Fishing license must always be carried and presented on request.
In Garnsviken, a trolling ban applies from ice break-up until 15/6.
The card does not entitle you to fishing with nets (seine nets excepted) or crayfish fishing.
As a member of the Sigtuna Fisheries Association, you get on leased water in Mälaren (see marked in blue and on the map):

Fishing with up to a maximum of 4 rods per boat.
Long lines may be laid with a maximum of 50 hooks.
In winter, you can fish with up to 10 fishing rods/ice fishing rods.
Max 3 pike/goose per day!
Note that minimum/maximum measurements apply to pike and pikeperch:
The fish must measure at least 45cm, or measure a maximum of 75cm! Fish that fall below or exceed these limits must be reintroduced as carefully as possible! This is to preserve the stocks and hopefully strengthen them!

The fizzing:

Pulling row with max. 2 rods.
Petrol engine ban applies to all of Fysingen.
In winter, you can fish with up to 5 fishing rods/ice fishing rods.
Max 3 pike/goose per day!

Marängsån and Oxundasjön:

The fish is not edible but offers good sport fishing.

Fishing from shore with a hand-held tackle.

As well as general regulations
As for other species, use common sense and don't take home more than you eat yourself!