Can Starfish Be Kept With Seahorses? Full Compatibility Guide.

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Seahorses are sedentary fish that are very docile and timid. They normally do best in species-specific tanks but can be successfully kept with other tankmates that are compatible. One tankmate we will be discussing is the starfish, can these marine invertebrates be kept with seahorses?

Starfish can be kept with a seahorse as they make for good tankmates. However, there are certain conditions that must be met to make this pairing work. The right choice of suitable species is required which will allow for both creatures to co-exist peaceably. After all, whichever tankmate you choose for your seahorse you should always proceed with caution.

At first glance, you may think that a starfish (sea star) should make for great tankmates in just about any aquarium.

They are well known for being passive and slow but not many know the full extent of their predatory aggression.

Starfish can be ferocious and highly aggressive. They can be described as opportunistic since they often target prey that are slow that cannot defend themselves.

Once they wrap their arms around their target they can totally digest them pretty easily.

Even though seahorses are not a direct target for starfish since they are always lurking around in the water or resting on some post, their tails are susceptible to becoming prey.

This is only a threat with bigger predatory starfish and these are the species to avoid at all costs.

Rather you go for small colorful species that often do well co-existing with seahorses. The smaller starfish are a great fit for seahorses and they are sought out by many seahorse keepers.

However, another caveat to getting smaller starfish is that they are not necessarily suitable for small seahorses like dwarfs (Hippocampus zosterae).

If you intend on keeping dwarf seahorses I would suggest you stay away from any starfish species since there can become easy targets for starfish to consume.

Most Compatible Starfish.

Mini Bright Red Fromia Starfish.

Scientific Name:Fromia milleporella
Seahorse Compatible:Yes
Care Level:Moderate
Minimum Tank Size:30-50 Gallons Per pair
Max Size:5 inches

The Red Fromia Starfish is one of the hardiest of the Starfish family. Covered in deep pigmented red these guys are great for adding pops of color to your aquarium.

They are omnivores and will help get rid of algae and leftover food that is scattered around.

These guys are very sensitive and must only be introduced into a well-established aquarium.

They are quite sensitive to changes in pH, temperature, and salinity and will therefore need stable water parameters to thrive.

NOTE: Fromia requires a very long and slow acclimation period prior to the introduction into the display aquarium.

Marble Starfish

Scientific Name:Fromia monilis
Seahorse Compatible:Yes
Care Level:Moderate
Minimum Tank Size:50 Gallon Tank
Max Size:5 inches

The marble starfish from the Fromia species are commonly known for their coloration and unique patterns.

It is constantly foraging for microorganisms and detritus to eat and will surely do a good job keeping your aquarium clean.

They generally live alone, but if the aquarium is large enough to support more than one, it will tolerate others of its own species.

They typically reside on the sandbed or rocks of an aquarium and are great for seahorse tanks and will do well cleaning after them.

They do best in a well-established aquarium with plenty of live rock for them to graze on.

Neon Orange/Red Sea Star.

Scientific Name:Echinaster luzonicus
Seahorse Compatible:Yes
Care Level:Moderate
Minimum Tank Size:1 per 30-Gallon tank
Max Size:6 inches

These are brightly colored sea stars that are less commonly available but are beautiful additions to a seahorse aquarium.

They typically reside in the sandbed and on rocks that are covered with algae.

It moves over the surface, eating the small microbes and other bits of common detritus that normally build up in a seahorse tank.

The Orange Sea Star is very intolerant of sudden changes in oxygen levels, salinity, and pH of the water, but cannot tolerate copper-based medications.

The drip acclimation method is highly recommended for all Sea Stars due to their intolerability to changes in water chemistry. It should never be exposed to air while handling.

Serpent Starfish

Scientific Name:Ophioderma spp.
Seahorse Compatible:Yes
Care Level:Low
Minimum Tank Size:30-Gallon per pair
Max Size:4-6 inches

Often called Caribbean Serpent Sea Stars or Tiger Serpent Starfish, they are nicely Colored Serpent Stars and come in a variety of colors.

These hardy starfish are great for eating leftover food in the aquarium making for perfect occupants in any a seahorse aquarium.

These scavengers typically reside in the sandbed under the rocks and come out during feeding time. 

They do well in an aquarium if provided with ample hiding places and plenty of room to roam.

An ideal setting with live rock, and a sandy bottom, mimics their natural habitat allowing for them to thrive.

Successfully Keeping Starfish.

There are many starfish species that make for great tankmates for seahorses, however, they have their own set of requirements that must be met for them to thrive.

These sea stars are very sensitive and have a high death rate when kept in captivity.

Hopefully, by following these few instructions you can provide the ideal environment for these bad guys to thrive.

Apart from the normal tank setup that is required these other requirements are needed to mimic their natural environment.

1. Well-Established Aquariums.

Starfish are very sensitive and should not be placed in a new aquarium. A new aquarium isn’t balanced being unsuitable for starfish.

