Anyone have information on freshwater flounder ?

[Doc Aquatic]

I have 15 of these flounders. I can’t find any information anywhere on them. I believe they may need to go to brackish tank but any information would be so helpful to me ! Thank you so much. 

[xXInkedPhoenixX]

These look hard to classify. Based on a little search I'm guessing either Achiris Achirus or Hypoclinemus mentalis. 

[Colu]

Do you no what species of flounder they are 

[Gator]

@Doc Aquatic; there is only one "Flatfish" Achirus Errans that can spend its' whole life in the home aquarium, all others live in salt or brackish water and swim into freshwater to spawn and do not do well in the home aquarium. Yours' looks like a fine specimen.

They are blackwater fish that prefer warm ( 80 to 85 degrees), soft, and acidic water. They only eat live food so it's best to keep some feeder Guppies in your tank so they'll have babies for the Brazilian Freshwater Sole to eat.  

[Gator]

@Doc Aquatic; I failed to mention that your fish will grow to about 4 inches and at that size, it will eat any fish it can fit into its; mouth.

Sorry

Gator

[Biotope Biologist]

That actually appears to be a tonguefish. I believe there are roughly 10 species in the aquarium trade masquerading as freshwater flounder.

 

Tonguefish and flatfish are extremely hard to classify without the specimen in hand because you need to look at the accessory dorsal branch as well as gill raker count. Going off coloration alone is incredibly inaccurate. I want to put it in the Achirus genus though based off what I can gather of vague mouth details and eye distance. 

 

Species doesn't really matter here because all of them are indeed brackish fish that are found in estuaries. This means salinity doesn't necessarily need to be consistent or high. I've heard of people keeping them successfully at as low as 1.005 with bumblee gobies. Granted gobies are liable to be prey for this ambush predator. However, tonguefish are lazy and prefer easier meals of worms and other inverts they can find in the sand. They have quite an adept nose, but poor eyesight.

 

Sand/mud is required substrate as these are very fragile fish and will cut themselves on any abrasives.

 

I've heard of the true freshwater variety @Gator is referring to showing up in rare instances. However they are distinct in that they have cirri around their mouth. Those could be cirri at the tip of the mouth, but to my eyes I think it's the mouth.

For reference "cirri" are the tufts on top of this blennies head that make it look like he just woke up.

Photo credit: Florida Museum

Edited November 14, 2021 by Biotope Biologist

[Doc Aquatic]

[StevesFishTanks]

I caught one that looked alot like that about 10 years ago. I put it in a freshwater sand bottom community tank of natives and wild caught fish. It went straight to the bottom and burrowed in the sand. I only saw its eyes in the sand one other time about a week later. Not sure if it eventually died or was always hiding. When we took the tank down we didn't find it. I never caught another. It was collected from freshwater but there are storm drains that can introduce saltwater to the lakes/ponds.

[Wingman12r]

Bringing up an old post, but I saw this Reddit post. Pic #7 is a freshwater flounder called a Hogchoker.

@Doc AquaticJust in case you hadn't learned anything more.

[Doc Aquatic]

Yes I think is hog choker. We have them in Narragansett bay here in RI 

[Tampa Jack]

Bringing this back up!!!   Calling all flounder keepers!

I have had a pair of these guys for over 7 years.   I have always labeled them as “Trinectes Maculatus”.  If you know these fish, and know them to not be that, let minnow!  I housed them in freshwater for the first 6 months but after that they got moved into a 40B that has sat between 1.006-1.008.  The bigger fish is right at 5.5”.   I have often left livebearers in the tanks along with some other brackish tolerable species.   I have only really had them eat live blackworms or frozen bloodworms/tubifex worms.    Sometimes I will dumb some “ghost/whisker” shrimp in if leaving town but have never visually observed them eating, chasing, or striking them, even though I’ve watched for hours shrimp walk across their backs.

The lack of available information on these guys is still astonishing to me becuase I have seen them sold in big chain pet stores.   7 years I’ve had them and love em!   
 

