Red Planaria Pest and Predators!

Today's binomial tongue twister is Convolutriloba retrogemma. To most of you, these words might as well be a magical incantation. If you do know this name, you've likely already done some research on Red Planaria, and will see these words as more of an unforgivable curse. Red Planaria also frequently get called Red Bugs, Rust Bugs, Flatworms and a few other names we can't mention because this is a family friendly column and expletives are involved.

So, what is Convolutriloba retrogemma? They're a super common acoel, which are a group of soft bodied, unsegmented worms that stay very small (less than 15mm) and live in all the world's oceans. Which means that sooner or later, they find their way into home aquariums. In the wild, they rarely cause much of an issue because there is an incomprehensible amount of space and predators. In the home aquarium, they can range from just being a nuisance, to being a quite serious problem. They can reproduce asexually, so you only need to get one into an aquarium for them to multiply, which they can do with alarming speed. They are omnivorous and will eat a lot of different things from detritus to copepods and rotifers (which you want for feeding your fish and other inverts). They're often reported eating corals, but more often than not, they are just irritating the corals to death in your tank. The biggest problem with Red Bugs is that they release a toxin when they die and if enough die at once, this can actually kill the other inhabitants of your display. No amount of wand waving will save your aquarium from this menace.

Now that we've established that you probably don't want them in your tank, the next question is how does one get rid of them? There are chemical solutions to this problem, like Flatworm Exit, but the issue with these solutions is that they cause a mass die-off of the bugs which we've already pointed out is bad. The other way is our preferred way, and that is to add a flatworm predator to your display, and there are several options for this. Some are more effective / famous than others, and there is some variability from fish to fish, even within a species.

One of the most effective and famous Red Planaria eaters are the Dragonettes. Some sources will tell you that only the Spotted Mandarin (often called Target Dragonet) will do this job, but in our experience, all of them will. These fish are also arguably the most beautiful of the Red Planaria predators. They stay small and are suitable for very small tanks (down to 20 gallons). They'll spend their whole day flitting around the bottom of the tanks and the rockwork, looking for something to eat, and if you have Red Worms, they are on the menu. Dragonettes are often kept with systems that have bustling refugiums to keep a constant supply of live food coming. They can sometimes be difficult to get started eating frozen foods in captivity, but they almost always love a Red Bug, and can be taught to take things like TMC Gamma Brine Plus as well as Rotifers and Copepods when the Planaria run out.

Red planaria only get to about two millimeters, so generally need small predators to notice them. One of the most effective of these predators doesn't often get the credit it deserves, but Springer's Damsel and Melanesian Blue Damsel are actually very effective at this job. The rest of the Chrysiptera will also eat Red Worms, but Chrysiptera springeri and Chrysiptera cymatilis seems the most effective for some reason. In addition to being beautiful, these fish are incredibly hardy and easy to feed / care for. They are noted for being one of the more peaceful of the Damselfish, but we still recommend keeping them with other boisterous tankmates. They stay pretty small (less than two inches long at maturity), and you don't need a tank bigger than 30 gallons or so to have one.

Likely the most famous Red Worm eater is the Sixline Wrasse (Pseudocheilinops hexataenia). These are voracious predators of pretty much any invertebrate small enough to fit in their mouths, and they are good for controlling just about any nuisance invert your tank might have, including Red Planaria. They are gorgeous, and interesting, swimming around like little spaceships; it seems completely effortless as they glide among your corals and rocks, hunting down new snacks. They are generally secretive and peaceful fish but can become territorial once acclimated to the home aquarium, and we suggest adding them later on in your tank's progression. They're easy to feed and reef safe. They'll appreciate plenty of rockwork to zip through and need a tank of about 55 gallons or more. Their max size is listed at four inches in most literature, but that would be an absolutely huge specimen; they'll reach maturity closer to two and a half inches. They are absolutely the fan favorite here for this job, and others. Oh yeah, did we mention, they are also stunningly beautiful? Almost every aquarist here has one in their tanks.

Less frequently, aquarists will use Halichorees and smaller (juvenile) Coris Wrasses to do this job. These options are more hit or miss; all these fish are great aquarium fish, but may or may not eat Red Planaria, seemingly based on individual fish preferences. If you want to go this route, we'd suggest sticking to Halichores genus wrasses and the most commonly utilized is the Yellow Chrysus Wrasse, which for years was inaccurately called the Yellow Coris. It's actually the Halichoeres chrysus. This is another beautiful fish that stays relatively small and is easy to care for. The largest one on record was five inches long, but they're much more likely to top out around four inches long or so. Yellow Chrysus will need a tank that's at least 55 gallons, and more would be better. They'll also need a soft sand bed at least an inch deep, which is where they will sleep and hide when startled. Most Halichoeres will do this job to some extent, but the most common options that have been known to eat Red Worms (and other pests) are the Green Wrasse (Halichores chloropterus) and the Melanurus Wrasse (Halichores melanurus). Both get to a similar size and have identical care requirements. Another benefit of wrasses from this family is their peaceful nature and they're usually very easy to get to eat pellet and frozen foods.

Red Planaria can be a problem, and the best way to not have the problem in the first place is to quarantine and perhaps dip all your corals. If you end up with Planaria problems, don't wait, they are much easier to control with fish if you add those fish early in the problem. There is also a nudibranch solution to Red Planaria plagues, known as Blue Velvet Nudibranchs (Chelidonura varians). These are very effective but only eat Red Bugs and so if you get one, you may need to remove it later once they eat all the Planaria. If you start seeing tiny little red spots on your rocks, glass and coral, remove as many as you can with your next water change, and then ask your LFS about adding a fish for biological control and you should get nip that problem in the bud! Tell them Quality Marine sent you!