How do fish kill eachother?

[Hybridfish7]

I never really see how it happens. How do they go from 0-100 like that? It always goes like, a little chasing and nipping both fish are in tact, I leave and come back a few hours later, one has no fins or scales, is missing an eye, and is upside down. How do they do that? Does one like catch the other or ram it or something? I can't imagine the "victim" just sitting there getting its eye and scales ripped off.

 

[Deadeye]

Part of it might have to do with the stress getting too high and if the fish being starved out it will start to slow/shut down. Once it gets too weak the aggressor is able to finish the job.
It also depends on what is happening. In the case of a predator, it just needs to get one good shot to kill the fish. For something like territorial aggression (especially in African cichlids) it seems like a constant thing until the aggressor finally decides to go for it, and I wouldn’t be surprised if the other fish don’t gang up as well.

 

[Milingu]

Stress - Constant stress kills any fish at a certain point and I guess is one of the main causes for alot of so called unexplainable death.

With cichlids I encountered everything from constant chasing over fin nipping to internal injuries from ramming to deadly bites.
I lost two Lufubuchromis males with the lower jaw disconnected from the head. Another male had rammed them so bad from underneath that the connection between angular and quadrate broke which lead to quite quick death.

 

[Rtc/tsn]

I never really see how it happens. How do they go from 0-100 like that? It always goes like, a little chasing and nipping both fish are in tact, I leave and come back a few hours later, one has no fins or scales, is missing an eye, and is upside down. How do they do that? Does one like catch the other or ram it or something? I can't imagine the "victim" just sitting there getting its eye and scales ripped off.

When you leave the room they pull out their tiny knives and guns and go ham on eachother, seriously though I imagine it’d chase the other around until it dies of stress or exhaustion

 

[jjohnwm]

Stress certainly weakens fish and depresses their immune systems; they gradually decline, usually contracting one or more diseases as the deconditioning progresses. Then, when dead or nearly so, they just get picked on, chewed, mauled and otherwise mutilated by many fish which weren't and aren't actually aggressive per se, but are rather simply...eating...

But the situation you are describing...everything is peachy at breakfast time, and then by supper you have a rotting corpse...is almost a specialty problem presented to cichlid owners, as well as those keeping a few other types of borderline-psychotic fish; piranhas, sunfish, maybe wolffish...

The story is very common. A guy loves cichlids, and decides that somehow his 100-gallon tank is different than all the others in the hobby, and so everything he has read about cichlids can be disregarded. A bunch of 1-inch cichlids go in, often species that are known to be very aggressive, and usually ones where each single individual will outgrow the tank within a year...but the tank has about a dozen of them. They "get along fine" for awhile, eating and growing and developing into mature killers, maybe pairing up and trying to breed, or maybe just getting bigger and crankier and more inclined to not play nice with others. Each one looks around thinking "This space is all mine!", probably interspersed with notions of "I can take that guy!" and "You're in my spot!"

One day the biggest...which usually also translates into the nastiest...just decides he has had enough, and goes on a rampage. Much blood, many deaths. Our hero comes home from work, looks into his tank...in which apparently nobody is continuing to "get along fine"...and wonders what happened...

Usually, the aquarist will start a thread, sometimes replete with pics of partial fish and empty eye-sockets and torn fins. The same day, another hobbyist will read that thread, decide "Nah...that guy did something wrong...that'll never happen to me!" and will immediately traipse off to the LFS, where he will buy 4 Jaguars, 4 Red Devils, a Flowerhorn, a Dovii and maybe a couple Piranhas 'cuz they're just so cool...

He might even know what's going to happen, but isn't concerned because, after all, these fish are just going into a "grow-out tank" and will eventually move into that 500-gallon he is planning on building after he moves...

...and so the Wheel of MFK begins another rotation...

As to how they physically do it, well...you've seen cichlids lip-locking as they sort out dominance issues and breeding hierarchies. When one of them is big, tough and psychotic...i.e. has grown into a typical adult male cichlid...and when the other one can never get more than a couple feet away, because 100 gallons or so just isn't that big compared to any natural environment and simply doesn't allow the loser to get away...lip-locking turns into grabbing whatever part of the sub-dominant fish can be grabbed, and simply shaking and biting until that part comes off. The loser isn't fighting anymore...it's instinctively trying to get away, but simply has nowhere to go.

