Few marine fish are absolutely aggressive under all circumstances---unless you count 'feeding' as aggression, which I personally don't. BUT--you can get into a serious case of aggression and mayhem because of your tank choice.
Size matters. Consider how calm you'd be if you had to be in constant view of a person you didn't like in the first place. And shape of the tank matters. Is there anywhere in your tank that one fish can lose sight of another and thus calm down after a little territorial discussion?
I have a wedge tank, triangular, which isn't the best shape for isolating fishes, but it's 105 gallons, which, considering my heavy maze of rockwork and use of spires of tall rocks, does give some relief from everybody being in everybody's face. Being able to get 'apart' is important. If you haven't got size, consider obstacles that can serve to obstruct view. Because I have the tank I have, I don't include fish that can get cranky about territory: blenny, goby, chromis (1), gramma (1), and clown pair. They don't fuss. Nobody gets bit. Worst quarrel is the female clown bashing the gramma with her tail in an attempt to claim the gramma's cave. It never amounts to more than that, and probably the clown will annoy the gramma enough to make him move.
The easiest type of tank to provide cool-down space for is long, so that there's plenty of room for fish to get apart and forget what they were doing (which they readily do: real out-of-sight, out-of-mind.)
This is why you get so many varied answers when you ask (with no details) can I keep an 'x' or a 'y' together in my tank. And why when one fish has a 10" growth potential and another has 2", that can be an issue. The space to move in does matter.
Size matters. Consider how calm you'd be if you had to be in constant view of a person you didn't like in the first place. And shape of the tank matters. Is there anywhere in your tank that one fish can lose sight of another and thus calm down after a little territorial discussion?
I have a wedge tank, triangular, which isn't the best shape for isolating fishes, but it's 105 gallons, which, considering my heavy maze of rockwork and use of spires of tall rocks, does give some relief from everybody being in everybody's face. Being able to get 'apart' is important. If you haven't got size, consider obstacles that can serve to obstruct view. Because I have the tank I have, I don't include fish that can get cranky about territory: blenny, goby, chromis (1), gramma (1), and clown pair. They don't fuss. Nobody gets bit. Worst quarrel is the female clown bashing the gramma with her tail in an attempt to claim the gramma's cave. It never amounts to more than that, and probably the clown will annoy the gramma enough to make him move.
The easiest type of tank to provide cool-down space for is long, so that there's plenty of room for fish to get apart and forget what they were doing (which they readily do: real out-of-sight, out-of-mind.)
This is why you get so many varied answers when you ask (with no details) can I keep an 'x' or a 'y' together in my tank. And why when one fish has a 10" growth potential and another has 2", that can be an issue. The space to move in does matter.
