Deciding which species to keep, especially when it is your first time keeping seahorses, is exciting and a common question new hobbyist ask. When new to seahorses, identifying species can be also be challenging. Many species look very similar and without knowing their original origin, can sometimes be difficult to identify. Some species such as Hippocampus kuda also have a wide natural distribution and locales can look very different. Some locales in the Kuda complex almost like completely separate species. We will discuss topics including why it is not recommend to mix seahorse species in the same aquarium, which seahorse species are commonly available captive bred, which are hardy to keep, stocking density, and more.
H. erectus, Lined seahorses
Mixing Seahorse Species-Why it is Not Recommended
Most people like diversity and for this reason a commonly asked question is can you keep multiple seahorse species together. We do not recommend mixing different seahorse species in the same aquarium. Seahorses from different areas of the world carry different micro fauna (bacteria, ect). Seahorses can have immunity to these and when introduced to another species which has not been previously exposed and with no immunity it can cause stress on the immune system. This can directly cause issues with them and also make the seahorse susceptible to other bacteria or issues that may normally not be harmful. Seahorses have a primitive immune system and are more susceptible to bacterial related issues compared to other fish which likely has to do with why we see this issue when species are mixed.
In short, mixing different species often results in one or both species not doing well. Sometimes issues happen right away and other times it happens months down the road. Some keepers are successful at mixing species but from troubleshooting with hobbyist it seems to rarely go well when mixing species in the same aquarium. Hobbyist often ask us why it matters if all the seahorses are captive bred and from the same farm. We do not mix species at our farm for this same reason. Different species are kept in different systems and therefore they have not been exposed to one another.
One exception to mixing species is H. Reidi and H. Erectus. These two species naturally overlap in their distribution. There is evidence these two species naturally hybridize as well. We have successfully kept these two species together at our farm for years with no issues. Many other hobbyist have as well and we do not hear of issues when these two species are kept together. While H. Reidi are a hardy seahorse to keep, their fry are not an easy species to raise making them very limited in availability as far as captive bred.
H. erectus H. reidi
Stocking Density and Aquarium Size
Having an idea of the number of seahorses you wish to keep is helpful when you are choosing your aquarium. For the larger seahorses species we generally recommend a 30 gallon minimum aquarium size for the first pair of seahorses with an additional 15 gallons for every additional pair you wish to keep. A larger aquarium if possible is even better. Seahorses really enjoy having space and will use the whole aquarium. Having extra water volume can create a more stable environment as well. While 30 gallons is the minimum recommended aquarium size a 40-50 gallon aquarium size would be even better.
A common misconception is seahorses need very tall aquariums to thrive and breed. Seahorses are vertically oriented fish with most aquarium kept species reaching about 5-7 inches in height. 18-30 inches deep works well for seahorses. When choosing and aquarium and what height to go with keep aquarium maintenance and cleaning in mind. 30 inches or more is very deep and can be difficult to work in when you are doing your regular maintenance. A lot of keepers do not take horizontal space into consideration. Seahorses like to move around and use their horizontal space as much as their vertical space. You don't want to cut them short on horizontal space by choosing an aquarium that is very tall. We prefer aquariums 18 inches or wider.
A lot of hobbyist do not realize how large seahorses can reach with maturity. As mentioned before, H. erectus seahorses for example, reach 5-7+ inches as adults. At this size they are pretty large fish hence the aquarium size recommendation. Seahorses eat more than the typical saltwater fish and are messy eaters.
Overstocking can lead to many issues. When the density is too high a build up of organics is likely to occur. Seahorses really like space and to not be over crowded. Crowding can cause stress as well as instability in the aquarium. It is also important to remember when you purchase captive bred seahorses they are juveniles and still growing. A lot of new hobbyist under estimate how large seahorses will eventually get. Larger fish means more bio-load so keep in mind they will grow when you are first stocking your aquarium. It will be much more challenging to maintain high water quality when the aquarium is overstocked.
H. erectus x H reidi Hybrid. Captive bred and raised at our farm.
Which Species of Seahorse to Keep?
Hardy and Commonly Available Seahorse Species
There are a limited number of seahorses available in the trade. In the United States, the most commonly available captive bred seahorse species is H. erectus. Others species include H. reidi, H. kuda, H. comes, H. abdominalis, H. zosterae, and occasionally some other species. H. erectus, H. reidi, H. comes and H. kuda have similar care requirements and are all hardy species that do well in the home aquarium given proper conditions. These four species reach approximately 5-7+ inches with maturity. H. erectus are considered one of the easier species to raise. If you are interested in breeding and raising seahorse fry this is a good species to start with. H. erectus are also a stunning species and full of personality.
