Fish aggression and death

[authentic]

My tank is sorted out as far as all of my fish are concerned ,everyone gets along as is.However the last few times I add a new fish they dont make it,, I know that it's a risk but my question is this ,,,I have alot of crabs snails etc...when I recently added a solarensis wrasse it immediately hid near the sand obviously waiting to feel comfortable to emerge ,,will a fish allow itself to be slowly attacked by crabs and be killed,,or is it more likely that my mystery wrasse attacked and the crabs got a meal ,,just wondering

 

[SPR1968]

This will happen as the fish establish territory and the following is a very good article that may help you understand why

https://www.advancedaquarist.com/2008/6/fish

I am well over stocked and I have the same issue, but this article made me think.

 

[authentic]

thanks,,good read

 

[4FordFamily]

Hello,

I see you have a mystery wrasse, they're known to be immensely aggressive, even to fish several times their size. A stock list would be helpful to assess this.

Alternatively, it could be that your inhabitants are resistant to parasites that new fish succumb to. This is very common, as new fish don't have the immune health or strength as the remaining fish in your tank that have built up a resistance over time. Fish that show no symptoms at all are effective "typhoid Marys" for new fish, or the new fish bring their own parasites that they succumb to while the residents seem completely unaffected. Sometimes you add the wrong parasite and you lose incumbent fish a well.