Octopus kanji: 章魚 vs 蛸 vs 鮹


I'm trying to determine the most appropriate kanji for タコ (octopus), and have
come across three possibilities:
[章魚](https://en.wiktionary.org/wiki/%E7%AB%A0%E9%AD%9A),
[蛸](https://en.wiktionary.org/wiki/%E8%9B%B8), and
[鮹](https://en.wiktionary.org/wiki/%E9%AE%B9).

  * According to [jisho.org](http://jisho.org/word/%E8%9B%B8), all three possibilities are read as たこ.
  * The Pocket Kenkyusha Japanese Dictionary ([ISBN 978-0-19-860748-9](https://duckduckgo.com/html/?q=!ISBN+978-0-19-860748-9)) includes 蛸.
  * The Collins English-Japanese Dictionary ([ISBN 0-00-719655-5](https://duckduckgo.com/html/?q=!ISBN+0-00-719655-5)) only gives タコ.

My question: How common is each variant, and are their meanings truly
equivalent? For example:

  * 英語でタコは「octopus」です。
  * 英語で章魚は「octopus」です。
  * 英語で蛸は「octopus」です。
  * 英語で鮹は「octopus」です。

My understanding is that any of the above could be considered _correct_
(though some would seem more unusual than others) and that they all have the
exact same meaning.




If you look at 漢字, then 蛸 is by far the most common option. This is confirmed
by the frequency data in the BCCWJ (Balanced Corpus of Contemporary Written
Japanese, via <http://nlb.ninjal.ac.jp>):

[code]

    タコ　 676 results
    蛸　　 129 results
    ダコ　  32 results
    章魚　  10 results
    鮹　　   2 results
    鱆　　   0 results
    
[/code]

タコ is still a lot more popular than any 漢字 version. (But that's to be expected
since, like many other 漢字 for animals, 蛸 is not 常用漢字 and 熟字訓 readings are very
rare.)

Of course, 蛸 can also be written in ひらがな. It's not easy to get numbers, but
even looking at たこやき alone, we already get big numbers:

[code]

    たこ焼　244 results
    タコ焼　 39 results
    蛸焼　　  1 result
    
[/code]

Just something to keep in mind when choosing whether to write in 漢字 or not.

* * *

_Edit._

The dictionary 大辞林 entry for たこ is

> **たこ** [1]  
>  【▼蛸・〈章魚〉・▼鮹】  
>  [...]

The notation ▼ means that the _kanji_ is not 常用漢字 and the angled brackets mean
that the reading is 熟字訓. As such, writing たこ as 蛸 or 章魚 or 鮹 wouldn't be seen
as incorrect, but unusual.




If you look at 漢字, then 蛸 is by far the most common option. This is confirmed
by the frequency data in the BCCWJ (Balanced Corpus of Contemporary Written
Japanese, via <http://nlb.ninjal.ac.jp>):

[code]

    タコ　 676 results
    蛸　　 129 results
    ダコ　  32 results
    章魚　  10 results
    鮹　　   2 results
    鱆　　   0 results
    
[/code]

タコ is still a lot more popular than any 漢字 version. (But that's to be expected
since, like many other 漢字 for animals, 蛸 is not 常用漢字 and 熟字訓 readings are very
rare.)

Of course, 蛸 can also be written in ひらがな. It's not easy to get numbers, but
even looking at たこやき alone, we already get big numbers:

[code]

    たこ焼　244 results
    タコ焼　 39 results
    蛸焼　　  1 result
    
[/code]

Just something to keep in mind when choosing whether to write in 漢字 or not.

* * *

_Edit._

The dictionary 大辞林 entry for たこ is

> **たこ** [1]  
>  【▼蛸・〈章魚〉・▼鮹】  
>  [...]

The notation ▼ means that the _kanji_ is not 常用漢字 and the angled brackets mean
that the reading is 熟字訓. As such, writing たこ as 蛸 or 章魚 or 鮹 wouldn't be seen
as incorrect, but unusual.

