Last weekend me and my dad got on a school of bluefish, all about 2-3 pounds, in the Potomac River.  Every fish looked healthy, spitting up bunker and going crazy just like always.  But every other fish would have these parasite looking "bugs" under their gill plates.  I have seen them on white perch also.  I was just wondering what these are, and if they have any affect on the fishes health, and/or safety of eating the fish.  Here is a picture of one circled.  The parasites seem to be about 1 to 2 inches long, and when I pull them off, they have six legs underneath and a mouth.

I haven't noticed these on any bluefish I've caught this year. Thats creepy though. I think parasites are probably my least favorite things on earth.  Leeches, chiggers,  ticks and now apparently their giant ocean-going  armor plated cousins.

Isopods, aka sea lice.

Isopods, aka sea lice.

Bingo.  I've never seen them that big though.  Oh wait, that's a little snapper blue.  Yea, they feed on the tongue mainly but can be found anywhere on the body.  Not harmful to the fish, indicates they are fresh in from the ocean as they don't survive once they've been up in the bays for a bit.

Ok thanks for the quick replies.   I have seen sealice on on rockfish but they were always really small.  

Last year the Porgies we caught off Brezzy Point were loaded with them

We used to call them gill bugs.  They work as bait...

Man that's gotta itch. Imagine not having opposable thumbs to try to get to that!   :-?

Whoa, that is a scary lookin bugger!

Thats nasty...

The isopod is Livonica ovalis.

Often occurs in these fishes.

It is an isopod, not a fish louse.

Has 7 pairs of legs, not 6.