How do fish mate and how to breed fish in the aquarium

Every life form can only sustain its population by reproducing its kind and different organisms have developed various means of doing this. Fish mating is one phenomenon that had been extensively studied by a host of scientists, and this has broadened our knowledge about how fish bring forth their young ones. More so, aquarists/breeders may also take pleasure in watching different species of fish share intimacy within their group. But irrespective of variation in the process of mating, there is a common end-result – every organism has a means of passing on specific traits to the next generation to ensure continuity. So, today, in this article, we shall be taking a look at the process of reproduction in fish with the view of addressing the question: “how do fish mate “? Also, I shall be discussing how to breed fish in the aquarium.

How do fish mate?

Since all fishes are not the same, it is not expected that they will do things in a similar way. It is, however, worth mentioning that fishes possess specific reproductive organs which make it possible for them to make babies. Most male fishes have two evenly sized testes – which may be fused partially or totally – while female fishes have ovaries.

The genital papilla which plays a vital role in the release of sex cells (either sperm or egg cells as the case may be) is another crucial reproductive feature in fishes. For anyone interested in breeding fish; the genital papilla is the fleshy tube present behind the anus, and its shape is often used in distinguishing between male and female fish. The genital papilla of male fish is usually elongated and pointed while in the female, it is broad and oval.

Now to answer the question on how fish mate; it is essential to state that there are two categories of fishes with regards to the mating process – the Live-bearer and Egg-layer.

1. Live-bearing: In this type of mating, the male fish transmits sperm into the female with the aid of the anal fin – sometimes called ‘gonopodium‘ since it is adapted for insemination. The released sperm then (internally) fertilize the eggs stored in the oviduct of the female. This event leads to the birth of fully formed fry that are ready for life in the wild after a couple of weeks – like 3 – 4 weeks. Examples of fishes in this category include platy, swordtail, cichlid, guppy, goodeids, etc.

Interestingly, female fishes that have once undergone the mating process do not necessarily have to copulate again to give birth. Some of them have been known to reproduce every month – with the influence or presence of the male fish. Aquarists who take delight in breeding fish oft settle for live-bearers not only because of their breeding orientation but for the fact that they can survive a wide range of water conditions – they are less problematic to breed.

N.B: Another consideration to look at when discussing live-bearers has to do with the development of the embryo. In this respect; there are viviparous live-bearing fishes as well as ovoviviparous live-bearing ones. Let me take some time to explain these terms.

The viviparous live-bearers are such that have developed a placenta-like structure which attaches the embryo to the mother, and also functions as a medium through the embryo obtains its nourishment [from the mother]. Examples of viviparous live-bearers are guppies, swordtails, goodeids, etc.

On the other hand, the embryo is not attached to the mother in ovoviviparous fishes. Instead, the embryo is nourished by the yolk sac [while it is still in the mother-fish]. So, summarily, ovoviviparous fishes get their eggs fertilized internally; the eggs develop and hatch within the mother and the young ones (fry) are given birth to alive after a while.

2. Egg-laying: Egg-laying involves the process whereby the female fish lays eggs that are then fertilized by the sperm of the male fish. This fertilization occurs externally, and it is termed ‘oviparity‘ in the biological world. Different species of fish have different manners of laying eggs; for instance, fishes such as betta, croaking gourami and paradise fish are notable for building bubble nest wherein fertilized eggs are kept before getting hatched. The nests are usually positioned around hiding spots that are close to the substrate. The bubble nesters are renowned for their excellent parental instinct with the male fish tending to the fertilized eggs in most cases.  

On the flip side, we have the egg scatterers – this group litter the surrounding (aquatic) environment with their eggs. The eggs so laid, are eventually fertilized by the male fish which keeps following after the female while the egg-laying process lasts. Examples of egg scatterers include tetras, barbs, danios, etc. Despite the fact that the parents (i.e., egg scatterers) do not offer any form of protection to the young ones, they are also more likely to feast on their brood. For this reason, it is expedient that you put the parents in a separate tank once the eggs begin to hatch – or even before then. Furthermore, there are also egg buriers (e.g., killifish, etc.); mouthbrooders (e.g., cardinal fish, cichlids, etc.) and egg depositors (e.g., dwarf cichlids, rainbow fish, etc.) under the egg-laying category.

Besides the egg-layers and live-bearers, there are alsohermaphroditic fishes – they bear both the male and female sex organs [in one body]. Talking about hermaphroditic fishes; there are those that exhibit the quality right from the cradle and remain like that all through their life (e.g., sea bass, goby, etc.), and these can cross-fertilize to reproduce their young ones.

Again, there are fish species that undergo a phenomenon known as ‘sequential hermaphroditism‘. In this case, a fish given birth to with a particular gender orientation can turn into the opposite sex after a couple of years. The process whereby a female (hermaphroditic) fish changes into a male is called ‘protogyny‘ while the switching of a male fish into a female is termed ‘protandry‘.

