Dark ghost of the river mouth. The black flounder looks like a common flounder dipped in charcoal. The upper side is deep, dark olive-brown to almost black. Faint irregular blotches mark the skin. The underside is clean, creamy white. This provides perfect camouflage against the dark, muddy bottoms of the tidal rivers it loves. It is a fish that disappears into the mud. Adventurers of the flatfish family. While other flounders stick to salty estuaries, the black flounder pushes far upstream. It sometimes travels kilometres into pure fresh water. It has a higher tolerance for low salinity than any other New Zealand flatfish. This allows it to colonise coastal lakes and the deep, slow stretches of lowland rivers. Other flatfish cannot follow. A fish that goes where others cannot. Black flounder have a muddy, earthy flavour. This reflects their dark, freshwater habitat. Some people love it. Others find it too strong. But if caught from clean, flowing water and purged overnight, the muddy taste fades. A firm, sweet fillet emerges. It is worth the effort. A fish that rewards patience. To catch a black flounder is to catch the explorer. It is the dark, river-going flatfish that pushes into fresh water. It looks for a quieter life away from the salt. Once common in lowland waterways, it is now vanished from many catchments. Dams, culverts and pollution have taken their toll. It is the flatfish of the forgotten river. The one that used to be common, before the dams went in and the cows came to the banks. The river is brown. The water is slow. The black flounder hides in the mud, dark against dark, invisible. The dam upstream blocks the passage. The flounder cannot go further. It does not know why. It just knows it cannot go home. It carries on.