Back To Basics When Breeding Fish
Make sure you have a pair, (1 male + 1 female). There is nothing worse than spending your hard-earned dollars buying a couple of fish to try and breed and ending up with a pair of fish of the same sex. Let's face it, to reproduce fish you need a male and a female. Two males won't do much without a little lady. So do your homework before you go out and buy whatever looks good. Find out how to differentiate between males and females of a species and get a pair that can do something. If you can't find out how to sex a fish and no one will help you, buy a school of them if you can afford it. Chances are if you buy 6 or more of a species you are more than likely to get a male and a female. Also any fish that naturally lives in a school will feel much happier if there are others of the same kind to hang out with.
Keep them well fed and looked after. If a fish is hungry all the time and its home is not suitable for its long-term survival, chances are it isn't going to do much in the reproduction area. Fish need feeding regularly to be able to grow to maturity and develop properly. Why would they be thinking about sex when they are hungry. Much better to eat any eggs produced and fill the stomach void, rather than bring others into the starving community. Feed the adult fish 3-5 times a day with a variety of dry, frozen and live foods, for at least 2 (preferably 4) weeks before you breed them. This allows the fish time to gain some condition and body fat, and develop good quality gametes (eggs & sperm) before they breed.
Maintain good water quality. Regular partial water changes (50-75% every day or every second day when feeding more often) and gravel cleaning the substrate whenever you do a water change, will help keep the tank cleaner and reduce the build up of harmful microscopic organisms associated with more food going into an aquarium. It will also help keep the nitrates lower. The big daily water changes help to stimulate fish and encourage them to breed. This is due to it simulating rainfall, and a lot of fishes breed during the wet season when there is lots of regular rain.
You should monitor the water quality (ammonia, nitrite, nitrate) if you want to breed fish. In the wild the water is generally free of these harmful chemicals and the pH stays relatively stable by comparison to aquariums. If you get lazy with tank maintenance you can pretty well rule out any chance you have of breeding any fish. Keep ammonia and nitrite levels on 0ppm, and nitrate levels as close to 0ppm as possible, and below 20ppm at all times.
Clean water of the required type is desirable. The water used in the breeding aquarium should be clean, well filtered and free of any harmful chemicals before the fish are introduced. It must also be to their liking and have the correct water chemistry (pH, GH
) and temperature. It is pointless trying to breed a fish in soft acidic water if it naturally occurs in hard alkaline water, and vice versa. Do your homework and find out the water chemistry of their natural habitat. The pH, temperature and hardness (GH
) are all important factors that must be catered to if you want to breed fish.
Use an aquarium of suitable size to accommodate any fish involved in the breeding procedure. Some fish get very boisterous during breeding. Therefore sufficient room should be available so any other fish in the tank can get out of the way if they need to. A tight fitting cover of some sort is required. Most fish can jump and if excited or spooked may well end up on the floor. Nothing destroys the moment more if one party decides to do a flying leap of death up and over the edge, never to return.
Separate sexes for 5-7 days before breeding. Its amazing how much more excited fish can get if they haven't seen a member of the opposite sex for a week. Segregating males from females for a week prior to breeding can result in more eggs being produced and the fish being more willing to breed. Females of some fish species can become egg bound if they are not able to expel eggs regularly so do not separate females from males for more than 7 days. Female rainbowfish should only be separated for about 5 days otherwise they will start expelling eggs with other females. Introduce the female fish into the breeding aquarium 12-24 hours before introducing the males. Introduce the female in the morning and the male fish in the evening if possible. The following morning there should be some action. Depending on the fish being bred it is best to remove the adults the day after they were introduced. If the species is not an avid egg eater, or if they spawn successively over several days, the adults can remain in the breeding tank for that period.
Provide ample spawning media. Aquatic plants, particularly Java moss, are commonly used for fish to spawn in. Artificial spawning mediums are becoming more popular due to their ability to be sterilised before being used. This allows for more control over possible egg contamination by fungus or eggs being damaged/ devoured by pests, worms, snails, hydra, etc. Whatever spawning medium is used, provide plenty of it. The more hiding places for eggs the less chance of the adults finding and eating them.
