Black flounder

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Black flounder
Drawing by Dr Tony Ayling
Drawing by Dr Tony Ayling
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Pleuronectiformes
Family: Pleuronectidae
Genus: Rhombosolea
Species: R. retiaria
Binomial name
Rhombosolea retiaria
Hutton, 1873

The black flounder, Rhombosolea retiaria, is a flatfish of the genus Rhombosolea, found around New Zealand in shallow enclosed waters such as estuaries, harbours, mudflats, and sandflats, and in coastal freshwater lakes. Their length is from 20 to 45 cm.

The black flounder is a righteye flounder meaning it has both eyes on the right side of the head and lies on its left side. It has the typical flattened oval shape of the flounder with the dorsal and anal fins forming a fringe around most of the body. The eyes and scales are small. They swim by means of slight undulations of their fins and the outer edges of the body, keeping in contact with the bottom and seeming to "slide".

The colouring is dark grey-green on the back with darker mottling and a variable number of red spots. The fins are olive green with red spots and there is an orange tinge on the hind portions of the dorsal and anal fins. On the undersurface the basic colour is olive-yellow with a brown edge on each scale.

The black flounder eats worms, small crustaceans, and organic matter found in mud. It is most abundant in fresh or brackish waters, especially in Lake Ellesmere in the South Island of New Zealand, where it grows to its greatest size. It lives to a maximum of 4 years. Like all flounders it is a popular foodfish.


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