Displacer Fish Swarm (3.5e Monster)

"The jungles rivers had always had an evil reputation. Many times natives entered them and never came back.  And some of the fish were strange things without scales, and random numbers of eyes..."

Displacer fish are slimy, vaguely fishlike creatures that share the Displacer Beasts ability to deflect light. They are also incredibly voracious carnivores. There are a great many rumors regarding them, as no spawning behavior has ever been observed, and they don't seem to migrate like many fish do. In fact their behavior is disturbingly un-fishlike and suggests higher intelligence. Rarely are they caught in fishing nets, and they seem to be able to remember people, even going so far as to stalk fishermen who have caught one of their own...

Displacer Fish understand Common but cannot currently speak.

Combat
Displacer Fish use pretty much the same tactics as any Piranha swarm. Their enhanced intelligence means they aren't dumb brutes though. They know when they're outmatched. and when fleeing is a good idea.

Distraction: Any living creature vulnerable to a swarm’s damage that begins its turn with a swarm in its square is nauseated for 1 round; a Fortitude save (DC 15) negates the effect. Spellcasting or concentrating on spells within the area of a swarm requires a Concentration check (DC 20 + spell level). Using skills that involve patience and concentration requires a DC 20 Concentration check.

Displacement : Any melee or ranged attack targeting the Displacer Fish has a 50% chance of missing unless the attacker has some means of locating them other than sight. See Invisibility doesn't negate this but True Seeing does.

Resistance to Ranged Attacks : Displacer Fish have a +2 Resistance Bonus to ranged magical attacks that specifically target them (except for ranged touch attacks).

Skills: Displacer Fish get a +8 Racial Bonus to Hide and Swim checks. They may always Take 10 on a Swim check, even if threatened or endangered. They may use the Run action while swimming in a straight line.