We can't help it Arthur, we're running out of zip-lock baggies trying to keep all these excess fish alive.

How about different behaviors for different types of fish: faster, slower, hide behind plants & other fish, etc.; what if certain fish don't breed or don't get along with certain other fish?

Wonderful! These additional fish behaviors are my dream to program. It's always about the time constraints. I also wanted them to pick at the gravel, etc.

I would love to see a data tracker that allows you to see the fish you have "discovered". When you unlock a level (type of fish) it could show you a "?" for the fish in that group you have not found. This would not leak info for the people you like the mystery, but would serve as record keeping (and save paper). It could be as simple as a photo album of fish. You don't get the "album" until you get the first fish that would be in the album.

If possible, a true screen saver where you could add the fish from your discovered files to screen saver tank. This could serve as a personal "trophy tank" that was not part of the game play.

Make it more like a realy aquarium. Like you can add live plants, ajust the lighting, water changes, etc. There are a ton. (This is comming from a person who as 3 tanks )

I just posted this in another forum, but it might be better off here. Everyone does want more tanks, and I think we understand that it makes the beginning of the game harder and more interesting to be contrained to only 3 tanks, however, after a while it would be fun to have more tanks available to us to really collect fish in. Maybe you could add additional tanks for ridiculous amounts of money. That way it isn't easy, and it probalby won't happen until we are well into our game, but we will be able to buy more tanks as we breed and sell fish in our quest for the magic fish. Or in my case, in my quest to have bred every type of fish. The additional tanks could start at 10,000 and go up for every one we want to purchase.

Like others, I have the urge to save all the pretty fish... The limitation to 3 tanks adds challenge, though.
What I would really like to see is a little more action in the store, since we spend so much time there. Even more of a change from one advertising level to another. Maybe the player's name on the door...
Also, a little more fanfare once all the magic fish have been discovered. I mean, all that work and you get simply a one line statement. Maybe music and jumping fish?
Additional fish behaviours would be cool too.