So cool! I was really hoping I’d find bluegills in the Marie Fish book, but I guess that family isn’t found in Rhode Island where she was doing her studies. I hear that fish crunching away though, amazing! I love it.
I have had the same issues with my little bit of hydrophone experimentation. I was asking a friend who knows way more about this stuff than I do and he suggested a small phantom-powered preamp as close to the microphone as possible would be the way to go. The shorter the distance between the preamp and the mic, the more amplification you can get out of the piezo disk without as much noise. (As I understood it anyway.)
I’d like to experiment with this, he said he could recommend a simple preamp circuit to build so I can pass that along at least – he’s on this forum too but I don’t know his username haha, so maybe he’ll chime in.