Dwarf Seahorses As Pets
They arrived via postal mail one blustery January afternoon, circa 1988. One pair of dwarf seahorses, ordered from the back of a Field & Stream magazine. I placed them in a 10 gallon tank with an undergravel filter, my first marine aquarium. Little did I know this was a completely inappropriate set up for them. Yet these hardy, thumbnail–sized seahorses thrived.
Much has changed regarding our understanding of seahorse care, and many other species are now commonly available. Yet the dwarf seahorse remains an ever popular, easy to care for aquarium pet. The basics of keeping them are quite simple as long as you follow a few guidelines.
Before getting into dwarf seahorse care, it’s important to understand a little bit about their biology.
Dwarf seahorses belong to the genus Hippocampus, which is the genus all seahorses belong to. Their species name, zosterae comes from the habitat they are usually found in. Zostrea is a type of seagrass, also know as eel grass. H. zosterae inhabit sea grass beds in the Atlantic ocean in the Gulf of Mexico and around Florida, though their habitat is not limited to just eel grass. They prefer protected areas where the water flow is buffered from the main ocean currents, usually lagoons and sheltered areas near reefs. They occasionally are found floating in seaweed as well.
True to their name, the dwarf seahorse only grows to around 1.5″-2″. Occasional oddball “large” dwarf seahorses are reported, but these are likely mis-identified juveniles of other species. Their main food in the wild is copepods, although other micro- and macro-scopic plankton is consumed. H. zosterae aren’t particularly long lived, having a life span between 12 and 18 month. However, they breed quite readily, and can produce three generations of seahorses per year in the wild. More in captivity where the seasons don’t influence breeding behavior.
Keeping dwarf seahorses have very basic housing requirements. They only need a small aquarium with a sponge filter to thrive. More complicated set-ups tend to be less successful. The reason for this is simple. Stronger filtration removes their food from the water column faster than they can eat it.
The size of the aquarium to house dwarf seahorses is the exact opposite of what you usually hear when keeping fish: You want to keep the aquarium appropriately small. The reason behind this is to maintain food density without compromising water quality. If you keep the seahorses in too large of an aquarium, you run the risk of them starving, or so much food being present that the majority of food isn’t eaten, and ends up fouling the water.
The specific size needed depends on the number of seahorses being kept. Below is a suggestion of the number of dwarf seahorses that can be kept comfortably in different aquarium sizes.
- 1 gallon: 2 – 3 to start, max 6 adults *Keeping an aquarium this small is a challenge to keep balanced, and shouldn’t be attempted by first time aquarium owners.
- 3 gallon: 4 – 6 to start, max 12 adults
- 5 gallon: 8 – 12 to start, max 20 adults
- 10 gallon: No fewer than 20 adults.
The tank should be set up and cycled before any seahorses are added. Cycling is the process of establishing the biological filtration that keeps the water clean. This is important especially since some vendors still suggest that dwarf seahorses can be added immediately to a new aquarium. While dwarves are frequently tough enough to withstand a cycle, ammonia burn and nitrite poisoning can cause long term complications. There is no point in risking the lives and health of this precious animal for a few weeks of cycling time.
Generally you don’t want to use live rock for cycling the dwarf aquarium. Two methods that are commonly used are fishless cycling with ammonia and fishless cycling with shrimp. These techniques are beyond the scope of this article, but you can read about them here: fishless cycling with ammonia, fishless cycling with shrimp
Dwarf seahorse are subtropical, but can handle a wide range of temperatures as long as the change isn’t too quick. you can expect to successfully keep them between the temperatures of 65 and 80 degrees, with 68-74 being optimal. This means they don’t need a heater if kept in a normally heated house. A thermometer is a must though, to monitor for large temperature swings and the temperature going outside of the safe zone.
Seahorses, while true marine fish, aren’t too picky about their salinity. Any specific gravity from 1.020 to 1.026 is acceptable as long as the change is made gradually. Take special care to replenish evaporated water every day. With a small tank, evaporation and replenishing water can cause wild swings in salinity. Check salinity on a regular basis to ensure it it is within the correct range.
Dwarves, just like large seahorses, need places to hitch. Many keepers opt for artificial decorations because of the risk of hydroids (see below.) Most basic aquarium plants work well. Macro Algae can be used but must be treated for hydroids. Live rock should be used with caution, as many pest can hitch hike in and harm the diminutive seahorse.
Feeding dwarf seahorses is probably the most tedious part of keeping them. Because of their size, they need to be feed tiny live food. Fortunately, brine shrimp hatched from eggs fits this description, and is easy to hatch. A small brine shrimp hatchery is easy to set up and maintain, and setup and feeding will only take roughly 15 minutes a day once you are familiar with the process.