A new aquarium will undergo a process of constant fluctuations that only come to equilibrium once the chemistry of the water remains within safe parameters.

Placing starfish in these environments will lead to their deterioration since they are too fragile to handle the fluctuations.

In fact, most starfish die when kept in captivity due to incorrect care and unsafe water parameters.

A well-established aquarium that’s chemically balanced is what’s needed for these fragile inverts to adjust properly.

Proper testing and procedures must be done before they are introduced to any closed system.

2. Proper Acclimation.

Another crucial step in keeping starfish successful is the practice of proper acclimation. This process is often performed incorrectly since hobbyists think they acclimate similarly to other marine life.

These invertebrates are more sensitive than fish to changes in water chemistry.

It is imperative to acclimate invertebrates in terms of specific gravity, temperature, and pH or else severe stress or trauma may result.

The only recommended method I recommend for starfish acclimation is the Drip Method.

You will need airline tubing, and a clean aquarium bucket (3-5 gallons) and you will need to monitor the entire process.

  • When your starfish arrive they should come in a tightly sealed plastic bag. Carefully empty the contents of the bag into the bucket being careful not to expose sensitive invertebrates to air.
  • Depending on the amount of water that came, you may need to tilt the bucket to make sure the creatures are fully submerged.
  • Using airline tubing, set up and run a siphon drip line from the main aquarium to the bucket. You can control flow by tying loose knots on the tube or adding a valve.
  • Begin a siphon by sucking (pulling) on one end of the airline tubing the side you’ll be placing into the bucket. When water begins flowing through the tubing, adjust the drip rate to about 2-4 drops per second.
  • When the water volume in the bucket doubles, discard half (do not empty in the aquarium) and begin the drip again until the volume doubles once more. This process should take about an hour.
  • At this point the invert should be transferred into the aquarium, gently remove them placing into the aquarium. Note, some invertebrates should not be exposed to air and must be submerged in water.

3. Water Parameters.

Echinoderms are very sensitive to marine pollutants and different species require water adjustments to accommodate them.

On average a starfish will require a powerful water filtration system as well as water temperatures ranging between 72 and 78 degrees Fahrenheit.

They enjoy water conditions with a pH of 8.1-8.4, hardness of around 8-12 dKH, and salinity of 1.023-1.025 specific gravity.

Any other changes in water parameters must be slow and steady if not it will cause stress and trauma which they may never recover from.

4. Substrate And Live Rock.

Starfish are slow bottom dwellers that require a suitable sandbed for them to graze upon. An inch or two of fine substrate should be ideal for these creatures to linger upon.

They also need Live rock which they graze on eating off all the debris that has settled on it. Rock also provides an escape for some starfish to hide.

You will need to add sufficient live rock that is firmly put together with lots of crevices and hidden gaps for them to lurk into.

5. Tank Size

Starfish require a lot of space since they graze the bottom of the aquarium seeking out their food.

While a 30-gallon may be sufficient for some, other species of stars require 50-100 gallon tanks in order to thrive.

Depending on the type of starfish you considering provide the right tank size since these invertebrates require ample space to house them and their exploration

Benefits Of Keeping Starfish.

  • A starfish will help maintain water quality since they consume organics and waste before it breaks down into harmful chemicals like ammonia which is toxic to seahorses.
  • Starfish is a good addition for clean-up crews helping to keep the aquarium clean. There are some that will help with algae and some with leftover food making maintenance easier.
  • They help clean and protect corals in the tank.
  • Starfish are great at cleaning the sandbed, these guys can smell food, and once it touches the substrate bottom they already devouring it. At least you don’t have to siphon the sand regularly.
  • They add great color and diversity to a seahorse aquarium which is aesthetically pleasing.
  • They keep nuisance algae in check, something that can be frustrating to deal with.

Potential Risks.

1. Choosing the wrong starfish that are incompatible with seahorses may result in the seahorse becoming prey. These are amongst the species that you should avoid at all costs like (Green Serpent starfish and Chocolate Chip)

2. Some starfish may eat your corals, macroalgae, and other smaller tankmates.

3. Some species have some of the lowest survival rates in the aquarium hobby making it unethical for most people to add them as occupants in a species-specific tank.

4. They don’t adapt well making them harder to keep alive. Most die within a year when in captivity.

5. Starfish should not be impulsive purchases as they require a lot of initial preparation for them to thrive.

6. They are not beginner friendly and should only be kept by enthusiasts with some kind of knowledge and experience.

Final Thoughts.

Starfish is a great addition to seahorse aquariums. They are colorful and gorgeous and add great diversity to your aquarium.

However, these guys need lots of preparation to provide a suitable environment for them to thrive, even with such effort it’s hard for them to adapt hence their high mortality rate.

I advise hobbyists or anyone who wants to keep starfish to first seek more knowledge about these invertebrates so you can provide the care they require.

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