Chauntea would be a good choice also. Although not specifically for fishing, she would be concerned with lumber (forrests), and as the Earth Mother, all forms of common subsistence are her perview (specifically agriculture, but I would think hunting, lumber, and fishing would also apply). I don't see why she wouldn't be someone that one could entreat for success while fishing.
An outside of the box idea could also be Istishia. Traditionally he's only concerned with Water Elementals, but his portfolio technically includes all water. An excerpt from Faiths and Avatars reads: "Istishia always sends a representative to accept offerings... These representatives can be anything form his priests to fish to water elementals. His gifts to his followers are most often the ability to travel easily through water, (or) the knowledge to find something hidden in water (such as fish)..." However, he is rather whimsical over whether he listens to his followers or not - as whimsical and random as the luck of fishermen...
