FishProfiles.com Message Forums

i never been able to figure out why, i often see aggresssive fish in lfs get along, but these same fishes which i know about and have are so aggressive.

for example, yesterday i was in a petland an i saw:

2 huge birchir,
1 jaradini arowana
2 silver arowanas

all in a holding 10 gallon.


now anyway stocking aside, i know from experience that jaradini arowanas should have kill the other silver arowanas.

and today i saw at another store, red devils in the same tank no problems, and in anohter tank i see a couple flowerhorns together, but mines is one of the most aggressivest cichlid i have personally seen.

and last example with arowanas, when i got my larger jaradini it was in a tank with 4-6 inch similar arowanas, and they should be aggressive but they are not.


my question is what makes the difference from being in a holding tank at a lfs compaired to my house.

For one thing, pet store fish usually do not stay in a tank very long. They haven't had the time to get comfortable with where they are, and so don't waste energy fighting. Instead they concentrate on survival in the unfamiliar and unfriendly conditions. Territorial fish don't get to spend time in a suitable aquarium, and don't have the chance to set up shop anywhere. Either their tank is too small, or there are too many other fish to allow for individual hangouts. Not only that, but lots of fish are introduced to a tank at the same time. Unless holdovers from another shipment are present, nothing has established itself, and all fish from a shipment are totally unfamiliar with the new digs.

There are other reasons too, such as the constant hands, nets, and equipment nosing around most of the tanks, dumb people who smack the glass, malfunctions, etc. A large part is just because life in a fish store is extremely stressful for fish, even those in display aquariums.

---

And when he gets to Heaven, to Saint Peter he will tell: "One more Marine reporting, Sir! I've served my time in Hell."

i had something like that in my mind, and it makes sense now.


thanks nick.

There's another reason why crowded fish in a store tone down their aggression. It's particularly applicable to Cichlids, which seem to be able to perform the appropriate calculations very finely, but probably applies to other fishes too.

Each additional fish in an aquarium produces a certain amount of pollutants. And, the fishes in the aquarium can gauge how crowded their home is by sensing the amounts of assorted pollutants. Territorial fishes then use this to calculate the risk involved in combat.

If you put, say, 4 Green Terrors in a 100 gallon aquarium, and let them grow up alongside each other, eventually territoriality will assert itself among the fishes. If the fishes decide among themselves that 100 gallons is enough for them all to coexist, then territorial behaviour will be primarily of a ritual nature. If, on the other hand, one or more individuals in the group arrive at the conclusion that there isn't enough space for everyone, then the biggest and toughest will solve the problem in typically efficient and brutal Green Terror fashion - namely by eliminating the unwanted competition.

Put 30 Green Terrors in the same aquarium, and the story is likely to be different. They'll all hate being crowded, but the instinct to launch into battle will be suppressed, because the much larger number of fishes will produce much more in the way of pollutants, and thus any fish that is tempted to engage in combat will gauge that the potential opposition, being much more numerous, makes the enterprise a LOT more risky. Not least because if the fish making the decision to attack ends up wounded, the chances are good that the other fishes will dispatch it. Taking on the odd one or two opponents, while it possesses certain risks, is a LOT less risky than initiating a fight when there's a small army of potential adversaries present, some of whom will be biding their time waiting for one to make a move before seizing the initiative and engaging in some culling of their own.

This is part of a whole collection of mechanisms governing aggression that was covered eloquently in the article Fish In Their Element by Dr Ashley Ward (Practical Fishkeeping, February 2004 issue, pages 4-8).

One of the features of that article, which I've discovered through personal experience definitely has an impact, is that the colour of the surroundings has an impact upon fish aggression. I wrote a piece entitled Green Is So Relaxing, which I posted in a previous incarnation of the Board, in which I explained this, and coupled it to some interesting behavioural discoveries in humans. Want to see your fishes become aggressive? Put them in a red container. This has been demonstrated repeatedly in experiments with Convict Cichlids (the Ashley Ward article covers this in detail). Likewise, yellow or white containers are not conducive to calm, and surprisingly, blue isn't as calming a colour as you may think for freshwater fishes, though for marine fishes it works very well. Black has a calming effect upon freshwater fishes, but the best colour to go for is green. The answer is pretty obvious - most freshwater fish habitats are awash with plant life. Whether it's algae coating the rocks of Lake Malawi where the Mbuna dwell, the Cryptocorynes of West African rainforest streams, the Amazon Swordplants and Cabomba of South America, or the Java Ferns of Asian biotopes, plant life is present in abundance, and so if you surround your fishes with shades of green, their behaviour will be much more natural, because for many fishes, green equals home and security. Bare dealer aquaria will stress the fishes thus contained, while an aquarium with luxuriant and thriving plant life (except in the cases of those fishes that destroy plants of course!) will be relaxing and soothing.

As an experiment, if you have a spare aquarium to press into service that can be fitted on the outside with different coloured backgrounds, compare the results of keeping various fishes against red, white, blue, black and green backgrounds for yourself. You'll probably find that your results match Dr Ward's.


Panda Catfish fan and keeper/breeder since Christmas 2002