Help fish ill?

[titchrules]

Hi.
We bought two silver sharks on Friday. One is happy and swimming around. Having lots of fun chasing after the guppies. The other seems to have a kink in his body and doesn't really swim properly. He just floats near or behind the filter. Often floating nose to the ground.
Is he poorly or just lazy?!
The water tests are fine. The other fish guppies and other shark are perfectly fine! Have I just bought a sick fish?

Both sharks came from the sane tank!
Thanks

[Esoteric Backbone]

Sounds like a deformity, probably from inbreeding.

[titchrules]

What do we do? He is now looking seriously not right no pet shop open now and I'm concerned if he is Sick he will make the other fish sick too.