Re:Aiptasia Eating Filefish (acreichthys tomentosus)

Pete Giwojna

Dear Debi:

Yeah, I’m beginning to think you may be talking about something other than Aiptasia rock anemones, Debi. If they are all so small that you need a magnifying glass to get a good look at them, they may well be something else altogether.

Aiptasia rock anemones are easily visible with the naked eye, and the larger specimens will have an oral disc with a diameter in excess of 1-2 inches. Likewise, the Majano pest anemones are even larger and more difficult to eradicate.

Judging from your description, it’s clear that your little pests with the retractable translucent stem and milky crown are cnidarians, and they are almost certainly hydrozoans of some sort, Debi. But their size suggest something other than Aiptasia glass anemones; if I had to make a guess, I would say you are most likely dealing with some sort of polypoid hydroids.

If that is indeed the case, it would be good news, Debi, since the hydroids are only problematic for the miniature seahorse species such as dwarf seahorses (Hippocampus zosterae). The dreaded ‘droids pose no threat to the larger seahorse species such as Ocean Rider Mustangs and Sunbursts (Hippocampus erectus) and, unlike Aiptasia anemones, hydroids should not undergo a population in a tank like yours.

Hydroids typically only get out of hand when they are in an aquarium that is receiving daily feedings of copepods or newly hatched baby brine shrimp (Artemia nauplii), which the hydroids require in order to thrive. Those are conditions that we normally only find in nursery tanks or dwarf seahorse tanks, so if you’re pests are hydroids, they should remain in small numbers and you needn’t worry about controlling them or eliminating them. But you should try to verify their identification, since there are so many different types of hydroids and they can appear vastly different depending on their stage of life and their diet.

The unexpected appearance of various crustaceans and microfauna in a SHOWLR tank is the very reason aquarists refer to these rocks as "live." It can be very difficult to accurately identify all of the mysterious life forms that may blossom from your live rock over the months and years, Debi, but 99% of them are harmless, benign, or beneficial to the aquarium and the pageant of life that appears in microcosm from the LR is fascinating to observe 100% of the time.

There are really only about four types of undesirable hitchhikers that sometimes sneak into our tanks concealed amidst the live rock or upon live sponges or live corals and which are problematic for large seahorses like Mustangs and Sunbursts, Debi, as outlined below:

(1) mantis shrimp;
(2) predatory crabs;
(3) fireworms and bristleworms;
(4) Aiptasia rock anemones, a.k.a. glass anemones.

With the exception of the four undesirable pests mentioned above, most anything else that emerges from your live rock or live sand will be benign or even beneficial for your aquarium, Debi, so you needn’t be too concerned at this point.

Reef Central ( is the place to go to identify all of the interesting critters that pop up from live rock or live sand or natural seawater. They have an excellent series of photo galleries on their site, including one devoted to Reef Tank Hitchhikers, so you might check in there and see if any of their photos look like the small anemone-like translucent white polyps you are worried about:

Reef Central has a discussion forum devoted just to seahorses, so it’s a good place to visit from time to time anyway.

Also, if you copy and paste the following URL into the Web browser on your computer, it will take you to another site with lots of photographs of aquariums hitchhikers that may help you to identify your mysterious tiny white bugs:

Let me know if you find any photos that look like your tiny milky white polyps with the translucent retractable steps to verify their identification, Debi (look closely at the photos of any hydroids anemones or polyps, in particular), and I will be happy to advise you whether they are harmless or should be removed from the aquarium.

Best of luck identifying your ministry hydrozoans, Debi!

Pete Giwojna, Ocean Rider Tech Support

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