And they're on a mission - a mission to catch fish.它们正在出任务，它们要去捕鱼

on a mission执行(某一)任务, 肩负(某一)使命

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

我们不是在度假,我们是在执行任务。

The French teenager became man on a mission.

这位法国的年轻人身上的担子重了。

catch fish扑鱼, 抓住鱼

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

他带领全家出海捕鱼。

You catch fish with a fishing rod.

你可以用钓竿逮鱼。

in such shallow water they ought to be safe.在这样的浅水处鱼群应该很安全

ought to be应当

That ought to be enough food for all of us.

那些该够我们大家吃的了。

The child with the cough ought to be in bed.

这患咳嗽的孩子应该睡在床上。