"The fish swim by moving their tails" is better.
it's > its

its

Yes, but the mistake hasn't been corrected yet.We can't change it.

@duran

I see you translated it anyway.
I find this bad policy because it gives some kind of backing or credibility to a mistake...

You are right. I thought it would be corrected, but not.

some corrections are YEARS behind...
What I do in this kind of case, for instance if I see the mistake after having translated, is I unlink my translation (after possibly linking it to another translation that is correct, in the same language or another...
Similarly, I do not translate sentences that have no owner, or that have an owner who is not native, or not credible...

Could you explain how to unlink to me, please? I have never unlinked one before. Thanks in advance.

@duran

since you are an advanced contributor, you can see a pair of scissors linking sentences. Clicking on it unlinks the corresponding sentence.
Take much care when you do it, because afterwards, the translation is lost.
Please comment before unlinking, to explain why you do it when it is not obvious...

Thank you, but I had clicked on the pair of scissors next to the sentence before receiving your explanation.I see that the translation is lost before commenting about it. Anything I can do now? Sorry.

I think it's commented well enough now...
Take care.

Lots of comments for one sentence. I guess I do need to fix my grammar...

But I learnt how to unlink thanks to you. I think you need to be more careful. That's all. Take care.:)