FOOD FOR THE BABIES
If everything goes to plan you will have a number of little tiny fry swimming around the breeding tank several days to a week or more after the parents were removed. Now it is time to feed the young.
Baby fish (known as fry) have very small mouths. This simply means that if they are to eat anything it also has to be small. In the wild fish fry will consume single celled algae (phytoplankton) and infusoria during the first few weeks of their lives. After they have grown a bit they graduate up to larger food sizes that include Rotifers, Cyclops and Daphnia and any small insects and their larvae. From here on they simply eat anything that fits in their mouths and is of nutritional value.
In an aquarium there is very little live food available for young fish. Therefore we the aquarist must provide a suitable substitute if we are to keep any fish fry alive. Infusoria and green water can be cultured with relative ease and for anyone with a large number of fry to feed, this is the cheapest and most practical thing to do. Alternatives to the above mentioned include prepared liquid and dry "Fry Foods" available from any good aquarium shop. These are suitable for the majority of baby fish and provide a readily accessible food substitute. They are available in packages that are easy to use and can be stored on the shelf waiting for when they are needed. The drawback to prepared foods is they are quite expensive and tend not to give quite as good results as live foods, (green water, infusoria and rotifers) when it comes to survival and growth rates of fry.
Green water is a mass bloom of single celled algae. To culture this, put a container of dechlorinated water out in the sun and add 1 level tablespoon of lawn fertiliser for every 20 litres (5 gallons) of water. Use fresh water for freshwater species and seawater for marine species. If possible aerate or circulate the mixture. It should go green and soupy quite quickly, (usually within a couple of weeks). Then take some of the green water and put it in with the baby fishes. Enough green water should be added to the fry tank to turn it a pale green colour. You also need to keep adding green water to the fry tank to keep the green tinge in it. If the water in the rearing tank goes clear, there will not be enough algae for the fry to eat and they die.
Algae cultures can be grown indoors and regularly are in scientific labs or aquaculture facilities. You have a couple of fluorescent lights above or next to some containers of water with fertiliser in. You either add an algae starter disc, available from aquaculture supply stores (like Florida Aqua Farms) or you just leave the containers of water open to the air. Algae spores will eventually land in the water and start the cultures.
If you need to get green water quickly, you can use a clean fish sponge and wipe some green algae off the inside of an aquarium and rinse the sponge out in the culture container. Within a week the water should start to go green and soupy.
Have the light on for 24 hours a day and aerate the water and fertiliser. Use an airline without an airstone to circulate the water. Tie a small lead weight to the airline to hold it on the bottom of the container of water.
When the water goes green and soupy you start adding a liquid aquarium plant fertiliser or an iron based aquarium fertiliser to keep the culture going.
You should start a new culture regularly by making up some clean tap water and fertiliser and adding some of the green water you already have.
You can use old green water cultures to grow rotifers, daphnia & cyclops.
Make sure the green water that gets added to the fry tank has a similar temperature to the fry tank so there are no sudden temperature changes.
Replace the water you take out of the green water culture container with some fresh dechlorinated water.
If you put fry into a container full of green water, make sure it is aerated so the fry don't suffocate at night, and have something in the water to buffer the pH. During the day when the tub of green water gets light, it will use all the carbon dioxide (CO2
) in the water and the pH will go up. At night the green water will use up all the oxygen (O2
) and release CO2
and the pH will drop. Aerating the green water culture will prevent this from happening and stop or reduce pH fluctuations.
An aquarium based plant fertilizer can be used to keep the culture going after it has been running for a while. Alternatively, start a new culture every few weeks so you have several cultures going at any time. This will provide you with plenty of green water and provide a back-up should one culture crash. *NB* put a cover on the container to stop insects making it their home.
