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Thinking about Coral (and Marine Invert) Sexual Reproduction & Breeding in Captive Systems
(in 3 "easy" steps... uh, maybe)

by Sara Mavinkurve

spawning Dendro, photo by T. Greene


Thinking about breeding? Maybe you are fascinated by "smoking" snails or maybe wild coral spawning videos make you blush. Or maybe you just want to advance the hobby for all of us. Whatever your reasons, thank you. The sad truth is that the reefs as we know them will be all but gone within the next 100 years. There will likely come a day when many species of reef animals are extinct everywhere but in our aquariums. And so there is a need, a responsibility even, for us reef aquarists to do everything we can to not only learn how to best care for these animals, but also to learn how to breed them in captivity. This may seem like a daunting task, but as the famous Chinese proverb goes "a journey of a thousand miles begins with a single step."

Step 1: Choose Your Candidate Well

Ideally, we should be thinking about how to breed any and all marine animals in captivity. However, if you choose an animal which has not yet been seen spawning in captivity, you will have little more to do than sit in front of your aquarium waiting for it to do so. Thus, it's best to start with an animal that is known to at least spawn in captivity (and ideally in your own aquarium).

You can further narrow down your choices based on how the animal reproduces...

Corals and Anemones:

Gender/Sex Assignment

If you thought human sexuality was complicated, you've probably never asked a coral about his/her/his-her/her-his/its sex life. When it comes to coral, even gender assignment is complicated. Some corals are "gonochoric" (having separate male and female colonies producing sperm and eggs respectively) while some are "hermaphroditic" (the same colony produces both eggs and sperm). To further complicate matters, some corals start off as male or female and then switch sexual roles after the release of sperm or eggs respectively. For the proper language: "Protandry" is when male turns to female and "protogyny" is when female turns to male.

Brooders vs. Broadcast Spawners

Corals are also either broadcast spawners or a brooders. Brooders are the easiest to try to raise because the egg and sperm meet inside the coral (internal fertilization). The coral then releases "planulae" (embryos) at spawning. Broadcast spawners release eggs and sperm separately (or in attached bundles) into the water to be externally fertilized. This can make them more challenging to breed since you will be the one who has to make sure the eggs and sperm get together. Just how challenging this is depends on how the eggs and sperm are released. Simultaneous hermaphrodites (releasing egg and sperm at the same time) can be good candidates to try and raise in captivity. Sequential hermaphrodites (the kinky gender switching corals) might be a little more difficult. The most difficult corals to attempt to breed in captivity are gonochoric, broadcast spawning corals. For these corals, you would have to have both a male and female colony and hope and pray that they spawn at the same time.

For a general overview of some corals of interest, please see here: Captive Closed System Coral Spawning Information

Errant Marine Invertebrates:

[Note: errant means "motile."] As with corals, there are similar characteristics to consider when choosing any other marine invertebrate to try to breed. There are additional concerns different kinds of invertebrates:


Crustaceans are gonochronic. The larger concern for these animals is the survivability of their larvae. Most marine ornamental crustacean larvae are very delicate and easily damaged and killed even in collection. Another challenge to crustacean larvae is that it's not always known what they eat. Some don't feed at all until after they "settle" (stop being larvae). Others have very particular feeding requirements. If you want to start out with an easier crustacean to breed, try one that has already been captive bred by a hobby aquarist (rather than only in labs).

Snails (Gastropoda and Polyplacophora)

Most (but not all) gastropods have separate male and female individuals. So you might be wondering "what about my smoking snails?" Well, not all gastropods mate. The popular Trochus sp. snails are broadcast spawners. For broadcast spawning snails, you will likely have to set up a species tank. You might also have to manually collect the gametes and aid in fertilization.


Most commonly, enchinoderms are gonochronic broadcast spawners. And this is the point where things start to sound redundant. The concerns here again are; the selection of both males and females (which are often visually identical), fertilization which may need aquarist assistance, and the survivability of the larvae.

Other Reef Critters

There are many marine animals which readily reproduce in aquariums without any assistance. Though interesting information to have, no one really needs to know much about bristle worms, hitch-hiker feather dusters, mini-bristle stars, hair or spaghetti worms, amphipods or other such populous critters in order to have them reproducing like rabbits in their tanks (except maybe that one should not run a UV sterilizer which can kill or damage swimming larvae). If you have such critters and don't know why they're not being fruitful, consider that your aquarium(s) are not providing an ideal environment for them (in terms of available food, habitat or general water parameters). Or, consider that you have a predator which may be feeding on the animals eggs and/or larvae.

