If you are to be successful at keeping marine life in your saltwater aquarium you will need to understand the concept of species compatibility.
This is one of the major areas that newbies to the hobby fail to address and can cause massive stress, injury and even death to your marine life.
There are a whole lot of different species in the tropical reef environment and all of them play different roles in their ecosystem from predators to prey, herbivores to carnivores. Not only this, species must be able to compete with other species for food and space.
You want a harmonious marine aquarium and therefore you need to carefully match your chosen species together to ensure that the tank environment remains peaceful in regards to territoriality and aggression.
Invertebrates are much simpler than fish when it comes to compatibility – the only real rule is to keep stony corals far enough away from each other so as not to start a stinging tentacle war when they encroach on each others space this can be very savage and even fatal.
Because most invertebrates don’t move around very much they usually get along fine with other invertebrates unless one preys on another in nature. The real trick with them is to match them well to reef-safe species of fish.
To a certain extent a particular marine fish species eating habits can dictate its behavior, but there is much more to compatibility than this.
The only way to anticipate how one species will react to another is to research it thoroughly.
As a general rule of thumb like species can go with like (for example algae eating species), but often times you cannot add more than one or two of the same species as territorial instincts come into play which will result in fighting.
A good way to avoid this type of behavior is to have enough space for fish to get away from each other and a few different areas fish can use as their home base.
There are 2 golden rules of marine fish compatibility:
1. A small fish that can fit into a larger fishes mouth may end up being an expensive treat.
2. The less related and similar looking fish are the more likely that they will get along well.
Compatibility issues usually fall into the following categories:
⪼ 1. The predator-prey relationship
⪼ 2. Opportunity feeders
⪼ 3. Fish protecting their mates
⪼ 4. Fish protecting their young
⪼ 5. Territorial behavior
Basically you will need to ensure if you keep any large, carnivorous predator species for example Groupers, Lionfish, that you do not also have small potential prey species that it may eat in its natural environment especially if it fits in the carnivores mouth.
Keep it with other like aggressive species, larger species or don’t get one at all. Watch your motile invertebrates too!
These are species like Triggerfish that will snack on anything if given the chance, so it is not advisable to keep them with invertebrates or other small species. Also there are quite a few types of fish that enjoy the occasional coral polyp snack that should be avoided in a reef set-up.
When you have a mating pair and you introduce another individual of the same species there will often be aggression from the same sexed fish of the pair towards the newcomer. Avoid this scenario as often they can fight to the death.
This one is also rather obvious, fish that are spawning will be very protective of their young; warding off all fish around their nesting area. This aggressive behavior can be countered with housing for the nesting species and plenty of space.
This is the most common form of incompatibility a marine aquarist will have to face.
When you put a few different fish into a new aquarium this is optimal because fish (all being new) will have not already established a territory or home range.
The problem lies in when you add a new aquarium inhabitant into an established aquarium community; it may well end up being harassed regardless of what species it is by the more territorial of its tank mates which essentially have a natural instinct to protect their territory that they have already established.
Territorial behavior is made worse if the new addition is a member of an existing species in your aquarium and is made better the less similar the new marine fish is to existing sizes, shapes and colors of fish already in your aquarium!
The general rule here is to only have one example of the same species in your aquarium if you want more its best to introduce them at the same time so they do not get victimized by the more established of their species.
There are a few ways territorial behavior can be remedied and you can save that species being harassed but you will need to get adventurous:
You can place the new addition inside a physical barrier (such as transparent plastic with holes) placed in the aquarium for a couple of weeks and remove this after all fish concerned have gotten used to each other. You can even do this using separate tanks placed close to each other.
Another option is to remove all established fish from the aquarium then rearrange all the aquascaping before placing them back in with your new addition at the same time, I have seen good success with this method.
As you can see compatibility can be a huge issue but if you do your homework correctly it shouldn’t be a problem, but there are always exceptions. If worst comes to worst you can always try asking your fish supplier if you can return your incompatible fish and swap it for a more compatible fish.