Do you think fish can get depressed?

You might think this to be a strange question but I want to tell you the following anecdote.

When it became clear that Resplandor was eating his babies after having transferred them to the bigger tank I had to act fast. So, I attached a 1 gallon hang on breeder to this tank and put him in there.

The water in this breeder box is turned over as fast as the main tank so same water parameters. I also siphoned out any debris that would settle on the bottom.

This was a temporary solution but as I had other things to do, he was in there somewhat longer than I wanted. After 4 days I noticed that he didn't swim around anymore and would only react to food. Two days later he didn't even react to food anymore and was lying listless in a corner.

I looked closely at him but no signs of disease whatsoever. I decided to put him in my community tank and within a day he was acting normal again! Exploring the tank, carrying out some hunting moves etc.

A case of depression, or something else?

I have read that this ocurrs when removing males. But it may also be due to stress in those breeder boxes.

What is depression? Brain chemistry. If you take a fish and put it in a poor environment, it certainly has its behavioral switches on a dimmer. If it uses resources to swim, its water fouls. When this happens in nature, usually via drought, fish can go into a dormant state, hanging on by using as few resources as possible, waiting for better conditions.
I think we do this to a lot of fish. More and more, I think the minimum tank size for any fish is ten times its body length. A lot of fish need more - a 3 inch wild krib type can hold a nine foot territory. When a fish goes into survival mode, we could call it depression. It often leads to stereotyped, compulsively repetitive behavior, immune system suppression and even premature death.

Well stated as usual Gary and I agree.

I am no expert on fish and depression, but I can tell you that, no matter what species, I believe that depression is seeing things 'too clearly' and that you see only the "negative" and/or the "scary' while any positives are out of reach. If you think about it, depression is expressed differently even for humans - with children and youth, sadness sometimes comes out as aggression and defiance, whereas with adults it is often expressed with exhaustion or lack of interest, etc. 

Who can honestly tell us how fish express this feeling? We do know that they can 'feel' and 'experience'. I truly believe that all living beings feel emotions...call me crazy...but hey, I'm okay with that - crazy is good! We, however, do what we can to keep these guys safe....and if that means planning a new line of attack, let's plan that line of attack...because, really, they depend on us while living in the glass box. 

Biulu - I know that you are a caring, helpful, observant, and cautious finned baby parent who acts when something goes wrong - keep watching and caring - and keep us updated ! I wish I had a better answer, but I thought I'd pass along my thoughts 

We see depression in boarding dogs way too often. I cannot help but believe it is the same with ALL living creatures, as it IS (or quickly becomes) a physical issue, not just something in our head.
There is a very fine line between emotional and/or physical well being, IMO.