Fishmon Spotted Eel immune to Sleepy Hammer?

I've not brought my Netgun (stupid) and nothing else will work without killing it.

Went through every crate to find something I can use, only thing I found was the Sleepy Toy hammer, I facetanked it and had to go for oxygen 3 times (max tank) but it didn't knock it out once?? I've seen people knock it out with a Tranquilizer Harpoon but obviously the Darts don't work.... But the Sleepy Hammer too??? That's just unfair lol