Do fish really know their numbers?

[Whitecloudminnowguy09]

People always say, keep this fish in a group no smaller than say, 6. But I do wonder, do fish really know that there is 6 of them, and that number is satsifactory for them to not get stressed. Fe, I have 4 peppered cories, after 2 died. Do they really know or care that two are missing and there is no longer 6 in the tank? All of them have their brighest (in this fishes case, darkest) colors and all look happy. It has been 2 months since the 2 passed, and I have had zero issues, with health or stress. Might sound like a stupid question, and may or may not have an easy answer, but would like some feedback on this.

 

[raylove]

Interesting question. Buy any group of fish and the odds are one individual will way outlast the others, sometimes by years. I've never noticed any signs of stress and living so long seems to confirm this. I imagine it's most important when settling in to a new environment, but once settled in, maybe not as important. Obviously some species are more nervous, and always will be, so those probably benefit from being in larger numbers even in familiar surroundings.
As you say, it's hard to tell and there probably isn't a straightforward answer!

 

[Essjay]

Some time ago Byron posted on this subject and he included a link to some research papers.

Effect of group size on behaviour and welfare of fish

The number of fish needed for species "x" to be healthy and less stressed in an aquarium is a topic that enters quite a number of threads on TFF. Some of us realize how vitally important the number of fish for a particular species really is, but having scientifically-controlled studies that...

www.fishforums.net

 

[anewbie]

6 is just a generalization. I actually prefer larger groups for many fishes so i have 13 clown loaches (really small for a group size that should be int he 100s); 25 or so cory sterbai (again the group size should be in the 100s but alas space constraints).

My hope when i setup a 12ftx5ft aquarium after i move i'll get 300 ruby tetra (the most lovely active tetra you can own) and a 8ftx5ft i hope to put in 200 jelly bean tetra.

6 pffffttt just a number that seem to fit smaller aquarium but is way too small for any reasonable group.

 

[GaryE]

You see a behavioural difference with larger numbers. Six is a number the hobby pulled out of its umm, nose. I think it was a discount number for pet stores, and a bare minimum. When I started in the hobby, we were told three was the number. That one was a destructive suggestion. So it became six.

The papers our late friend Byron posted are really interesting to look at.

You can keep tiny herds, packs, flocks etc of social animals, but the general consensus is you see different behaviour in group situations.

 

[Innesfan]

The scientific paper that described a species I'm very fond of, Pethia setnai,("Indigo Barbs") included some interesting details that are relevant here. The authors noted that in the wild the species is found in loose shoals of 8-10 lorded over by a dominant male. I have found that keeping them in smaller numbers exacerbates male aggression, and in larger numbers several are apparently excluded from the family and huddle in the tank corners. It would be invaluable if this 'in situ' information were available for more species.

 

[anewbie]

The scientific paper that described a species I'm very fond of, Pethia setnai,("Indigo Barbs") included some interesting details that are relevant here. The authors noted that in the wild the species is found in loose shoals of 8-10 lorded over by a dominant male. I have found that keeping them in smaller numbers exacerbates male aggression, and in larger numbers several are apparently excluded from the family and huddle in the tank corners. It would be invaluable if this 'in situ' information were available for more species.

Yes it is a pity we dont' have more money for research. I was mentioning TDS effect on fishes but unfortunately the only papers i found were game fishes (salmon, trout...) after all who wants to fund research for the sake of research.

I presume that the 8-10 individuals are either females or junvies of course if you have 30 do they break into 3 shoals ?

Naturally Mrs google just use standard number and sez buy 6 (or more).

 

[Innesfan]

I presume that the 8-10 individuals are either females or junvies of course if you have 30 do they break into 3 shoals ?

Naturally Mrs google just use standard number and sez buy 6 (or more).

I suspect there are alpha and beta males. That is certainly the case in my 75g. The beta males are part of the pack but congregate with the ladies. They aren't driven into the corners by alpha guy.

 

[plebian]

ruby tetra (the most lovely active tetra you can own)

My Paracheirodon simulans care to dispute that claim.

 

[GaryE]

What we have to bear in mind is Pethia is one Genus, and if 8-10 works for them, friends have reported spending all day with shoals of cardinals in the millions passing by. A friend described a group of corys (I don't know which species) passing by his feet in enormous numbers, taking a long time to move down the stream while he stood in wonder.

I'd hate to be a person who thought he knew everything. That would be boring. I would, however, like to know a lot more about fish behaviour in the wild. It's interesting. My limited experience "in the field" has already stood a lot of my aquarist's lore on its head, almost always in ways that are inconvenient. We do like to generalize. Could it be we make 'rules' for captive fish in ways that please us, and not them!!! Gods forbid humans would be like that. Six is a convenient number. Ten starts taking space, and 20 is worse.

I don't know how much I've learned about fish in this hobby, but man, it'll teach you a lot a lot people.

 

[GaryE]

ON another level, experiments have shown some fish species (Gambusia affinis being one) will choose to passageway that leads to the highest number of others of their species. But they couldn't see and there was a door in the experiment. They consistently count the dots on the door and choose the one with the highest number, even when the info is false. So it isn't smell or chemical signalling - they can be fooled. They seem to count.

I've watched them in Florida, and they seem to move in groups of a couple dozen at most, and often were around 10. That makes sense for a micro-predator. If I were a Gambusia affinis (I'm an introvert), I'd always choose the door with the fewest dots. Then again, if I were a fish I would have been devoured sometime around 1960.

They count, and many species recognize individuals. I just added a small group of Hoplisoma panda to my herd, as I took in my daughter's fish due to a move. You could see the new fish being checked out closely, and while it may have been random, the first fish to join them were their offspring I raised here. My store bought pandas took about 15 more minutes before they all sat and looked at each other, before going off to swim like happy fools.

 

[Whitecloudminnowguy09]

All great feed back, and interesting info. Thought I would make a poll, although I know many have different opinions, it would be cool to see the amount of votes for each choice in the poll.

 

[Rusty_Shackleford]

Fish learned to count in.....schools.

 

[GaryE]

What about 10 or more, which is what I do if I can afford it? The numbers offered are too low. 3 is a discredited number I put in to show how wrong we used to be.

 

[Rusty_Shackleford]

My thought process is to get as many as can fit in the space you have. Honestly for schooling fish, for me it's a minimum of 12.