And they're on a mission - a mission to catch fish.它們正在出任務，它們要去捕魚

on a mission執行(某一)任務, 肩負(某一)使命

We are not on a vacation, we're on a mission.

我們不是在度假,我們是在執行任務。

The French teenager became man on a mission.

這位法國的年輕人身上的擔子重了。

catch fish撲魚, 抓住魚

He led the whole family out to sea to catch fish.

他帶領全家出海捕魚。

You catch fish with a fishing rod.

你可以用釣竿逮魚。

in such shallow water they ought to be safe.在這樣的淺水處魚群應該很安全

ought to be應當

That ought to be enough food for all of us.

那些該夠我們大家吃的了。

The child with the cough ought to be in bed.

這患咳嗽的孩子應該睡在床上。