Isopod ID (pics and clip)

[LgTas]

Does not roll into a ball
Has forward facing predatory eyes

Was swimming in my DT with multiple fish that usually would snack on something like this.

Video of Isopod

 

[Nick711]

Looks like a Cirolanid.
You saw it swimming during the day? They’re nocturnal as far as I know & latch on fish (detrimental). Did you recently add LR?

 

[LgTas]

Looks like a Cirolanid.
You saw it swimming during the day? They’re nocturnal as far as I know & latch on fish (detrimental). Did you recently add LR?

It was swimming in the morning with the lights off. Established tank but I use NSW. Last batch was collected well off shore so potentially came in through that?

 

[JoJosReef]

Does not roll into a ball
Has forward facing predatory eyes

Was swimming in my DT with multiple fish that usually would snack on something like this.

Video of Isopod

That looks like a cirolanid. Eyes of a cirolanid look so much more sinister than a spheromatid.

Good guy:

BAD guy:

 

[Nick711]

It was swimming in the morning with the lights off. Established tank but I use NSW. Last batch was collected well off shore so potentially came in through that?

Yes, unfortunately it is a Cirolanid. It’s highly likely you have more than 1 in your tank (I had 50+ from only 8# of gulf live rock). I would suggest observing your tank tonight during lights off to see if you find more. They jitter through the water in a somewhat jerking motion so they should be rather easy to spot despite their size (size also varies quite significantly). I won’t sugar coat it, these guys are a pain to eradicate, but maybe first see how many more you come across and if any are latching to your fish.

 

[JoJosReef]

The potentially optimistic view is that you say it may have arrived from your collection of natural sea water. They usually come in mass from live rock, so you might have just picked up a straggler in the water. Still, I would get it/them out asap just in case it's ready to lay a million eggs in your rocks!