Dear Brandon:
There are two primary issues you will need to address if you want to attempt to keep dwarf seahorses (Hippocampus zosterae) in your sealed PalmTop pico reef tank that I can foresee — the water flow and the issue of hydroids.
Dwarf seahorses are ambush predators that lie in wait until suitable prey passes within striking distance, whereupon they will slurp up micro crustaceans from the water column that pass within reach. They are deliberate feeders and when there is a appreciable water current that whisks potential prey past them too fast for them to target and slurp up, they are unable to eat. In order to avoid this sort of complication, you would need to greatly reduce or attenuate the water circulation in your pico tank, and this is going to be contrary to the needs of the SPS corals, which require strong water movement in order to thrive. I am thinking that it’s going to be very difficult to find a flow rate or achieve a water circulation pattern that would both be suitable for the live corals and allow the dwarf seahorses to feed upon rotifers, Artemia nauplii, and other micro crustaceans from the water column undisturbed.
Secondly, in order to keep the dwarf seahorses well fed, you will need to supplement the available pods and microfauna in the pico reef with regular feedings of rotifers or newly hatched brine shrimp, and, sooner or later, this WILL trigger an explosion of hydroids in any reef tank, regardless of how mature it may be or how uncommon hydroids are in such a system initially.
Sooner or later hydroids will appear in any marine aquarium that is receiving regular feedings of rotifers, copepods, or baby brine shrimp or plankton suitable for feeding dwarf seahorses. It’s inevitable because the hydroids can can gain entry into the aquarium in many ways. For example, they are notorious hitchhikers. Both the colonial polyp stage and the free-swimming micro-jellies can thumb a ride on live rock, macroalgae, hitching posts, sand or gravel, specimens of all kinds, or within so much as a single drop of natural seawater (Abbott, 2003). Beware of fuzzy looking seashells! Very often hydrozoans come in on the shells of the hermit crabs or snails we purchase as aquarium janitors (Abbott, 2003). Or they may be introduced with live foods, or even among Artemia cysts, in some cases it seems. They can even be transferred from tank to tank in the aerosol mist arising from an airstone or the bubble stream of a protein skimmer.
It can be very challenging to identify hydroids because there are about a zillion different species of hydrozoans and the different types have different characteristics and are often vary remarkably in appearance. There is considerable variation within the species as well, and the same type of hydroids can appear vastly different depending on the size of the colony and its stage of development, conditions in the aquarium, and their predominant diet. And, of course, the different stages of the life cycle of these amazing animals are so entirely different that they were long believed to be different types of cnidarians altogether, and different species names were often assigned to the same hydroid in different phases of its life cycle. Because they are so difficult to identify and are not easy to distinguished with the naked eye during their initial stages, hydroids often go undetected in nursery and rearing tanks until they begin to take a toll on the fry.
The typical hydroid colony has a stem with a variable number of polyps growing on it, and each of these polyps bears numerous tentacles that are liberally studded with knobby nematocysts (batteries of deadly stinging cells). There are many different kinds of hydroids and they appear in the aquarium in many different guises: many colonies are stalked; some have fingerlike projections, others look like tiny pink fuzzy balls or appear like cobwebs (the webbing kind usually spread along the bottom or grow on the aquarium glass along the substrate). The "snowflake" type of hydroids seem to be particularly common in aquaria, whereas other species look more like crystal chandeliers, and some species form bushy colonies as they grow that serve as microhabitats for Caprellid skeleton shrimp and other tiny crustaceans.
Even a large hydroid colony appears harmless to the naked eye of the untrained observer. It takes a much closer look to reveal the dreaded ‘droid’s lethal nature, as described below:
"Studying the colony under high magnification, one soon becomes lost in an extraordinarily complex, living world–a microcosm in which a beautiful but deadly ballet is conducted on a microscopic scale (Rudloe, 1971). Hungry polyps, some resembling snapdragons, others looking more like daisies or tulips, expand their knobby, translucent tentacles, slowly flexing and languidly waving them about, lulling the observer with their slow-motion ballet — until they abruptly and quite unexpectedly snap up a bit of planktonic life, stinging it, drawing it in with one violent contraction, digesting it, and then re-expanding like a blossoming flower to hunt again (Rudloe, 1971). There are many such polyps in a colony, hundreds of them, each of which is armed with many tentacles and countless nematocysts, and at any given moment, some of them will be dormant and still, some will be expanded and lazily casting about for prey (Rudloe, 1971), and still others actively feeding (Abbott, 2003)."