For any overview of various reef invertebrates breeding and/or spawning in captivity, please see here:
Captive Sexual Reproduction of Errant Invertebrates

Summary of Step 1:

bis 1. This should be obvious, but make sure you choose an animal which you have experience caring for consistently and successfully.
1. Know if you animal is gonochronic or hermaphroditic
2. Know what is needed for egg fertilization (Does fertilization require your assistance in any way?)
3. Consider survivability of premature stages (such as planulae, larvae, fertillzed eggs, etc.)
4. How will the premature stages need your help? (Will they need special housing and/or feeding?)

Step 2: Tender Loving Care

No matter what your candidate animal, the next step is to provide the absolute best conditions for it/them to grow and be as healthy as possible. Even if spawning is something you will have to induce (as is often the case with urchins), the healthier and happier the animal, the healthier will be its gametes (eggs and sperm).


Creating ideal conditions may include obtaining the appropriate male to female ratio (if known). But more generally, it means pampering the animal as much as possible. Learn everything there is to learn about your animal. Don't stop at hobby focused publications. Search for academic articles and textbooks for even more information (if available). Attempt to recreate the animal's ideal habitat as best you can. Be sure to feed the animal WELL. This doesn't just mean feeding generously, but also feeding quality foods of the right nutrition, size and variety.

Protection from Predators:

Eggs, planulae, larvae and juveniles of many (if not most) marine animals are great snacks for other aquarium inhabitants. Fish love to eat shrimp and crustacean larvae. Many crustaceans love to eat snail eggs or juveniles. You will need to know how to protect your animal's eggs, larvae, planulae or juveniles from being eaten (either by other animals or even the parents themselves--depending on the type of animal).

Protection from Competition:

Usually, whether your animal is a coral or crab, you won't want your animal wasting stress and energy on competition with other animals. Your corals should be given plenty of space to grow and fully extend. Your errant invertebrates should not be housed with other animals which might compete for space and/or food.

Consider a "Species" Tank:

When it comes to getting animals to breed, there are a lot of advantages to using a species tank. This doesn't necessarily mean that your candidate animals are the only animals in the tank. It's more important that the animals are the only ones of their kind in the tank (i.e. the only coral or the only fish, crab, snail, etc.) Simply put, no interest of any other animal in the tank should be at odds with (or in competition with) the interests of your candidate animal. For instance, a Fungia species tank is still functionally a species tank even if you have a few harmless snails and/or worms in the same tank. In some cases, there may even be animals which do better in the company of another animal (clown fish and their host anemone being the most obvious example-- at least for the clown fish).

IMPORTANT NOTE: When some corals (and other animals) spawn in an aquarium, they can drastically change water chemistry (especially pH). This change in water chemistry (and/or possible toxicity of the spawn itself) can kill other animals in the tank. Again, this is just another reason to set up a species tank.

Step 3: Have a Plan

You're going to need to prepare for spawning, hatching and/or "birthing" events. Best case scenario you'll be able to predict when your animal is about to spawn or release larvae. More likely, you won't know until it's happening. Thus it's important to always be prepared. Always have extra sea water, extra tanks and containers, tubing, lights, pumps, etc. on hand for whatever situation might arise where you'll need them.

Gametes, Planulae, and/or Larvae Collection

For most animals, there will be some stage of the reproductive cycle which will require you to collect gametes, planulae and/or larvae, etc. Know how you will do this ahead of time. In the case of corals releasing planulae, you may want to build an appropriate container to put the coral in just before you think it will spawn (or as it starts spawning). In the case of crustacean larvae, you could build a larvae trap. If the larvae are particularly delicate, you will likely need a kreisel (or other specialized housing) ready to move the larvae into as soon as they are released. Whatever the plan is, be prepared in advance.

Note: Most animals spawn at night (many at a particular time- such as around midnight). Unless you have a trap or system set up to gather gametes/planulae/larvae in your absence, you might want to start staying up late around the days when you expect your animals to spawn.

Start Culturing Food Now

In many cases, larvae/juveniles will be a surprise. If they are feeding organisms, you will need to have rotifers or baby brine shrimp on hand to start feeding them right away. Even if you do know when you will need these cultured foods, it's wise to start culturing them well in advance.

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