Hormone use in commercial fish breeding, how prevalent is it…

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Magnum Man

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Jun 21, 2023
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Southern MN
I’m going to start on food fish, then move into aquarium fish.. so supposedly the supplier of Tilapia I’ve been using, claims no hormones are used in their production, but claim many other producers in the industry, use it to produce more male tilapia, as the harvest weight is almost double, on a male, over a female, in a set time, and you can buy them sexed as males because of the production gains…

I’m not very good at sexing fish, but on the Emperor Tetras ( Nematobrycon palmeri )
and their line bred offspring, the males have blue eyes, and the females green… I have 10-12 of these and their crosses, and I’ve only identified 2 females… wondering if the commercial breeders may use hormones, which on purpose or not, effect the male / female ratios… I thought I had read somewhere, that often harder to breed species, get a little chemical help… most people prefer males for the prettier colors, so it makes dollars and cents if they can produce more males… and at that point, the producers probably would prefer we didn’t breed them…
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I read there is ongoing research on using hormones for sex control particularly in the salmon industry.
As you can imagine, it's a dirty secret of the trade. No one likes to admit to it, but the anecdotal evidence is there.
I have had a fancy Discus breeder try to teach me to use a hypodermic to spawn his fish - he thought I was an idiot because I didn't inject the Apistogramma I bred at the time. His claim was that most Russian Discus breeders used hormones to get the numbers they needed, I can't vouch for that. And I said no.
I have used, once to see if it worked, hormones with Thai writing on the jar. It was what they used to make linebred gourmis extremely red, and yes, it worked. I was hoping to myth bust, but noooo.
Since in most (not all) fish, the male has colour and finnage, there have long been strong rumours of farms using methyl testosterone to make males. In many fish, sex is determined after hatching, and gender expresses itself according to environmental conditions. I can manipulate the sex ratios of some of my killifish and of many dwarf Cichlids through temperature at raising. I have a species that seems to have different ratios depending on minerals in the water - if I raise the minerals in the rearing tanks, I get 95% males. My goal is to learn that to avoid it - I want 50/50 ratios and I'm not a seller. I breed to keep fish going.
I just moved 11 Aphyosemion ottogartneri yesterday, and had 9 beautiful males. 2 females lets me keep them going, but it's cutting it fine.
What are the consequences? In many jurisdictions, sale of the fish for food could be illegal. Probably not. Frankly though, it's very hard to prove. If I were an unethical fish farmer under pressure to deliver only males of a species, and to deliver them cheaply to the box stores, would I cheat and use easily available hormones?

With the ottogartneri killies, I started with 11 fry, so I know what I got was natural. In many cases though, young male fish will kill females, and aggression in the stupidly small breeder nets and tiny tanks hobbyists sometimes use is blamed for skewed ratios by the time you can sex them. I do see so many male only batches coming from farms though. You wander through some of the lower quality pet stores, and you'd swear there are only males in this world.
most of my fish are pretty difficult to sex... so I would guess this isn't as noticeable for most aquarists... the Nematobrycon palmeri, are unique in the eye color difference...

where this really hit me in the face, was when I was looking to raise Tilapia... I don't think I want to eat fish exposed to extra hormones...

these are a few paragraphs from Lakeway Tilapias website...

"No hormones​

Think that hormone use is rare? Think again. The state of New Mexico actually requires that all fish be treated with testosterone! Under the FDA, tilapia producers are not required to disclose such hormone usage. However, it is a federal crime to ship fish intended for human consumption after making false statements about hormones, so the companies that use them just don't talk about it. Lakeway Tilapia does not use hormones of any kind at any time. Our tilapia are 100% natural.

Our organically raised Blue food grade tilapia fingerlings are ready for grow-out. They are between 30 and 40 days old and average about one gram in weight. They will grow to over one pound and will be ready for harvesting in approximately seven months. As a result of the grading process, our food grade fingerlings are predominantly male. Food grade Blue fingerlings™ can also be used in aquaponics systems however their faster growth rate may result in greater fish waste which may require additional filtration depending on your system design."

