It can be quite a while before you get that second Greenfin Spotanus. The common eggs cost $120 and I've had to buy at least 10 batches of them before I've got another Greenfin Spotanus. You'd be better off using the $1200 to research the environment and then you could sell more delicate and more expensive fish.

These are my top tips for making lots of money early on in the game:

Breed the Spined Fruitfish with the greenfin spotanus. The spined fruitfish may already be in your tank unless you are playing on Hard difficulty, in which case you will have to breed it. Alternatively, breeding a Spined Spotanus and a Greenfin Fruitfish will produce the same result. There are lots of other matches too but I've chose the two that are most likely available to you at the beginning of the game.

The offspring will be the speckled leaffish (a magic fish) and you will have time for the fish to mature so it can be sold. Make sure that you sell the offspring otherwise their health deterioates and they will die.

Until you've researched level 2 environment, you will want to keep breeding the fruitfish and spotanus and sell the offspring for around $70. I usually keep 4 or 5 fruitfish per tank and breed them with the single greenfin spotanus.

Don't forget that you can use your Sale tank to breed fish. To avoid selling the 'breeding' fish by mistake, increase the price by $1000 and they won't sell if you accidently click Sell Fish.

First priority after you start to earn money is to buy the second tank.

Second priority is to research environment. When level 2 is researched you can sell the fruitfish (remember to reduce the price) and breed the leaffish.

After you have researched level 2 environment, find the Oriental Goldbulb. You will be able to sell this for about $100. More importantly, this fish breeds very quickly and the offspring will grow quicker because of the magic qualities of the fish.

Buying and placing ornaments in your sale tank will make your customers happy and they'll be more likely to buy. To get more customers you need to research marketing.

You may find that the fish sell slowly because of lack of customers. Either 1. speed up the sales by reducing the price of the speckled leaffish to $50 or 2. leave the selling screen running and go and do something else. The fish will carry on selling while you browse the internet etc. providing you don't close the screen.

None of the individual fish will sell for $1000s. The maximum price that I've found a fish to sell for is $475 but you'll need to research level 3 environment for that one.