When we think of flatfishes like flounders, plaice, butts and tongues, we actually think of the sea and edible fishes. However, it is little known that several species are also purely freshwater dwellers. Among the Achiridae (American sole) in South America, for example, 26 species are known from freshwater, but many of them are euryhaline, i.e. they live in the sea, brackish water and freshwater. Among the species living exclusively in freshwater is Apionichthys nattereri, which we were able to import from Peru.

The animals were sent to us as Apionichthys finis, a closely related species, which also occurs only in freshwater and is also reported for Peru; a first comparison on the day of import with the original description of A. finis from 1912 did not raise any concerns at first. One week later we found time to study the animals more intensively. The revision of the genus Apionichthys by Ramos from 2003, which we consulted, quickly showed that our animals must be A. nattereri. In contrast to A. finis, the dorsal, caudal and anal fins of A. nattereri are clearly distinguishable from each other, but nevertheless connected. In A. finis the three fins are separated from each other. The identification became unambiguous when an animal attached itself to the front glass of the photographic aquarium. The black border on the blind side of the flatfish is characteristic for A. nattereri and does not occur in any other species.

Quite droll are the tiny eyes sitting on stalks and the no less tiny mouth. However, you don’t often get to see the pretty spotted pattern of the animals in a properly set up aquarium, because like all flatfishes, these animals spend a large part of the day buried in fine sand.

Apionichthys nattereri grows to about 25 cm in length, making it one of the largest members of the genus. The species is found throughout the Amazon basin. There is no information about the reproduction. The animals are certainly egg-layers without brood care, but how, where and when the fish spawn and the larvae develop is unknown. Examination of the ear stones (otoliths) of two related freshwater species, namely A. finis and Hypoclinemus mentalis, revealed that these two species probably spawn in freshwater and never live in the sea, even as larvae (Matsushita et al., 2020).

For our customers: the animals have code 207075 on our stocklist. Please note that we only supply wholesale. Only a few specimens available!

Text & photos: Frank Schäfer

Literature:

Eigenmann, C. H. (1912): The freshwater fishes of British Guiana, including a study of the ecological grouping of species, and the relation of the fauna of the plateau to that of the lowlands. Memoirs of the Carnegie Museum v. 5 (no. 1): i-xxii + 1-578, Pls. 1-103.

Matsushita, Y., Miyoshi, K., Kabeya, N., Sanada, S., Yazawa, R., Haga, Y., Satoh, S., Yamamoto, Y, Strüssmann, C. A., Luckenbach, J. A. & Yoshizaki, G. (2020): Flatfishes colonised freshwater environments by acquisition of various DHA biosynthetic pathways. Communications biology, 3(1), 1-9.

Ramos, R. T. C. (2003): Systematic review of Apionichthys (Pleuronectiformes: Achiridae), with description of four new species. Ichthyological Exploration of Freshwaters v. 14 (no. 2): 97-126.

Flounders and tongues belong to a group of fishes that are rarely seen in the aquarium hobby. Whereas flounders have a well developed, clearly visible caudal fin, in the tongues the dorsal, ventral and caudal fins are melted. The species Euryglossa panoides, which is by chance imported from India and Vietnam belongs to the tongues. The fish can reach a maximum size of about 20 cm, but even in the wild the rarely get that big, but stay about half that length. It can be kept in pure freshwater, but if the total hardness is below 10° DGH, a salt addition of about 5 ‰ is highly recommended. It is very important that the fish can burry itself in fine sand, for otherwise it wil get skin diseaeses like fungus and others. The most preferred food is tubifex and bloodworm.(Photo F. Schäfer, Text K. Diehl)

Angaben zum Tier
Herkunft	Indien-Vietnam
Name	Euryglossa panoides

Many
species of flatfish (of course not all of them) are wanderers between
two worlds. They are very tolerant against different salinities and can
live as happy in pure freshwater as in pure marine water. The common
European Flounder (Platichthys flesus) for example is found occasionally
as far upwards as Basel in the Rhine. However, they always return to
the sea to spawn.

The
small Indian Tongue (Euryglossa panoides, also sometimes referred to as
Brachirus panoides) has a similar way of life. Most often the adults
are found in the river mouths. So we suggest a slight salt addition for
the long-time keeping. The nice juveniles we currently have in stock
have been collected in pure freshwater. The species attains a maximum
length of about 20 cm.

For our customers: the animals have code 415921 on our stocklist. Please note that we exclusively supply the wholesale trade.

Text & photos: Frank Schäfer

The flatfishes (Pleuronectiformes) are a quite successfull order of fishes, comprising 11 families, 108 genera and about 572 species. Most of them are marine, only 4 species are known to live completely in fresh water, but many species are found in the brackish water of the lower reaches of rivers at least during their youth. Many species are of great importance as food fish for human consumption, but in the aquarium hobby these fish are almost unknown.

We were able now to import a species from Colombia for the first time ever, which probably represents a member of the genus Cyclopsetta. Our specimens are currently between 8 and 12 cm long and thrive very well in slightly brackish water (2.5 g salt/litre).

There are four accepted species in Cyclopsetta and our specimens are most similar to C. querna, which has a wide distribution in the western Pacific from the Gulf of California to Peru. C. querna is the largest species of the genus and can reach a maximum length reported of about 40 cm; however, the common length of fish collected in the wild is around 25 cm.

It is extremely fascinating to observe these fishes in the aquarium. They are predatory fish that prefer small fish as prey. As soon as a Cyclopsetta has discovered a potential prey, it erects from the bottom by stretching the back. Then it literally explodes from the bottom like a bullet and catches the food fish – even fast swimmers like zebra barbs have no chance to escape. After the hunt the flatfish slides back to the bottom.

For our customers: the fish have code 290903 on our stocklist. Please note that we exclusively supply the wholesale trade.

Lexicon: Cyclopsetta: the name refers to the cycloid scales of the members of this genus, combined with the genus name “psetta”, which is another genus of flatfish. querna: Latin, means “oaken” or “tanned”.

Suggestion of a common name: Toothed Flounder

Text & photos: Frank Schäfer

Angaben zum Tier
Herkunft	Kolumbien / Colombia
Verfügbare Größe in cm	8-12

For our customers: the animals have code 412934 on our stocklist.

Angaben zum Tier
Herkunft	Thailand