All living things reproduce; this is an essential part of survival for each species to ensure they do not become extinct. Freshwater and saltwater fish are no exception.

The “Do Nothing” Approach

The easiest approach is to “do nothing” and let nature take its course. Your fish will do all the work. They will date, mate and have children all on their own. The first part of fish courtship is not too different from the mammal world where the males chase the females, except this activity happens in water and usually in the morning. After several hours of chasing, it’s time for romance. At this point, things are a bit different. The female releases her eggs, and the male fish immediately fertilizes them by spraying them with milt. Milt is the seminal fluid of fish and other water-dwelling animals who reproduce by spraying this fluid, which contains the sperm, onto roe (fish eggs).”

That’s it for the parents. The eggs are “sticky” and those fortunate enough to stick to submerged plants such as Hornwort, Cabomba, and Anacharis have the possibility of developing and hatching in 3-7 days. The parents and any other fish and many types of aquatic insects will still consume as many eggs as they can find. Eggs which sink to the bottom of the pond will not hatch. They will be consumed or succumb to a fungus as the pond debris settles on them.

This “do nothing” approach may seem heartless but it is how Mother Nature has been operating for millennia, only the luckiest, toughest and strongest eggs survive to hatch. Furthermore, a mature female goldfish lays anywhere from 500 to 1,000 eggs. If every egg survived, the limited space of most backyard fish ponds could not sustain the population. In short time, the entire ecosystem of the pond would “crash” and all the fish, including the parents, would die.

You can increase your chances of baby fish survival in the “do nothing” approach by doing a “little something” and that is to have plenty of submerged grasses in your pond. As described above, those eggs that were able to stick to the grasses have a better chance of hatching and surviving predation.

The “Do Something” Approach

The second approach to fish breeding in a water garden, involves a bit more effort on your part, this is the 'do something' approach that we are going to talk about below.

Breeding fish in a home aquarium isn’t as easy as simply sticking a male and female of the same species together and hoping for the best—it requires careful preparation and monitoring. After you’ve researched the specific mating habits and preferred living conditions of the species you’re trying to propagate, your first step will be to select a healthy parent candidate of each sex. You’ll then need to carefully engineer key tank conditions like water temperature, pH level, lighting, and surrounding flora to make them more favorable for mating. These environmental changes help “set the mood” for the parent fish and ensure a successful coupling.

Much like many other animals, most fish require both a male and a female to create new life; however some fish are asexual and can reproduce alone.
For fish to reproduce, sperm and an egg must be combined to create new life. Whilst there are a few different ways in which this can occur, one common factor is the reproductive organs involved; the ovaries and the testes.

The vast majority of fish are dioecious (the sexes are separated), females have ovaries and males have testes. There are a few species which contain both sets of organs (hermaphrodites); we’ll discuss this later in the article. Some species also have secondary organs known as genital papilla. This is a small fleshy tube found at the back of the anus from which sperm is released.

Similarly to insects, birds and reptiles, in oviparous fish, the embryo develops inside the egg, but outsideof the parent’s body. Over 90 percent of bony fish are oviparous reproducers.

This method of breeding requires the female to lay eggs, which will then be fertilized by the male.

Most females can lay large amounts of eggs at one time, because it takes much less energy than growing an embryo in an egg inside her body. The number of eggs a female is able to produce during a spawning season is called the ‘fecundity’. The fecundity of a fish is closely related to the weight and length of the fish.

As an example, the Mola (Ocean Sunfish) releases around 300 million eggs in a spawning season whereas the Silver Arowana only lay around 50-250 eggs per season.

The fertilization can be done in a number of different ways; either by the male rubbing his sexual organs on the eggs, releasing sperm, or releasing sperm into the water to join the eggs in the zooplankton layer (if the eggs have been laid in that way).

Egg-layers fall into one of these categories:

– Mouthbrooders:Eggs are laid in water then collected in the mouth once fertilized. (Bettas, Cardinal fish, Blennies, Gobbies & freshwater Cichlids).
– Nest Builders:Made from plant materials or a bubble nest, usually built by the male and the female then deposits her eggs there and the male fertilizes them. (Bettas, Gouramis, Bluegills & Stickle-backs).
– Egg Scatterers:Sticky eggs are laid in an area usually under cover; non-sticky eggs are laid in open water. The male then fertilizes the eggs by swimming through and spraying semen in the area. (Cardinal tetras, Zebra Danios, Tiger Bards, Koi & Goldfish).
– Egg Depositors:Eggs are laid in one spot, the male then swims past and fertilizes them. (Killifish, Dwarf Cichlids, Clownfish & Rainbowfish).
– Egg Buriers:Eggs are buried in the substrate and the male then dives into the substrate to fertilize the eggs. (Killifish).

