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Fish

Monkey Goby

Neogobius fluviatilis

Monkey Goby

Overview

The tubenose goby (*Proterorhinus semilunaris*) is a small-sized representative of the Gobiidae family, adapted to life in the quiet waters of the Delta. It is distinguished by its "nose-like" appearance and preference for vegetation-rich areas, unlike its relatives which prefer rocky or sandy zones. It is a discreet but very common fish in the channels and pools within the Danube Delta.

Physical Characteristics

Fusiform (spindle-shaped) body, more elongated and less dorso-ventrally compressed than other goby species — a more hydrodynamic form facilitating active swimming. Moderately large head with bulging eyes on the upper surface. Two distinct dorsal fins — the first short with spines, the second long with soft rays. The defining Gobiidae characteristic: pelvic fins completely fused into a functional adhesive disc allowing attachment to substrate even in strong currents. Colouration relatively uniform and discreet: brownish-grey, dark grey, or olive on back and flanks, paler on the belly. Key diagnostic character: no large spots or distinct transverse bands on the body (unlike the round goby or other species). Usual dimensions 10–15 cm, maximum 20 cm.

Habitat & Distribution

A native Ponto-Caspian species originating from the Black Sea, Azov, and Caspian basins. In Romania, present in the lower Danube from Iron Gate to the mouth, throughout the Danube Delta, and occasionally in the coastal Black Sea. Habitat is extremely varied: rivers with slow to moderate current, delta lakes and marshes, natural and artificial channels, brackish zones. Almost ubiquitous in the Delta. Has become invasive in the upper Danube (Germany, Austria), Sava (Croatia), and other European rivers through vessel-mediated transport.

Behavior & Diet

An opportunistic benthic carnivore with a varied diet: benthic invertebrates (insect larvae, chironomids, amphipods, isopods), small molluscs, crustaceans, fish eggs and fry, and occasionally very small fish. Not a strict ambush predator — actively searches for food on the bottom. Maximum activity at dusk and night. Uses its ventral disc for attachment to substrate in current. Prey for predatory fish (pike-perch, perch, pike), piscivorous birds, and aquatic mammals.

Life Cycle & Reproduction

Sexual maturity at 1–2 years, at 8–12 cm. Spawning in spring and summer (May–July) when water temperature exceeds 12–15°C. The male prepares a nest under stones, in cavities, or among roots and attracts females. A female deposits 200–1500 adhesive eggs on the nest surface. The male aggressively guards the nest for 2–3 weeks, fanning the eggs and removing dead ones. Hatching after 10–20 days. Fast growth: 8–10 cm in the first year. Lifespan 4–5 years.

Conservation Status

Least Concern (LC) in its native range. Extremely abundant in Romania with no major threats. Important ecological role as prey for valuable species and as a regulator of benthic invertebrates. In invasive range (upper Danube, Sava), it competes with native species for food and habitat, consumes eggs and fry of native fish. No special protective or control measures in Romania.

Sources

  • FishBase: Neogobius fluviatilis
  • Wikipedia: Monkey goby
  • Scientific publications on Ponto-Caspian gobies