Pyriel, if you are heading to the torrens, Places I have caught natives as mentioned above are paradise interchange-St Peters, then down Lockleys way. Further up Gorge Rd some of the creeks e.g. 6th creek, Galaxis, brown and rainbow trout, and other little natives. The Onk has same sort of thing, don't know about tandanus and rainbows. Ive heard these have been stocked in the torrens by Native hobbyists. A lot of the wetlands that have been created in the Sailsbury/Mawson Lakes areas have a lot of little natives especially carp gudgeons and congolli. Sweep netting like karl mentioned or using the box like shrimp nets full of different fishy foods will get you a good catch. Winter is a bit slower but still ok with spring/summer best.
Good luck!!