Is it possible that Ancistrus catfish attach themselves to other fish?
A pearlscale goldfish has some dark "moon" on the cheek and is somewhat frightened. Is it possible that an Ancistrus catfish has attached itself to the cheek of a veiltail goldfish?
yes, this is actually possible. Some loricariids tend to attach themselves to other fish occasionally, which may lead to skin damages. Keeping tropical fish and goldfish together is not ideal anyway; you should therefore consider keeping the fish in separate tanks.
Dr. Bodo Schnell