Sole Fish – Freshwater

Freshwater Sole Fish – a very unique looking and interesting fish to have in your tank.  They are peaceful but a picky and slow moving fish when feeding, thus recommend for the advanced aquarist.  Adult size 20 cm, minimum tank size 200 litres.

Sole fish (Brachirus panoides) are sometimes referred to as flounders because they share a flat and somewhat rounded appearance. Sometimes they are also called tonguefish due to similar ‘tongue-like’ characteristics. However both these names are not accurate for sole fish. Both Flounders and Tonguefish have distinct anatomical features and are classified in distinct and separate families. Flounders are mostly saltwater fish, and are a more distant relative to the sole fish. True Soles on the other hand, are closely related to both the American Soles of the Achiridae family and the Tonguefish of the family Cynoglossidae, also called “tongue soles”.

Behaviour

The intriguing anatomy of sole fish is that they are flattened, or compressed laterally. They literally swim on their left side on the bottom of their environment. After they are born, their left eye migrates over to the right side and points up, leaving the left side or ‘bottom’ side blind.

This Freshwater Sole is an interesting species that will do quite well in an aquarium if given the correct environment. However don’t jump into getting one of these fish unless you are ready to dedicate time and energy to its care. These are picky, slow moving fish when feeding, and you have to make sure they get their fill. They will normally feed late at night when the other fish aren’t interested in eating.

They will spend most of their time on the bottom of your tank, although they may occasionally stick to the sides.

Tank Conditions

Freshwater Sole are seen on the bottom of estuaries and in the lower courses of rivers. These fish tend to live in pure freshwater as well as brackish water. They will normally stay covered with sand or mud most of the day and hunt at night. Soles camouflaged themselves in a combination of colors that match their surroundings, making them very hard to spot.

They do require a fairly large tank of at least 200 litres, and a high quality canister filter. These fish are sensitive to low oxygen levels and require air stones to keep the oxygen level high.

They spend virtually all of their time on the bottom so special care needs to be given to the bottom of your tank. To feel secure, they should be able to bury themselves which means that very fine gravel or sand is the substrate of choice. It is not unusual to see only a pair of eyes poking up through the sand. Adding some rock or wood decor is fine, but should be kept to the back and sides of the tank so they have an open, uncluttered area for burrowing.

Compatibility

They will eat tiny fish so make sure any tank mates are too large to be able to fit into their mouths.  This fish is not aggressive but since it is a predator care is needed when choosing tank mates. The other concern when keeping them in a community tank is making sure they get enough food. They are not aggressive eaters and are slow to find food. Avoid fishes like loaches and catfish, but daytime active fish like livebearers and gobies are good tank mates.

Fish Compatibility Chart

Feeding

The biggest issue with Sole is getting them enough food. They are nocturnal hunters and will not eat at all during the day and since they tend to be slow moving that by the time they start to eat, the food has often already been consumed by the other fish. They prefer live foods and are not to be considered a scavenger when it comes to food.

Since they are carnivores, the Freshwater Sole will eat all types of protein foods. Feed a diet of live or fresh frozen foods such as brine shrimp, mysids, black worms, earthworms or bloodworms. Some specimens, once comfortable in their new home will accept catfish pellets and chunks of prawn or white fish. Some may also eat a bit of algae, but it will be very little and they are not scavengers. They are not aggressive feeders so food may have to be poured directly on top of them to make sure they get enough to eat. They will also eat tiny fish so make sure any tank mates are too large to be able to fit into their mouths.

For best success feed them at night when they are normally ready to hunt and their natural instincts are intact. It is very important to monitor how much they actually consume, and to make sure that the animates to not take their food.

Diet Type: Carnivore
Flake Food: No
Tablet / Pellet: Occasionally – click for a list of Sinking Pellets at Rebel Pets.
Live foods (fishes, shrimps, worms): Most of Diet
Vegetable Food: Some of Diet – Some species may eat a bit of algae, but it will be very little and they are not scavengers.
Meaty Food: Most of Diet – click for a list of Fish Food for Carnivores at Rebel Pets.
Feeding Frequency: Daily

Care

The Freshwater Sole prefers freshwater or slightly brackish water.  If you don’t know what species you have (some Soles prefer brackish water), keeping the water slightly brackish is a safe bet for all species. A specific gravity of around 1.005, is fine and the freshwater species can handle this little bit of salt. Provide weekly partial water changes as needed, generally about 25 – 50%. Water changes can be quite variable, depending on salinity, tank size, and stocking density (bio-load).

These fish are very sensitive to low oxygen concentrations in their water, but are very long lived in the right environment. That being said the mortality rate is often high in most home aquariums. This has nothing to do with the health of the fish, but the inability of the aquarist to make sure they are getting their share of food. Its not uncommon for them to die of starvation.

As with most fish the Freshwater Sole are prone to skin flukes, parasitic infestations (protozoa, worms, etc.), ichthyobodo infection, parasitic infestations (protozoa, worms, etc.), bacterial infections (general), and bacterial disease. Anything you add to your tank has the possibility of bringing disease to your tank. Not only other fish but plants, substrate, and decorations can harbor bacteria. Take great care and make sure to properly clean or quarantine anything that you add to an established tank so not to upset the balance.

See Fish Disease Diagnosis and Treatment at Rebel Pets for help with diagnosing and treating diseases.