I know this is going to sound really weird! But I was confronted with this claim and the person strongly had faith in it! I said faith since he couldn't provide any evidence.
- Is there any kind of fish that is forced to hold his urine when in deep water ?
- If yes, is there any relationship between the case with fish's scale ?
- Does that make the fish's meat not proper (poisonous) to eat ?
I don't know what depth would be proper to define here but I guess the matter to be rare and not so important to define.