The nassarius snail, N. vibex, is a small member of the mollusk phylum and is a fairly common addition to the saltwater aquarium as part of the cleanup crew. They are amusing to watch. By day, they bury themselves in the sand, with just a tiny periscope-like piece of flesh left sticking out of the tank.
When you feed your fish, you’ll think you rang a dinner bell, because these snails will come crawling out from the sand bed like zombies from the night of the living dead. But are they really an essential part of the reef cleanup crew? That appears to be where the controversy about this snail resides.
If you plan to keep them in your tank, you should have a deep sand bed. These critters aren’t really appropriate for a bare bottom reef tank. Nassarius snails (or pretty much any small snail, for that matter), are not compatible with hermit crabs, because those arthropods may prey on the mollusks, turning them into escargot and turning their shells into a mobile home.
If you’re like me, I think of snails as being useful to keep the problem algae population of my tank down. But that’s not the case with the nassarius snail. These snails don’t eat algae they eat carrion, which is a fancy word for dead fish and detritus/fish waste. That’s right, not only do they crawl out of the substrate like a zombie, but it also has a craving for flesh, not algae. To that point, they may be somewhat useful in cleaning up uneaten meaty foods left in the aquarium, like Mysid shrimp or brine shrimp.
Do Nassarius snails eat other snails?
No, they are scavenging, carnivorous mollusks that eat dead carcasses, not other living snails, with a single major exception. If the snail in question is already dead, then, yes. But these gentle creatures are not generally predatory.
Will Nassarius snails eat diatoms?
No, Nassarius snails are kind of like tiny, underwater vultures…with shells…ok that was a stretch. They will not eat diatoms. They are carnivorous scavengers. If you are looking for a snail that will eat diatoms, check out Nerite or Trochus snails. Because they stir up the sand bed, they may indirectly make it more difficult for diatoms to grow on the sandbed. The Lawnmower blenny and Kole tang are also known to eat diatoms.
Their presence in a saltwater aquarium does likely provide two indirect pressures on diatom or other algae growth in the reef tank.
- Their constant motion, burying themselves in the sand and coming back out, and searching for food does churn up the surfaces of the substrate, likely keeping things a bit cleaner due to mechanical disruption of the substrate the diatoms would otherwise be trying to grow on.
- The removal of detritus and waste that would otherwise contribute to the pollution in the tank that would potentially fuel diatom or problem algae growth likely removes a factor that would otherwise contribute to algal growth.
How big do Nassarius snails get?
Nassarius snails are small and grow only to about a half-inch in size when fully-grown.
No, Nassarius snails are not poisonous.
Are Nassarius snails nocturnal?
Nassarius snails are generally much more active at night, although they will emerge from the sand when they smell food.
Nassarius snails burrow into a substrate when they are not active, so you should have some sort of soft substrates like sand or mud.
Do they breed in captivity?
Aquarium owners report and post that a happy group of snails has laid eggs in their tanks (on the aquarium glass, for example), but this is a very difficult species to raise in captivity. The most likely result is that they’ve created a natural zooplankton bloom in your tank, feeding some of the other invertebrates (or fish). The eggs generally hatch after a few days (~3-5).
Are nassarius snails useful?
That depends on what clean-up-crew role you need help with. Nassarius snails are not that useful in getting rid of problem algae, but if dead fish carcasses or too much meaty food, rotting in your tank are your problem…then, yes, they are useful. They are also very useful in stirring up the sandbed, keeping oxygen levels high in the substrate.
In all seriousness, the nassarius snail can be a bit helpful. The fact that these cleanup critters zoom out from the sand bed at the first sign of feeding your tank is a signal to me that they will and do eat excess (I assume meaty) foods.
The challenge with keeping them in your tank is that they may help clean up excess meaty foods, but if you don’t have a lot of excess food (probably a good thing) they may starve.
Yes, they are quite adept at righting themselves if they fall over. They do this by changing their center of gravity by stretching as far as they can out of the opening in their shell.
Are they part of my cleanup crew?
In the past, I have added them to my tank, but I do not have them in my tank currently.
Best aquarium conditions
These mollusks do best in a tank with the usual, stable aquarium water parameters:
Temperature: High 70s Fahrenheit
Salinity: ~1.025 specific gravity
Ammonia, Nitrates, Nitrites: Fully cycled aquarium, near-zero levels
Never use copper, in a tank you either have snails or other invertebrates now or hope to have them in the future.
Since their natural behavior is to bury themselves in the sand (with their siphon sticking out/up), it is also likely best to keep them in a tank with a deep sand bed or in a refugium (…with a deep sand bed).
For more information
- Shimmer, Ronald. Marine Snails. CORAL magazine. July/August 2015.
- Best herbivores. Worst herbivores. CORAL magazine. July/August 2015.
Check out these carrion eaters in action:
How many Nassarius snails do I need per gallon?
It is difficult to give a one-size-fits-all recommendation about how many Nassarius snails you might need for your aquarium, but the answer is certainly: not many. Their primary food is a dead fish carcass, which, you should generally not have a lot of, in your fish tank. As such, most tanks would likely not need more than a few (3-5), perhaps more for very large tanks.
Nassarius snails are:
- peaceful and easy to add to any tank with a sandy substrate
- interesting to watch
- helpful at aerating the aquarium sand and cleaning up waste in the tank
- certainly not an algae eater
For further exploration, it would be interesting to see if adding these carrion-eating snails would help to keep bristle worm populations in check, by competing for the same food. There is no research to support that, just a hypothesis based on the niche (and how competition works in other unwanted pest areas, like controlling aquarium algae.
But, if you hate bristle worms, give these nassarius snails a try and see if you can replace those worms.
If you were interested in this snail because you thought it would help you with problem algae, check out the Cerith snail instead.
If you want more help Building a Better Saltwater Aquarium, please
Shimmer, Ronald. Marine Snails. CORAL magazine. July/August 2015.
Best herbivores. Worst herbivores. CORAL magazine. July/August 2015.
Sprung, Julian. Invertebrates: A Quick Reference Guide. Ricordea Publishing. Miami, FL 2001.