I found the third level of fish eggs rather disappointing...or is it just me? Now I have been buying level 2 eggs and adding growth hormone and then magic juice. Seems to be funner than level 3. I also have not really figured out what the seahorse does.... I have him/her, but what the heck? I am currently playing 5 games, two of them I have all the magic fish but am playing each game differently. One is all plants, plus the upgraded food, and such.
One is no plants or accoutrements at all, just food and such. One is all the add ons, except the plants...
oh sheeeesh, I don't remember the other two!! lol
I am currently working on all types of each species...
This game turned out to be a lot more involved than I thought, I love it!

To me level two and three eggs are a waist of money. They are only one if not two breedings away from your basic eggs. JMHO. Once you get five different fish, you can pretty much make what ever fish you want, if you know the right combo.

I have bought many many fish eggs and can't get a pink shark...can I breed one?

Yes, you can. The easiest combination is to breed a Silky Shark with an Orange Shark.