Suggestions for a breeding project?

[arowfanaticII]

how about stingrays those are easy!

 

[Damascus]

how about stingrays those are easy!

Would have to strongly disagree here.
If you define :

Keeping MASSIVE aquariums
Spending hundreds every month on food and electric
And the input of an initial 1000s of $

As "easy", then maybe consider breeding rays. You will still not be able to compete with imported rays from overseas unless you have a specie that is attractive and no one else has.

This is not an easy, cheap or realistic undertaking for anyone to consider first.

 

[Hybridfish7]

Rainbow cichlids could be fun. They are like convicts but not as common.
Nanolutae, cutteri, or sajica are all convict relatives that would work too.

Nanolutea might be a bit problematic, they're easy as long as you have a mature tank with stuff for the adults and fry to graze on. Very susceptible to stress related diseases. Cutteri are fun too, very cool colony dynamics and behavior, but you will have a very hard time selling unwanted fry. I personally suggest something along the lines of Honduran red points if you want to do cichlids, as they are easy to breed and sell. Since you're working with a 75 or 125, you could even do something like hypsophrys nicaraguensis or some kind of herichthys, as those will give you cool behaviors and you'll be able to sell them. I wouldn't bother breeding small stuff in a big tank, unless your intention is having a lot of them as permanent residents. Plecos especially, you will never be able to catch fry. It's hard to get food to them in a big tank unless you already have a swarm that's waiting for food wherever you drop it in there.

 

[fishdance]

Due to colour and peaceful nature, most tetra species are always in demand (for sales) and look great in huge schools (to keep) but neons or rummynose especially popular.

 

[Disturbed.)]

Not sure if you were asking about other plecos for a 20 or just other fish for for a 20. Easy begginer fish for 20g rare corys. Razor the eggs off the glass and move to a nursery tank. Another easy one would be Celestial Pearl Danios for your 20g thought. They are in demand, short lived and won't breed in hobby tanks because they eat their own eggs and fry. But all you need for even a 10g breeder tank is happy fish and craft netting elevated off the bottom so the eggs don't get eaten. Move the parents to another 10 rinse and repeat.
For the 55 small Africans cichlids in a bare tank with air powered egg tumblers can be fun and easy.
Have fun but be careful of this rabbit hole. You won't produce fish cheaper then they can be shipped in from Asia. You may spend more money on the breeding tank upkeep than you will receive in store credits. And ultimately this is how you end up with a fish room and being served divorce papers lol