Aggression In and Out of School
Tiger Barbs, friends and relatives

Ing posted January 14, 1999 10:02 PM ET (US)

I have six tiger barbs. At times I see two of them nose to nose with each other and they start spinning round and round. Can anyone explain this behavior for me?


RTR posted January 14, 1999 10:14 PM ET (US)

I have seen the same behavior, and considered it male dominance behavior. Were your two fish males? Mine were. Similar to the two males head-to-tail spinning common with Rosy Barbs, and kissing in Kissing Gouramis- though I can't say if those are always males or not .


Ing posted January 14, 1999 11:55 PM ET (US)

Yes, I believe they were males. Are they just having fun or are they serious about this?


Randall posted January 15, 1999 10:39 PM ET (US)

I saw two of my male Tiger Barbs doing the same thing tonight. It was fun to watch. Very interesting fish, those Tiger Barbs. I have 5 in a community tank. They do harass the other fish somewhat. Rather than get rid of them, I purchased another tank that I am going to move them into and add some more.


Big Kal posted on January 15, 1999 07:54 PM ET (US)

I have had three rosy barbs for maybe a month now and just today I saw them "biting" each other playfully, or so I thought. They were looking rather playful but yet, aggressive but I really didn't think anything of it. Now one of the barbs is barely alive, it's swimming upside down and around and doing flips, it's most likely going to die. What would cause such behavior?


Schools are a defensive device for fish. It is difficult for a predator to target one fish in a school. So this behavior has become hard-wired over time, it has become instinctive to a number of fish, and we cannot overcome that instinct in our tanks. Some fish show schooling only when very small, as do Cichlid fry. Others may school well into "teenage", such as Synodontis nigriventris, the familiar Upside-down Catfish, but do so less as sexually mature adults. Many fish school, not in the tight groupings we imagine for schooling, but as loose aggregates with only minimum obvious coordination of movement. Corydorus catfish and Otocinclus Catfish both fall into that category once acclimated to our tanks, where they "learn" that predation threat is low. We do not see them as a school, but they do. If stressed they will fall into tighter coordination and show overt, obvious schooling behavior and synchronized swimming. Without the security offered by the school, fish that maintain this behavior throughout their life will not be "normal" or "happy" in our tanks. They may survive, but subject to constant low-level stress, they will not thrive.

There is more than one type of interaction within a school. Many of the Characins (Tetras) that school have no rank structure or hierarchy within the school. Other fish, most familiarly the Barbs, do have structured schools. Males in particular have a rank order. There is one fish, the alpha male, who "bows" (gives way) to no one. The other males in the aggregation will each have their own distinct rank as well. The beta male (note: beta, second letter of the Greek alphabet, not Betta, the Siamese Fighting Fish) will bow to the alpha, but no other. Similar ranks will exist for the gamma, delta, and so on to the effective omega, low man on the totem pole (a mistaken analogy, as that is really the prime pole position, or so I've been told). These fish have a hierarchy and each "knows" its position in the school organization chart. This is exactly like pecking order in chickens.

The aggression shown among conspecifics (fish of the same kind, the same genus and species) within a school is similar to the territorial aggression shown among substrate-associated cichlids. There aggression provides each fish with feeding or breeding area in a fixed location with discernible (at least to the fish) boundaries. With the schooling fish like Barbs, some aggression serves to space the individuals in the school (for wider access to food?), but still maintain the coherence and security of the group. This is not in a fixed location, but is movable in space as the group swims around, providing 3-D personal space for each member of the school. You could imagine the school to be like a cluster of same-sized soap bubbles, each bubble marking the personal space of a single fish. The cluster can change in shape and form thru rearrangement of the bubbles, while the individual bubbles hold their size without losing contact with the cluster. Few of our tanks allow sufficient room to really show full-scale schooling behavior other than for the smallest fish. With fish such as Tiger Barbs, the personal space requirement is still there. As is the aggression that defines that space.

Given that aggression to a certain degree is inherent in these fish, that aggression must have release. In a group of conspecifics, aggression is released in establishing and maintaining the "pecking order". The alpha fish works his off defending his rank against the beta fish, and less often, the gamma fish. The beta will in turn challenge the individual above him in rank, and defend his rank against the fish below him, and so on down the list. The omega fish can only challenge above his rank, but can also display to the females, so long as a higher-ranking male doesn't catch him. These challenges are what Ing, Randall, and I reported in the first four posts quoted above.

Okay, fine, but what does this mean for our tanks? It means that Tiger Barbs and their relatives can be expected to show some aggression, and that in an effective school it will be dissipated among the conspecifics. The kicker is, how big is an effective school? Well, like many things in aquaria, it depends. It depends on the size of the tank, the presence or absence of perceived threats, and the proportion of males and females in the school. Three fish do not make a school for Barbs, even ones of lower aggression than Tigers. See Big Kal's quotation above for sad proof of that. These fish will release or work off their aggressive instincts or urges. If there are not enough fish to spread the aggression around, the lower ranked individuals may be battered or even killed. In tanks, they cannot flee. If there are too few members in the school, the aggressive urges may be taken out against other fish in the tank. We have all heard the stories of Tigers nipping fins or worse on unrelated tank-mates. On that point, Angelfish do not count. Expecting a hyperkinetic fish of any sort to resist the invitation of those long fin extensions is just too much. With sufficient numbers, aggression is spread around and is ritualized- no serious nipping or lasting damage results. Conspecifics speak the same language of threat display- my colors are brighter than yours, I'm bigger and meaner, spread my fins better, and just try to keep up with me in a head-to-head or head-to-tail (really caudal peduncle) spinning contest. Other fish do not know what they are talking about, do not respond properly, so they are harassed. Randall's post was good on that. I have said before in posts, and I have seen others do the same, that six in a minimum number. In the future I may say eight. Randall had five and still saw aggression against non-Tiger tank-mates. A margin of one fish is too small. If the tank were large, and there were some fish large enough to be seen as a threat, five or six might well be enough. I don't think I would chance it.

Tiger Barbs are very active fish. Given their aggression levels, they really are better in a species tank. Picture a 40L (48" long) with a dozen Tigers, three Clown Loaches, and a couple of Ancistrus lurking in the Anubias and Java Fern-covered tangle of driftwood along the back of the tank. That would be a very showy, highly kinetic tank. If you must keep them in a community setting, better count on six to eight Tigers, six for the less aggressive Barbs.