Infusoria for fish culture purposes are generally single celled animals called Paramecium. Numerous recipes for their growth are available. The most common being crushed lettuce leaves in a bucket of water and then left to grow for a few weeks. Any non-toxic plant matter (spinach, silverbeet, cabbage, broccoli, lawn clippings, hay, oak leaves, maple leaves, eucalypt leaves, sliced banana or banana peel, sliced apple or apple peel, etc) can be used instead of lettuce leaves. I recommend lettuce because they are cheap and readily available in most parts of the world, and they break down quickly and easily and at a similar rate.
The only plants you can't use are poisonous plants and plants that produce a white sap when the leaves get picked or broken. And avoid citrus (lemon, lime, orange, mandarin) or citrus peel, onions, spring onions, leeks, shallots, garlic and potatoe.
Use a large plastic container (at least 40 litres) full of dechlorinated water and add one whole lettuce for every 20 litres (5 gallons) of water. Tap water is preferred so you get a pure culture of infusoria. You need to add a lot of plant matter to the water, 1 whole lettuce per 20 litres or an equivalent amount of plant matter. You would need about 5-6 large spinach plants or a couple of bunches of silverbeet to equal 1 whole lettuce. If you get a 10 litre (2.5 gallon) bucket and fill that with leaves or lawn clippings, that would be about the same as a lettuce.
Rinse the leaves well (make sure they are free of chemicals & pesticides) and crush them up before adding. Have an airstone bubbling away in the culture. Put a lid on the container and leave it to bubble away for a few weeks.
The water initially goes dark and smells awful as the leaves break down and bacteria starts to feed on the rotting leaves. If the culture is not aerated during this time it goes black and becomes anaerobic, and it stinks. Aeration prevents this from happening. After a couple of weeks, infusoria start to grow in the culture and they eat the bacteria. When this happens the water will start to clear and develop a slight yellow tinge from the tannins in the leaves. The water will not smell bad and if you remove the airstone for 10 minutes and allow all the rotten plant matter to settle to the bottom of the container, you will see tiny white specks moving about in groups. These are the infusoria.
You can scoop these out using a fine mesh net (5 micron net), or syphon them out, or just use a small plastic container to scoop these clusters out. You add the infusoria to the fry tank and the fish eat them as their first food.
If you use a container to scoop the infusoria out, you should check the temperature, pH and ammonia levels in the water. The pH will usually be below 7.0 and there will usually be ammonia in the water. If there is a pH difference or high levels of ammonia in the infusoria water, you should try to reduce the amount of water added to the fry rearing tank.
Once you have an infusoria culture producing fry food, you can keep it going by adding a few crushed up lettuce leaves (or other plant matter) every few days, and the new leaves break down and provide food for the bacteria, which provide food for the infusoria. If you don't add new leaves each day or every couple of days, the bacteria eventually stop growing and the paramecium run out of food and you run out of paramecium to feed to the fry.
The new leaves only have to be added after the culture is established and you do not have to add leaves while it is developing. The new leaves are simply to extend the cultures life and keep it going for a few weeks, which is usually long enough for the fry to be moved onto newly hatched brineshrimp.
If you have several cultures going you can harvest from one in the morning, one at lunch and one at night. This gives the cultures more time to recover between harvests and gives you a back up culture if one crashes, which can happen in really hot weather or it you forget to put the airstone back in.
Cultures also die after a period of time so if you plan on breeding fish you should start new cultures every few weeks to ensure you have a plentiful supply of fry food when you get fry, and to use as a back up if a culture crashes or becomes infested with insect larvae. Mozzie larvae love infusoria cultures and one female mosquito can lay hundreds of eggs in a culture and the larvae will eat all the infusoria.
Infusoria cultures do not need a light source and can be cultured indoors where there is normal room light or in dark sheds. The only time you need light is to see the infusoria so you can collect them.
