The Linux version does not capture the mouse correctly. It captures the mouse but still if it hits the borders of the screen, you can not pan the view any further.
I wanted to try the windows version with wine but the downloaded ZIP file only contains the .exe which complains about a missing UnityPlayer.dll. If I install that one it complains about a missing data directory.
I somehow also missed the point that you already have all the fish on you. I wandered around the scene (battling the malfunctioning mouse movement) and wondered where to find the fish that I should drop until I accidentally "jumped" over a box once, dropping the fish. Maybe this could be made more obvious?