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Marcos Avila
Moderators
Joined: 05 Feb 2003
Location: Santo Andre (Brazil)
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 Posted: 2008.02.27(Wed)3:19 Post subject: Female mosquitofish can count up to 4! |
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Quantity discrimination in female mosquitofish
Christian Agrillo, Marco Dadda and Angelo Bisazza
Animal Cognition 10 (2007) 63-70.
| Quote: | | The ability in animals to count and represent different numbers of objects has received a great deal of attention in the past few decades. Cumulative evidence from comparative studies on number discriminations report obvious analogies among human babies, non-human primates and birds and are consistent with the hypothesis of two distinct and widespread mechanisms, one for counting small numbers (<4) precisely, and one for quantifying large numbers approximately. We investigated the ability to discriminate among different numerosities, in a distantly related species, the mosquitofish, by using the spontaneous choice of a gravid female to join large groups of females as protection from a sexually harassing male. In one experiment, we found that females were able to discriminate between two shoals with a 1:2 numerosity ratio (2 vs. 4, 4 vs. 8 and 8 vs. 16 fish) but failed to discriminate a 2:3 ratio (8 vs. 12 fish). In the second experiment, we studied the ability to discriminate between shoals that differed by one element; females were able to select the larger shoal when the paired numbers were 2 vs. 3 or 3 vs. 4 but not 4 vs. 5 or 5 vs. 6. Our study indicates that numerical abilities in fish are comparable with those of other non-verbal creatures studied; results are in agreement with the hypothesis of the existence of two distinct systems for quantity discrimination in vertebrates. |
I don't know if this was part of the original intention of the study, but note that the results fit extremely well with what we aquarists feel about our fish, and recommend here on the board. We often say "this is a group fish, it prefers to be in numbers of 5 or more"...and here's a study demonstrating that, at least for these little female Gambusias, that's exactly right! They can count up to 4 and therefore know perfectly well when there aren't sufficient numbers in the group. After that they can no longer count right, therefore 5, 6, and 7 are essentially the same as 4, although according to the study, they can still perceive large differences such as between 8 and 16. But in this case I think it's no longer a matter of counting, they can visually tell that the latter group is larger and give preference to joining it.
So, assuming that the result can be extended to other species such as tetras, cories, etc...it's a nice and solid support for the customary insistence that we try to keep these species in groups of 5 or more... 
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Slimy
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Joined: 20 Nov 2007
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| Posted: 2008.02.27(Wed)3:41 Post subject: |
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That's really interesting. After reading this I thought back about something I noticed about my tetras... When I originally bought the pristella tetras it was a group of 10. Shortly after I added them to my tank they seem to separate with 8 in a group and 2 that kept trying to get back in and would be chased off.
After a week or two they finally settled into two groups of 6 and 4. Incidentally the school of 4 is all males. I figured they had behaved like most other males and had been kicked out 
Since then I had to uproot and remove two large swords and change the landscape so the school is a large 10 again. I suspect it was brought on by the nervousness (immediately after the uprooting all 10 fish were grouped in a school the size of a lemon!). Now that they are comfortably again, I'm curious to see if it'll split and settle into 6/4 or 5/5 ...
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Dusko
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Joined: 13 Feb 2006
Location: Sweden
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| Posted: 2008.03.04(Tue)13:19 Post subject: |
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Great find Marcos 
That is interesting. I was observing my Rasbora hengeli, 14 of them and they seem to shoal all together. I am not sure this applies to all fish, f.ex Corydoras. We could do some tests then
Regards, Dusko.
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Brattess
New Members
Joined: 08 Mar 2008
Location: Canada
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| Posted: 2008.03.08(Sat)23:09 Post subject: |
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This is something that hobbyists can test in their own fishrooms and come to a reasonable conclusion without huge numbers and a lab. It will be fun to try, thanks!
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Brattess
http://www.CanadianAquariumConnection.com |
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Skittles
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Joined: 21 Jun 2006
Location: Alberta,Canada
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| Posted: 2008.03.17(Mon)18:52 Post subject: |
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Thats very interesting thanks for sharing! Thanks for posting the link too, I'm interested in reading their methods 
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Skittles
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Joined: 21 Jun 2006
Location: Alberta,Canada
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| Posted: 2008.03.17(Mon)19:12 Post subject: |
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Interestingly their results where the fish could distinguish between a 1:2 ratio but not a 2:3 ratio was similar to a study done with 6 month old infants!
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geoff
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Joined: 24 Feb 2005
Location: SE QLD
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| Posted: 2008.03.24(Mon)6:00 Post subject: |
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Actually I doubt these fish are counting at all. I received a similar reply on MASA ( The article HERE
anyone! AND MASA LINK members only unfortunatly  ) and I found out that the fish could only tell proportions, I think these fish are only seeing that (in comparing between 2, 3) 'oh! that school looks a half bigger than the other school. better join that one!' because if I flashed two squares at someone, then three at that person again. Even if they couldn't tell how many squares I flashed (unlikly) they'd still know that the 'three square' card has more squares on it.
Ps. I am soon going to conduct my own test upon this worthy quest!
Jeff
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