These fish show up occasionally in many LFS – regularly but seasonally in mine.  I confess a fascination with them dating back many years.  My first efforts to keep them were in the dark ages, when I actually kept community tanks.  Big mistake – huge!  I knew little about their needs, but learned fast that they are fin nippers.  I learned this perhaps most easily because I was not feeding them properly either, so they showed their lack of suitability for a community tank by shredding tankmates' fins before they died, likely of starvation. 

Okay, in the LFS you see this fish plastered to the wall of the tank.  If its belly is toward you, it is unmarked, but actually looks something like a Rainbowfish profile plastered flat on the wall of the tank, and with no visible eye.  The anal fin is very broad-based, coming well forward on the fish’s profile, but much shorter than the dorsal, which comes farther forward than any other fish I know, well down on what would be the fish’s face.  If you have the “dorsal' view of a "flounder" on the side or rear wall of the tank, the unpaired fins are less obvious as the body’s camouflage coloration (mottled with black/dark brown blotches) extends into the fins uninterrupted.  Close looks show there are eyes, both on the same side of the body, protruding like a frog's, but much less noticeable.  The mouth is still pretty well where it should be, giving the whole creature a strange asymmetry. Whether flounder or sole - the differences are technical, it is a flatfish.  The ones I kept were identified as Trinectes maculatus,commonly known as "hogchokers". These are born as "normal" fish.  Then one eye migrates around to the other (right) side of the body, ending with both eyes on the same side, now to be the "top"' of the fish as it settles out for life resting on the other side on or in the substrate, or swimming just over the substrate.  Showy?  Not at all.  Active?  Only at mealtimes.  Irresistible?  For me, just about.

Eventually I learned that these beasts are not true freshwater fish, but are least brackish to possibly marine at maturity (not unlike several of the brackish puffers, monos, and some other ""brackish"' fish we keep).  Fine, I've done puffers for years.  So we set light brackish water for them, or if in fresh at the LFS, gradually bring them up in pH and hardness to a minimum pH 8.0 - 8.2 and GH at least 12 - 14 (or more).  To accomplish both, we should use marine mix in the water.  I kept mine at specific gravity 1.003 - 1.008.   They are obviously bottom-dwellers, and from their cryptic coloration, probably hiders or lurkers.  Okay, then I had no fine-grained marine sand available, so used the finest grade of silica sand I could get.  Today I’d use marine sugar sand instead, or the finest grades of aragonite - to help maintain the buffering.  The swimming motion of these beasts is wonderful – they move with a rippling motion of the unpaired dorsal & ventral fins (now peripheral fins I suppose), rather as do knifefishes and the round rays. 

Rumor has it that there is a true freshwater flounder from somewhere in the Amazon basin, but I've never seen the fish in person and have only seen two offering of them in the time I have been on the Web.  They were quite expensive.

Feeding is not really difficult If you are willing to do live and some frozen (a bit of training is needed for non-live foods).  From the LFS, blackworms are taken greedily, as are adult brine shrimp (but less avidly in my experience).  Frozen bloodworms (midge/fly larvae, not really a worm) are taken as well.  Be sure to rinse these under the tap to minimize organic pollution of the tank water.  After adapting to captivity, thawed frozen chopped clam or squid is taken as well.  Probably any textured meaty frozen food would do.  Although nipping by these fish is obviously a response to visual clues, they seem to have an acute sense of taste as well, as they react quickly to the presence of even rinsed frozen food in the tank.

Photo courtesy of Aqualand pets plus

I have read that they can get to ~8" in captivity.  My three made about 4" or a bit over in a year and a half to two years before I traded them off.  They started life with me in a 20-long, later were moved to a 33XL.  Both tanks were canister filtered, lower tier (i.e., near the floor and therefore cooler).  Routine water changes were my then-standard 25-33% per week.  Now I would boost that to 33-50% weekly to keep the nitrate titer minimized, or perhaps add an algae bed filter but that is a high upkeep device for me.  As I had brackish puffers at the same time, aged premixed water of the correct specific gravity was kept on hand.  Marine salts need time to dissolve, even if only at brackish densities, so preplanning helps.  As these are brackish water fish, as is the case also for marines, it is better in my opinion to keep stocking densities well lower than is common in freshwater.  Both setups were of course my traditional "empty tanks", in that I could see the fish (or at least their eyes) and nobody else could.   Even when I fed them you could not see them for long.

Not a fish for everybody, the flatfish are interesting, low maintenance other than the live and frozen feeding requirement, if you think you can deal with an empty-appearing tank.  If you keep other light brackish tanks, and other fish needing or requiring these same foods, they are really low-care.  But you can't keep anybody else with them, or I couldn't.  These are, in my experience, strictly species oddballs, kept for the curiosity of them and their secretive lifestyle on an open sand or silt plain.

For more information on the fish in the wild, see:

Hogchoker, Trinectes maculates

They are found all along the East and Gulf Coasts of North America, obviously having a wide range of acceptable temperatures.

Robert T. Ricketts, a.k.a. RTR