Latin name

Acanthogobius flavimanus

Other names

Mahaze, Japanese river goby, oriental goby, spotted goby.

Identification

The gill covers are covered with scales at the top; the cheeks have very few scales and are very small, sometimes almost imperceptible, especially in young individuals. The throat is covered with small scales. The scales on the top of the head reach up to the eyes. The base of the flipper is covered with scales. The eyes are set high.  The collar (edge) of the venter is without lobes. Corners of mouth perpendicular to anterior edge of eye. Lips not widened to corners of mouth. Length of head 28.5-30.7% of body length. Width of flat forehead less than longitudinal diameter of eye. This species can be identified by the arrangement of pores on the head, spines and rays on the dorsal fins, and scales and papillae on the head. The yellow pelvic fins also distinguish it from related species.

Features of fish fins

The pelvic fins fuse to form a sucker. Dorsal fins two, extended to a distance less than the longitudinal diameter of the eye. The pelvic fins do not reach the anus, the pectoral fins reach the vertical of the posterior end of the first dorsal fin. 

Fish colouring

Light brown fish with darker saddles and spots. The pelvic fins are yellow. 

Distribution

Northwest Pacific: Russian Far East (from the Amur to Peter the Great Bay), Korean Peninsula, Bohai Sea, Yellow Sea and East China Sea in China, Hokkaido to Kyushu in Japan. It has spread beyond its natural range (Australia, Mexico, Florida and California in the USA) where it has become an introduced and often invasive species.

Habitat

Marine, freshwater, brackish, amphidromous species, depth range 1 to 6 m. Ground dweller, lives on muddy or sandy substrates. It tolerates fresh and salt water well and rapid movement between the two. It can live in a wide variety of aquatic habitats. Adults can spend their entire lives in fresh water, while larvae usually develop in salt water.

Size

Reaches 25-30 centimetres in length. Normal length is 14.5 centimetres.

Behavior

This fish spends most of the year in rivers and streams. In winter it moves down to saltier areas such as bays and estuaries, where it breeds. 

Food and feeding habits

The diet includes many species of small organisms such as copepods, amphipods, mantis shrimp, mysids, small fish and polychaetes. It is also known to feed on fly larvae, bivalves such as Corbicula fluminea, ostracods and various types of detritus.

Reproduction

Spawning takes place at temperatures between 7°C and 13°C. Females can lay up to 37,000 eggs. Each egg is about 5.5 millimetres long. The eggs are laid in a nest, a burrow up to 35 centimetres deep built by the male. The nest can be guarded by both males and females. Under optimal conditions, the young hatch in about 28 days. They usually live up to 3 years, but some individuals may live longer.

Fishing

Anglers using goby as bait. 

Relationship with a person

It is a pest fish. For example, it is illegal to sell or keep it in the Australian state of New South Wales. It is sometimes kept in aquariums as an ornamental fish. It is used in Chinese medicine.