From my experience in keeping various cichlids + other semi-aggressive non-cichlid fish, I've managed to divide a fish's "aggression" into distinct categories that in my opinion better profile a fish and its compatibility with others.
Here's the categories:
1) Fighting ability:
how strong is the fish at sparring/lip-locking with others? this will often determine who is the tank boss
2) Potential for damage:
can the fish kill other fish and if so how? some cichlids try to outright kill others in one go, while others like mbuna nip fins until the victim is stressed to death. this category determines whether you should add this fish or not, and often fish with high potential for damage should be avoided (highly toothed fish like piranha) while those with low potential for damage may have mouths that are too weak to give them a chance against other fish (ex. blood parrots and rainbow sharks)
3) Predatory instinct:
often people believe predatory instinct and aggression are the same which is completely wrong. a South American leaf fish (pure predator) will get killed by an herbivorous mbuna. this category is more for determining whether a fish's mouth is large enough to swallow a tank mate (therefore being more careful with tank mates for catfish etc.)
4) Attack/harassing ability:
fish that are high in this category are the ones fish keepers find the most annoying. these are fish that chase around tank mates for no defensive reason and include fin-nippers and others like leporinus. generally we like to avoid these fish as they cause havoc.
5) Defensive ability:
can this fish hold its own against larger fish? I personally love cichlids that are high in defensive ability and low in harassing ability because these fish are durable enough to withstand any extra-aggressive tank mates but will not go out of their way to chase and bully other fish. my favorite example of this category are convict cichlids.
6) territorialness:
does this fish stick to its own cave or does it swim across the tank a lot? I tend to find territorial fish to be more defensive as they spend all their time in the cave and won't leave it to harass other fish. thus fish that are high in this category tend to be defensive, though there are exceptions.
Here's the categories:
1) Fighting ability:
how strong is the fish at sparring/lip-locking with others? this will often determine who is the tank boss
2) Potential for damage:
can the fish kill other fish and if so how? some cichlids try to outright kill others in one go, while others like mbuna nip fins until the victim is stressed to death. this category determines whether you should add this fish or not, and often fish with high potential for damage should be avoided (highly toothed fish like piranha) while those with low potential for damage may have mouths that are too weak to give them a chance against other fish (ex. blood parrots and rainbow sharks)
3) Predatory instinct:
often people believe predatory instinct and aggression are the same which is completely wrong. a South American leaf fish (pure predator) will get killed by an herbivorous mbuna. this category is more for determining whether a fish's mouth is large enough to swallow a tank mate (therefore being more careful with tank mates for catfish etc.)
4) Attack/harassing ability:
fish that are high in this category are the ones fish keepers find the most annoying. these are fish that chase around tank mates for no defensive reason and include fin-nippers and others like leporinus. generally we like to avoid these fish as they cause havoc.
5) Defensive ability:
can this fish hold its own against larger fish? I personally love cichlids that are high in defensive ability and low in harassing ability because these fish are durable enough to withstand any extra-aggressive tank mates but will not go out of their way to chase and bully other fish. my favorite example of this category are convict cichlids.
6) territorialness:
does this fish stick to its own cave or does it swim across the tank a lot? I tend to find territorial fish to be more defensive as they spend all their time in the cave and won't leave it to harass other fish. thus fish that are high in this category tend to be defensive, though there are exceptions.
