They're pretty passive, so perhaps they mostly attempt to flee until cornered?
Actually, a scorpion fish's preferred defense is to pretend to be a lump of coral until the threat goes away, any rely on its poison spines to deter attacks if it fails to hide.
Scorpion fish are very cryptic, so we should give them a racial bonus to Hide in reef environments. We might want to give them Camouflage or a "Hide in Plain Sight" variant too.
How's this:
Skills: Hide +14*, Listen +2, Move Silently +2, Spot +2, Swim +5
A little, stout bodied fish resembling a rock with fins, with a row of spines running down its back.
Scorpionfish are slow-moving bottom dwellers that most commonly live in reefs. The spines of these fish are coated in a venomous slime that causes excruciating pain to any creature injured by a spine, which gives them their name.
A scorpionfish's resemblance to a rock or piece of coral makes them extraordinarily hard to spot among the reefs where they prefer to live. They are usually red or brown in color.
Most types of scorpionfish are very small, typically 4 to 8 inches in length and an ounce or two in weight, the largest species can grow up to 18 inches long and 5 pounds in weight.
Combat
Scorpionfish are not aggressive. If they see an enemy they hide, freezing in place until the threat departs. Should this fail, they rely on their venomous spines to defend them.
Skills: A scorpionfish has a +8 racial bonus on any Swim check to perform some 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 scorpionfish has a +8 racial bonus to Hide checks in a reef environment.