Re:Dwarf Seahorses for a beginner

Dear hero:

In looking over your proposed setup, it is apparent that you have indeed done some advance research with regard to dwarf seahorses (Hippocampus zosterae) but it is also apparent that you still have much to learn about their aquarium requirements as well, and it was very wise of you to present your plans on a discussion forum such as this for feedback before you proceed.

It is clear from the aquarium you have selected, the type of filtration and water circulation you are planning on installing into the gutted Biocube, and the list of tankmates that you hope to keep that your intent is to design an aquarium system that will be good for live corals as well as dwarf seahorses, and I believe that is a fundamental flaw in your system. The fly in the ointment with the type of dwarf seahorse tank you hope to achieve, hero, is the issue of hydroids. Any aquarium that includes live sand and assorted live corals, and that will meet the feeding requirements of the dwarf seahorses, which require copious amounts of bite-size live foods (Artemia nauplii, larval copepods, larval Mysis, etc.) on a daily basis, is going to have chronic problems with the deadly hydroids and I just don’t see any possible way around that.

In the reading and research on dwarf seahorses you have done, hero, I know you must already be all-too familiar with the danger that hydroids present for these pint-size pigmy ponies, so please bear with me while I rehash the issue on this forum. This is what I normally advise seahorse keepers with regard to hydrozoans:

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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 filter feeding invertebrates. It’s inevitable because the hydrozoans 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, there is a simple way to eradicate them and get the situation under control again:

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. 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, 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.
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Okay, hero, that’s the quick rundown on hydroids. An outbreak of hydroids is devastating to dwarf seahorses, which are sensitive to their stings, and an outbreak of the hydrozoans would be inevitable in the type of aquarium you are planning. Unfortunately, the one sure cure for eliminating the hydroids — treating the tank with fenbendazole (brand name Panacur) — would be deadly to the live corals, polyps, and featherdusters worms that you hope to keep in your aquarium. In other words, once the hydroids appear — which I believe would be sooner rather than later — you would face the dilemma of either sacrificing the dwarf seahorses for the sake of the live corals and featherdusters or sacrificing the live corals and featherdusters for the sake of the dwarf seahorses.

So, before you learn about the harmful effects of hydroids in a dwarf seahorse tank the hard way, hero, I suggest that you rethink your fundamental aquarium design. This is what I propose: I have a great deal of information about dwarf seahorses available off list — informative articles, species summaries, descriptions of all sorts of aquarium setups that have proven to be very successful with dwarf seahorses, detailed information on their natural history, breeding and rearing, compatible tankmates, diverse food sources for dwarves, etc. — in files that are much too large to be presented in a simple forum such as this. I suggest that you contact me off list ([email protected] is my e-mail address) and I will gladly load you up with all of the additional information mentioned above, which you can then digest at your leisure. After you’ve had an opportunity to study the new material on dwarf seahorses I provide, you will then be in a better position to revise your aquarium design, and I would be very happy to discuss your revised dwarf seahorse setup with you at that time.

You stated that you want your seahorses to have a very natural, safe aquarium, hero, but an aquarium with live corals would be neither natural nor safe for these pigmy ponies. In the wild, dwarf seahorses are found in shallow seagrass beds, not on coral reefs or patch reefs with live corals and gorgonians. So if you want to mimic their natural environment, I would recommend setting up a tank with lush beds of colorful macroalgae that will simulate their natural seagrass habitat. If hydroids appear in a dwarf seahorse tank that is heavily planted with macroalgae, the tank could simply be treated with fenbendazole to destroy the hydroids without harming the ponies or the beds of macroalgae, so it would be a natural, safe setup for your dwarf seahorses.

Also, I must advise you that you should plan to do without a Mandarin dragonet in your revised dwarf seahorse tank. The Mandarin would not molest the dwarf seahorses in any way, but it would be doomed to a slow death by starvation in any aquarium small enough to be suitable for dwarf seahorses.

Don’t get me wrong — I absolutely love the psychedelic coloration and peaceful nature of Mandarin dragonets! There’s no disputing that they are gorgeous little fishes and make ideal tankmates for seahorses in the right type of setup. They are docile, slow-moving, passive fish that are beautifully marked and very deliberate feeders. And they are quite hardy fish providing they can be fed properly. They have a heavy slime coat that seems to make them quite resistant to protozoan parasites such as Cryptocaryon irritans.

But, as you know, in order to do well, mandarins need a large, well-established aquarium loaded with live rock or live rock rubble that’s teeming with copepods and amphipods. Mandrins must have continuous opportunities to graze on suitable live foods or they generally slowly waste away and starve to death. In the right system, they can thrive, and will often learn to take small pieces of frozen Mysis, but they do best in well-established reef systems or aquariums with at least 1 pound of live rock or LR rubble per gallon, a mature sand bed, and a refugium that can continually replenish the pod population in the tank. Those are typically the conditions that are necessary to assure they have adequate suitable live prey.

Mandarins are bottom feeders that normally do not take food from the water column, so select an aquarium with a large foot print that can accommodate plenty of live sand, small pieces of live rock, live rock rubble, and macroalgae. If you want to maintain more than one Mandrin, and keep a male/female in top condition, the larger the aquarium (and therefore the more extensive pod hunting ground the Mandarins will enjoy) the better. Nowadays, no conscientious hobbyist would consider keeping a Mandarin dragonet in an aquarium smaller than 50 gallons, and most hobbyists would opt for a tank of 100 gallons or more for the sake of the Mandarins.

Please contact me off list, hero, and I will send you the additional information about dwarf seahorses for your ongoing research and you can proceed from there, armed with new information to guide you.

Best wishes with all your fishes, hero!

Respectfully,
Pete Giwojna