Fish stalls can be stolen from with at least level 42 Thieving, granting 42 experience. Thieving from the stalls in Rellekka requires completion of The Fremennik Trials quest. Thieving from the stalls in Miscellania and Etceteria also require completion of the quest, as one cannot access the islands until the quest is completed. Thieving from the stalls in Miscellania and Etceteria will lower your approval rating if you are managing the kingdom.