Shoal Sizes

[leighton_87]

One of the most common things I read on this forum is that shoaling/schooling fish should be in groups of 6 or more - my question is why?

I'm not saying I disagree with this and it's advice I've given myself but does anyone know the science behind why.

I've had a bit of a search and found that some research has been done in the area (http/link.springer.com/article/10.1007%2Fs10071-008-0140-9?LI=true) which suggests that fish can distinguish between shoal sizes. Although the ability of the fish diminishes as shoal sizes increase and the cut-off mentioned is 4. So in the example a fish could tell the difference between a shoal of 1 for fish or 2 fish but couldn't tell the difference between 4 fish or 5 fish - suggesting to me that a fish would be just as happy in a group of 5 (4 other fish) as they would be I a group of 6.

However, the article goes on to say that while a fish cannot tell the difference between 4 and 5 they can tell the difference between 4 and 8 and would choose a shoal of 8 given the option.

Therefore why do we choose 6 and not 5, and why do we stop at 6?

 

[Mikey1]

Therefore why do we choose 6 and not 5, and why do we stop at 6?

 
who exactly do you referring to as "we" ?

 
you also have not said exactly what fish you are referring to....
 
you cant lump ALL shoaling/schooling fish into the same category....

 

[leighton_87]

Therefore why do we choose 6 and not 5, and why do we stop at 6?

 who exactly do you referring to as "we" ?  you also have not said exactly what fish you are referring to.... you cant lump ALL shoaling/schooling fish into the same category....

I'm talking about the vast majority of advice given on here and on many places on the net - scroll down the forums and whatever shoaling species your talking about someone will say you need at least 6 of them to make them happy (tetras and corys being a prime example but not the only ones)

For the sake of argument lets talk about corys

Many people on the forum (I include myself in this) say you need to keep them in groups of 6. My question is why?

I've posted this in the scientific section as I was wanted to know any research or facts that supports the number 6 vs any other number that could be chosen.

If you don't agree with 6 then what number would you say and why? i'n looking for facts and research to support any choices. I know you're a very experienced fishkeeper Mikey and it the number you keep might be based on experience but I'm wondering if anyone out there knows the facts/research that supports the numbers chosen.

 

[Livewire88]

I think the behavior displayed by fish that are in larger groups tells its own story. 
 
For example if you have a group of 4-5 fish that like to be kept in larger numbers they will be more shy at that number than they would be when kept in a larger group. 
 
Before I upped the number of my Gold Laser Corydoras from 3 to 7 they would hide away till feed time, now that they are 7 strong they are always patrolling the tank together. 

 

[leighton_87]

And if you upped that number to 14 would they be that much happier again? These fish live in hundreds if not thousands in the wild - I'm just wondering if there is any logic behind the number 6.

I'm not questioning anyone's fishkeeping here I'm just here to learn.

So far in this hobby I've picked up what I've learnt from forums and sites such as seriously fish but I feel I'm just scratching the surface and want to learn so much more. They way I've always learnt is to ask why? I think the best way to learn is not to remember what you've read elsewhere but to understand why something is true.

On a slight tangent I'd never considered oto's as a schooling fish until I saw this - http/m.youtube.com/#/watch?feature=player_embedded&v=EOK5stRPq1E&desktop_uri=%2Fwatch%3Fv%3DEOK5stRPq1E%26feature%3Dplayer_embedded

This is as close as your likely to see to 'natural' behaviour in an aquarium.

 

[fluttermoth]

And if you upped that number to 14 would they be that much happier again? These fish live in hundreds if not thousands in the wild - I'm just wondering if there is any logic behind the number 6.

 

Yes, I think you would! My largest shoal is of 42 green neons, that were added, over a period of months, in multiples of six (my LFS sells 'six for the price of five' on most shoaling fish) and I certainly noticed a significant difference in behaviour when I went from twelve to eighteen.
 
I think the 'six minimum' guideline is a piece of received wisdom, possibly from a long time ago, before the true nature of shoalers had been looked into; quite possibly based on assumptions of how high a number fish could count.

 

[TwoTankAmin]

Most people are wrong.
 
I have no idea who made up the number six. But there is absolutely no rationale for it. In nature these fish often school in the100s.
 
That study does not indicate what you say it does. What is said was mosquitofish females could tell the difference between 1, 2, 3 and 4 fish but not make such distinctions when bigger numbers were involved. It also said that the research seemed to support the idea that there are two distinct abilities regarding number. One for small numbers- 4 or fewer- and then another for big schools.
 
