flats, where they feed on plankton and small benthic organisms until they mature.

While not a primary target for large-scale commercial fisheries, Gerres longirostris holds local importance in artisanal fishing communities, valued for its delicate flesh and role in subsistence diets. However, it faces significant threats from habitat degradation, including mangrove deforestation, coastal pollution, and sedimentation from urban development. These activities disrupt the shallow-water ecosystems it relies on for feeding and reproduction. As a species that bridges the gap between marine and freshwater environments, it serves as an indicator of estuarine health. Conservation efforts focused on preserving mangrove habitats, promoting sustainable fishing practices, and reducing pollution are crucial to safeguarding this unique mojarra and the biodiverse ecosystems it inhabits. By protecting Gerres longirostris, we also support the resilience of coastal communities and the intricate web of life in tropical and subtropical waters.