Haletta semifasciata, the Blue weed whiting, is a species of weed whiting endemic to Australia where it is only found along the southern coast. It is found in brackish and marine waters in sheltered locations at depths of from 1 to 7 metres (3.3 to 23.0 ft). This species inhabits areas with a substrate of sand with beds of seagrass where it feeds on small invertebrates and on algae and the seagrasses themselves. This species grows to a length of 29 centimetres (11 in) SL.