 
Here is a piece of research from 1982 published in Scientific American. It concludes that:

"....it is possible to formulate a useful working definition of a school: It is a group of three or more fish in which each member constantly adjusts its speed and direction to match those of the other members of the school."

http/www.colby.edu/biology/BI358j/Readings/Partridge%201982.pdf
 
I currently have about 30 rummy nose, in the past I have had a school of 65 cardinal tetras. There is nothing quite the same as seeing them in bigger groups. If you want to see 6 colorful things scrambling about, go watch a hockey team. If you want to keep schoolers, think bigger numbers.
 
And there is lots of research on schooling fish. Here are some 102,000 results on Google Scholar http/scholar.google.com/scholar?as_vis=1&q=schooling+fish&hl=en&as_sdt=1,33  or if you want to limit it to fw fish try this one (only 29,400 results)  http/scholar.google.com/scholar?hl=en&as_sdt=1,33&as_vis=1&q=schooling+freshwater+fish

 

[leighton_87]

Thanks I think this is going to involve a lot of reading over the next few days (maybe at the weekend) to see if I can get through a few of those articles.

I find it interesting that if I made a post saying I have 4 corys and they seem healthy and happy one of the first replies I would get is "fish are very good at hiding when they are stressed and they should really be kept in a group of 6 where they will be less stressed" and while this might be true I'm thinking they be much happier in a group of 12 or 18 or 100.

Interestingly here is a follow-up article to he mosquito fish study I found - http/www.plosone.org/article/info:doi/10.1371/journal.pone.0015232

 

[TwoTankAmin]

There is a difference between what it takes to get schooling behavior and in what size schools fish "feel" the most comfortable. From what I can tell, in the wild it would take at least 3 to perform schooling behavior but also that the fish would prefer to be in the largest size group they can. As long as they can tell the difference if faced with a choice.
 
Now it is one thing to see how some fish behave in a laboratory, but I wonder who/what in the wild is going to organize such choices for fish? I can't really imagine a few cardinal tetras swimming along together and suddenly on the right they see 200 other cards in a school and to the left another group of 150 and then deciding which group to join.
 
To play these in full screen for a much better view, click on the YouTube icon on the bottom right of each vid and then the full screen icon at YouTube

 
http/www.youtube.com/watch?v=cWIVCdLOImw
 
http/www.youtube.com/watch?v=HzKa7d-Ha7Q

 

[This Old Spouse]

Whenever I give the advice about how many cory, etc., my usual response is "at least 6" and I would like to say "or as many as your tank can handle." I don't think I have any shoals that are precisely 6. I truly wish I could have many more cory, for example, but having a trusted LFS 2-4 hours in one direction makes that difficult. My next plan of action is to place an order so the fish are in the store a good week before I get there. 
 
Most people can't afford (in tank size or money) to have a really decent shoal of fish, but most can have at least 6. I have 13 tiger barbs who seem quite content at that number. At 6 they bickered all the time. 
 
I just think 6 was the number someone came up with at some point and everyone uses it now.

 

[Mikey1]

I have no idea who made up the number six. But there is absolutely no rationale for it. In nature these fish often school in the100s.

 
you cant compare shoal sizes in the wild to a tank....in the wild fish are not confined to a 3-4 foot swimming space
 
the number 6 is often recommended because thats a good "average" size, for the "average" fishkeeper, with an "average" sized tank, with "average" knowledge....the number is a generalization....it may change from tank to tank and person to person....same goes for many questions in this hobby, just like the infamous question "how often should i do water changes?"....too many different variables come into play.....the question can not have one "blanket" answer that covers every tank and every fishkeeper....
 
shoaling fish feel more comfortable and calm in large groups....they get nervous and stressed when alone, or 1 or 2....in most cases the bigger the group, the better....having said this, you cant group ALL shoaling fish into one category....these recommendations may change depending on the fish....like i said, many different factors to consider....
 
in my opinion, if your tank is not big enough for you to keep at least 6 shoaling type fish, then you shouldnt keep them at all....just thats just my jacka$$ 2 cent opinion....

 

[This Old Spouse]

 

[frapadoodle]

I agree with 'average' idea. But has been said, that usually comes with the caveat of 'at least'.
I do agree with This Old Spouse, that it should be as many as you can keep safely and healthy in your tank.

 

[TwoTankAmin]

Mikey- my question to you then is why is the number 6, why is it not 5 or not 7. Why is 6 the exact number? Where did it come from. And since it would be impossible do define the average fish keeper, I do wonder that the average tanks size is? And If you have an answer, could yo explain how it was determined. I mean is it some made up number or is there some reasonable way to know the answer.
 
The scientific study I linked to says it takes 3 to show schooling behavior. If this is the case, why would that not be the minimum number?
 
I am only asking as this is the Scientific Section as opposed to the Tropical Discussion area.
 
I would also think that shoaling, or schooling, behavior basically means synchronized swimming. I doubt it matters to which schoolers one refers in that regard. They either school or they don't.