Do fish really know their numbers?

Boundava · Jul 17, 2026

I know my SAE know when there numbers are down. Had one oopsie and went from 5 SAE to 2. The 2 fought like

until I brought their numbers back up, now they gladly follow each other around in the 125.

I have had striped and black kuhli (pangio) loaches for a decade. I love both but lately the striped have been hard to come by. With the black I probably have just under 20 in my 33 gallon and they are one fish where more is merrier. They are out all the time, franticly looping from substrate to top of tank and back down again, usually in 3 or 4s.

For me it is also "the more the merrier". If I am at the store looking to get 10 of something and they have 13, I will get all of them and not leave the 3 in the tank for who knows how long.

Innesfan · Jul 17, 2026

GaryE said:
What we have to bear in mind is Pethia is one Genus, and if 8-10 works for them,

Obviously. It is species specific. I wasn't even speaking for all Pethia, just P. setnai. I tried one Pethia species, P. erythromycter, "The Lipstick Barb," a striking, tiny thing with fiercely territorial males. 8-10 of them would not work unless you had 500 gallons...maybe.

We've seen enough youtube clips of various Paracheirodon, Hoplisoma, Hemigrammus, Petitella, etc in huge swarms in the wild that we know for many of these species, if you have the tank space, more is better. The option I'd check on the poll, if it were there, would be "Depends on the species."