In an aquarium or pond, successful breeding largely depends on nutrition and environmental conditions that are sometimes very specific. In the wild, these conditions might be seasonal changes, water conditions, the amount of daylight, and the availability of specific food sources. The amount of daylight is generally less important in tropical species because hours of sunlight in tropical regions near the equator stay fairly constant year round. Temperate-water and cold-water fish, such as goldfish and koi, may be more affected by shorter and longer days of the seasons farther north or south. Certain conditions often trigger a particular species to breed. For instance, during the wet season in the tropics, rains may wash extra nutrients into the swollen rivers, leading to a greater abundance of available food and plants, which can be ideal breeding conditions for fish.

In aquarium and pond fish, healthy breeding stock must be of spawning age. You will need to research the nutritional and environmental needs of the particular species you want to breed. These conditions are almost as varied as the number of fish species (see Table: Types of Fish Reproduction). Proper substrate, cover, temperature, pH, live foods, lighting, and number of fish are all likely considerations.

Sexing Fish

Determining the sex of a fish can be difficult or easy, depending on whether physical differences are visible. Males of some species may be larger and showier than females. Information on how to sex a particular species may be obtained from your veterinarian, books, hobby magazines, the Internet, and other sources.
Live Bearers

Fish reproduce by bearing live young or by laying eggs. Livebearers give birth to fully formed and functional young called fry. The eggs are fertilized and hatch within the female. Most livebearers have fewer and larger fry than egg layers because the fry need to be more developed and large enough to fend for themselves after birth. Most species of livebearers kept in home aquariums are generally easy to breed. Identifying sexes is usually easy as well. Males are generally larger and have larger, longer, more ornate, and more colorful fins than females. For instance, only male swordtails have the “sword” on their tails, and male guppies have larger, more flowing tails that are brightly colored.

Fry should be separated from adults because the adults (including the parents) tend to eat them. Small live or frozen food and crushed flakes are good for feeding fry. Species of freshwater livebearers include mollies, platys, swordtails, and guppies from the Americas and the 20 or so halfbeak species from Asia.
Egg Layers

Egg layers spawn by several means, including egg scattering, egg depositing, egg burying, nest building, and mouthbrooding. In all cases, eggs are laid and fertilized outside the body. Nest-builders and mouthbrooders are generally good parents, protecting the eggs and fry from aggressors. Many cichlid species, such as freshwater angelfish, are nest-builders.

Egg scatterers, egg depositors, and egg buriers may or may not defend the eggs and fry. Usually the fry need to be separated from the adults to prevent the larger fish from eating them. Egg-scatterer females lay sticky eggs in various places within a certain area (often in areas that provide some sort of cover), while others set nonsticky eggs adrift in open water. Egg depositors pick one general spot to lay sticky eggs, usually on the bottom substrate and sometimes on the aquarium glass. In salt water, clownfish are depositors, guard their eggs and fry, and are the most likely species to be bred by hobbyists. Egg buriers either dive into soft substrate or the male pushes the female into the soft substrate to lay. The male then dives in to fertilize the eggs. In a tank breeding environment, peat moss is often a good choice for the substrate.
Care for Newborns

Usually fry should be separated from the adult fish and placed in a nursery environment. Mouthbrooders will eventually expel the fry even when the fry are still quite vulnerable. Removing fry from outdoor ponds can be difficult. Ideally, a separate, smaller aquarium should be set up to receive them. Conditions should generally be kept much as they are in the main aquarium or pond. There should be some kind of cover for the fry so they are safe, secure, and free from stress. The aquarium should be filtered, but the pump should not be so powerful that it sucks in the fry. Several commercial baby fish foods are available. Alternatively, finely crushed flake and tiny live or frozen foods can be fed.

Another option is to purchase a nursery. Nurseries are made of a box frame with a fine mesh netting for the walls and floor, or plastic grids for the same purpose. They are usually built to hang from the top lip of the aquarium into the water. The mesh or grid prevents the fry from escaping while keeping them safe from the larger fish. The open top allows access for feeding and other purposes.

UNISEX FISH

Some species of fish reproduce by themselves. These fish are females, and so are the young they give birth to. It’s debatable whether this can actually be called ‘mating’ but it is certainly a way to reproduce. The females may mate with males, but the sperm is not used for reproduction.

Hermaphrodites possess both male and female reproductive organs. Typically fish are born one sex and at a later age will switch to the opposite gender.

A female switching to a male is called a protogynous hermaphrodite; males switching to females are classified as protandrous hermaphrodites. Both of these types of reproducers still need a fish of the opposite sex to reproduce.

A clownfish is a great example of a hermaphrodite. A group of clownfish will include one large male, and one large female, the rest of the group are small males. Once the female leaves the group, her partner will turn into a female and the next largest fish will become the new partner.

A small amount of species, fall into the classification of synchronous hermaphroditism, which means they can produce eggs and sperm at the same time, for example the Mangrove Killifish.