A tank of snails (mystery snails are frequently used) that are kept and fed on lettuce or other plant matter, will produce infusoria as well. The infusoria feeds on bacteria that eats the rotting snail poo. The infusoria can be harvested and fed to fry. For a snail tank to produce quantities of infusoria you need to reduce or remove the filtration in their tank. This can be a problem if lots of snails are kept as the water quality can deteriorate quite quickly. Air stones bubbling away and frequent water changes will help keep the water suitable for the snails, but not filter out all the infusoria.
Rotifers are multi-celled animals that are quite small, ranging in size from 20 microns to an inch in length. Some require a microscope to be seen. Others can be seen with the naked eye but exact details are difficult to see clearly without some ocular help. Rotifers will feed and grow in green water and infusoria cultures. This isn't a problem for most, however it can annoy those trying to keep pure cultures of a certain plant/ animal.
To culture rotifers, obtain some cysts (dormant eggs) and add them to a container of green water. Have an airstone bubbling away gently in one corner of the container. Shortly after being added to water the cysts will hatch and within a few weeks you will have a thriving colony of rotifers. Once a culture is going you should start new cultures every few weeks. One way to do this is to take a couple of litres of green water and live rotifers from an established culture and add that to a new container of green water. This will provide you with alternative sources when the older culture crashes and dies off.
When a culture does die off you can drain the water out but keep the sediment on the bottom. Allow the sediment to dry out for several weeks. The sediment will contain rotifer cysts and can be used to start a new culture if it is added to some clean green water. If you don't want to start a new culture straight away, you can freeze the sediment in a plastic bag or put it in the bottom of the fridge and the cysts can remain dormant like this for years.
Rotifer cysts can be obtained from various aquaculture suppliers including Florida Aqua Farms, (see the following link).
Resting Rotifer Cultures – Florida Aqua Farms
To harvest the small species of rotifers, you can use a fine mesh net (5-10 micron) or scoop them out with some green water and add it to the rearing tank. The bigger species can be caught out with a normal aquarium fish net.
DAPHNIA & CYCLOPS
Daphnia and cyclops can be collected from ponds during various times of the year and kept for short periods in containers of aquarium water that is gently aerated. They can be cultured in the same way as rotifers (in containers of green water or infusoria) and will supply you with a year round source of small live fish food. Surplus Daphnia can be frozen in ice cube trays and used when live Daphnia is not available.
When conditions are good, the female Daphnia produces live babies (clones) that make a great food source for small fish. When conditions deteriorate the females produce eggs that go dormant and can survive drying out. These eggs can be left to dry out for several months before being added to containers of green water to start new cultures. Alternatively scoop some live Daphnia out of a culture and add them to a new container of green water and they will continue to grow there.
To harvest Daphnia you use a fine mesh aquarium fish net to scoop out the babies, or a course mesh aquarium fish net to catch the adults. You can also scoop them out in some water but nets are more efficient.
Brine shrimp eggs are readily available from pet shops and can be hatched out in salt water to provide a valuable source of food for young fish. Most nutritional value from brine shrimp is obtained during the first two days after hatching while they still have their yolk sac.
Dry brineshrimp eggs should be kept dry and in an air tight container in the fridge or freezer to maximise their shelf life.
A simple brineshrimp hatchery can be made out of a 2 litre plastic drink bottle. Cut the top off the bottle and throw the top bit away. Half fill the bottle with sea water or salt water made to the same salinity as sea water. You can buy a hydrometer from any pet shop to measure salinity in water. You can use rock salt, sea salt, or swimming pool salt for this. Put an airstone in the container and add 1/4 of a level teaspoon of dry brineshrimp eggs to the salt water. Put the container somewhere warm, I had mine on top of an aquarium. The eggs are brown and take 24-48 hours to hatch, depending on temperature. In warmer water (28-30C) they hatch faster than in cooler water (20C). When you see orange dots in the water, the eggs have hatched. The orange dots are the baby brineshrimp called nauplii.
