Claim: Pelvic fin structures (paired fins located on the ventral surface of fish) can be extremely specialized in actinopterygians, with Gobiids and lumpsuckers modifying their pelvic fins into a sucker disk that allow them to adhere to the substrate or climb structures, such as waterfalls.
Evidence: Pelvic fins or ventral fins are paired fins located on the ventral surface of fish. Pelvic fin structures can be extremely specialized in actinopterygians. Gobiids and lumpsuckers modify their pelvic fins into a sucker disk that allow them to adhere to the substrate or climb structures, such as waterfalls.