underwater fish detector

I would like to create an underwater fish detector - completely operating underwater (personal project)
The enclosure will be a waterproof hollow cylinder (possible material to use are: acrylic, Polycarbonate or PVC), a PCB will be sealed inside that enclosure containing the sensor (CH201 with narrow FoV horn).
The fish can pass through that hollow and will be detected while passing. the inner diameter of the enclosure will be in the centimeter range to allow one fish to pass at a time.
I would like to check the practicality of this solution based on your chip. Could acoustic wave move from the inside of the enclosure and pass through the thin enclosure to the water, hit moving object and be detected again? I am not very interested in accurate measurement so just the change in the received value can be noticeable or not depending on your point of view?
Note: I attached a picture showcasing the idea - please ignore the optional receiver i placed in the picture