Fishermen caught a large number of elvers at the river mouth during their upstream journey.

elvers 是名词 elver 的复数形式，elver 指"幼鳗"，特指鳗鱼从海洋洄游到淡水时的幼体阶段。这个词来自古英语，与"鳗鱼"(eel)同源。