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Theory question. Suppose you have a shoal where some really sustained fighting and persecution breaks out. One fish is dominant and causes a lot of trouble, and another clearly less dominant is suffering somewhat. You decide that seperation is the only way to go. Which fish do you remove to maintain the social dynamic of the shoal for the better, and why?

Im aware that there are some different behaviours out here for diffent species,and you may choose a particular species of fish to comment on or go for a general approach.

What do you do?

Last edited by longhairedgit at 29-Nov-2005 06:44

Sell Tickets.

Sorry, am not awake yet...
Either remove the bully, or the weakest fish.

Or, pull all the fish out and add more territories to the tank, re-add all the fish and observe. May not always fix the problem, but worth a shot.


The Amazon Nut...

Remove all the fish & re-do the tank. Then i would isolate the weakest fish & put the rest back in the tank.


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I would say it depends on "what would happen next" in nature.

With that I mean:

a) Would the weak fish leave the shoal and swim far away? In that case he should be removed from the tank.
b) Would the weak fish fall back into his appropriate position within the shoal? Then leave him in the tank. If he just doesn’t get it, well tough luck.

Ingo

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Proud Member of the New Jersey Aquatic Gardeners Club

In this case, is it likely that the dominant one would simply pick a different target?

"I am a believer in punctuality, though it makes me very lonely" EV Lucas

Easy toss the aggresor out completly. If this is done sometimes another fish takes over the dominant role.

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It's too broad a subject to approach as a general question. I'd have to be given a particular species (and one that I'm familiar with) before I could go into details.

Last edited by Cup_of_Lifenoodles at 30-Nov-2005 01:25

Ok , I thought the answers might be a bit muted on this one, but I guess the answer depends mainly on your goals for a particular shoal. Theres a few factors to consider.
(ps. I said you could choose a species.)

1) Breeding potential and Heredity.

Very dominant fish often breed extremely well, females in many species find them impressive, and perhaps breeding success is more probable with such fish.Obviously when a fish is so aggressive as to be considered virtually psychotic, it either does have a problem with hyper aggression (probably a mental complaint) or the tank is of insufficient size or decoration for the task at hand , or the male/female balance may be off. Extremely aggressive fish may have some limitations as good long term projects for breeding, because if the fish is excessively aggressive, chances are its also easily stressed and the strain of being an alpha male/female can actually shorten its life. If you keep rare species obviously a fish that kills others is not always a great idea.

2)Age issues.

The persecution from a dominant male may be so severe because his only competition of the same sex may be a much smaller or younger fish. Obviously in a situation where male competition is considered essential for breeding, males of equal size and strength should be considered.Potential breeding females may not be yet of age , so the dominant male may be trying to impress them all the harder because of their lack of interest.He doesnt know hes going to have to wait a few months whether he likes it or not.To suit the dynamic of the shoal in this case perhaps removing the dominant animal may be beneficial, at least until the other fish have increased in size and maturity.

3) Provocative triggers.

People with hybrids and selectively bred animals may experience standard colourations that match breeding condition or aggressive threat colouration. A given animal may be in aggressive colouration whether it intends to be or not. This means that in the mind of the aggressor fish, the suboordinate never actually backs down. Sometimes lighting, a mixture of species or even the presence of another currently breeding species ( hormone release into water) may cause a triggering of unusually violent competition.

Food competition.

!Everything is mine! Some fish dominate food resources whether they are hungry or not. This is rarely the norm for most species. Any fish trying to get to food may be attacked.

Health

Fish often persecute weak fish. It can be to eliminate easily removed potential future competition, or quite simply its the reaction: "youre sick - get the hell away from me!"

The health of a shoal can be a difficult thing to manage. For some species living in a shoal is essential, not to do so is so stressful that it may literally end their lives. So do you go with the stronger fish, or the weaker fish? The stronger fish may be the sole cause of the weaker fish's failure, or it may be that the weaker fish is literally incapable of ever amounting to much. How do you tell?

Natural selection.(or unnatural selection)

Do you think it is right that the weaker fish die? Can aquarium life in any way have similar enough perameters to nature to keep a species strong via allowing mating and dominance struggles to carry on in a tank?

