i got one more fish bed ?

[Craftlady]

Since this is not the typical flat oval cat bed, I would use the recommended foam. You wont have the appropriate thickness or strength to keep it upright. All your sides of the fish need to be strong so that the fish doesnt collaspe. Otherswise they cant get in the bed.
Here is bed she is trying to make, then my explaination will make sense to use the correct foam.