The simplest set up is a pop bottle hatchery. It uses a inverted 2 liter soda bottle and is extremely inexpensive, yet simple. You will need:
- Soda bottle
- Airline hose
- Air pump
- Coffee filters
- Turkey baster
You’ll want to take the 2ltr bottle and cut about 1/3rd of the bottom off. Keep the bottom. Tighten the cap and turn the bottle upside-down. You should be able to take the bottom you cut off and rest the bottle inside of it. Fill that bottle half way full of saltwater at 1.026 (natural salinity level). A more detailed guide to making your hatchery here: pop bottle hatchery.
Put an airline hose in the bottle to the bottom, and set the air to vigorously turn the water just a bit. You don’t want it so high that it could destroy the newly hatched brine shrimp. Now, place a lap pointed at the bottle – light is required to activate the enzyme in the brine shrimp egg that causes the egg to hatch. Add approximately 1/4 tsp of brine shrimp eggs.
After approximately 24 hours, the eggs will have hatched. Take the airline out, and let the brine shrimp sit for 15 minutes or so with the light off or in a darkened area. The brine shrimp will settle to the bottom, while the egg shells will float to the top. Once they’ve separated, take the turkey baster and suck out the brine shrimp from the bottom (they will be bright orange). Then line your funnel with a coffee filter, and filter the brine shrimp you took out with the baster in the funnel with the coffee filter. Once the hatch water has drained, give them a rinse with fresh water. You can now add the baby brine shrimp to the tank.
Enriching Brine Shrimp
While feeding newly hatched brine shrimp can work for a time, it’s lacking in many of the essential nutrients that dwarf seahorses need to thrive. Enriching adds those nutrients to the baby brine shrimp.
The most important nutrient is the unsaturated fatty acid DHA. It’s one of the Omega 3 lipids that makes fish oil so healthy. Newly hatched artemia is high in EPA, a different Omega 3 lipid, but completely lacks DHA. DHA is essential for all marine fish as they cannot produce it on their own. The way to correct this is through enriching.
Enriching requires setting up a second hatchery for the baby brine shrimp. This can be another soda bottle hatchery, or it can be a jar. I recommend a 1 gallon jar for this, up cycling old pretzel or pickle jars.
There are a number of ways to enrich, but the most basic is taking new water, and placing the rinsed brine shrimp into that water. Add an airline that creates vigorous bubbling. Add a small amount of enrichment product, just enough to tint the water.
After approximately 24 hours, remove the airline, and rinse the brine shrimp the same way your rinsed them the first time. They may require multiple rinsing to remove excess enrichment. I usually rinse twice as many times as with fresh brine shrimp.
You want any enrichment source that has DHA in addition to EPA. Zoecon, Selcon, and SELCO Boost are easier to find than other product, but they don’t disclose the DHA/EPA ratio, and have questionable shelf stability. Selcon is rumored to have only a one month shelf life, even when handled properly. All these should be refrigerated, though I’ve seen many stores offering these unrefrigerated. Omega-3 lipids have poor shelf stability and break down quickly into harmful compounds.
Marine phytoplanktons can also be used for enriching if they are high in DHA. Two common “phytos”, Nannochloropsis and tetraselmis do not contain DHA. Isochrysis is used in many hatcheries and is high in DHA and would be a good option for enriching brine shrimp. There are many others such as Rhodomonas, Chaetoceros, & Pavlova are just a few that are sometimes seen in the hobby.
You’ll eventually figure out the right balance of how much brine shrimp to add to the aquarium, but you’re looking to add enough so that the seahorses can eat pretty much constantly but not so much that there is a lot left over at the next feeding. You can put the unused baby brine shrimp in the fridge in fresh salt water for a second feeding later in the day. Dwarves should be fed a minimum of twice a day, 3 times being ideal. You can also set up a second hatchery, but refrigerating the unused baby brine shrimp is usually sufficient.
Dwarves need constant access to food, which means they have to be feed at least every day. They can not go prolonged periods without food, so if the aquarist is leaving town, they need to have someone pet sit who is prepared to hatch out live brine shrimp every day. They also do not work very well as office pets, as going a whole weekend without food could spell disaster for dwarf seahorses.
If you plan on keeping dwarf seahorses, sooner or later you will have babies. That’s just a fact of keeping the marine equivalent of guppies. Fortunately, the babies are extremely easy to raise. They can even be raised in the same aquarium with the same food as the parents.
Like other seahorses, it is the male that becomes pregnant. They are gregarious by nature, and don’t pair bond. In the wild, their breeding is limited by the seasons, but in the home aquarium they can breed constantly. The male can have a brood every 10 days, and can have 5-30 at a time. Most spawns are generally around 10 or so babies at a time. The babies hitch at birth, and will often be found hanging from the male’s head, snout, tail, etc… at birthing time.
Raising the young can be as simple as adding enough food to make sure that the babies are sufficiently fed. However, higher success rates are often achieved by raising the babies separately. It’s unclear why this might be; lack competition for food or possible unnoticed aquarium pests may be to blame. Raising the babies separately is quite simple though. All they need is a cycled aquarium set up like their parents. A bare bottom aquarium is even easier to keep clean for raising babies, and makes changing out the tank for each new brood much easier.
