in regards to water, they can be caught in ponds/lakes and out of loch raven and pretty boy, so freshwater in not a problem for em.
as far as keeping them in a pond, they wouldnt be much. maybe fun to feed but you wouldnt see much besides like a dark fish shape.
Regulations are 5 per person per day. Minimum size of 9"s. what u do with em after you catch em is up to you i believe as long as they are not released into a non private body of water, as transferring fish from one place to another is illegal.