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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.

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    $\begingroup$ Shouldn't a majority be 50% + 1? Also are you referring to species or to total numbers? $\endgroup$
    – kmm
    Mar 12, 2012 at 1:33
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    $\begingroup$ @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) $\endgroup$
    – DVK
    Mar 12, 2012 at 1:49
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    $\begingroup$ (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. $\endgroup$
    – dmm
    Sep 26, 2013 at 22:14
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    $\begingroup$ aren't they just much smaller and softer so harder to see clearly as scales? $\endgroup$
    – rg255
    Sep 27, 2013 at 5:51
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    $\begingroup$ @nico The description of majority you just presented is in fact erroneous. en.wikipedia.org/wiki/Majority#Erroneous_definitions $\endgroup$
    – user22020
    Jul 28, 2017 at 16:08

2 Answers 2

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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

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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,

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    $\begingroup$ I can't find reference to it is not good justification. $\endgroup$
    – John
    Mar 29, 2018 at 15:34

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