So we as consumers, are eating hormone adulterated products from Tilapia to Milk... I guess we shouldn't be surprised how un-naturally produced, are aquarium fish are...
BTW... on my yellow tail African river tetras Alestopetersius caudalis... I bought 6-9 months ago, I ordered 4 of them... & lucky or not, I got 1 male, & 3 females... since I have no desire right now to breed them, I was disappointed, as the females are plain silver fish, with no interesting characteristics, while the males can be quite spectacular... & I would guess as @GaryE ... explained several things, including temperatures can influence the sex, so there are likely "conditions" that could produce a higher percentage of females, which could have a negative effect on sales, on fish like the yellow tails...
The use of hormones in this manner is appalling. The good news is that most forms of testosterone cannot be absorbed through the GI tract.
I would guess that "The state of New Mexico actually requires that all fish be treated with testosterone!" is done to reduce the numbers / potentential of invasive fish... if they were all males, little to no chance of reproduction in native waters... Florida, among other southern states has a problem with invasive Tilapia... only issue there, is the consumption of hormone adulterated fish
One effect on wild fish is behaviour. The holding stations can be small, and males crammed together may kill each other, or nip each other (lousy for sales). Killie imports are often male heavy, as in places they gather, males often display to females, who sensibly stay in leaf litter. So a pass of the net tends to catch males, who are higher in the water column. I bought a breeding pair of SA killies once by identifying the one female in a batch of 50 fish.

Plus, local fishers sometimes assume no one wants females, or simply can't sex the fish because they are too small when caught.

Most wholesalers say they won't guarantee their sexing of fish. They dip a net and you get what you get. It's frustrating when hobbyists order fish then try to save money with minimal numbers. Somehow, people think it's logical that if 300 fish get sent from SA or Africa, there'll be 150 of each sex. It doesn't work like that!

If you intend to breed fish, it's an investment. You buy as many as you can afford. The importer may have received 300 fish, with 290 of them one sex. If they make pairs, those pairs cost a lot.

The colour hormone I experimented with was used to turn a dwarf gourami linebred variety flaming red. Not long after arrival, the fish would start to fade, but they sold like crazy. Have you ever had a bright red fish lose its colour? Bingo.

I would guess that "The state of New Mexico actually requires that all fish be treated with testosterone!" is done to reduce the numbers / potentential of invasive fish... if they were all males, little to no chance of reproduction in native waters... Florida, among other southern states has a problem with invasive Tilapia... only issue there, is the consumption of hormone adulterated fish
That makes sense to me. Tilapia have been the agent of a lot of extinctions, with humans who introduce or let them escape as the cause.
Male & Female pair of Black Linebred Nematobrycon palmeri... makes it easy to see if your male & female numbers balance out
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.


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.


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.
Fish breeding is no longer the interest it was about 20 years ago, and the hobby has swung to a straight consumer model. I tend to think that among the species where sex can easily be influenced by well timed hormone treatments, the hunt for prettier males is the motivation. Sometimes, it's to block breeders - when Melanotaenia praecox, the dwarf neon rainbow was first introduced in the hobby, it was a couple of years before I saw a female in a store. The same was true for rosaline barbs.

As one wholesaler said to me about praecox "It's good. You don't want some &^&^&^& hobbyist breeding them and selling them to stores." They still sell well now that females are available, so maybe there was paranoia there, but it's an attitude.

If you care about nature, and how our fish live in it, then there is no reason to chemically alter fish for breeding, colour or gender. The aquarium industry is busily churning out glofish, blood parrots, grotesque bettas, balloon fish - I don't think it can be accused of an interest in nature or education. We prefer to buy them, so we're right in there. It's straight ahead market driven.

I've known aquarium store owners who tried to be ethical and who refused to sell balloons or deformed fish, and they had customers shouting at them for being poorly stocked. It's a cut-throat, consumer driven business, and if they can get an angle with hypodermic needles, batches of hormones, raising fish in antibiotics to force growth, etc, they'll do it.
If they don't, the box store, near monopolies won't buy from them and they'll go bankrupt. Ethically bred and raised fish are slightly more expensive to raise, and the market doesn't like slightly more expensive at source.
I’m not trying to advertise here, but the seller I prefer to buy from, blatantly states his fish are more expensive, and has a video out explaining why… treatment of the fish…

I still have to buy from other sources, as he doesn’t get everything that “I” want, when “I” want it… so yes, even if I’m trying to be ethical, it’s still a consumer driven market
I also buy from more expensive sources, because I know how they operate. But we're such a miniscule segment of the market. In any business there will be a tiny sector aiming at quality, and selling for a bit more. The difference isn't huge, especially when the death and disease rates are factored in. If you pay $20 for 5 fish and 4 die while the other needs $20 in meds, while I pay $6 a fish and 4 out of 5 live with no meds, I'm ahead.
I ordered 6 more Nematobrycon palmeri... will see if I get any green eyes ;)
Emperor tetras aren't sold as male only, in fact no tetras are. They are bred and the shops get males and females. If you order online, ask the supplier for 3 prs (3 males & 3 females).

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