The feeding or nutritive zooids are the distinct individual animals in a hydroid colony that are responsible for capturing and digesting prey; as such, they bear the nematocyst-studded tentacles. But you need high magnification in order to appreciate the true beauty of living hydrozoans, or to differentiate between different species of hydroids, or to observe the zooids going about their deadly business.
Hydroids are insidious because they start out so small and insignificant, yet spread so quickly under ideal conditions (e.g., a nursery tank or dwarf seahorse tank receiving daily feedings of Artemia nauplii). Many species can spread asexually by fragmentation as a microscopic speck of the parent colony. All of the troublesome types have a mobile hydromedusae stage, which look like miniscule micro-jellyfish, and can spread sexually in this way as well (Rudloe, 1971). The mobile medusae swim about with a herky-jerky, pulsating motion and are often mistaken for tiny bubbles due to their silvery, transparent, hemispherical bodies (Rudloe, 1977). These tiny jellies often go unrecognized until they begin to settle and are discovered adhering to the tank walls. They will have a large "dot" in the middle of their bodies and smaller ones at the base of their nematocysts (Abbott, 2003). Both the polyp stage and the medusa stage sting (Rudloe, 1977) and are capable of killing or injuring seahorse fry. Multiple stings can kill the babies outright, but they are often only injured by the nematocysts, which damage their integument and leave them vulnerable to secondary infections. Many times it is a secondary bacterial or fungal infection that sets in at the site of the injury which kills the fry.
Once they find their way into a dwarf seahorse setup or nursery tank, hydroids can explode to plague proportions very quickly because conditions are ideal for their growth: perfect temperatures, an abundance of planktonic prey that is renewed every few hours, and a complete absence of predators.
When hydroids become a problem in the nursery or dwarf tank, Brandon, which is inevitable in a reef system, the only really effective treatment for eradicating hydroids is to treat the tank with fenbendazole (brand name Panacur), but unfortunately, this medication would also devastate many of the corals in the aquarium, as discussed below:
Eliminating Hydroids
Hydroids can be controlled in the aquarium by using a medication known as fenbendazole to treat the tank over a period of days. Fenbendazole (brand name Panacur) is an inexpensive anthelmintic agent (dewormer) used for large animals such as horses, and the de-worming granules can be obtained without a prescription from stores that carry agricultural products (e.g., farm and ranch equipment, farming supplies and products, veterinary supplies, livestock and horse supplies, livestock and horse feed). If you live in a rural area, those would be good places to obtain it as well.
However, there are a couple of things you should keep in mind when treating an aquarium with fenbendazole, Brandon. Administering a regimen of fenbendazole (FBZ) or Panacur will eradicate any hydroids, Aiptasia rock anemones, or bristleworms from live rock or live sand, thereby rendering them completely seahorse safe. The recommended dose is 1/8 teaspoon of the horse dewormer granules (22.2% fenbendazole) per 10 gallons of water. Dose aquarium with 1/8 teaspoon/10 gallons every other day until you have administered a total of 3 such treatments (Liisa Coit, pers. com.). Even one dose will do a fine job of eradicating bristeworms, but Aiptasia rock anemones and hydroids are a bit tougher and may require 2-3 doses to eliminate entirely.
Because fenbendazole is essentially a de-worming agent, it will destroy any bristleworms, flat worms, spaghetti worms or the like. The FBZ or Panacur treatments are best administered to the live rock in a bucket or hospital tank before the LR is introduced in the main tank. Otherwise, the massive die-off of the worm population in the aquarium may require large water changes in order to prevent a dangerous ammonia spike! And after the treatment is completed, its a good idea to add a portion of newly purchased live sand to the system in order to help restore its normal diversity of fauna and microfauna again (Liisa Coit, pers. com.).