Plastic multi coloured airstones are the best airstones to use because they can be taken apart and the salt and old egg shells can be removed. Many brands of these airstones also have a small lead weight in the bottom that helps hold the airstone at the bottom of the container.
To harvest the baby brineshrimp, you remove the airstone, wait 5 minutes for the eggs and nauplii to separate, and then use an eye dropper to suck the nauplii out and feed them to the fish. The nauplii are attracted to light, so having a light on one side of the culture will encourage the baby shrimp to gather in one spot and makes them easier to syphon out.
Try not to put the brown eggs into the rearing tanks because fry can choke on them.
A plastic plant mister can be filled with freshwater and used to wash the salt and eggs off the sides of the hatchery throughout the day.
After you have fed the nauplii to the fish fry, put the airstone back in the hatching container and wait until the fry need feeding again before removing the airstone and sucking out more nauplii.
A couple of days after the eggs have hatched the culture will start to go off due to the egg shells rotting in the water. When this happens you tip out the remaining culture onto the garden and wash the container and airstone/ airline and make them nice and clean. Then you can re-use the container to start a new culture.
You should start a new culture every day or every second day and use up all the nauplii within 48 hours of the eggs hatching because that is when they have the most nutritional value. You can feed surplus nauplii to adult guppies, dwarf gouramis, tetras, barbs, rainbowfish, virtually any fish less than 5 inches long will eat newly hatched brineshrimp.
DECAPSULATED BRINESHRIMP EGGS
You can get decapsulated brineshrimp eggs and these don’t rot in the water. Decapsulated eggs have had the shell removed and you can either hatch them out normally in salt water, or feed the eggs directly to the fish.
If you want to decapuslate your own brineshrimp eggs you can do it quite easily. You add some dry eggs to a bottle or container of fresh water, and add some bleach or granular chlorine. You swirl this solution around until the brown eggs go orange. The bleach dissolves the brown egg shell leaving behind the orange egg. At which point you gently pour the orange eggs into a fine mesh net and rinse under some tap water. After a few minutes rinsing you put them in a container of freshwater and add a double dose of dechlorinator and swirl around for a couple more minutes. Then one more rinse under the tap before adding the eggs to some salt water to hatch.
This takes a bit of practice and if you leave the eggs in bleach for too long you kill them. If you don't leave the eggs in the bleach for long enough you have white egg shells in the hatching container.
You can use different concentrations of bleach and find one that works for you. Stronger bleach solutions will dissolve the egg shell faster so you have to watch the eggs for the changing colour.
Microworms can be cultured in instant porridge. Get a small plastic container and spread a thin layer of oatmeal across the bottom. Add enough tap water to just cover the oatmeal and then put it in the microwave for a couple of minutes. After a minute in the microwave you remove the container and stir it up before putting it back in the microwave for another minute or so. Remove the oatmeal and mix it again before spreading it out in several small plastic containers (1-2 litre icecream containers work well for this). You have a 5-6mm (1/4 inch) layer of oatmeal on the bottom of each container and let it cool, this only takes a few minutes. Then you add a teaspoon of microworms (from a starter culture bought online or at pet shops) to each container of oatmeal and put the lid on it. Allow the culture to grow for a week and the worms will spread over the oatmeal and grow up the sides of the container. Use your finger to carefully wipe some of the worms off the side of the container and wiggle your finger about in the fry rearing tank. The worms are tiny and wash off in the water and the fry eat them.
You can add more than a teaspoon of worms to each culture if you have access to a lot of worms but a teaspoon is the minimum you want to add. Drip the worms around the porridge/ oatmeal so they cover more of it faster.
You can feed dry Baker's Yeast (available from any supermarket) to the worms to help give them a boost. Normally yeast is only added one time, a few days after a culture has been started. You can add yeast every few days but too much yeast can cause cultures to crash so I normally only add it one time or if a culture is doing well, I might add it once a week while the culture is doing well.
Have several cultures going and start new cultures each week. Keep cultures cool but not too cold, and avoid really hot weather. Normal room temperatures that suit people, are ideal for microworms.
