June 5, 2023

Black Flounder – Rhombosolea retiaria

Black Flounder – Rhombosolea retiaria

By Allan Burgess

A Freshwater Flounder

The black flounder is often caught in modern and brackish water, significantly spherical river mouths. Based mostly on Arthur W. Parrott throughout the Queer and Unusual Fishes of New Zealand, before now huge parts of this species have been taken in Lake Ellesmere, Canterbury, on the mouths of the rivers that enter the lake, largely amongst weeds. They’re moreover fairly widespread in Lake Wairarapa and Onoke. Surprisingly they will journey very prolonged distances up rivers see beneath; The place do you uncover black flounder?

Dimension of Black Flounder

Their widespread measurement is 200 to 250 mm. They are going to attain a measurement of 450 mm nonetheless there are few knowledge of big black flounders (McDowall, 1990). Based mostly on Tony Ayling throughout the Collins Info to the Sea Fishes of New Zealand, huge black flounders as a lot as 450 mm and weighing 2kg are typically caught in Lake Ellesmere, Canterbury.

Colouration of Black Flounder

The black flounder species is actually probably the most vibrant and engaging of the flatfishes. Colouration can differ pretty a bit with no two fish wanting exactly alike. Based mostly on David H Graham in A Treasury of New Zealand Fishes, “the colour is darkish, uninteresting inexperienced with purple spots which differ from the dimensions of a mere dot to spots as huge as a shilling”. A shilling measured 23.6 millimetres all through.

The distribution of the brick purple spots can differ with practically every specimen in dimension and distribution. Typically the purple spots have a smaller pale cream-coloured spot of their centres. Some have spots throughout the eyes and nostril. Whereas some individuals may need spots on their tail and fin membranes, others, identical to the one pictured above in a watercolour by Frank Edward Clark, do not.

The underside of the black flounder is a yellowish-olive shade with each scale being tipped with brown. The undersides of various specimens can often be a muddy grey. David H. Graham notes that he moreover seen black flounders throughout the fish markets that had purple spots every huge and small on their undersides. Some specimens had many purple spots on their bellies, whereas others had only some.

Graham, who was at one time a biologist on the Marine Fisheries Investigation and Natural Station and Hatchery at Portobello in Dunedin, found that when dwell black flounders have been launched into the station’s holding tanks, they’d a lot much less administration over altering their shade to go nicely with their habitat than each the sand-flounder or the greenback flounder.

Graham moreover mentions being shocked to see many black flounders throughout the Christchurch Fish Market that had been caught in lakes with elements of their fins, and in some cases with their complete tail missing. Graham was suggested this was attributable to the ravages of eels.

The black flounder has an oval-shaped physique. The dorsal fin has between 65 and 67 rays, The anal fin has from 43 to 45 rays.

What Do Black Flounders Eat?

Investigation of the stomach contents of black flounders has confirmed they’d been feeding on weed, worms and typically muddy ooze from the underside. They eat practically one thing found throughout the mud along with crustaceans like shrimps and crabs, along with worms, bugs, snails, and practically any pure supplies. Moreover they eat small fish and are recognized to feed intently on whitebait throughout the spring.

The place do you uncover Black Flounder?

They’re found all through the New Zealand coast. It is additional prevalent on every the east and west coasts of the South Island and reduce North Island. They’re moreover found throughout the Waikato River.

Black flounder is simply current in New Zealand.

They’re caught in bays alongside the coast, in estuaries and in harbours. They’re catadromous fish. This suggests they’re born in saltwater, then migrate into freshwater as juveniles the place they turn into adults sooner than migrating once more into the ocean to spawn.

Black flounder are additionally known as river flounder. They’re typically caught inside or near river mouths and could be caught in lowland lakes. Black flounders are well-known for travelling many kilometres upstream and residing pretty happily in freshwater.

Yellowbelly flounders are a similar New Zealand flatfish that moreover enters river estuaries and lowland rivers nonetheless not just like the black flounder, do not enterprise previous the intertidal zone to dwell in freshwater.

Based mostly on Ron M. McDowall in New Zealand Freshwater Fishes – A Pure Historic previous and Info, “there are tales of black flounder at Ohura, 250 km up the Whanganui River, near the confluence of the Moawhanga and Rangitikei Rivers, 88 km from the ocean; on the Manawatu Gorge, 100 km up the Manawatu River; on the Burke Hut, on the Landsborough, a tributary of the Haast (60 km upstream – Walton, 1935); about 60 km up the Clarence River, in North Canterbury; throughout the headwaters of the Grey River, close to Springs Junction; and throughout the Pomahaka and Tuapeka Rivers, throughout the Clutha.”

With a view to penetrate these prolonged distances upstream the black flounder ought to navigate strong fast flowing water and rapids.

