I have been playing fish tycoon for a while and I have yet to make enough money to keep the fragile species! What is a good way to make money? I have seen people with codes and hacks, I have tried them but they never seem to work for me! I have tried breeding the same fish so they wouldn't die of old age, and I got farther than I ever had, but then all of a sudden things went downhill even though I did the same things I did in the first place! HELP!

The most important thing is to focus on getting the second tank (so you can breed more fish; more fish = more money) and researching better Fish Environment (so that the more valuable hybrids will thrive). People have posted a lot of good strategies for making money early in the game, such as those described in this thread.

Find the Canary Fire-Arrow. You can sell this fish for over 300 dollars each.

But first you need to research fish environment to level 3.

I suggest that you breed lots of Speckled Leaffish and sell them for around 60 dollars each. If you only have level one environment then you will need to sell them when they reach adulthood (age 20) and you may need to top up their health by buying fish vitamins, otherwise they will die. But this is the quickest way to make money so that the environment can be researched.

It is not necessary to get the 2nd tank early in the game as you can breed fish in your sale tank. However, if you want to prevent certain breeds from being sold accidently, e.g. the Greenfin Spotanus and Spined Fruitfish, then you need to increase the price of these fish dramatically. (I add a couple of 9's to the fish price).