How to Overcome the Death of a Fish

https://www.wikihow.com/Overcome-the-Death-of-a-Fish

“Take time to grieve. There is nothing strange or wrong with mourning the passing of a living being that was important to you, indeed it is a natural reaction. Don’t feel the need to hurry up and get over the death of your fish. People need different amounts of time to grieve – there is no set amount of time when grieving should end. Take the time that you need to work through this” 

Mourning the Loss of a Fish

https://fishbreeds.net/mourning-the-loss-of-a-fish/

“Your Other Fish Will Mourn As Well.

Animals know when their companions are missing and a mated fish pair will certainly notice if their mate is not around. Don’t be surprised if your fish appears to be processing their way through the stages of grief as well. It may help to get a new mate to help them get through the grief more quickly. Keep in mind though that you won’t want to just dump a new fish into the tank. Acclimate them to one another through fish screening.”