# Are all flatfish of the same handedness? **URL:** \ **Category:** Factual Questions\ **Created:** [February 9, 2004, 12:33pm UTC](https://boards.straightdope.com/t/are-all-flatfish-of-the-same-handedness/228259 "2004-02-09T12:33:20Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![zut](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/zut/32/2875_2.png) [@zut](https://boards.straightdope.com/u/zut)\ **Post date:** [February 9, 2004, 12:33pm UTC](https://boards.straightdope.com/t/are-all-flatfish-of-the-same-handedness/228259/1 "2004-02-09T12:33:20Z")
I think, from a cursory look at a series of pictures, that most flatfish lie on their left side (that is, the “left” as compared to a typical fish). Are there any exceptions? If so, is it because some _species_ are left- or right-handed, or are there _individuals_ within a single species that are left- and right-handed? If the former, what would cause such an evolutionary divergence? If not, are there any reasons that an occasional opposite-handed mutant (I’m thinking of the occasional human being who has reversed internal organs) would not be successful within the flatfish population? ---
**Author:** ![Polycarp](https://avatars.discourse-cdn.com/v4/letter/p/82dd89/32.png) [@Polycarp](https://boards.straightdope.com/u/Polycarp)\ **Post date:** [February 9, 2004, 12:56pm UTC](https://boards.straightdope.com/t/are-all-flatfish-of-the-same-handedness/228259/2 "2004-02-09T12:56:38Z")
For most flatfishes, individual species or genera will go one way or the other, but it’s an amazing mix. Here’s a list of the families in Order Pleuronectiformes, the flatfish, with “sinistral” or “dextral” tagged to each to indicate whether “top” is what was originally left or right side. Suborder Psettodidei Family Psettodidae, two primitive species from Indonesia and Africa, go either way Suborder Pleuronectoidea Family Citharidae, go either way Family Scophthalmidae, sinistral Family Bothidae, “left-eyed” flounders, sinistral, and “California halibut,” a species that goes either way Family Pleuronectidae, “right-eyed” flounders and halibuts, dextral Suborder Soleoidei Family Soleidae, the soles, dextral Family Cynoglossidae, the tongue soles, sinistral ---
**Author:** ![Desmostylus](https://avatars.discourse-cdn.com/v4/letter/d/c57346/32.png) [@Desmostylus](https://boards.straightdope.com/u/Desmostylus)\ **Post date:** [February 9, 2004, 1:02pm UTC](https://boards.straightdope.com/t/are-all-flatfish-of-the-same-handedness/228259/3 "2004-02-09T13:02:40Z")
> [@](#): > > [Order Pleuronectiformes (Heterostomata) = > Flatfish: plaice, flounders, soles & relatives.](http://www.solaster-mb.org/mb/pleuronectiformes.htm) > > Family Scophthalmidae = Turbot, brill, topknots and relatives > > Flatfish that lie on the **right** side so that the eyes are on the left flank. Both pelvic fins are elongate > > Family Bothidae = Scaldfish & relatives > > Flatfish that lie on the **right** side so that the eyes are on the left flank. The pelvic fin base on the left flank is longer than that on the right. > > Family Pleuronectidae = Plaice, flounders and relatives > > Flatfish that usually lie on the **left** side, so the eyes are on the right flank; lips conspicuous. > > Family Soleidae > > Flatfish that **usually** lie on the **left** side, so the eyes are on the right flank; oval shape, small mouth and eyes. > > Most species spend much of their time on or within sand. > [@](#): > > [The asymmetrical genetic determination of laterality: flatfish, frogs and human handedness.](http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=1802645&dopt=Abstract) > > The determination of the left-right body axis is unlike that of the two other axes because left-right positional information is not required to specify mirror-image structures on the two sides. When the left and right sides of the body are not mirror symmetrical such positional information is required, as is a mechanism for reading that information. There are several possible gradient schemes for left-right information, including symmetrical gradients from which the information is extracted by spatial differentiation. **The genetic mechanisms for the control of handedness are not known**. There is no evidence for ‘left-handed’ and ‘right-handed’ genes, only for mutations that can interfere with handedness in a non-specific manner. * * * ---
