Sol Negro (1988)

A millenary spell, passed down from father to son, turned the muscular Bully into a fish and the indomitable Monica into a hawk. Each full moon one of them transforms and the other recovers its normal form, which prevents them from being together. Only an extraordinary phenomenon can break the spell, an eclipse of the sun ... the BLACK SUN (Sol Negro)

To break the spell, Bully must first free Monica from her cage to, turned into a fish, arrive together in time to the sacred underwater temple of the sun, a grotto located in the submerged city of Hidrionis, just at the moment in which it occurs the eclipse.