Converting Unity models to Source?

Is this possible to do? And if so, how? Because I need to convert some Unity models to Source for my gamemode.

You extract the models and then convert them to source. Now if you would be more specific and told us exactly what you want from where we can help you out.

All the fish from the game Feed & Grow Fish.

Get Unity asset viewer, it will let you open the asset files of the game.
You can also get unity obfuscator to open the unity3d files.

It just tells me

when I try to open a file, happens with every single one of the files and it also tells me to update when I start the program even tho I cant download a newer version than 2.1…

If traditional extraction fails, try ninjaripper.

Well, got it to work, only that I need to open every single dds file to see what it is and there is over 500 of them and each one takes 5 seconds to open or so…