Octopus kanji: 章魚 vs 蛸 vs 鮹

Question

I'm trying to determine the most appropriate kanji for タコ (octopus), and have come across three possibilities: 章魚, 蛸, and 鮹.

• According to jisho.org, all three possibilities are read as たこ.
• The Pocket Kenkyusha Japanese Dictionary (ISBN 978-0-19-860748-9) includes 蛸.
• The Collins English-Japanese Dictionary (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.

Answer 1

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):

タコ　 676 results
蛸　　 129 results
ダコ　  32 results
章魚　  10 results
鮹　　   2 results
鱆　　   0 results

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:

たこ焼　244 results
タコ焼　 39 results
蛸焼　　  1 result

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

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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.