The smallhead stickleback (Gasterosteus microcephalus), or resident threespined stickleback, is a fish species, which widespread in the basin of the Pacific Ocean: Japan, also Mexico.

Freshwater demersal fish, up to 5.5 cm (2.2 in) length.

Habits small streams, where feeds on aquatic insects and other invertebrates.

[1] This taxon is regarded by some authorities as a synonym of the three-spined stickleback (G. aculeatus),[2] and others treat it as a subspecies of the three-spined stickleback, G. a.

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