Not all seahorse keepers are satisfied with a species only tank. For those who choose to keep a more diverse aquarium environment, it's important to put the seahorses' needs first and select tankmates with caution. With careful planning and consideration, seahorse tanks are no longer confined to being species only, but can house a wide variety of life. Seahorse tanks are becoming more and more beautiful by the day, with many keepers diving into setups containing seahorses, and peaceful fish, as well as many species of corals and macro algae.
Over the past few years, the thousands of members of seahorse.org continue to share their experiences and observations in keeping seahorses with other species. Using this continually growing knowledge base, we have attempted to compile an exhaustive list as to what is safe, and what is not. There will always be some exceptions based on the "personality" of individual specimens, but for the most part, we hope this list will be a helpful and accurate guide. Please bear in mind that it is best to become familiar with keeping seahorses, and that your seahorses should always be well established in the system before adding tankmates.
The rating system is generally based on the following criteria: temperament/territoriality, swimming patterns, food competition, venoms or toxins, and in some cases, the species' inability to survive in home aquaria. One must bear in mind that there may be some exceptions to a rating based on the temperament of certain specimens, however, the ratings are based on the USUAL specimen's behavior.
0 - represents close to zero risk. There is no competition for food. The fish are mostly benthic. There is not an issue with aggression. Corals would not have the ability to sting.
1 - still pretty safe. There could be some, albeit minor competition for food. The fish will be found in the water column but are not fast swimmers, and therefore, less likely to cause seahorse stress. There are really no issues with aggression to speak of. Corals are still no danger to the seahorses although the corals may contain feeding tentacles (no sweepers).
2 - these are a bit riskier, and you should proceed with caution. Many of the fish will be more present in the water column and may have faster or more erratic swimming patterns. There may be some competition for food as well as a possible chance for aggression towards the seahorses from the fish and inverts.
3 - I wouldn't keep any of these critters with my seahorses, but you're welcome to try. 3's are on the dangerous side. The fish will not only be in the water column but often have a distinct presence. There is a good chance for food competition and aggression. The corals have the ability to sting or typically don't do well. If you're planning to try anything that is ranked as a 3, please have alternative plans to house the species if a problem arises.
4 - these specimens either have no business in a seahorse tank, or should not be kept in captive systems due to failure to thrive.
If you have any questions, or would like to contribute your own observations of species listed or not listed, please visit the Tankmate forum here on Seahorse.Org.