facultative Not limited to; not depend on. Opposite of obligatory, e.g. Oncorhynchus mykiss is a facultative marine fish, being capable of entering freshwater.

• 兼性的不仅限于；不仰赖。相对于必须的，例如虹鳟是一种兼性海生鱼类，能够进入淡水存活。