Most fish may not only perceive a new tank addition as a territorial threat, but when it comes to feeding time it can be perceived as a food competitor as well. This can particularly happen if the newly added fish is of the same species, or is similar in shape, color, or size. And don't forget, in some cases new additions can be perceived as a food source themselves.
For these reasons it is important to know what types of foods any particular group or species of fish likes to eat, and which of the three basic feeding categories they fall into.
Carnivores - Meat Eaters or Opportunistic Predators
This category includes Cardinalfishes, Dottybacks, Eels, Frogfishes or Anglers, Grammas, Groupers, Hamlets, Hawkfishes, Scorpionfishes, Puffers and Porcupinefishes, Pipefishes, Sea Basses, Sharks, Snappers, Soldierfishes, Squirrelfishes, and Triggers.
The general rule to keeping carnivores, which are hunters of live prey, generalized bottom feeders and opportunistic predators, is to be sure that other tank inhabitants kept with them are large enough NOT to fit into their mouths, or that you are NOT adding something that is on their diet preference list. Now these fish usually will not attempt to eat other tankmates that are larger than they can eat, but the occasional mishap does occur.
Carnivores will eat smaller fishes, crustaceans, and various types of motile invertebrates. Even though fish in this group are not considered to be coral eaters, some individual specimens may decide to pick at certain types of sessile invertebrates like tube worms, clams or other bivalves. And, because some species in this group can grow quite large, physical damage to corals can also result.
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