Mesonoemacheilus triangularis or Nemacheilus periyarensis is a species of stone loach endemic to the Western Ghats in southern Karnataka, Kerala, and Tamil Nadu, India. It is a fairly common species occurring in streams with gravel, cobbles and bedrock with some sand as the substrate. This fish grows to a length of 5.8 centimetres (2.3 in) SL and can be found in the aquarium trade.