 

[Biotope Biologist]

Yours look very healthy and they are actually several species of brackish tonguefish. 
 

Their state of origin is unknown as they are all wild caught. Some come from the Atlantic coast some from the southern pacific coast. None of which are true freshwater but like many Flounder species the adults head up stream to lay their eggs. Babies are full freshwater or brackish and look just like regular fish. After about 8 weeks their eyes migrate to one side or the other based on which species of flatfish it is. 
 

anadromous fish are very rarely successfully bred in captivity due to their complex life cycle. Silver sharks are another one that up until very recently Petsmart used to sell. Which is an anadromous catfish that hail from Central America. 

[Tampa Jack]

moving them to brackish was the best thing that happened for them.   They started to grow immediately and become much more active, especially at night.   Super cool fish, I just hate not being able to keep plants alive in my brackish tank.    Ive tried sooooo many plants and while some tolerated it for a while, eventually they would just stuggle to grow or look good.   A smart man would go down to the river with my salinity test, find whats growing in 1.008 and bring it home lol

[ArthurLK11]

I can guarantee you that is not a species of tonguefish (Cynoglossidae). It is way too circular and not long enough. Trinectes maculatus seems to match the best, with possibly Achirus lineatus being in the discussion. That of course is assuming they are from the east coast of the US. I didn't look into any other areas of the world. Either way, both of those species live in saltwater and swim upstream to spawn. The juveniles live in freshwater and slowly move their way into saltwater as they age. Good move moving them to brackish. 

[Tampa Jack]

On 10/2/2024 at 7:06 PM, ArthurLK11 said:

I can guarantee you that is not a species of tonguefish (Cynoglossidae). It is way too circular and not long enough. Trinectes maculatus seems to match the best, with possibly Achirus lineatus being in the discussion. That of course is assuming they are from the east coast of the US. I didn't look into any other areas of the world. Either way, both of those species live in saltwater and swim upstream to spawn. The juveniles live in freshwater and slowly move their way into saltwater as they age. Good move moving them to brackish. 

I agree with this.   The body shape and markings point to Trinectes maculatus for me.   The Achirus seems to have a more rounded back half that these don't possess.

[Biotope Biologist]

On 10/2/2024 at 4:06 PM, ArthurLK11 said:

I can guarantee you that is not a species of tonguefish (Cynoglossidae). It is way too circular and not long enough. Trinectes maculatus seems to match the best, with possibly Achirus lineatus being in the discussion. That of course is assuming they are from the east coast of the US. I didn't look into any other areas of the world. Either way, both of those species live in saltwater and swim upstream to spawn. The juveniles live in freshwater and slowly move their way into saltwater as they age. Good move moving them to brackish. 

Tonguefish are not always elongated. At least not our pacific coast ones. Which I am going to say I wouldn’t even bother trying to pinpoint species even with a dichotomous key without knowing their water of origin you will have a hard time identifying them. Many many flatfish share identical mottling patterns and body shape. It’s best using lateral line, rays, and gill rakers.
 

many of the ‘freshwater’ saltwater species you see in the trade are brackish and inhabit estuaries. They can withstand freshwater for a time but likely face long term stress in freshwater. Again this is also highly debated as we are finding out bullsharks and other estuarine species can spend prolonged amounts of time in full freshwater. We are talking years timetables.

 

Here is where common names also get tripped up. Hogchokers on the east coast are an estuarine sole but hogchokers on the pacific coast are tonguefish. Would really like to know where that etymology comes from too

[Mississippi fish guy]

On 10/3/2024 at 10:52 AM, Biotope Biologist said:

Here is where common names also get tripped up. Hogchokers on the east coast are an estuarine sole but hogchokers on the pacific coast are tonguefish. Would really like to know where that etymology comes from too

If you mean the etymology of hogchocker I seem to remember reading that people had fed them to hogs and they would flatten in the hog throat choking it to death so I think that is where hogchoker came from. Please correct me if I’m wrong.