first dorsal fin
/ˈfɜːst ɐsˈɪstənt ˈkamɹəɹ ˈɒpəɹˌeɪtə/
n
English · first dorsal fin中文 · 第一背鳍Español · aleta dorsal anteriorFrançais · première nageoire dorsale
意味：Swimming appendage formed of a membrane and usually prickly rays located on the middle anterior dorsal portion of the body; it provides stability.