**Author:** ![Xema](https://avatars.discourse-cdn.com/v4/letter/x/9de053/32.png) [@Xema](https://boards.straightdope.com/u/Xema)\ **Post date:** [February 10, 2004, 12:22am UTC](https://boards.straightdope.com/t/are-all-flatfish-of-the-same-handedness/228259/4 "2004-02-10T00:22:07Z")
I have no info for flatfish, but I do for lobsters. They have one “pincher” claw and one “crusher” claw. These are definitely available on either side. ---
**Author:** ![zut](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/zut/32/2875_2.png) [@zut](https://boards.straightdope.com/u/zut)\ **Post date:** [February 10, 2004, 1:59am UTC](https://boards.straightdope.com/t/are-all-flatfish-of-the-same-handedness/228259/5 "2004-02-10T01:59:21Z")
Thanks for the info; that’s pretty interesting. I was curious about flatfish particularly (as opposed to lobsters, for example) because it seems like a relatively severe modification is required for the fish to “flop” from one side to t’other, as opposed to the (seemingly) relatively simple pincher/crusher alteration. I was curious whether the genetics worked out to allow fish of both handednesses to interbreed (as it does, apparently). ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [February 10, 2004, 3:02am UTC](https://boards.straightdope.com/t/are-all-flatfish-of-the-same-handedness/228259/6 "2004-02-10T03:02:19Z")
> [@](#): > > I have no info for flatfish, but I do for lobsters. They have one “pincher” claw and one “crusher” claw. These are definitely available on either side. Unless it’s a spiny lobster (_panulirus interruptus_). (Incidentally, I like spiny lobster better than lobsters with claws. I don’t know if it’s because of the species, or because they were fresher.) I was watching a show about dolphins. There is a group of bottlenosed dolphins in, IIRC, the Carolinas that form up line-abreast to push fish to the shore of estuaries with their “bow waves”. Interestingly, they always land on their right sides. Over time, the teeth on the right side of their mouths will wear down because of the sand and mud they tak in whilst catching the fish. I’ve never caught a flatfish; but I saw some dead ones on the shore of Terrel Creek, so it’s likely I’ll get some when I start fishing. I don’t recall which side of them was the top side. Question: How does one clean a flatfish? When I was young and caught trout and catfish, I’d slit them up the belly. Are flatfish cleaned the same way? Or are they cleaned by cutting up the side? ---
**Author:** ![GuanoLad](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/guanolad/32/42_2.png) [@GuanoLad](https://boards.straightdope.com/u/GuanoLad)\ **Post date:** [February 10, 2004, 3:38am UTC](https://boards.straightdope.com/t/are-all-flatfish-of-the-same-handedness/228259/7 "2004-02-10T03:38:20Z")
I think the problem here is that fish don’t have hands. If you look up left-finnedness, you might have more luck. 🙂 Actually, this is a fascinating subject. Don’t the eyes also pair up on the up-facing side? I think that’s the freakiest part. ---
**Author:** ![donkeyoatey](https://avatars.discourse-cdn.com/v4/letter/d/e47c2d/32.png) [@donkeyoatey](https://boards.straightdope.com/u/donkeyoatey)\ **Post date:** [February 10, 2004, 4:19am UTC](https://boards.straightdope.com/t/are-all-flatfish-of-the-same-handedness/228259/8 "2004-02-10T04:19:12Z")
> [@Johnny L.A.](#): > > Question: How does one clean a flatfish? When I was young and caught trout and catfish, I’d slit them up the belly. Are flatfish cleaned the same way? Or are they cleaned by cutting up the side? [Here](http://saltfishing.about.com/library/weekly/aa000704c.htm) you go **Johnny**. (your second guess is correct)