Sometimes, the switch in sexual/gender orientation is as a result of prevailing circumstances. For example, in a scenario whereby a group of hermaphroditic fishes is suddenly deprived of the opposite sex – say, female – one of the remaining – take that to be a male fish – can become a female and is ready for mating to make babies. A very good example of this is the clownfish.

How to breed fish in the aquarium

Before I delve fully into the next item on the plate, there are few things you need to grasp beforehand. Firstly, when breeding fish, it is essential to take note of their size and age – these two factors are fundamental to the success of the breeding process. And, of course, you have to be able to distinguish between the male and female fish. Note that in order to prepare the fish for spawning, it is advisable that you feed them with a diet rich in protein. Making them robust [in a healthy manner] somewhat increases the success rate of breeding. You should feed them this way for 3 – 5 days, and also make sure that the male and female fish are not occupying the same tank.

Additionally, the sexual behavior and lifestyle of the fish should not be overlooked. It is not the same way you will be breed a danio, which lacks parental instinct that you would breed betta. For the former, it is evident that leaving the fry with the parent could spell doom for the young ones hence providing a separate should not be a second thought. Apart from this, male fish of certain species do not like the female being around them [or the freshly fertilized eggs] immediately after spawning is completed. On the whole, good knowledge of the lifestyle of the fish that you have chosen to breed will help you set up the breeding tank as appropriate.

Setting up the breeding tank

As the fish is away from its natural habitat and now dwelling in the aquarium you have made for it, you will have to provide it with the right (environmental) conditions. So, when setting up a breeding tank or preparing an aquarium for breeding, it is vital that you simulate the conditions feasible within the fish’s habitat during spawning season.

With the breeding tank in place, the next port of call is to equip it with items such as plants, caves, rocks and so on. By the way, a 37.5l tank with a good lid will make a perfect breeding tank for fish. A substrate of sand or gravel – or a mix of both – is also essential. One thing you should keep in mind is that ‘it’s different strokes for different folks‘; while some fishes may desire a soft substrate for mating, others prefer hard surfaces like a rock. But you should forget that coarse stones can be injurious to the eggs and fry so, it would be logical to avoid putting such (stones) in the breeding tank.

Furthermore, you should integrate a 75 gallon aquarium filter into the tank to generate the right current for raising the offspring – the sponge filter is the most widely used in this respect. You may read a detailed sunsun canister filter review to get detailed performance and specifications of the canister filter.

Still on tank set-up; do keep in mind that the breeding tank should be in an area with dim or low light – or a shaded part of the room. Likewise, the lighting of the tank should be lowered or put out completely as bright light may disrupt the breeding process.

Conditioning the water

To begin with, that you have to vary the water parameters does not mean you should suddenly introduce the breeding stock into unfamiliar terrain. The change should follow a gradual routine to allow the fish time to acclimatize to the new water condition. Hence, the water hardness, temperature, and pH should be maintained at the normal range at the very instant the fish is put into the breeding tank. Then, you can start increasing the temperature as time goes by. This is why you should incorporate a temperature-regulating device into the aquarium. Plus, a pH – and water hardness – device(s) should not be left out.

You may have to look out for the appropriate temperature for breeding the specific aquarium fish in your care. However, temperature rise of 50C and pH value of 6.0 – 7.0 are usually ideal for breeding most aquarium fish species. These conditions will help preserve the sperm of the male fish, and also, ensure optimum egg production by the female fish. Additionally, in some cases, the water level in the tank is dropped in anticipation of spawning. Notwithstanding, it will be of great benefit to know the level/layer of water that your pet loves to mate at.

Dissolved oxygen should not be lacking in the tank – so, you will have to watch out for that. In the same vein, the level of nitrogen and ammonia should be put in check as both compounds are detrimental to the health of the fish especially, the fry at this point.


Irrespective of the behavioral pattern of any species of aquarium fish, it’s best that you separate the parent stock from the fry. The reason is simple: it will avail the young ones the space to live out their lives and compete evenly without any intimidation. Again, they will be saved from the danger of being eaten by relatively bigger fishes. That said, you should not forget to return the temperature to the normal range [fitting for your fish species] once spawning is over, and also provide the fry with the right kind of feeds for their growth and development.

In wrapping this article up; I cannot overemphasize the need for you to do extensive research on the fish species you intend to breed. This will save you some stress and put you in charge of the situation. You can yet seek the advice of an expert in the field of fisheries with particular attention on breeding. One last piece of advice: seeing the brood swim about in the aquarium could be thrilling; however, the number of fry within the group may be more than you can handle so, it will not be a bad idea to make some money selling some (of them) off. 

Matt Hook

Matt hook has been a passionate aquarist since he was 5 and now he is professional aquarist. Through this blog he plans share his knowledge to beginners. Feel free to contact him if you have any queries.