Fenbendazole does not have any adverse effects on biological filtration, but be aware that it is death to many Cnidarians besides hydroids. Mushrooms and related corals are generally not affected, but expect it to have dire effects on other corals (e.g., sinularias), polyps, gorgonians, and anemones. In general, any Cnidarians with polyps that resemble the stalked family of Hydrozoans are likely to be hit hard by fenbendazole, so don’t use this treatment in a reef tank!
Also be aware that fenbendazole seems to soak into the porous live rock and be absorbed indefinitely. I know one hobbyist who transferred a small piece of live rock that had been treated with fenbendazole (Panacur) months earlier into a reef tank, where it killed the resident starfish and Astrea snails. So enough of the medication may be retained within treated live rock to impact sensitive animals months after the fenbendazole was administered. Don’t treat live rock intended for reef systems with fenbendazole (Panacur)!
At the lower dosage recommended for nursery tanks and dwarf seahorse tanks with fry (1/16 tsp. per 10 gallons), fenbendazole normally does not harm cleaner shrimp and decorative shrimp. With the exception of Astrids (Astrea), Coit and Worden have found it does not usually affect the types of snails typically used as cleanup crews (e.g., Nassarius, Ceriths, and Nerites). It will kill starfish but copepods, hermit crabs, and shrimp are normally not affected.
Macroalgae such as the feathery or long-bladed varieties of Caulerpa or Hawaiian Ogo (Gracilaria) are not harmed by exposure to fenbendazole at even triple the normal dose. In fact, if you will be using Caulerpa in your nursery tanks to provide hitching posts for the fry and serve as a form of natural filtration, it’s a very wise precaution indeed to treat them with a regimen of fenbendazole beforehand.
So fenbendazole (FBZ) or Panacur is primarily useful for ridding bare-bottomed nursery tanks and dwarf seahorses setups of hyrdroids and Aiptasia anemones, ridding Caulerpa and other macroalge of hydroids or Aiptasia before its goes into the aquarium, and cleansing live rock of bristleworms, hydroids, and Aiptasia rock anemones before it is introduced to the aquarium.
It can also be used to eradicate bristleworms, hydroids, an Aiptasia from an established aquarium if it does not house sensitive animals such as live corals and gorgonians, starfish, Astrea snails, or tubeworms and other desirable worms that may be harmed by FBZ, providing you monitor the ammonia levels closely and are prepared to deal with the ammonia spike that may result from the sudden death of the worm population.
In summation, sir, if the aquarium with a hydroid problem will be housing live corals at some point, it would be best not to treat it with fenbendazole. And you may not need to be concerned about the hydroids in the first place, since as long as you keep them out of your nursery tanks, hydroids won’t present a problem for large seahorses like Mustangs and Sunbursts (Hippocampus erectus) at all. They are impervious to their stings. In fact, in the wild, seahorses often encourage algae, small bryozoans and other encrusting organisms, including hydroids, to grow on their exoskeleton in order to enhance their camouflage (Vincent 1990). The hydroids are only a problem for baby seahorses in nursery tanks or for the tiny dwarf seahorses, which are susceptible to their stings.
In short, Brandon, even if you can overcome the problem with water flow, I suspect that you are going to have an ongoing battle with hydroids in a pico reef tank that houses dwarf seahorses, and you may then find yourself in the difficult position of either sacrificing the pigmy ponies for the sake of the live corals or treating the tank with fenbendazole and sacrificing many of the corals for the sake of the seahorses.
This is an interesting project, sir, and worth experimenting with, but I cannot see how you will be able to overcome the hydroid issue in the long run in such a setup…
Best wishes with all your fishes (and invertebrates), Brandon! Please keep us posted if you try keeping dwarf seahorses in these interesting ecosystems — I know we would all be interested in the results of this most interesting experiment.
Respectfully,
Pete Giwojna
Ocean Rider, Inc. is an Organic Hawaiian-Based Seahorse Aqua-Farm & Aquarium that Follows Strict Good Farming Practices in Raising Seahorses and Other Aquatic Life.
