Good news, fellow basement biotechnologists,
It is stated that active Vibrio Cholerae growth was detectable when the water temperature rose above 20°C
"All of the three vibrios were demonstrated in Norwegian mussels (at fewer than 100 bacteria /gram) and in Norwegian seawater (up to 30,000/litre) during the course of the study. They were first and foremost demonstrable when the water temperature rose above 20°C.
Read more at: http://phys.org/news154708942.html#jCp"
So, if you leave your fish in the basement (if not heated, so ~10-15°C in winter), Vibrio Cholerae shouldn't grow much and may be outcompetet by other bacteria. Of course it will still be safer to incubate it in the fridge.