H. erectus with cirri, Lined Seahorse H. kuda, Spotted Seahorse
H. reidi, Longsnout seahorse H. comes, Tiger Tail Seahorse
H. abdominalis, commonly called pot belly seahorses, are seen in the trade but not as commonly kept as some of the other species. These are among the largest seahorse species reaching up to 10-12 inches. Pot belly seahorses are native to Australia and New Zealand. They are a very unique species and considered a cooler water species. The recommended temperature range for this species is 65-67 F so a chiller is necessary. A 100 gallon aquarium is the minimum aquarium size we recommend for this species since they reach such large sizes. They will really enjoy the space so if you can provide them an even larger aquarium, go for it. Tank-mates with Pot Bellies is more limited since they are a cold-water species.
H. abdominalis, Pot belly seahorses. Photo credit Felicia McCaulley.
Dwarf Seahorses-H. zosterae
H. zosterae, Dwarf seahorses, are one of the smallest seahorse species and native to the western Atlantic including Florida, Bermuda, Bahamas, and the Gulf of Mexico. This species is commonly found in the shallow seagrass beds including Zostera which is how they got their species. name, H. zosterae. Their maximum adult size is 1-1.5 inches. Given proper conditions, Dwarf seahorses breed easily in captivity producing small broods of large fry. Brood sizes range from approximately 4-20 fry per brood. Male Dwarf seahorses are pregnant for approximately 12-14 days. They produce large fry making them one of the easier species to raise. This is a really neat species but they have unique feeding and care requirements we will discuss later. For this reason, they are not a species for every seahorse keeper.
Dwarf Seahorses-Unique Feeding Habits
Dwarf seahorses being so small, have a quick metabolism and different feeding habits compared to other seahorse species. They rarely taken frozen prepared foods. From our experience, we highly recommend feeding Dwarf seahorses live enriched Artemia nauplii (baby brine shrimp). Feeding live Artemia nauplii will allow your Dwarf seahorses to graze throughout the day. Allowing them to constantly feed throughout the day is recommended since they have a quick metabolism. This type of grazing is not possible with frozen food. Like any raw seafood, food fish foods will also begin to quickly spoil and degrade your water quality and produce harmful bacteria if left in the aquarium. Most hobbyist who keep Dwarf seahorses have a herd of them. They are very social and having larger herds such as a dozen or more can actually be easier to maintain. They are not active eaters and therefore the Artemia nauplii needs to be pretty dense to ensure they are properly fed. Having a larger herd will help make sure all the food is consumed at this high concentration and not have a lot of excess waste.
Dwarf Seahorses Need a Different Type of Setup than the Larger Seahorse Species
Since Dwarf seahorses are so small and need their food concentrated, a 4-7 gallon aquarium typically works well. An aquarium properly setup in the size range can easily maintain a herd of ~25-50 Dwarf seahorses. A common question we get asked is if Dwarf seahorses can be mixed with other seahorse species. The short answer is, it is not recommended. A properly setup Dwarf seahorse aquarium is not a good setup for other seahorse species. For this reason we do not recommend mixing Dwarf seahorses with other species including H. erectus even though their distribution naturally overlaps and the possible immunity issues we discussed earlier may not be an issue with these two species. Artemia nauplii can also irritate the gills of larger adult seahorse species also making them not compatible tank-mates. Water flow is likely going to also be lower in a Dwarf seahorse aquarium and this probably will not be enough for larger species. Larger seahorses have higher oxygen demands. Since Dwarf seahorses have such unique care requirements, especially feeding, we highly recommend keeping them in a dedicated species only aquarium and not mixing them with other seahorse species.
Occasionally other species become available in the trade. In the early 2000's all species in the genus Hippocampus were listed CITES appendix II. CITES is an international agreement between governments and regulates wildlife trade. All seahorses are the genus Hippocampus. This listing stems from the potential for this species to be over-harvested for TCM (traditional Chinese Medicine). Since their trade is highly monitored because of this CITES listing imports into the United States is not as common as it once was in the past for all seahorses including wild collected, captive bred, and net-pinned raised specimens. Since importing seahorses is a complex process with them being CITES II listed, the availability is often limited and less diverse now days.
Some captive bred specimens we see available from time to time include H. barbouri, H. ingens, and some others.
H. barbouri H. ingens
We hope you find this article helpful in deciding which seahorse species you want to keep. We want you to be successful and if you have any questions please reach out. We are happy to help.
H. erectus at our farm