Premise: How to identify and care for lionhead goldfish<br>Check the fish you are preparing to buy, or if it is already in your tank, observe it. Lionhead goldfish have the following as physical traits : [substeps] Lionhead goldfish completely lack a stabilizing dorsal fin. If your fish has a dorsal fin, it is most certainly not a lionhead.
Hypothesis: A fish is not a lionhead if it has a fin