Pajama Cardinal Fishes Are Breeding in My Saltwater Aquarium! How to Do This in Your Aquarium

Wow! This morning, as I performed my "check in" procedure on a 650-gallon saltwater coral reef aquarium, I was pleased to discover (and film) a male Pajama Cardinal fish carrying a brand new batch of eggs in its mouth. This phenomenon is referred to as mouth brooding, and fish that use this breeding strategy are referred to as mouth brooders.

Pajama Cardinal fish are a very hardy and easy fish for beginners to keep. And if you are consistent at maintaining a stress-free environment for them, you will likely end up with laying eggs (as long as you have a male / female pair).

But for some people, this experience is elusive or just occasional, which can be frustrating, especially if you want it to happen. So here I am going to give you a few points on how to make that happen.

For starters, the key is a low stress environment in your saltwater aquarium. I know this may sound vague, but pay attention here. So what makes a low stress environment?
– undetectable ammonia (less than 0.15 ppm)
– undetectable nitrite (less than 0.10 ppm)
– stable pH in the range of 8.1 – 8.4
– stable alkalinity in the range of 3.0 – 4.5 meq / l (150 – 225ppm)
– stable temperature in range of 77-81F (I usually aim for 78F)
– stable salinity in range of 32 – 35 ppt
– no noticeable aggression; this means fish can get away from one another and no one is forced to cower in a corner; problematic aggression that would prevent your Pajama Cardinals from breeding would be if you had too many in too small an an environment, or if another fish were picking on them and injuring them. The other potential source of aggression would be from other species of cardinal fish (compatibility).

Once you at least have achieved a low stress environment, including plenty of shelter and ideal water quality and all the parameters I listed above – once you have realized that – you will be able to turn breeding behavior on and off like a switch – with diet .

– (quantity) enough food: I know this sounds vague, but the rule of thumb here is that all other factors being stable and ideal – food will be your on / off switch for breeding. If you want to stop breeding, reduce feeding. If you want to turn on breeding behavior, increase feeding quantity. The ideal for consistent and robust breeding is two feedings per day (morning and evening). But you can go as low as one feeding per day. In this case you may want to feed a bid heavier (remember not to over feed – no unheaten food left in the tank after 5 minutes).

– (quality) varied diet w / abundance of high protein food; A varied and diverse diet is key here (quality of diet). We typically will feed, the following (Nori sea weed, spirulina flakes, New Life Spectrum pellets 1mm sinking, frozen mysis shrimp ( is my favorite), spirulina-enriched frozen adult brine shrimp (San Francisco Bay Brand). So you may be saying "that seems like a lot of different foods" …. and …. it works.

So maybe now you're saying, that's not so complicated after all. Remember, the simple key to focus on here is a stable, low-stress environment. After all, that's what people want too. Enjoy.