Gobiomorphus coxii, or Cox's gudgeon, is a species of sleeper goby in the family Eleotridae which is native to the upland rivers of south eastern Australia. Description Gobiomorphus coxii is dark brown to greenish-brown in colour on the back and flanks, this colouration fades to pale brown or cream on the underside. The scales on the lower flanks are mottled with blue, gold and yellow and there is a single black spot above the base of the pectoral fin. The juveniles have series of elongated blotches on their flanks which merge as they nature to create a wide, dusky, mid-lateral stripe. The head is dark brown with the lower jaw and throat often coloured black and with two indistinct, dark stripes radiating from the rear of the orbit across operculum. Its fins vary from colourless to blackish-grey and the dorsal fins have between one and three dark stripes with a yellow or orange background colour. The margins of the fin are frequently fin margins yellow and the caudal fin is marked with many dark spots which are arranged in irregular bands. The body of Gobiomorphus coxii is nearly cylindrical and tapers towards the tail, the head is large with a blunt, round snout and the quite small eyes are positioned high on the head. The mouth is relatively large, oblique and turned upwards with the lips ending lust below the front part of the eyes. They have jaws armed with bands of fine, pointed teeth. The cheek and operculum have lines of papillae which are also found around the preopercular margin and on each side of snout to above the eye. There are 3-5 large pores on the preopercular margin. It has two dorsal fins, the first, anterior dorsal fin, is rounded and has notches between its six spines and the second, posterior dorsal fin, is taller and slightly longer. The anal fin is below the second dorsal fin but it is smaller and rounder. The caudal fin is quite large and is, truncated while the pectoral fins are also large and are rounded and the rather long, pointed pelvic fins are located on the thorax. Males grow to a maximum standard length of but are more commonly , but the females grow larger than the males. Distribution and habitat Gobiomorphis coxii is endemic to eastern Australia from southern Queensland to Gippsland. It also occurs in the Swan River in