Keeping Your New “Freshwater” Flounder 
Aqualand’s inside info on Achirus lineatus

 
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Flounder Factoids

Origin

USA

Temperature

70-85o

Lighting

Needs no special lights

Attitude

Seemingly shy and retiring

Security

Blends into the substrate

Foods

Start on live worms or small fishes

Size

Six inch max -- long not across

Water

Prefers slightly brackish water

Breeding Comments

Prolific breeder in the wild

LA
Bottom view of a 1.25-inch freshwater flounder.

LA
Two-inch freshwater flounder.

LA
Bottom view of a 4.5-inch freshwater flounder.

Common Name.  Though often called “freshwater” flounders, these guys do better in brackish water.  We’ve also heard them called “puppy tongues” down south.  In some areas they call them “hog chokers.”  Seems farmers feed these as trash fish to their hogs.  Hogs have trouble swallowing them, thus the name. (?)  Actually, hogs have very little trouble swallowing anything.

LA
Top view of 4-inch freshwater flounder.  Those eyeballs just bug out at you.  Ridiculously expensive.

Appeal.  Like the other flounders, these weird little guys have both eyes on one side of their bodies.  Their left eye migrates to the right side of their bodies.  The left side becomes its whitish underbelly.  They spend all their time lying on their underbellies.

LA
Freshwater flounders flip sand on their backs to hide from monsters (you).

LA
Other freshwater flounders blend in by digging in.

 

Color.  Freshwater flounders try to blend into whatever’s on the bottom.  They can control the size of their various pigment pores to change from dark to light in the greys and browns.  Some develop spots to complete the camouflage.

LA
Freshwater flounder bellies really show up.

Sort of a “Sucker Fish.”  Freshwater flounders frequently plaster their bodies to the glass sides of their aquaria.  They suck on the sides so strongly you’ll usually have difficulty netting them.  Some you need to pry off the sides.  Once in a plastic bag, you often need to slit the bag open to get them out.  Flounders can really hold on to flat surfaces.  But, unlike the plecostomids and other algae eaters, these guys ignore your algae.  They want live meat.

LA
Don't confuse flounders with these Borneo suckers (sometimes called Hong Kong otocinclus).

LA
Sold to us as tongue fish.  They cost five times more than freshwater flounders.

LA
Even with sand on top they still look like freshwater flounders.

LA
Four-inch long freshwater flounder about as big as they get

Size.  Few people grow freshwater flounders to any size because they keep them incorrectly.  The largest we ever saw was three inches across.  Flounders fare poorly in a regular community tank.  Beginners give them the wrong kind of water and expect them to eat fish food.  Most won’t eat flakes at first.

Habitat.  Ten-gallon aquariums work fine as starter tanks.  Flounders need more room as they grow.  They also prefer a sand bottom.  In the wild, flounders congregate on mud flats.  Do not attempt this at home.

LA
Since bumblebee gobies and freshwater flounders share the same needs, feel free to mix them.

LA
Flounders can change their color at will.

Brackish Water.  Adult flounders spawn in the mouths of rivers (where rivers empty into the ocean).  The extremely tiny fry migrate upstream.  You usually find flounders on the market at the one to two-inch size – well beyond the fry stage.  They start wanting more salt in their water as they grow larger.  Give them at least two teaspoons per gallon.  Increase the amount of salt as your flounders increase in size.

LA
Neither freshwater flounders nor bees like the flakes you see.  Both like the brine shrimp.  

 

Foods.  If it’s small and moves, freshwater flounders try to eat it.  Live blackworms or small earthworms work well to start with.  Add some feeder white clouds also.  They’d probably also enjoy ghost shrimp as they grow.  You can eventually convert them over to frozen brine shrimp and frozen bloodworms.  Some eventually convert to eating flakes or sinking pellets.  Most community fishes will eat all the flakes before the flounders start looking for them.  Flounders have an eating advantage at night.

Provide Cover?  If you keep flounders with bigger fishes, you may want to provide a cave or two.  However, in a tank with small neons, the neons need the cover.  Freshwater flounders can overpower the smaller fishes at night.

Tank Mates.  Feel free to mix these guys with other medium-sized brackish water fishes – African butterflies, dragon gobies, African ropefish (if your flounder’s too big to swallow), mollies, and other livebearers (because they like salt also).  Livebearers also provide additional live food periodically.

LA
Freshwater flounder -- an intriguing fish that always catches your eye.


LA
This guys from Peru.  Seems a bit bigger than our USA flounders.

LA
Don't know if the Peruvians are the same flounder species as our guys or not.

LA
Two of these Peruvian flounders almost fill this 10-gallom tank.

LA
Flounders usually appear on the market at about an inch.  They like to hide under the sand.

Last Words.  You needn’t worry too much about temp.  Like other USA fishes, freshwater flounders adapt to a wide range of temps.  Just keep it steady.  Set your heater to take care of their tank mates.  LA.
 

Ron Kruger, October 5, 2010
Hello Larry,
It's been a while since I've been in Des Moines! 
I was reading your write up about flounders. 
I've always found them to be very slow eaters, but snatch up food quickly once they find it.  Usually any other fish in the same tank will eat up all the food before flounders have a chance to find it.  I've always basically "hand fed" them with a modified eye dropper......  an eye dropper where I've attached a long tube that would reach to the bottom of the tank.  That way while other fish are busy feeding at the surface, I can place frozen brine shrimp right at the flounder's mouth.  Otherwise they should have a tank to themselves.  Once the flounders learn this, mine would always shoot up the sides of the tank and wait to be fed at the water's surface, stuck to the sides of the tank, where I would then "hand feed" them with the eye dropper.  Their stomachs then get huge as they fill up on brine shrimp. 
I hope all is well with you!  I was laid off April 2009 and so far doing okay without the stress of a job.  My dad is still living at the house in Altoona.
Take care!

A:  I'll add your info to my flounder page.  Being "job-free" can decrease your stress in some ways but increase it in other ways.  LA

 

LA
Two 3-inch flounders, November 8, 2012.

LA
Top view of one.

LA
Underside of same guy.

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