Concerning the fishing in French Guiana, you do not need any licence, and there is no restriction of any kind.
However, each type of fishing requires a particular sort of material :
Very few boats take people out deep sea fishing (around Devil's Islands or further out around the shrimp boats), so a reservation is required...
They usually take 5-8 fisheman onboard that share the price of the day. That includes the fishing equipment and bait (food and drinks are not provided).
Freelance can help you to put up a fishing group and for the reservations...
The price is approximatly 90 euros per person.