Maintaining Peace in your Aquarium
A coral reef is a highly stratified environment. The complex and convoluted structure creates a variety of micro-environments in which different fish live, feed, mate, etc. This inherently creates competition. The crazy diversity of color and patterns we see on the reef by it’s inhabitants is meant to help organisms tell one another apart, to advertise defense mechanisms such as toxins or dangerous spines, and to basically keep animals from unnecessary injury. They instinctively know not to eat for example the yellow boxfish and not to mess with the striped lionfish.
In nature, fish will try to avoid those who might prey upon them but this is not always possible in an aquarium, especially if the tank is overcrowded. It is quite possible that the competition will turn deadly, which we obviously want to avoid. Specifically in aquariums, fish primarily show aggression towards each other for reasons related to food. It’s common in an aquarium to see an elevation in aggression between tank mates when they see people around the top of the aquarium at feeding time or if the fish are left unfed for a few days. Dominant fish are competing for the chance to be the first to eat and to eat the most. This can be exacerbated when adding new fish to the tank.
Knowing what factors cause aggression can greatly reduce (but not eliminate) problems. The guide below will give you a reasonable background however this area of aquarium science is complex; like people, all of these fish can be taken on an individual basis with a range possible behaviors within the species hardwiring. There is a spectrum of natural and husbandry/aquarium induced patterns and nature vs. nurture is a real factor in a fishes "personality". Healthy Aquatics is available for consulting and education if you want to explore fish behavior more thoroughly or you are having trouble with your fishes behaviors, feel free to contact us.
Categories of Fish
Smaller fish have a complex social structure that needs to be considered
Larger reef fish are often ominvores that can show aggression toward other fish or damage reefs depending on their situation
Trigger fish, pufferfish, and eels generally don't have psychology but tend to be interested in eating most things which they can chase down (small fish the the case of some eels and everything in the case of triggers and puffers). Some eels are considered invertebrate eaters (zebra and snowflake morays have conical crunching teeth) but can still get in the habit of trapping and eating fish at night. Not many other fish mess with a puffer or trigger.
Wrasses often don't have problems with other fish but a few species have been known to turn to the dark side and pick on smaller fish and/or other wrasses. When in trouble, wrasses often just dive into the sand, avoiding the aggressive behaviors of other reef fish. often a new wrasse may disappear into the substrate for days as it acclimates. Wrasses will often eat whatever fits in their mouth. Mystery, leopard, dragon, paddlefin wrasses, and even any of the large coris wrasses have been known to eat hermit crabs and snails and even run down little fish like neon gobies. Fairy wrasses are usually very well behaved but may fight new fairy wrasses if added at different times. Dragon wrasses especially are notorious for moving things around your tank and setting up a territory against other wrasses. Beware of buying cleaner wrasses as they have a very high chance of starving to death because they are never weaned onto aquarium food.
Ambush Predators: Groupers, lionfish, etc. A famous aquarist once gave a presentation explaining that killer whales are reef-safe by making the argument that they don't eat corals and most inverts. Groupers and lionfish can be considered reef-safe so long as animals you have don’t fit in their mouths. They leave other fish alone and are left alone. A blood shrimp is a very expensive snack. In this category is also any of the grunts or fast silvery swimming fishes like lookdowns and yellow jacks (though hopefully you don’t get any of these pilot type fish for your home aquarium as they get to be 3 ft. long).
Specific Tricky Fish that often have tragic experiences along with information on how to keep them alive