When selecting inhabitants for a saltwater tank, there are many important factors to consider. Depending on what you want your tank to look like, or how you already have it set up, you should carefully consider which fish you add to your tank. Although mixing predators and prey isn't the only consideration, if you have a desired species or mix of fish in mind, you may need to make some changes to your tank or plan ahead so all the fish are happy in their new environment.
Ideal Tank Conditions
All fish, no matter the setting, require a home with good water quality and a good diet. However, not all species are created to live within the same home. Before you bring any fish home, or before you even purchase your aquarium, do your research on what fish you would like in your ideal setup.
Some fish species like to have a bunch of their brethren in close proximity, whereas other species need to have room to call their own. Some species may have different requirements given if they were wild-caught or bred in captivity. Clownfish are well known for living in a herd and can share their space well. Damselfish need to have their own cave or they will not flourish in your aquarium. In the wild, these fish are known for charging divers who venture too close to their rocky homes. The territorial damsel sees themselves reflected in the diver's goggles and charges! This requirement is entirely species-dependent.
And territory doesn't only mean having a place to hide and protect. Sometimes fish just need room to move! That cute little golden puffer you added to a 60 gallon tank will eventually grow into a 1'+-long giant that needs over 150 gallons for themselves. Never put a fish in a tank and tell yourself, 'I'll get a bigger tank later,' because most people won't. Plan ahead or don't add that particular fish!
All fish are not created structurally equal or prefer the same environment. If fish are in a tank with inappropriate water flow, they risk overexertion or poor water quality. Depending on the mix of species, you may be walking a fine line between too much and too little flow.
Many saltwater fish, such as tangs and triggerfish, can easily maneuver all throughout an aquarium and have no problem swimming up against a current. Some even enjoy the exercise and you can make feeding time less crowded if a powerhead blows the food around evenly. However, other less mobile fish, such as jawfish and blennies, cannot swim against a powerful flow for long periods of time. Sure, they can dart out at feeding time, but they spend most of their time in their rocky outcroppings or buried in the substrate. Water flow must be directed all over the tank environment in order to promote good water quality, but keep in mind that some spots may need to be lower flow.
Any decor you add to your tank will manipulate how water moves throughout your aquarium. Smaller and nano saltwater tanks are especially susceptible to high water flow since the reverberations will bounce back against the sides of the tank. An easy way to check the flow of your aquarium is to add some small, neutrally buoyant tub toys, or a ping-pong ball filled with water and see where they land in the tank. They should not increase significantly in momentum and not end up in the same place every time.
Tying into territory, some fish like to have different types of places to hide. Without a place for them to settle in, they will become stressed and likely die due to starvation and secondary infections. Some species, such as blennies, like having rocky outcroppings with shallow caves, and damsel fish like tiny caves tucked away deep inside. Substrate may be a cover for species such as jawfish. They will require soft sand, not hard gravel, since they will move it around to make their underground homes.
The biggest advocate for co-habitating with specialized housing are clownfish. There are multiple species of clownfish with some preferring specific types of anemones to make their homes. This symbiotic partnership keeps the anemones free of particulates and pathogens, while the clownfish have a safe home to raise their young and hide from predators.
Keeping anemones and other soft corals in an aquarium come with their own list of requirements and parameters, so take those into consideration when designing your tank. They will require certain light parameters and areas of low water flow to keep from being knocked off their rocks. And just because they are sessile does not mean they won't wander if they don't like their intended spot!
If making more fish is in your plans, you will need even more room! Breeding pairs will need to have a safe place to store their eggs, either in a cave, tucked around a coral, or stuck to the sides of their tank. Some parents will even store the eggs in their mouths until the baby fish hatch, but they themselves will become reclusive. Some species will viciously defend their young, while others take a more lax approach. And other species can't wait to nibble on a tasty egg snack!
Be sure to do your research prior to starting a breeding program, keeping in mind you will need to find a new home for your new fish if your tank is not big enough.
The Ideal Saltwater Mixed-Species Tank
After taking the above considerations and adding them all together, what does your tank look like? Is it too big for what you planned? What kind of decor and substrate will you need to buy? Do you really want to have a breeding pair in that tank that's already maxed out in size?
Usually, the biggest consideration for a mixed-species tank is size. No matter what your setup looks like or fish it contains, a bigger aquarium, with a larger water volume, is always a better way to go. Having more water adds extra cushioning for lapses in maintenance. We know you do your best, but there will always come a time where something comes up and your tank just slips from your mind. That extra volume will take care of your fish until you get back.
If your tank size has become too much for your to manage, re-evaluate your priorities. Maybe you should look at smaller fish that don't have expansive territories? Or fish that don't need to have a network of caves that messes up your water flow? If you just have to have fish that require a massive tank and you don't have the space, get a membership to your local aquarium rather than forcing a situation that cannot flourish.
Gold-Star Tank Mates
These easy-going fish are happy in smaller territories and get along with many other species.
Banggai or Kaudern's Cardinalfish (Pterapogon kauderni)
These easy-going fish are slower swimmers and can enjoy a variety of habitats. They may be found in their caves during the night and out swimming during the day. They are easily bred in captivity and enjoy a varied diet.
Neon Blue Goby (Elactinus oceanops)
Don't dismiss this fish by it's small size! The electric blue coloration makes this goby a vibrant addition to any tank. They do not require much water volume and can take up tiny caves ignored by larger fish. They do well as a single fish or matched pair.
Ocellaris Clownfish (Amphiprion ocellaris)
There are many different varieties of clownfish that would suite many reef aquariums. These easy-going reef fish like to have an anemone to call home, but get along well with many species of fish. When clownfish are born, they are all males and the largest fish in a group will change to female.
Incompatible Tank Mates (link to other article)
These fish do not play well with others and require lots of water. Careful planning is required to bring these fish home.
Clown Triggerfish (Balistoides conspicillum)
Requiring a tank minimum of 300 gallons, triggerfish are known live rock and coral nibblers. Their beak can easily crush all the rocks you carefully arranged and they need similarly large, aggressive tankmates.
Goldbar Wrasse (Thalassoma hebraicum)
There are various temperaments throughout the wrasse family, but the vibrant Goldbar Wrasse, with its distinctive golden bar behind its operculum, is one of the most aggressive. Requiring a tank of 125 gallons and up, these fish are very territorial and do not take new additions well. If you are going to add them to your aquarium, add them LAST.
Black Banded Cat Shark (Chiloscyllium punctatum)
All sharks and rays require a large volume of water. Although some species are not very aggressive, they are more sensitive to poor water quality and inappropriate tank conditions.
Overall, there is no one right way to setup an aquarium. Do your research before buying anything in order to make sure all species will thrive in their new homes.