what ARE aggressive fish? A discussion....

[Sk8r]

I've had 'community' tanks, 'aggressive' tanks, including a piranha tank, a tank with a small bass---and I have arrived at an odd conclusion. The most aggressive fish I ever kept was a goldfish, which would eat ANY non-goldfish you put it with...

So what defines an aggressive fish and are they harder/easier to keep than community fish?

First, among freshwater fishes there are some dedicated herbivores---mollies, etc---that are everybody's lunch if not protected, and you can generally put another into the tank with no problem of it being attacked.

NOT so in salt water. Even the otherwise gentle mandarin will kill another mandarin that gets dumped into its tank, and you can't readily think of a quieter, less argumentative fish than a mandarin.

I think the 'aggressive' tag does apply to a few fishes like, say, the big triggers, notorious for going out of their way to attack, and apt to eat any tankmate.

But for nasty persistence in taking pieces out of tankmates, you could equally well add the false cleaner goby, only an inch long, but making its living by biting pieces off any fish that swims by. In a small tank---well, you get the picture.

Some species only bother their own kind: the yellow watchman will bluster and gape at everybody that doesn't scare him into his burrow, but will bust a gasket getting at a potential rival. Some blennies also do this.

Some species are stealth predators, and wait for other fish to go to sleep. Eels are good at this maneuver.

Some species will become reconciled to what is new: I had a 2" long highfin goby sump-dive; thought he was dead. Bought a new one to go with my female. The other guy showed up. I put him in. Two days of WWIII. Mouth-measuring, nipping, but no fins missing. The third guy took to hanging out near the couple. After 2 weeks he shares their burrow, or shacks up with the jawfish.

Some species will kill each other until they adjust their own number to fit the tank: firefish, chromis.

Some species just pick on each other and chase continually, but never seem to kill each other off: damsels.

Some species are really nasty when mating: clowns can turn from funny little guys into maniac terrors. I've seen a clown grab an unoffending fish and stuff him alive into his anemone, fatally. And people have, with reason, compared the female maroon clown to a queen trigger with attitude. They will attack the owner who puts a hand near them...let alone a tankmate.

How do you stop aggression? A newly suggested method [thank you, Prugs]: a mirror, to distract one fish into obsessing on his own image.
Turning out the lights on a fight. When a new day dawns [every day is a new world if you're a duck] the fish may 'forget' they've never seen each other until yesterday. What's old news---isn't attacked, in some cases.
Putting the aggressor into qt for 2 weeks, then returning him to the tank as 'the new guy'.

Anyway, this being a topic on which there's a lot of difference from freshwater, and in which there are some odd assumptions, I thought people might like to discuss or ask questions.

 

[barbra]

I think you make an outstanding point. I have nothing in my tank as aggressive as my yellow tang defending his piece of Nori. Or even the act of eating the Nori, which he attacks with the same fervor that you might see a shark display on a large kill.

In freshwater when I think of aggression I think of Oscars immediately. Any animal that will chew your hand off under normal circumstances is considered by me to be aggressive. But that is mostly because I think as people we define aggressive creatures as those that are aggressive to ourselves. Ants are quite aggressive, but rarely does it impact human life, so we think of them as being easily squashed out.

Do you think it is fair to say that nearly everything is aggressive when it comes to looking out for it's own interests, even though the aggression may be harmless or even comical to the observer?

 

[luke33]

I think your mixing the words territorial and aggresive. Agressive to me means a clown trigger destroying a fish just to destroy it. Territorial means to me a angel being in my tank and introducing another angel. The original will chase and harass the angel for a day or up to a couple weeks and the end result will be death or they will be fine....the same with tangs. Some would consider that aggressive behavior but its really just teritorial behavior. And the word aggresive isn't really true either. Its not aggression that causes the trigger to kill, its just insticts in there genetic makeup. But many may disagree. But an interesting topic to talk about. The cichlid family is pry the most interesting when it comes to agression.

 

[papagimp]

I agree with luke's comment, some differences between aggressive and territorial. I'd also use a mirror with caution. many fish are aggressive or territorial with conspecifics and may attack a mirror image. much like a betta fish would. It's risky but better he kills himself than everybody else.

 

[barbra]

Granted one must define the terms prior to arguing a point, but there is such a thing as Territorial Aggression. An attempt to separate the two is missing the point.

 

[Sk8r]

Well, and there's just simply---food chain. Any fish that can fit into another's mouth and down its gullet...probably will.
But it's not saying a combtooth blenny [dentition like a brontosaurus] isn't going to do damage in a territorial fight: he's almost entirely an algae eater, but may take exception re mating, feeding area.
A mandarin really has no territory I've ever detected: they just wander, eating pods, and may wander right through a fight, oblivious. Most other fishes seem to pick a 'geological' feature, like a rock or coral head [in the wild] as 'theirs', and they hang pretty close to it. I think one the major problem people have with damsels is that a damsel has a VERY large territory, and people with small tanks who get advised into a damsel are often shocked at the behavior. In a 100g, a damsel may defend, say, 1/3 of the tank, but his chases peter out away from 'his' rock, and he will return to that base and wait for the next intrusion or food, whichever comes first.

WHich brings me to one other way of breaking up a perpetual fight when introducing a new fish: move the rockwork. Territories have to be redefined.

Re mirrors: we had a decorative mirror near our tank when we set up. Wrong! Our yellow watchman nearly killed himself trying to get that 'fish.' We had to move it, because he'd rather kill that fish than eat.

 

[luke33]

The perfect freshwater fish that shows agression=snakehead, but this isn't its fault, there just eating machines. Its the genetic makeup in it that says if something will fit in your mouth eat it, no matter if your hungry or not. Many times you'll catch a bass with a plastic worm and when you get him out of the water he'll be fat as crap with shad coming out his mouth......is he agressive i guess but its more instict than anything. When taking a fish from an ocean and adding it to a tank, hard telling what is going to happen.

 

[Sk8r]

: When taking a fish from an ocean and adding it to a tank, hard telling what is going to happen.
---luke33

So true.

There *is* however, one convenient help: liveaquaria.com, on the left side of their 'marine fish' sales display, has a little 'compatibility chart' that is a real help, even to people who've been decades at this...it's the collected experience of people who have learned what will actually happen in various combinations of fishes and inverts.

I can, for instance, tell you that a ghost eel, which is rated 'hard to feed' prefers live food, hunts at night, lives in rocks by day, and got 300.00 worth of my smaller fish before I caught him and got him back to the store. In the 'die and learn' school of aquatics...

One really good resource is just to run a flag up in the fishy sections of RC and ask other members what they've found.

 

[3rdimension]

How do you stop aggression? A newly suggested method [thank you, Prugs]: a mirror, to distract one fish into obsessing on his own image.

I did this today in my 125 gallon FOWLR tank. I noticed a decent size chunk out of the tail fin of my passer angelfish from my clown trigger fish this morning. So I mounted a 24"x30" wall mirror on one end of the tank. The Trigger won't go anywhere near that end of the tank anymore, meanwhile the passer angel is obsessed with it's own reflection thinking it's another fish. Like an invisible barrier! Works wonders! Hopefully it'll last a while because I really don't want to get rid of the clown trigger.

 

[chrisfont23]

Cherry barbs are the worst