how do you tell if cod is bad
Confidence votes 84.7K. Cod fish is bad if: 1  it has yellow spots and transparent parts on the surface instead of an even, light surface. 2  there is a coating of slime on the surface; the surface should be shiny and dry.f the catfish has a strong fishy smell, it has gone bad. You can  also tell by looking at it, if you see areas that appear  discolored, it is likely bad.