ALSO NOTE THAT:

● For most species, it is imperative that the water be in very good condition. The water parameters may also matter as some species refuse to mate except if the pH, temperature, and other parameters are within certain values. Other species could care less and will mate in mud (not really, but you get the point). Research your fish to see if they are picky or not. If they are picky, try your best to offer them the water parameters they like. Even if the fish you are trying to breed are not especially picky, you should still make sure that the water condition in your breeding tank is as high as possible.

● Some fish also require a certain kind of environment. For example, some like to mate and lay eggs in caves while others prefer flat rocks or planted areas. If you do not have any caves in your aquarium, they may be less likely to mate. Some cichlids like to mate on flat rocks so you should provide them with one or two. Others like to mate in high current areas while some species require very still water. Do your research before mating your fish to make sure that you have created the proper breeding environment.

● Some fish can be induced to mate by performing a water change. When you take out the water, allow it to remain low for a little while. Then refill it with slightly cooler water (2-3 degrees F). This drop in temperature simulates a rain and causes some species to mate like crazy – this is especially true with some Amazon River species. Some other species may mate when you raise the water temperature slightly. There are numerous spawning triggers, so research effective ones for your specific species.

● Some species require that you find a particular mating pair. In these instances, it is best to buy from a breeder who is selling them as mating pairs or observe fish at a fish store to find ones that seem to be swimming together constantly. If you cannot purchase a mating pair you can try purchasing a group of juveniles and raise them together, waiting for them to pair off naturally.

● The diet you offer your fish before breeding them is also very important. Feeding your fish a high-quality diet to prepare them for breeding is referred to as “conditioning”. The types of food you offer will vary depending on the type of fish, but generally you should feed a variety of rich foods like live and frozen foods. Live brine shrimp are an excellent option because they are high in protein but are also very easy to raise. Some fish will also appreciate fresh vegetables – especially herbivorous species. Just be sure to do your homework so you know what kind of food the specific species you have prefers. You should plan to condition your fish for at least two weeks before trying to breed them to make sure they are in good health and condition.

One of the major problems with fish breeding is that the fry (newly hatched fish) are often consumed by either the parents or other tank mates. You should research your specific species to see if they will eat their own. If they will not and you have a species tank (meaning that only one species of fish is kept in the tank) then the babies should be fine. If the parents are likely to eat their young, or if you have other species in the tank, you should attempt to either remove the eggs once they are laid, remove the mother if she is either a mouth-brooder or live bearer (more on what this means later), or remove the fry after they are born.

You do not have to remove the fry from the breeding tank or remove other fish from the tank. However, to give the babies a chance to survive from predators, you should provide them with enough cover that they can hide until they grow big enough to handle themselves. In a live-bearer situation, this might include having a great deal of plants floating at the surface of your aquarium. For fish such as African cichlids, this may include a great deal of rock work. Research the specific species you are trying to breed to determine what kind of cover is best.

Another option to protect your fry if you do not have an extra tank for them is to use a tank divider. Tank dividers usually consist of clear plastic with small holes in it that allows the water to flow through the divider. If you use a tank divider you won’t have to worry about buying a separate filter or heater and you can keep your fry in the same tank. The downside of tank dividers is that the holes may be large enough that newly hatched fry can swim through them, putting them at risk for being eaten. You can remedy this by covering the tank divider in fine mesh until the fry have grown larger than the holes.

WHAT TO FEED THE FRY

When the fry first hatch out of their eggs they will still have part of their yolk sac attached. If you see your fry free swimming, but still having a yolk sack, make sure you do not feed them until they have fully absorbed their yolk sacks. Once these sacks are absorbed, it is important to feed the fry an adequate and nutritious diet. New fry typically feed off of live brine shrimp or crushed up flakes (finely crushed). To feed crushed up flakes, just put some flakes in a plastic bag and crush them into very fine pieces.

To hatch your own brine shrimp, add 1 teaspoon of BBS eggs to a mason jar of water. Let this sit for one hour and then add 1 tablespoon of aquarium salt. Put a small bubbler in it and place it under a desk lamp for 24 hours – you will have tons of baby brine shrimp after this time period.

Some fry cannot eat brine shrimp and crushed flakes because their mouths are so small in the beginning. Therefore, things like infusoria (a general term for microscopic or near-microscopic aquatic life) need to be fed. An easy way to make infusoria is to crush green vegetables (like lettuce, for example) and add them to water. Let the water sit until it becomes green (1-2 days) and then you have your infusoria. You can feed the fry with an eye dropper or baster.

CONCLUSION

Breeding fish and raising fry can be some of the most fun an aquarist can have. It truly is fascinating to watch each species with their individual rituals and methods. If you have never tried to get your fish to breed, I highly recommend it.

As a side note, you may be wondering what to do with all the fry. Some people sell theirs (just don’t expect to become rich off of it). Also, most local fish stores will either give you cash or store credit for your fry, but most will only accept them after they have reached a certain size. Also, the more exotic the species, the more likely you are to get a fish store that wants them (in other words, you are more likely to get credit for some cichlid fry than some danio fry).