Remember to always use a lure when fishing it increases your chance to catch fish and not trash.
Also if you are farming fish in uldum then you have a chance to catch other useful fish like Deepsea Sagefish,and Fathom Eel. all sell very well you should also pick up a few volatile waters on your fishing journey which are always welcome.
Lavascale Catfish can be used to make
Lavascale fillet, which needs a cooking skills of 450.
Lacascale Minestone, which needs a cooking skill of 500.
Seafood Magnifique Feast, which needs a cooking skills of 525