Home | Aquarium Livestock | Spawning Fish and Fish Eggs in the Aquarium – A Guide for Beginners

Spawning Fish and Fish Eggs in the Aquarium – A Guide for Beginners

Bettas Spawning under bubble nestWhat could be more exciting for an aquarist than seeing a pair of fish spawn or finding a mass of eggs in the tank? Many beginner aquarists may not realize that their fish have formed a pair, what the fish are doing if they show a courtship ritual or that they are preparing an area to lay thier eggs. When eggs or babies appear, someone new the game may have lots of questions and concerns about what (if anything) they need to do for a successful hatch or to raise the fry.

Chances are you’re doing something right if you have a pair of fish that are prepared to spawn in the tank. Typically conditions must be favorable (clean water, ideal spawning chemistry, ect.) for the fish to be interested in breeding to begin with. If you’ve reached this point you’ll want to know what happens next.

Fish in Love

Taking a short step back, let’s look at how you got to this point. You may have purposfully purchased a male and female in hopes that they would pair up to mate, or you may have gotten lucky when the fish bagger netted you the specified number you asked for, ending up with at least one pair. Some species of fish show sexual dimorphism, when mature males and females display different colors, fin-types, size or body shape. This is common in Malawi Cichlids, Killifish, livebearers and some other groups. More often fish are sexually isomorphic, meaning males and females are virtually impossible to tell apart visually. Some may show minute differences, but only a well-trained eye may be able to spot them. Once the fish were placed in your tank and made themselves at home, you may have noticed that two fish seemed particulary friendly, swimming together or camping out in a favorite area of the tank.  You may have also noticed one fish swimming around the other, shaking or performing some other little dance for the other that was noticeably different from typical swimming and hovering…this was probably the male fish courting the female, enticing her to spawn with him. Some fish change in color or shape when they are ready to spawn. Another indication may have been one or both of the fish creating a nest in the substrate by moving gravel or sand or otherwise grooming an area in anticipation of egg arrival. Regardless if you noticed any of these things or not, the time has arrived!

Breeding Strategies

Male and Female gouramies showing sexual dimorphismFish employ several strategies in spawning, so what to look for will depend on the type of fish you have.  Most are egg-layers; the male fertilizes the eggs externally. The eggs may be scattered, deposited or buried, depending on the species. Scattered eggs either fall to the substrate, float to the surface or stick to plants, rock or whatever else they come in contact with. The eggs hatch quickly and the fry are on their own to survive. Egg depositors lay their eggs on a surface for fertilization (glass, wood, rock, plants, ect). Some of these fish tend their eggs and fry, some don’t. They may keep the clutch in the open or some fish prefer to keep their eggs and fry in caves or crevices so they only have to defend the opening of the brooding area. These eggs are often defended and tended by both parents and hatch after a few days. The parents often continue to protect the fry for some time after they emerge.  Depositors such as some catfish and killifish lay the eggs and then leave, not tending the eggs or fry. Species that bury thier eggs are usually from areas where drought is common. The eggs are deposited and buried so they are protected when the area is dry. The eggs remain covered until it rains and conditions become favorable again for a successful hatch.

Mouth-brooding is a specialized method whereas the eggs or fry are sucked up and carried in the female’s mouth for several days or weeks. Many African Cichlids are mouth-brooders. Females lay the eggs then suck them into their mouth (these eggs are also fertilized in the mouth) or wait for the eggs to hatch in a pit where they take in the new fry to protect them. As the fry grow, you can observe their tiny bodies in the mother’s mouth when she opens it! The fry are released when they are ready to swim off on their own.

Other common aquarium fish create specialized nests where they can easily tend their fry. Bettas, for example create elaborate clusters of bubbles where they deposit their eggs. Other fish have skipped the egg-laying step and produce live young. These include guppies, mollies and swordtails!

Egg Issues

Once eggs are laid, there is a crucial window of time that can determine a successful hatch. There are several things that can happen that will prevent new arrivals. First of all, some fish eat their eggs. Whether attented or not eggs are a tasty snack, so other fish in the tank will try their best to snatch what they can. Factor in an inexperienced parent fish that hasn’t learned not to cannibalize the eggs or how to protect them effectively, and initial spawns may have a 100 percent mortality. 

Have your eggs turned white or opaque? Chances are these eggs were “blank” or infertile. It’s normal for at least some of the eggs to be infertile, though the fertile rate should increase as the fish continue to spawn. If the number of fertile eggs does not improve, several things can be considered for adjustment to help. Obviously, check the water quality first to rule out any issues there. Be sure the water isn’t too hard, as this Clownfish Embryosmay cause issues as the eggs develop, particularly in Amazon and other soft-water species. Adjust water flow away from the area where the pair is hanging out, too much flow can wash away the sperm, resulting in low fertility rate. It is also possible that the male itself is infertile or too closely related to the female. It may be time to find a new mate for your female if several clutches fail.

Eggs are also prone to bacterial and fungal infections. Pristine water quality can be the first defense against such infections, but they can still occur. The eggs will turn white or become blanketed in whitish or grey mold-like material. In the early stages you may be able to treat the eggs with a mild methylene blue treatment, but handling of the eggs can damage or perpetuate the problem.

Eventually you and your fish will probably have a successful hatch! 

Next time, I’ll talk about raising the brood.



Clownfish embryos image referenced from wikipedia and originally posted by Silke Baron
Spawning Bettas image referenced from wikipedia and originally posted by ZooFari


  1. avatar

    Very useful.thankyou.

  2. avatar

    I have a mix of fish in my tank, we recently bought two new ones. Now there are eggs at scatt red at the top of the tank. The eggs are transparent with small white fish body like things in them. Are they fertilized eggs or not?

  3. avatar

    Hi Serena, It is difficult to say without seeing them or having more information about your tank. What types of fish do you have? Do you have both males and females? Most fish wouldn’t scatter eggs at the top of the tank. If you are able to get photos of the “eggs” that you are seeing, you can email us with more info about your tank at fish@thatpetplace.com and one of our Fish Room staff members will get back to you.

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