Barracuda (CR 1/2)

Medium Animal (Aquatic)
Alignment: Always neutral
Initiative: +3 (Dex); Senses: low-light vision, scent, Listen +3, and Spot +4

AC: 14 (+3 Dex, +1 natural), touch 13, flat-footed 11
Hit Dice: 2d8 (9 hp)
Fort +3, Ref +6, Will +1
Speed: Swim 60 ft.
Space: 5 ft./5 ft.
Base Attack +1; Grapple +1
Attack: Bite +4 melee
Full Attack: Bite +4 melee
Damage: Bite 1d4
Special Attacks/Actions: Sprint
Abilities: Str 11, Dex 17, Con 10, Int 1, Wis 12, Cha 2
Special Qualities:
Feats: Weapon Finesse
Skills: Listen +3, Spot +4, and Swim +8
Advancement: 3-6 HD (Medium)
Climate/Terrain: Warm aquatic
Organization: Solitary, pair, or school (3-6)
Treasure/Possessions: None

Source: Stormwrack

Sprint (Ex): A barracuda can move up to three times its normal speed (180 feet) when it makes a charge.

Skills: A barracuda has a +8 racial bonus on any Swim check to perform a special action or avoid a hazard. It can always choose to take 10 on a Swim check, even if distracted or endangered. It can use the run action while swimming, provided it swims in a straight line.

A barracuda is unnervingly quick, drifting motionless one moment, then darting forward in a blinding rush to snap at prey.

Aquatic Subtype

Creatures with the aquatic subtype always have swim speeds and thus can move in water without making Swim checks. An aquatic creature can breathe underwater. It cannot also breathe air unless it has the amphibious special quality.