Empire gudgeon (Hypseleotris compressa)

H. compressa has an elongated body which can be up to 12 cm (4.7 in) long. The males are larger than the females. The fish does not have a lateral line, but does have ctenoid scales.

Its color varies, but the fish generally has a yellowish-tan to golden-brown head, although it can occasionally be a dark brown. Its abdomen is usually a whitish-red color. During the off-breeding seasons, males can be identified by prominent, variously colored bands on their anal and dorsal fins. The caudal fin is a "dusky" colour, and the pectoral and pelvic fins have no colour. During the breeding season, the male's colors brighten significantly, turning a red-orange colour, and they sometimes appear to glow. The male fish uses his colors to attract a mate. The species can quickly change color as needed.