A fish killed by the smell of an overweight guy farting in a pond would not have any distinct physical appearance changes. The smell from a fart, even if it were particularly pungent, would not directly cause any harm to fish in terms of altering their physical characteristics. However, it is highly unlikely for a fish to be killed solely by the smell of a fart. Fish are more sensitive to changes in water quality, such as pollution or lack of oxygen, which can contribute to their well-being or mortality.