Showpiece fish in your tank---good idea? or not?

Serial killer fish in your tank...what triggers them?
I kind of wince when I hear the phrase 'showpiece fish'. Most tend to be of a pushy species, and if you don't give them enough room...your other fish start disappearing. They don't even have to be that huge a fish---if your tank size makes them feel cramped, they just start adjusting the aquarium population until they feel calmer in the traffic flow. Your other fish, in a healthy tank, just start not reporting for feeding. Sometimes you'll find them deceased. Sometimes the snails and worms will get them first. The culprit? Butter wouldn't melt.

Then with some species you get the day they truly run amok and start taking the tails off everything in sight.

Be SURE your tank size will be ample. Fish grow. And when they get to a certain size, either you start having quiet disappearances, usually one a week. Or some day for no reason but barometric pressure or a change in the tank, you get the St. Valentine's Day massacre, so fast, so persistent and so general it's hard to stop the mayhem.

Amateur aquarists aren't the only ones who get caught by this. Back in the Jurassic, I paid a visit to our national aquarium in DC, on the morning the piranha tank went ballistic. There was fish confetti every which way in a tank the size of a delivery van. What happened? I asked the keepers. They theorized the temperature might have risen a tad, maybe making oxygen short. Those fish had lived with each other for years. My own suspicion is that it wasn't the first temperature glitch, but over the years, all those fish had grown, and one morning the dominant in the tank went bozo.

So pay attention to the stated adult size and also to the tank size requirements. Some dealers give these. But even so---err on the side of small. Yes, you can have one damsel in a 50 gallon tank. You can safely have 8 in a 100 gallon tank---as long as you're (with the exception of chromis) getting one of a kind. So you see it's not a straight line progression.

Remember, fish don't really come in 'community' and 'aggressive' in salt water tanks. What they come in is size. One species' aggression could be a feeding behavior. Another's could be territoriality. Is a humpback whale aggressive when it swallows a school of baitfish? Well, you could say he is. If you're a baitfish.

Just try not to push limits with your tank size. You're buying fish that will grow. And grow pretty quickly. You're likely to be at this hobby a long time. Your 3-head hammer may become a tankful in a few years. Your baby rabbit may become a 10" problem in a few years. And no body, no store and no zoo, wants a 10" rabbit or a dinner-plate-sized tang.