Just a few things to get those brain cells ticking over.Whats your experience?

To get the ball rolling I have to say that ive found particularly with rainbows it helps to remove the dominant fish, with tiger barbs to remove the weaker, and with a lot of tetras to remove the stronger.It may have something to do with the fact that the species have different levels of stressful degradation in their shoals to which there are a few different dynamics and thusly ways of handling it.

Do you think this has a positive impact on multigenerational breeding or not?

Besides it might help beginners and a few experts alike to find out why their fish occasionally or regularly beat the hell out of each other , and what to do if it happens.



Last edited by longhairedgit at 30-Nov-2005 04:36

1st...ill make sure i have at least the minimum number of the shoal, less tends to be more stressful for the group...if i have the number and yet, theres still a bully, ill take that one out.

hi there, i had this problem, one dominant fish who wreaked havoc in my tank, when i removed him all the fish enjoyed the peace.
So i'd say remove the bully, in my case it worked for me and my tank.

Hmm. A difficult and involved question.

In the case of my Beckford's Pencil Fish, I discovered that if they are in an aquarium bereft of any other fishes that look threatening (i.e., larger fishes such as a Pearl Gourami or an Angel Fish) then they can undergo a complete change in personality, and start behaving more like Mbuna than characins! In fact, mine started behaving like Black Belt Cichlids, and the dominant males systematically wiped out all my females, before turning their attentions on each other. Thanks to that experience, I wouldn't recommend putting a shoal of Beckford's Pencils in anything less than a 4ft aquarium, so that there's plenty of scope for the fishes lower in the pecking order to stay away from trouble. I won't be getting ny more Beckford's Pencils for a while, until I have a 4ft aquarium in which to put them, and I'll try and make sure that it's furnished in such a manner as to provide plenty of hiding places for any individuals that find themselves being harassed.

The key to this is space. Despite being small fishes, Beckford's Pencils, in my experience, demand a fair degree more space than the 'typical' shoaling characin. Needless to say, I'm of the opinion that the textbooks need a LOT of revising with respect to this species! Moreover, I'd recommend getting no fewer than twelve of them at a time to make sure that any aggression is spread more thinly among the resident population, because thanks to the experiences I've had in keeping these things for nearly two years, I'm convinced that in a setup where there are no 'predators' (i.e., fishes that trigger a tight shoaling response to a perceived threat) they exhibit a behaviour that bears a fair degree of resemblance to the hyperdominance syndrome seen among some Mbunas.

However, I suspect that even a fish such as the Cardinal Tetra can start becoming snappy if it's crowded. Therefore my first answer is to ask how much space your shoaling fishes have. If they have sufficient space to move around in, they'll be less likely to engage in internecine warfare.

Second, are these fishes a species in which there is noticeable sexual dimorphism? Only I am beginning to suspect that this is a factor too - fishes in which the males and females are obviously different may exhibit this kind of behaviour to a greater degree than those fishes in which sexual differences are far less obvious. So, for example, I'd keep an eye on Black Phantom Tetras (particularly in a small aquarium) in case they too exhibit the same kind of behaviour. I noticed it in my Lemons - the males adopt 'landmarks' in the aquarium and engage in macho 'jousting' contests with each other. However, in the case of Lemons, it was mostly show and ritual - their flashing passes at each other looked spectacular but resulted in no damage.

I'd also advise at this point that if you have two or more shoaling species that exhibit this behaviour in the same aquarium, then one of those species may (again on the basis of my experience with the psychotic Beckford's Pencils) become more aggressive with conspecifics and indeed with other shoaling fishes because the 'landmarks' available for display are limited. Again, some species will need more space because of this, and consequently if anyone contemplates mixing Black Phantoms and Beckford's Pencils, I'd only recommend that in a 4ft setup or larger just in case one or other of the species decides to 'go Mbuna' on you!


Panda Catfish fan and keeper/breeder since Christmas 2002

Perhaps a far smaller male may result in some squabbles, but it is in my experience that two evenly matched males will display far more aggression and whose squabbles may have far more injurous results.