I'm stealing this from another conversion:
Str 15, Dex 17, Con 15, Int 1, Wis 12, Cha 2
3HD
Lamprey CR 1/2
N Small animal (aquatic)
Init +3; Senses blindsense; Listen +2, Spot +2
Defense
AC 15, touch 14, flat-footed 12
(+3 Dex, +1 natural, +1 size)
hp 5 (1 HD)
Fort +3, Ref +5, Will +1
Weakness susceptible to fire
Offense
Spd swim 30 ft.
Melee bite +4 (1d3-1)
Space 5 ft.; Reach 5 ft.
Special Attacks attach, blood drain
Statistics
Str 9, Dex 17, Con 13, Int 1, Wis 12, Cha 2
Base Atk +0; Grp -5 (-1 attached)
Feats Weapon Finesse
Skills Listen +2, Spot +2, Swim +9
Special Abilities
Attach (Ex) A lamprey that hits with its bite attack latches onto the victim’s body. An attached lamprey loses its Dexterity bonus to AC and can use blood drain on subsequent rounds. An attached lamprey can be struck by a weapon or grappled, but it receives a +4 bonus when opposing grapple checks. To remove a lamprey through grappling, the victim must successfully pin the lamprey. A lamprey receives a +4 bonus to any grapple check to resist a pin due to the incredible strength of its mouth.
Blindsense (Ex) A lamprey can locate creatures underwater within a 30-foot radius. This ability works only when the lamprey is underwater.
Blood Drain (Ex) Once a lamprey has attached itself to a victim, it can drain blood at the start of each subsequent round. A lamprey inflicts 1 point of Constitution damage each round it remains attached.
Susceptible to Fire (Ex) Lampreys make their saving throws against fire-based attacks with a -2 penalty.
Skills A lamprey 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.