European Carp, Cyprinus carpio, are native to central Asia. They were first introduced into Australia in the mid 1800’s, but remained confirmed to two locations , Sydney and the Murrumbidgee Irrigation Area.These two different populations were different strains of one species and showed no signs of spreading. In the early 1960’s a fish farmer illegally introduced a new strain and it has rapidly colonised watercourses throughout Australia. A recent genetic study has identified a fourth stain , Koi, which is present in the wild in the ACT and Tas. The feral Koi lacks the bright orange and black colouration seen in aquarium Koi. Coloured Koi have also been caught in the Euroa Arboretum dam in recent times.
Carp are present in the majority of slopes and lowland rivers and creek , and in upland streams as well. They often comprise between 70% and 90% of the fish biomass in lakes and rivers. The streams of the Strathbogie Ranges are generally free of Carp . They are usually associated with warm , slow-moving water and are rarely found in clear , cool fast flowing streams. Carp feed by ‘mumbling’ in the sediment on the banks and bottoms of water bodies. This involves sucking in the sediments , sorting out the edible items and expelling the sediments through gill openings. Dietary items include zooplankton , insect larvae, crustaceans, molluscs and to a lesser extent plant material . When carp are seems gasping at the water surface , they are not taking oxygen but rather feeding on zooplankton.
The impacts of Carp on native fish are not clear but their feeding behaviour has led to considerable concern that they may be increasing turbidity levels in waterways. Blue Green algae blooms occur when water quality decreases . Carp caught while fishing should not be released back into waterways, but dispatched humanely.
Reference : Fishes of the Goulburn Broken Catchment . “A guide to the native and alien fish of the Goulburn Broken Catchment”. Free Publication 2012 . Contact GBCMA Shepparton Office for a copy .