There's no reason to use hormones or any other chemicals to breed fish, birds or any other animals. They are all easy to breed if you provide them with the right conditions.
I used to breed Australian finches and was extremely good with certain species. I kept my finches in colonies because they naturally lived in colonies in the wild. They regularly produced 4 batches of eggs per year. Most other breeders were getting 1 or 2 batches a year. I had 6-10prs of each species in a large aviary and they got a really good diet including lots of green feed (including green grass seeds), clean water, vitamin and mineral supplements, and protection from the elements. The bird shops in Perth would take any of my birds and they wanted as many as they could get.
Organisms need the following to flourish.
1) A clean, safe, predator free and disease free environment. If an organism is stressed or getting sick because of a dirty environment it won't be thinking about breeding. Likewise if it is being continually harassed by anything, including predators, it won't be thinking about breeding. A clean safe environment that is set up for that particular species is essential for the long term health of the organism.
2) An environment with a suitable climate is essential. To breed fish you need to give them the proper pH, GH, KH, salinity and temperature for the species being kept. You are unlikely to breed a wild caught fish that naturally occurs in soft acid water if you keep it in hard alkaline water (and vice versa). If the temperature is too low or too high the fish won't breed. Keeping fish in a tank that is too small won't help anything except disease outbreaks and poor water quality. Having too many fish in a tank won't help and leads to fighting and disease. Give the fish a suitably sized home with the correct water chemistry and temperature, and they will be more likely to breed.
3) Lots of good quality food that they can digest. If an animal is hungry, it's not going to breed. The exception to this is humans who breed even though there isn't enough food to feed themselves, let alone their kids. But for all other organisms on this planet, if there isn't enough food for the animals, they won't build up fat reserves and come into breeding condition, and they won't breed.
Fish being used for breeding purposes should be fed 3-5 times a day for several weeks before they are bred. They should get high quality food that they can digest and they naturally eat in the wild. You are unlikely to get fish to breed by feeding them fish flakes 5 times a day because it's not the best food, but can be used as part of a varied diet. Vegetarian fishes need plant matter, predators need meat, and omnivores need plant and meat. With fish you can use insects and insect larvae, various crustaceans, worms, and a range of other foods available from pet shops or the seafood isle at a supermarket. If the fish are hungry, they won't be thinking about breeding and if someone in the tank does shed a batch of eggs, everyone else eats them.
4) Clean water to drink or live in. If you don't have clean safe water, you're not going to be happy or well. Same deal with fish, they need a clean environment to live in and animals need clean water to drink. The water needs to be free of diseases, harmful chemical and pollutants.
If you provide any animal with these 4 basic requirements, they will breed without the need for any outside interference.
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Using hormones to breed fish like Tilapia is stupid and a complete waste of time and money. Like all cichlids they are easy to breed. One of the reasons people keep cichlids is because they are easy to breed. I personally like watching the brood care and colouration on some cichlids. But you don't need hormones to breed cichlids. Why New Mexico makes it compulsory to add hormones to their fish is beyond me but it should be illegal.
As for using hormones to produce males only, I haven't heard of that and would think the hormones would be applied to the water that the eggs were in so the developing embryos get the chemical and turn into males. However, I doubt this would be legal in most civilised countries.
Tilapia are a pest species in lots of countries including Australia and New Guinea. People have deliberately released them here for whatever reason. In New Guinea they were introduces into local waterways as a food fish. However, the locals don't like the taste or texture of them and the fish have subsequently decimated the endemic fish populations.
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Most fish can be easily sexed if you know what to look for. Males generally have bigger fins and brighter colours for showing off. Males are generally slimmer than females that are carrying eggs. There can be colour differences between males and females (Melanotaenia boesemani or Glossolepis incisus, male dwarf gouramis are colourful and females are silver). With emperor tetras, they have different eye colours but the males get a filament in the middle of the tail. Male Congo tetras also get a small filament in the middle of their tail. Most livebearers have different shaped anal fins. Male salamanderfish have different shaped anal fins and don't grow as large as the females. Sharks (like jaws) and stingrays have different shaped anal fins. Male rainbow sharks have a black edge to the anal fin. A lot of male suckermouth catfish get bristles on their face or pectoral fins. A lot of male catfish like Hoplosternum species have a longer thicker pectoral fin rays and it can be a different colour to the female's fin rays. Male goldfish are slimmer than females and develop small white dots on their gill covers and pectoral fins when in breeding condition. Male neon tetras have a straight blue line whereas females have a kink about half way along the body in their blue line. This is caused by eggs making the females fatter and distorting the shape of the blue line.
A lot of female fishes eat more food per feeding than the same size males. I have no idea why this is the case but years ago I did experiments on the amount of food fish eat and found females at 20-30% more than males. I assume it's to help them get the nutrition to develop eggs, which require more energy to make compared to sperm.
There's also behavioural differences and male fishes will often display and flare their fins out to show off to each other and the impress the females. If you see a fish with its fins flared out and the fish is swimming excitedly next to another one, you can be pretty sure one is a male.
With crustaceans, male crabs have a narrow pointy tail and females have a wider/ broader tail.
Male freshwater crayfish have 2 small bumps on their lower legs (1 bump per leg). Females have 2 bumps on their upper (2nd) set of legs counted from the head to the tail, (1 bump per leg).
It's just a matter of learning how to sex different species and over time you can see the differences quite easily even if you are looking at 100 fish in a tank.
