They are only an inch long. 而虾虎鱼身长只有不到3厘米

173. ..which they will certainly need.
     这正是它们需要的
174. Because the only way...is up.
     华山一条路 它们必须登上顶端
175. It is 30 metres to the top.
     垂直落差高达30米
176. They are only an inch long.
     而虾虎鱼身长只有不到3厘米
177. This is the equivalent of a human being scaling a waterfall
     相当于人类去攀登
178. over a mile high.
     近两公里高的瀑布
179. Millions attempt the climb...
     数以百万计的虾虎鱼向顶端进发

来自《行星地球 第三季 第四集 Planet Earth S03E04 淡水》第 176 行