There are a lot of things we love about saltwater aquariums—the vibrant colors, the soothing ambiance they lend a room, the joy of watching living things grow as you feed and care for them. But one of the things about aquariums that we enjoy the most is how we can see fish, coral, and other creatures interact with each other in a dynamic setting.
An active aquarium where fish playfully dart around and hide in all the nooks and crannies, coral shift and grow as part of a changing landscape, invertebrates dig through the sand and climb through the reefs, and every member of the aquarium community interacts with the others as like a cog in a larger whole—this is every hobbyist’s dream, capturing a small bit of the wonder and excitement of marine life.
But sometimes encouraging such interaction can be difficult. There are thousands of species of fish, coral, and other organisms that you can use to populate your aquarium, and not all of them are equally compatible. While some livestock will share space and coexist peacefully, others will exhibit aggression and territorialism, or even attack and kill each other. There’s a lot of care that needs to be put into the composition of your tank to not only ensure not only the safety of its inhabitants but also to encourage interaction among them.
Here are some basic guidelines to help get you started in your efforts to build a dynamic, lively aquarium.
Species of Fish
The first and most obvious factor affecting the interactions within your aquarium is the makeup of the livestock populating it. The way many of your tank’s inhabitants will interact is largely based around the 
relationships that inherently exist between their species. This presents a whole series of challenges as you handpick each species you introduce into your aquarium.
Luckily, there are many sources that provide handy compatibility charts laying out the relative compatibilities of different types of fish for both freshwater and saltwater aquariums.
Generally, you want fish that can stand on equal ground but not be in direct competition. Look for species of similar sizes so they can’t bully one another as much, and with similar behaviors but occupying different swim levels in the aquarium so that they aren’t competing for the same space. This also means that it’s good to have species of different colors, so that they aren’t competing for the same hiding spots.
Coral also requires similar care. While coral provides constantly-shifting spaces for your fish to hide in and interact with, many species have long sweeper tentacles that can reach across to neighboring corals and sting them, damaging and possibly killing them with necrosis-causing nematocysts. Some corals, like Rhizotrochus typus, can even devour whole fish. Learn about how each species of coral defends its space and the rate at which it expands before you go filling your tank with too many aggressive species and turning your aquarium into a warzone.
Resources
How an organism behaves in your aquarium has to do with more than just its species though. While its species does influence how the individual acts, the change in environment from the wild and into your aquarium can profoundly impact its behavior. A fish that is relatively docile in the wild, when displaced into an unfamiliar environment with limited space, food, and mates, can become far more aggressive than it had been previously. That’s why your allocation of resources becomes an important tool in discouraging violence and encouraging positive interaction.
The key to maintaining healthy activity in your aquarium is in making sure all of your livestock get ample and varied resources.
For fish and other creatures, this means maintaining a proper sex ration for that species, so that, for example, a group of males doesn’t start bullying or attacking the others to defend their claim to a limited number of females.
It also means a sufficient but varied feeding schedule. Of course, you should make sure that your livestock all have enough to eat that they aren’t in vicious competition. But you should also consider varying your times and locations of feeding, dropping food in at different points. This keeps a small subset of fish from dominating the feeding points and encourages the fish to move throughout the aquarium, exploring different sections.
Layout
Another important way to encourage your livestock to move throughout the aquarium and balance their interactions is in the physical layout of your aquarium. An overcrowded tank pits livestock against each other, and a tank that doesn’t change lets them grow reclusive, so you have to balance these elements to establish an active environment.
The organisms whose interactions are most dependent on layout are corals. Their growth patterns depend largely on the texture and form of the rockwork they grow onto, and so the shape and spacing of the areas where you place your coral will dictate whether they come into conflict and what sorts of structures they form for other creatures to interact with. You need to consider how you position your coral so that they have enough space and resources without competition. For example, plate corals like Montipora capricornis can grow to cast shade on lower levels of the aquarium, depriving coral on those levels of much-needed light.
As with food, it’s also wise to occasionally vary the layout of your aquarium, changing and adding new elements. This keeps your fish, starfish, or whatever other organisms you keep in your tank from growing sedentary, keeping to their little holes and corners. It encourages them to continue to actively explore the aquarium as they encounter new elements, same as they would in the wild. This also has the added benefit of shaking up their territories, forcing them all to keep reestablishing their home spheres and keeping individuals from territorial dominance. For this reason, it’s recommended that you alter the environment every time you introduce new organisms, so that they are on equal footing with the existing inhabitants and have a chance to integrate rather than be bullied into submission by them.
By following these guidelines, you will encourage the livestock living in your aquarium to not only peacefully coexist but to freely explore and interact with the home you’ve made for them. However, there are still thousands of species out there, and even individuals within a species can differ in behavior. On top of that, there’s any number of layouts and combinations you can put together in your tank.
That said, it’s understandable that you might want some assistance picking out just the right inhabitants and environment for your aquarium. If you want to discuss fish husbandry, look into the species available, or explore any aspect of building your freshwater or saltwater aquarium, we at Living Art Aquatics are here to help. Simply call Cory at 847-737-5151 or contact us with a description of what you need. For all aquarium-related needs in the Chicagoland area, Living Art Aquatics in Crystal Lake provides the expertise necessary to bring your underwater world to life.