Hello David, welcome aboard!
I'm from Fortaleza and I've yet to catch my first peacock bass. I don't have a car so it's hard to reach the lakes/rivers. I know about two fishing guides but I'm not sure if they are still in business (probably), they don't have websites anymore. I could try to find their phone numbers, call them and ask for info/rates. Here you won't find monster peacock bass, but I've seen pictures of some nice fish. Visit the link below for some pics:
http://www.arpia.com.br/noticias_200...anoceara.shtml
The pictures were taken by some guys from the south of Brazil, they hired one of the fishing guides I was talking about and went to a lake in Trairi called "Açude Água Boa".
A fishing license is needed but I've never seen gov people asking for the licenses. It costs about $10 (R$20).
There are a few rivers with peacock bass, but I think you will have greater success fishing the lakes for them. My wife's cousin told me there is peacock bass in the Acarau River.
Another freshwater fish common here is the trahira. I've also heard people talking about the "piau", I think they're referring to "piau-três-pintas"
Snook is found in some rivers near the beach... I've yet to fish for it.
I've only caught catfish from the surf so far
I don't know about the Rio Curu (the river between Trairi and Paracuru)
I think you can hike along the rivers, I just don't know if it's safe (especially since you will carry your Nikon)