Thanks to the ol' Gogen, I found the information that I will provide in a breakdown.
烏賊 Breakdown!烏 i= Crow
Why: An old Chinese legend claims that squid like to play possum on the surface of the water, hoping to lure in hungry black feathered carrion so that they can wrap them in in a tentaclely death grip. Thus the kanji for crow+enemy.
Now as to the verbal component of ika, nobody knows for sure, but some think it may have something to do with words like ikatsui (stern) or ikameshii (stern), or perhaps with word bits like i (expressing white)+ ka (expressing katai, or hard). All I know is ika wrestler is an awesome concept.
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