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Based on pictures, it seems to me that a vast majority of fish species that have scales do NOT have scales on their heads.

Is that fact true?

To make this properly answerable:

  • lets' define a "majority" as >70% of fish species. But frankly, I'm more interested in actual numerical answer than whether it passes some arbitrary threshold or not.

  • The universe which I'm interested in measuring the percentage are fish species that have "normal" (Cycloid and ctenoid is the technical term, I believe?) scales on their bodies.

    If that's not specific enough, you can restrict the universe to species in Actinopterygii (ray-finned) that have scales.

fileunderwater
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DVK
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    Shouldn't a majority be 50% + 1? Also are you referring to species or to total numbers? – kmm Mar 12 '12 at 01:33
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    @Kevin - species, as the first bullet point notes. As far as 70% vs 50%+, the question came out of an argument, for which mere 50%+ would not be a convincing enough number, whereas 70% would. And without a specific number, this would be a bad SE question (too vague) – DVK Mar 12 '12 at 01:49
  • @DVK: there is really no argument that 50%+1 > 50%-1, hence it is the majority. But I'm just nitpicking. – nico Jun 06 '13 at 21:39
  • Would also be nice to know (or at least think about) whether if this is the case it's because of synapomorphy (i.e. shared heritage) or convergence. – Oreotrephes Sep 27 '13 at 00:07
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    aren't they just much smaller and softer so harder to see clearly as scales? – rg255 Sep 27 '13 at 05:51
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    (Should be comment, but rep=1.) This might be helpful (from Wikipedia): "The same genes involved in tooth and hair development in mammals are also involved in scale development." Mammals tend to have less hair on their face than on their bodies. If you can track down the reason for that, then you might have the same reason for fish, and then could use that to reason out your estimate. – dmm Sep 26 '13 at 22:14
  • A lot of fishes have scales on the opercle ("cheek"), and sometimes inferior to the orbit of the eye--but they are often very small. I'm not sure about overall patterns, or how common they might be. I could see a hydrodynamic reason for not having scales rostrally to avoid inducing drag, but not sure the literature agrees with the answer. – Kara Apr 07 '17 at 02:48
  • The only Actinopterygii that I know of which do not have scales on their head are of the order Cypriniformes, which includes fish such as minnows and carp, as well as of the order Anguilliformes, which includes various Eels. There are ~4000 species of order cypriniformes, and ~900 species of order anguilliformes.

    As mentioned by @Ell, most fish have scales on their heads, they're just really small/fine. Example actinopterygii that exhibit this are salmon and trout.

    Source: F.H. Pough, C.M. Janis, & J.B. Heiser 2013. Vertebrate Life, 9th ed. Prentice Hall., Chapters: 5-6, 8-9.

     –  Jul 28 '17 at 15:57
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    @nico The description of majority you just presented is in fact erroneous. https://en.wikipedia.org/wiki/Majority#Erroneous_definitions –  Jul 28 '17 at 16:08
  • @Charles I was not the one who defined majority, just said that 50%+1 > 50%-1 , which is purely a math statement :) – nico Jul 31 '17 at 14:04
  • Ah, my mistake. I suppose that clarification should be directed towards @kmm. –  Jul 31 '17 at 14:09
  • I know Chondrichthyes (sharks and rays) have scales on hte head, their entire body is covered in tiny placoid scales. Don't know about other fish with different scale types. – John Mar 29 '18 at 15:42

2 Answers2

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I certainly agree with your general observation, but not being an ichthyologist, I can only offer a partial answer, based on a particular family of fish. Within the family Tripterygiidae, most species lack scales on their head, or have highly modified types of scales. A comparative study of 48 species showed that only 2 have "normal" scales of their head (Jawad, 2005).

The squamation pattern of the bases of the fins varies among species. The head is usually devoid of scales except for two species that have squamation with body- type scales (Matanui bathytaton (Hardy, 1989) and Norfolkia clarkei). Several species have head ctenoid scales modified into tiny spicules of different shapes (Acantha- nectes rufus Holleman & Buxton, 1993, Apopterygion oculus Fricke & Roberts, 1994, Axoclinus carminalis, Ceratobregma acanthops, Cremnochorites capensis, Ennea- nectes boehlkei Rosenblatt, 1960, Forsterygion malcolmi Hardy, 1987, Forsterygion varium (Forster, 1801), Karalepis stewarti, Matanui bathytaton, Norfolkia clarkei, Notoclinops caerulepunctus Hardy, 1989).

So far, I haven't found a broader comparative study, to support your general question. Someone more knowledge in the area and the literature can perhaps offer a more general answer. This is at least an indication that your observation might be correct.

Reference
Jawad. 2005. Comparative scale morphology and squamation patterns in triplefins (Pisces: Teleostei: Perciformes: Tripterygiidae). Tuhinga 16 (1), 137-168

fileunderwater
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Based on a lack of written evidence, in searching Google and Google Scholar, I believe fish have scales on their heads, where I'm defining 'scales' as 'solid, protective bony scales' [see below], and I'm assuming the fish heads are covered with solid protective bony Big scales. I think a lack of scales on fish heads would be a fish fact that wouldn't be too difficult to find.

  1. Some fish lack scales altogether, such as gobies and toadfish: https://www.slideshare.net/gurya87/types-of-scales-in-fishes-44959366

  2. This wikipedia article mentions scales repeatedly [examples below] but says nothing about a lack of scales on fish heads -https://en.wikipedia.org/wiki/Fish_anatomy

a. The dermis is covered with overlapping scales.

b. The dermis of bony fish typically contains relatively little of the connective tissue found in tetrapods. Instead, in most species, it is largely replaced by solid, protective bony scales.

c. The outer body of many fish is covered with scales,

Helen
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