When that unlucky fish stops moving, the big guy takes a breath, looks around, and then it's..."Hey! What are you looking at???" and away we go again.

Cichlids are great, aren't they? Personally, I just find most of them too stressful; I don't want to fretfully check each tank every day hoping that "it" didn't finally happen...but "it" happens too often for my taste, so I just avoid most of them.

 

[neutrino]

But the situation you are describing...everything is peachy at breakfast time, and then by supper you have a rotting corpse...

Agree. Bullying and stress can cause bloat or other problems that kill the weaker fish over time, but witnessing posturing or lip locking, then the next morning or a few hours later one is dead is not just stress. In nature, once the stronger, more dominant-- or more psycho-- fish gets the advantage is when the weaker fish would retreat and be chased off, with the stronger fish returning to guard his territory. When there's nowhere to go in a tank is when the weaker fish gets beat on and either dies from its injuries or is killed outright. Whether it happens by being battered or being literally torn up depends on things like the temperament and dentition of 'superior' fish.

 

[duanes]

I agree, with the others about stress and the lack of space in almost all aquariums.
Stress is one of the most important factors, as are the hormones that occur during spawning to ensure defense of fry.
Although eviserating each other is common in predatory species in aquariums, many of the other seemingly non-aggressive species are killed by stress, that may not show any wounds or battering at all.
Some just intimidate others into death.
I've had a dominant Acarichthys heckelli kill all others of its species in a 150 ga tank, with not a sign of battering
But It especially comes into play when different cichlid species are attempted to be kept together in what may seem like an adequate tank space to the aquarist, but to the fish themselves is far from being remotely sufficient.
I have watched a pair of 10" JDs defend an area the equivalent of 250 gallons in nature in the Cenotes of Mexico.
But It usually doesn't end in death there, because there are often thousands of gallons of escape room, to make an unscathed getaway for the subordinate.
Or the same can be said for a female, if the males spawning hormone boost gets out of control, even a 6 ft tank may not enough space to make that clean getaway, for her.
This is why many pro breeders will keep only one pair cichlids in a 6 ft tank, but also add egg crate incomplete dividers that allow females a route of escape to avoid over zealous males.

 

[duanes]

One other factor, most cichlids will not break off chasing another cichlid from their territory, until about 4 ft from the middle of it(4ft x 4 ft).
So if a tank like a 75 is 4ft by 2 ft, in reality, there is no space for escape, even a 6 ft x 2, only offers a small area beyond the 4 ft, but......if the dominant individual can still see the rival, that 6 ft (that extra 2 ft may not be enough to slow the dominant territorial owners aggression)

 

[esoxlucius]

This thread seems to me like an advert on why not to keep fish in an aquarium......and we're a fish keeping forum!! Lol.

I don't know whether i've just been lucky over the decades i've kept fish, or perhaps just super skillful, that sounds better lol, but I've never ever had a tank, of any size, where any of my fish butchered one another. The odd smaller fish getting taken by a bigger fish yes, but no in house fighting to the death type situations.

But saying that I've never ever kept any of the notoriously aggressive cichlids, only mild mannered ones.

Now is a good a time as any to ask this question because the master of cichlids is already involved in this thread. duanes , there must be a part of you that thinks that most cichlids should never even be kept in home aquariums, even very large tanks, simply because cichlid territories can cover a fair bit of space, something that most aquariums can never cater for.

We all go on about fish care, but to me cichlids get the biggest bum deal of any fish we keep. Not enough aquarists have the remotest idea when it comes to territories for these fish.

 

[Backfromthedead]

Ime, chasing and nipping fins can go on for a long time without necessarily harming the fish. It's when they start going for actual bites out of the body that death occurs.

With many fish, like cichlids, I think the outer jaw is adapted for both feeding and nipping competitors/hierarchical behavior. I believe that when they start taking lethal bites with the stronger pharyngeal jaw it is intentional and premeditated.

In other words I think nips can be distinguished from bites as separate levels of territorial/hierarchical behavior with different intentions.