Based mostly on McDowall, the black flounder is type of totally unstudied. Nothing is known about their breeding, nonetheless McDowall suspected that “each the adults lay their eggs in rivers and these are washed downstream to the ocean, or additional seemingly, the adults migrate downstream to the ocean, to spawn.” This seems the greater than probably as a result of the numbers of black flounder current in freshwater decline all through winter.

Black flounders are recognized to journey very prolonged distances at sea. There are tales from the Freshwater Division of the outdated New Zealand Marine Division that black flounders tagged in Lake Ellesmere have later been recaptured a number of of km down the coast to the south. In a single case 176 days later off the Nuggets in South Otago, 370 km away, and one different was recaught throughout the Shag River 270 km south of Lake Ellesmere 265 days later.


The black flounder most definitely lays lots of of very small eggs.

The eggs, which float near the ground of the ocean, hatch probably a few days after spawning. For his or her first few weeks, they’re found throughout the ground plankton. At this stage, they nonetheless have their eyes on both facet of their heads and swim upright like common fish.

As soon as they attain 10 mm in measurement a metamorphosis takes place. The eye on the left side migrates over the snout to the proper side. at this stage, the tiny flounder sinks to the underside to start out life as a flatfish. The black flounder lays on its left side. Black flounders shouldn’t current in freshwater until after this metamorphosis has occurred.

Very small juvenile black flounders solely 10-15 mm prolonged are found shifting into rivers by means of the spring.

It is unknown for constructive whether or not or not the adults die rapidly after spawning or return to freshwater.

How do you Catch Black Flounder?

The old-time Maori would catch black flounder by web or spear (Elsdon Biggest, 1929). Lately they’re caught by set netting and acquired commercially nonetheless solely in small numbers.

Flounders spend most of their lives hiding on the bottom the place they feed. With their eyes extreme on their heads they’re capable of scan their setting very efficiently. They modify their pores and pores and skin shade to match the substrate and may shimmy their dorsal and anal fins to partially bury themselves every to stay away from being seen by predators and to ambush small fishes. When disturbed they’re capable of beautiful quick bursts of tempo.

Are Black Flounders Good Consuming?

Black flounder is taken under consideration to be great consuming. Nonetheless, they do not preserve along with completely different flounder species and so should be processed or eaten as rapidly as potential after seize.

As with all flatfish, probably the most well-liked methodology of cooking them is after gutting place the whole fish in a frying pan with butter. Put together dinner one side then flip over and prepare dinner dinner the alternative side. Then place it on a plate and eat both facet with a fork leaving the bones in place. Add solely pepper and lemon juice each all through or after cooking.

Throughout the outdated time, black or seen flounder was recognized to Maori as mohoao. They’ve been taken between Might and August in Lake Ellesmere/Te Waihora. It is the fattest of the flatfish found there. They’ve been as quickly as caught by Maori in considerable numbers and preserved for future use. When caught they’ve been cleaned and the heads reduce off. They could then be hung up by the tail on racks to dry. A tricky roof could be constructed over them to keep up the rain off.

When required for meals they is likely to be pounded to soften them. They could then be roasted, broiled or steamed (Elsdon Biggest, 1929).

The black flounder was on no account as fairly a number of as a result of the sand flounder or yellowbelly flounder at any time.

Correct Eye Flounder

A Correct Eye Flounder: in case you preserve the darkish increased side of a black flounder, generally called the ocular side, coping with you with the highest to the proper, the gills will probably be on the bottom.

The black flounder is one in every of a much bigger group of flatfishes current in New Zealand which contains:

Black Flounder Rhombosolea retiaria,

Yellow-Abdomen flounder Rhombosolea leporina,

Sand Flounder Rhombosolea plebeia,

Buck Flounder Rhombosolea tapirina,

Lemon Sole Pelotretis flavilatus,

New Zealand Sole (widespread sole) Peltorhamphus novaezeelandiae,

Observed Flounder Azygopus pinnifasciatus,

Brill Colistium guntheri

Turbot Colistium nudipinnis.


Te Waihora Mahinga Kai: a compilation of data and summary of present evaluation on freshwater fishes in Te Waihora. Prepared for the Whakaora Te Waihora Companions by NIWA

A Treasury of New Zealand Fishes By David H. Graham

The Queer and the Unusual Fishes of New Zealand by Arthur W. Parrott.

Collins Info To The Sea Fishes of New Zealand by Tony Ayling, illustrated by Geoffrey J. Cox.

Handbook of New Zealand Marine Fishers by Larry Paul and John Moreland, Illustrated by Eric Heath.

New Zealand Freshwater Fishes – A Pure Historic previous and Info by R.M. McDowall.

A Photographic Info to Freshwater Fishes of New Zealand by Stella McQueen, with footage by Rod Morris.

Fishing Methods and Devices of the Maori by Elsdon Biggest.