What Are the Best Fish for a Coldwater Marine Aquarium?

By PetMD Editorial on May 3, 2019

Without a doubt, the marine aquarium fish trade is dominated by tropical reef species. This has been the case for several decades now. That notwithstanding, there has been a steady growth of interest in various types of coldwater marine aquaria.

Coldwater marine aquaria systems might be defined as any aquarium that functions optimally below room temperature (thereby necessitating the use of a powerful aquarium chiller). This type of system can be used to house either deep-water or temperate (i.e., high-latitude) species. Of these, temperate rocky shore biotopes are the most popular style of setup.

Fish That Are Suited for Temperate Rocky Shore Environments

Perhaps the most notable feature of temperate rocky shore environments (particularly in the intertidal zones) is their instability. These areas are subject to huge swings of temperature, pH, salinity, sunlight exposure and water depth (both daily and seasonal).

Thus, any animals that naturally occur in these habitats are well-adapted to rapid and/or extreme fluctuation of environmental conditions. This makes them very well suited to the sometimes wildly unstable conditions of a saltwater aquarium.

Given the hardiness, personality and sometimes beautiful coloration exhibited by so many temperate inshore fishes, it is certainly possible for an aquarist of any experience level to succeed with, and thoroughly enjoy, coldwater marine fish aquarium keeping.

While larger, extraordinarily attractive animals, like the flag rockfish (Sebastes rubrivinctus), Garibaldi fish (Hypsypops rubicundus) or ornate boxfish (Aracana ornata), most definitely can be amazing aquarium subjects, their need for extra-large aquaria eliminates them from many coldwater aquarists' wish lists.

So instead, let’s focus on those smaller species that can happily reside in a tank as small as 20 gallons. Here are just a few examples of temperate fish species that are desirable for an appropriately chilled and filtered system.

Species of Coldwater Marine Fish

Many species of coldwater marine fish are available in the aquarium fish trade. These may come either from coldwater aquarium livestock specialty dealers or as incidentals in tropical shipments.

Kamoharai Blenny

For those that prefer to buy/keep captive-bred fish, there are a few fantastic temperate options. For example, while once considered rare and unusual, the kamoharai blenny (Meiacanthus kamoharai) is now fairly easy to acquire. Its black and icy blue striping add a strikingly bold contrast to the pale reds and oranges prevalent in coldwater aquarium corals and anemones.

Eastern Hulafish

Also available as captive-bred, on occasion, is the eastern hulafish (Trachinops taeniatus). Like the kamoharai blenny, this little red and gold striped beauty is technically a subtropical species that doesn't require aggressively chilled water; something more like 65-70 degrees Fahrenheit will do.

Sailfin Molly

While not usually thought of as either coldwater or marine, the sailfin molly (Poecilia latipinna) naturally inhabits marshes, salty swamps and estuaries from Mexico to North Carolina. This euryhaline (lives in a wide range of salinities) and eurythermal (lives at a wide range of temperatures) species can thus be used in subtropical marine systems.

While several varieties of this widely aquacultured fish are certainly attractive enough to use as ornamentals, the most promising application for the species in coldwater aquaria is as pioneer specimens during the lengthy cycling period so typical of coldwater systems.

Rock Gunnel

As far as aquarium fish go, the rock gunnel (Pholis gunnellus) has got to be among the toughest. Adapted to the high shore, this eel-like species can tolerate very extreme conditions. If kept wet, it can even survive for quite a while out of water (even so, use a tight-fitting lid, because they can be sneaky!).

Bay Pipe Fish

The bay pipe fish (Syngnathus griseolineatus) is a great choice of coldwater syngnathid. This strange, slow-moving fish is a perfect addition to eel grass or surf grass biotopes, where the animal blends in perfectly due to its bright green coloration and slim body profile. Perhaps the only truly special requirements of this fish are modest water flow, live foods (brine shrimp and copepods) and completely peaceful tankmates.

Fluffy Sculpin, Catalina Goby and Zebra Goby

According to Josh Groves, who helps manage the popular online special interest group Coldwater Marine Aquarium Owners, the most popular temperate marine fish to keep in smaller aquariums would be "a toss-up between the fluffy sculpin (Oligocottus snyderi) and the very beautiful Catalina goby (Lythrypnus dalli).”

“Both have a place in my heart as two of the most active, puppy dog-like fish I have ever encountered!" says Groves. Very similar to the Catalina goby in appearance and habit is the zebra goby (Lythrypnus zebra).

Developing Live Nitrifying Bacteria in Temperate Systems

Due to the lower water temperatures, populations of nitrifying bacteria (which remove toxic ammonia and nitrite) can take a considerable amount of time to develop in temperate systems. Because fish are the primary waste producers in most aquaria, it is a very good idea to add a dose of Dr. Tim's Aquatics live nitrifying bacteria for saltwater aquariums.

Aside from this, practicing good marine aquarium husbandry and keeping the water cool, there's little else to keeping these beautiful and interesting creatures!

By Kenneth Wingerter

Featured Image: iStock.com/bugking88

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