Both size and gender of mud crabs influence the outcomes of interference interactions

► We observed interference interactions between mud crabs (Scylla serrata) in tanks. ► Crabs fed less and avoided more when with larger male than larger female crabs. ► Female crabs avoided male crabs of equal size more than female crabs of equal size. ► Male crabs of equal size spent the most time fighting. ► Protection of large male crabs in reserves may lead to more intense competition.