Getting started...
Large Animal (Aquatic)
Hit Dice: 8d8+x (x hp)
Initiative: +x
Speed: Swim 30 ft. (6 squares)
Armor Class: 12? (-1 size, +x Dex, +x natural), touch x, flat-footed x
Base Attack/Grapple: +6/+x
Attack: Bite +x melee (1d8+x)
Full Attack: Bite +x melee (1d8+x)
Space/Reach: 10 ft./5 ft.
Special Attacks: -
Special Qualities: Low-light vision
Saves: Fort +6, Ref +6, Will +2
Abilities: Str x, Dex x, Con x, Int 1, Wis x, Cha x
Skills: 11 ranks (Swim +8 from swim speed)
Feats: 3
Environment: Any aquatic
Organization: Solitary or pair
Challenge Rating: x
Treasure: None
Alignment: Always neutral
Advancement: 9-16 HD (Large); 17-24 HD (Huge)
Level Adjustment: -
Ability scores of other Large and bigger fish:
Dire Barracuda: Str 19, Dex 15, Con 14, Int 1, Wis 12, Cha 2
Ramfish (magical beast): Str 21, Dex 13, Con 18, Int 2, Wis 14, Cha 5
Giant Catfish: Str 17, Dex 15, Con 13, Int 1, Wis 12, Cha 2
Masher (Huge): Str 27, Dex 12, Con 19, Int 1, Wis 10, Cha 8
Giant Gar (Huge): Str 24, Dex 14, Con 20, Int 1, Wis 10, Cha 1
So...
Str 17-20, Dex 14-16, Con 13-16, Int 1, Wis 10-12, Cha 1-2