If a culture does not have many worms, you sometimes get fungus growing over the oatmeal. You can take worms from this culture and use them to start a new culture before throwing the furry culture away. Wash the culture containers out in hot soapy water (dishwasher) between uses. Open the cultures up each day for a minute to let fresh air get into them. You do not need to have holes in the lid of the culture and insects will sometimes get into the cultures if you do have holes in the lid.
When cultures start to go off, the oatmeal worm mixtures starts to turn brown and then black and it smells unpleasant. Start new cultures before this happens and dispose of cultures that have gone black or dark brown.
EMERGENCY FRY FOOD
Some fry like labyrinth fry (Bettas & Gouramis) and Iriatherina werneri are very small when they first hatch and need green water or infusoria. If you can't get these you can hard boil an egg. Remove the shell and white part and dispose of these. Push the yellow yolk through a handkerchief into a small container of dechlorinated water. Put the lid on the container and shake it up, then use an eye dropper to suck some of the egg yolk solution out and put it in the tank with the babies. Do this 3-5 times per day for the first 2 weeks then start adding newly hatched brineshrimp.
Boil another egg each day and make a new solution each day. Keep the solution in the fridge when not using it. Take the solution out of the fridge and let it warm up to room temperature for 10 minutes or so before using it in the fry tank.
Do regular partial water changes on the fry tank or have a small air operated sponge filter in it to keep the water clean. The egg yolk can cause ammonia levels to go up and without water changes or a filter the fry will die from polluted water.
FEEDING THE FRY
When I set up a breeding tank I will put a small air operated sponge filter and an air stone in it. These are left in the tank throughout the entire breeding and rearing process. They help keep the water clean, highly oxygenated, and free of ammonia and nitrite. They also help keep the food moving through the water. The filter is run at normal flow while the adults are in the tank, however when they are removed from the tank, the flow rate is reduced and then the filter is only operated at a slow rate when the eggs first hatch, and is gradually increased as the fry grow and food size increases.
When the fish have spawned and the adults have been removed, you should lower the water level in the rearing tank if possible. Obviously make sure there is enough water to cover the heater and for the filter to work. But with a rearing tank that has newly hatched fry in, you should try to reduce the water level to about 4-6 inches. This means any food in the water (green water or infusoria) will be more confined and the fry don't have to swim as far to find the food. Each day when you add green water and infusoria, the water level will naturally rise and the tank will slowly fill up over a few weeks. If the water level gets too high you can carefully remove some of the water from the rearing tank so it is not too deep and so the fry and food stay closer together.
When feeding young fish, provide a sufficient amount of food so they can feed easily without having to expend too much energy doing so. Don't however, feed excessively so the fry end up competing for space and oxygen with the food. It takes a bit of practice to work out how much is enough but practice does make perfect. I generally feed the fry so they are all full, then add a bit more food so they can pick at it over the next few hours.
Another thing to do when feeding fish is continue feeding the current food for a week or two after any new food is offered. Make sure all the fry are eating the new food before discontinuing the old food. If you suddenly change from one food to another, a number of fish may not be ready or willing to accept it straight away and fatalities may occur. At the very least growth rates will be slowed by those not accepting the new food straight away.
Most fishes that scatter eggs in plants have small fry that need infusoria or green water for the first 1-2 weeks. After this time they can go onto newly hatched brineshrimp. Brineshrimp nauplii are attracted to light and will normally swim up to the surface if there is a light on the aquarium. The fish fry also live at the surface during the first month or so of life because this is where the plankton normally lives. The fish fry make up part of the plankton. So it is beneficial to have a low wattage light source above the rearing tank when feeding brineshrimp nauplii to young fry.
It is also a good idea to keep the water shallow (about 4-6 inches) when first offering brineshrimp nauplii. Again this puts the fry closer to the nauplii so the fry don't have to swim as far to get food.
