My biscuit starfish has a growing chunk of flesh taken out

[joeybemate]

I noticed yesterday that my biscuit starfish had a chunk of flesh taken out of it. Today I noticed that it had gotten bigger. Could my fish be eating it or is it more likely a parasitic problem? Or something else?

Other fish: 2 clownfish, 1 banggai cardinal, 2 pajama cardinals, 1 lawnmower blenny.
I also have two peppermint shrimp and a bunch of others in my cleanup crew.

Parameters: Nitrates: 0.1 phosphates: 0.02 Mg: 1200 Ca:300 KH:8.2 PH:8.2 SG: 1.024

 

[Jeff4777]

A fish could nip him. It certainly happened to one of mine once and it recovered fully. I suspect a tang that was nipping for algae. However judging by your picture it looks much more like deterioration than a physical injury. Also his central disk/stomach looks a bit sunken in, even though one of the legs are bent up. I've had the best luck keeping sea stars at about 1.025 sg. Have a few Fromia stars closing in on 3 years.

Usually if they start deteriorating there isn't too much you can do to save it.

 

[CStrickland]

How long have you had the starfish for?

 

[joeybemate]

I've had it for 2 months

 

[CStrickland]

I'm not sure, but I think biscuits are like a broad name that often includes diff stars. I feel like most of them need to be fed in the manner of a chocolate chip, as opposed to fromias/linckias that don't really take food reliably. Has he been eating well?

 

[joeybemate]

I've not been target feeding him I just thought I'd let him find food for himself and didn't realise that there were particular feeding requirements. I did a lot of research for my linckia starfish and concluded that there wasn't a whole lot of information about feeding them and the information I found was a bit ambiguous, but it seemed that they ate detritus and film algae and often didn't respond to food for them. How can I better care for it in future?

What I think may have been the issue is if he wandered too close to the bta that hosts my clowns, and they got protective and nipped it? They've nipped at my hand before when I've gotten close to it, and he was right next to it when I first noticed the injury.

 

[joeybemate]

It moves around a lot, and I see a lot of its feet, and it extends its feelers at the end of its arms a fair bit which I took as signs of health.