"I just GAVE you your allowance!"
"But I was hungryyy. I ate it!"

Are these live fish, or metallic models of ones?
I'm curious what their wallets look like....

A money pouch would work fine in either case.

Is this a case of using a foodstuff as currency or a unit of account like using rice in feudal Japan, or is there something inherently valuable about these fish aside from being useful as food?

I'd imagine that business must be brisk, as you'd want to spend or eat your money as soon as possible. Likely a lot of business is conducted right at the dock, with fishermen trading their "money" for goods as part of the offloading process.

No. But they could have fish shaped coins like that.

"I have a high net worth."

"I heard the traders say 'currency' so I figured they meant something in the current."

"I tried burying my fish beneath the garden and the crops got better. I guess that proves the money's really worth something."

*A group of serious otter investors listen intently as the High Fishlord proclaims a series of 0.25% fish slices.*

Great idea. Each easily recognizable and also useable by people without sight or color blind since each has a distinct shape.

A HUGE BATTLESHIP
"PLATINUM SALMON"
IS APPROACHING FAST