You should continue feeding green water and or infusoria while you are offering brineshrimp nauplii. Baby fish grow at different rates and female fish usually have slightly smaller mouths than males. Some of the fry will be smaller than others and the smaller fry and female fry will not always be able to take the brineshrimp nauplii at the same time as the bigger fry or the male fry. By feeding green water/ infusoria and newly hatched brineshrimp together, the smaller fry can continue to get food (green water and infusoria) and the bigger fry will move onto the brineshrimp nauplii.
When fish fry eat newly hatched brineshrimp, their belly will be orange and is very noticeable. When ALL the fry have fat orange bellies from the brineshrimp nauplii, you can stop feeding green water and infusoria if you like.
After all the fry have been eating newly hatched brineshrimp for a week, you can increase the water level and start doing water changes. You can also add microworms, vinegar eels, rotifers and other small food.
Once the fry have grown a bit and are quite adept at taking daphnia and brine shrimp, more types of food can be offered. Normal foods offered to the adult fish can be used just make it available in a smaller size for the smaller fish.
Prepare any live foods well before you breed the fish. It takes several weeks to get green water and infusoria cultures started. With some foods, new cultures should be started every few days so there is always sufficient quantities available when it is needed. It is difficult to feed fish fry if you don't have any food ready for them. Commercially prepared fry foods come in handy under these circumstances. They can be waiting on the shelf ready to go and will give you time to get other foods ready.
KEEPING THE REARING TANK CLEAN
Adult as well as juvenile fish require water changes and a portion of the aquarium water should be replaced on a regular basis to keep their home clean. Initially when the fry are only a few weeks old you should start doing small 10% water changes each day or every few days. Once the fry are readily eating brineshrimp nauplii you can increase the size of the water changes to about 50% each day. If you have lots of fry in the tank you can do 75% water changes each day. Large regular water changes should continue until the fry have reached maturity, at which time you can reduce the number of water changes to a couple of times a week or whatever your normal water change schedule is.
Any water that is added to the fry tank (or any other live fish holding facility for that matter), should be free of chlorine or chloramine before it is added, and have the same PH, hardness and temperature. Gravel cleaning should be done every time a water change is done.
Baby fish produce a hormone to stop others around them growing. Regular water changes help prevent the accumulation of this chemical and other chemicals, (i.e. nitrate, phosphate, etc) and this allows all the fish to grow more rapidly and at a more even rate, helping to prevent big variations in overall fish size.
When you have large numbers of fish in a small container the fish end up suffering. If your adult fish were prolific and happened to provide you with many hundreds of young, they will need room to grow. When the fry have grown a bit you can start moving them into larger quarters. Have another tank set up with the same water parameters and transfer some of the fish into it. This allows for more room to move and a better growth rate.
Whilst you are moving fish around, check for deformities. Too many times I have been to pet shops and seen fish swimming around in the tanks. Some are perfect with nice fins and a good body shape and colour, while others are blind in one eye or only have one dorsal fin where there should be two. Others have bent or twisted bodies. None of these fish would survive in the wild and are of absolutely no use as future breeding stock. If you have a fish that doesn't look like it is supposed to because it is mutated or deformed, destroy it as nature would so only the best survive. Producing 10 high quality fish is much better than producing 100s of duds that should be fed off to the nearest Barramundi.
Putting poor quality fish on the market is only putting that species of fish in jeopardy and making it more likely to meet extinction. No one would buy them except to pity them and you will get a bad name as a fish supplier if you offer poor quality fish for sale.
Don't cross breed fish to make a new variety. As tempting as it may seem, fish are how they are, because that is what evolution has produced. They are the refinement of hundreds of thousands of years of trial and error, and are fine the way they are.
Finally, breed fish because you want to, not just for financial gain. Watch as the eggs develop and hatch. Then observe as each day the tiny semi transparent fry get bigger and start to develop colour. Gradually as they get bigger and older they mature and are then suitable to start the cycle of life all over again.