Whether you rear them in tank or on their own nursery, after about 6 weeks, they will start reaching sexual maturity and many will start acting amorous towards the opposite sex. Sexing starts to be possible, though some late bloomers may not show a pouch for a couple more weeks.
Acquiring Dwarf Seahorses
Dwarf seahorses are rarely sold in local fish stores so the beginning aquarist may wonder what to do about getting them. Even the occasional store that does get them in, they rarely have the knowledge or appropriate conditions to keep them alive. For that reason, its usually best to go through a mail order vendor.
I no longer recommend ccritters due to poor packaging and poor customer support. Please think twice before purchasing wild seahorses.
Many Florida fish collectors, including those that sell on Ebay, do very little to take care of the animals before they get to you. Never let them be shipped with anything less than overnight. Many vendors claim they will do fine with slower shipping methods, but that’s largely because it’s often cheaper to replace the whole bunch than to pay for overnight shipping. Aquabid is another source to avoid for dwarf seahorses; the same type of catch and sell vendors use that site to sell seahorses without any concern for their wellbeing.
No article on dwarf seahorses is complete without a discussion of hydroids. Hydroids are tiny stinging animals that resemble anemones and jellyfish depending on the stage in their lifecycle. They are present in most marine aquariums, but only become a problem when they are feed a constant supply of small, free floating foods. When that happens, the can spread in such large numbers that they literally cover every surface of the aquarium.
This poses a problem for dwarf seahorses for two reasons. In such large numbers, they can quickly consume all the food in the aquarium. However, a much bigger threat comes from stinging cells. Their sting isn’t particularly potent to most animals, but for the tiny dwarf seahorse, the sting can be deadly.
Eradicating hydroids is fortunately very simple. They are susceptible to the medication “fenbendazole”. It can be purchased at farm supply stores or online under the brand name “pancur”, which is a dewormer for horses, cats and dogs. Dosage is as follows:
1/8 teaspoon of the horse dewormer granules (22.2% fenbendazole) per 10 gallons of water. 25% water change 24 hours later.
Many people opt for artificial decorations to avoid hydroids. You can remove the animals in questions and replace them after a partial water change and running carbon for 48 hours; however you run the risk of reintroducing hydroids back into the tank.
Just how do you know if you have hydroids? The first symptom is food disappearing faster than it used to. If you notice that, start looking in the tank for small jellyfish no bigger than 1/4 inch. This is the free swimming stage of hydroids. If you don’t find that, then look for brown or clear “fuzz” growing in the tank. It will be a dense mat, and on observing closely, you should see them stinging and consuming the brine shrimp you add to the tank. If you find you have hydroids, don’t panic, just follow the above guidelines for treating the tank.
Because of their small size, animals that are normally safe with seahorses can be a potential threat. Scavengers, such as hermit crabs and cleaner shrimp, can easily overcome and kill a dwarf seahorse. Even those tank mates that are okay with adult dwarves can easily consume baby dwarves. For that reason, people rarely keep other fish with their dwarves. I have experimented with a few different fish, and found that your cleaner gobies and firefish are the safest, though will sometimes eat babies. Some small pipefish do well with dwarf seahorses as well, though may have a tendency to eat fry.
Snails are probably the best clean up crew. Nassarius snails can be used for cleaning up waste in the sand bed. Some people have said they’ve had success with small hermits but I would recommend against it. Some small shrimp, such as sexy shrimp and anemone shrimp can be kept, with caution, with dwarf seahorses. Most other clean up animals are inappropriate for dwarf seahorses.
Maintenance is extremely important in dwarf seahorse aquariums. It is probably one of the trickiest aspects of keeping them. Because the amount of food that goes into the aquarium, their water is fouled easily. 25% water changes every other week are a bare minimum, and a weekly schedule is ideal.
Keeping the filter media clean is difficult with dwarf seahorses. Be sure to clean any mechanical and biological media before it gets clogged up. Some sponge filters work better than others at this.
I recommend Hydro sponge filters. They are more expensive, but they tend to clog less frequently. Many knock-off brands of sponge filters use any sponge like material, whereas hydro uses specialized sponges with the right porosity to keep small particles from clogging the sponge filter quickly. They do still need to be cleaned, but less frequently than many others.
To clean sponge filters, rinse in a bucket of old aquarium water during the water change. Squeezing the sponge filter in the bucket will help remove the organic matter that has built up in the sponge filter. If the water becomes significantly dirtied, you may want to use fresh saltwater for a second rinse. Then move up your maintenance schedule to include more frequent cleanings.
Updated 05/09/2015: Updates include the new sections regarding maintenance and enriching, along with minor tweaks to text in order to provide improved suggestions and best practices.
Updated 08/09/2015: Minor grammatical and editorial changes for clarity.