keep a gill open

[Hongdung]

Hello,
I read a fantasy fiction and I see a sentence bellow: "I keep a gill open for any kraken -related incidents". Could you help me to explain what does it mean? I don't know the meaning of phrase "keep a gill open. Thank you.
Jung

[Skrej]

It's a play on words. We have phrases such as 'keep your ears open' meaning to be listening for something.

Here, since the speaker is apparently a fish or some other kind of under-water dweller, I guess it's supposed to be the aquatic equivalent.

A Kraken is a legendary sea monster, so the speaker is always interested in hearing about any incidents involving the kraken.
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[Hongdung]

Thank you, Skrei. Yes, "he" is a merman, hehe.