fish louse
noun
1- an aquatic crustacean which is a parasite of fish, typically attached to the skin or gills（寄生在鱼皮或鱼鳃上的）鱼虱：
1.1
- a free-swimming crustacean with a shield-like carapace and a pair of suckers (class Branchiura: several genera, in particular Argulus).鲺（鳃尾纲：数属, 尤指鲺属）。
1.2
- an elongated crustacean that becomes permanently attached to the host and typically highly modified (class Copepoda: several orders and numerous species).剑水溞（桡足纲：数目, 众多种）。