Quantity of Fish for 20 Long?

[dwalk77]

My tank dimensions are 35.43" x 11.81" x 11.81" and it holds about 21 gallons. I've decided I want to go with a 1-species tank of fish that are about 1" in size.
I have a few options I like that should fit my water parameters, but I'm more hung up on quantity right now.

I've heard 12 is a good minimum for shoaling fish, but I've also heard "more is better", so wondering if I should or shouldn't go with more than that with my tank dimensions.
Anybody have any advice on that?

I guess you could say I have a "moderate" amount of hardscape and plants, maybe 30% of the tank, but it's mostly open for fish to swim

Thanks!

 

[AdoraBelle Dearheart]

Which options are you thinking of? Generally, the smaller the fish, the more of them you can and should have, if they're a shoaling/schooling species (I always get those terms mixed up, but you know what I mean).

Also, consider that while you want a good number for schooling species, it's better as a rule to understock a tank rather than fill to max capacity. But if you plant a decent amount of live plants, that can help too, since they help to process the waste. Most of the nano group also appreciate a lot of planting, since it helps them feel safe. If you follow a typical aquascaping structure, with tall plants at the back, medium sized in the middle, small at the front, then it still allows for a lot of open swimming space, but also a decent amount of planting and hiding places.

 

[Back in the fold]

Yes ! ! ! A species only tank. That's the best way to go.

 

[Byron]

It would help to know any species you may have in mind. Numbers are not the main issue when stocking, it is species, and having sufficient space for that species in a decent-sized group.

A simple example. If one wants the species Danio margaritatus it requires a group of 20 to be at its best. If the tank were a 10g, this would be too many fish. But the solution is not to have only 10, but none of this species. This is in the best interests of the fish, and that is what absolutely should take precedence.

A 20g long is good space for a number of small-sized species, and the vast majority of such fish are shoaling. This is programed into the species' genetics, and the individual fish "expect" a group. Scientific studies have clearly shown that a group of 10 will be healthier, better adjusted, and live a normal lifespan, all else being equal. As opposed to a group of five or six; these limited groups show increased aggression, and a latency to feed. So numbers do matter, and yes, the more the better in general thinking, but there are no shoaling fish I know of that should ever have fewer than 10-12. If there is no room for a proper-sized shoal, turn to another species. The fish will otherwise be the losers.

 

[dwalk77]

Which options are you thinking of?

It would help to know any species you may have in mind. Numbers are not the main issue when stocking, it is species, and having sufficient space for that species in a decent-sized group.

Based on previous recommendations, Celestichthys margaritatus and Paracheirodon innesi were a few I was considering.
Any thoughts on an appropriate quantity for my tank size?

Thanks!

 

[Byron]

Based on previous recommendations, Celestichthys margaritatus and Paracheirodon innesi were a few I was considering.
Any thoughts on an appropriate quantity for my tank size?

Thanks!

These have somewhat differing parameter requirements, so it would help to know the GH and pH. But as for numbers, the Danio margaritatus (now moved to this genus from Celestichthys) needs 20 which is fine. If Paracheirodon innesi is chosen, and is the only species, I would do 20-25.

 

[dwalk77]

These have somewhat differing parameter requirements, so it would help to know the GH and pH. But as for numbers, the Danio margaritatus (now moved to this genus from Celestichthys) needs 20 which is fine. If Paracheirodon innesi is chosen, and is the only species, I would do 20-25.

Okay, thanks. Sure, the GH is 150 ppm and PH is 7. Based on that, you previously recommended Paracheirodon innesi and @AdoraBelle Dearheart recommended the Danio margaritatus.
So do you think I should avoid the Danio?

 

[Fishmanic]

lots of neon tetras would make a nice display

 

[AdoraBelle Dearheart]

Okay, thanks. Sure, the GH is 150 ppm and PH is 7. Based on that, you previously recommended Paracheirodon innesi and @AdoraBelle Dearheart recommended the Danio margaritatus.
So do you think I should avoid the Danio?

No, he didn't say to avoid them! Just gave some idea of minimum group numbers that work for each species, if you're going with this tank and species only

 

[dwalk77]

No, he didn't say to avoid them! Just gave some idea of minimum group numbers that work for each species, if you're going with this tank and species only

He didn't say to avoid them, but he did say they have differing water parameters - which to me is an implication that one fish could be a better fit for my tank than the other. I just didn't want to make assumptions!

 

[Byron]

Given the GH at 8 dH (=150 ppm) and pH of 7, either species should be fine. In the numbers previously suggested. The D. margaritatus on their own with 20. If you go with the P. innesi, you could do 15 rather than 20 with a second species included, something small, or you could stay with the neons.

 

[Aqua67]

AqAdvisor will help you determine the number of fish based on your tank size and your filtration capabilities.

http://aqadvisor.com/

 

[Naughts]

AqAdvisor will help you determine the number of fish based on your tank size and your filtration capabilities.

http://aqadvisor.com/

Aquadvisor is OK as a rough starting point. It's nowhere near as clever as Byron though!!!

 

[Byron]

The problem with any site like AqAdvisor is that it cannot possibly take into consideration all the factors that must be considered. As I alluded to in post #4 above, the fish mass is not the primary factor, but the needs of the fish. If the minimum needs cannot be met, then the fish is not going to work in the tank.

 

[sharkweek178]

It would help to know any species you may have in mind. Numbers are not the main issue when stocking, it is species, and having sufficient space for that species in a decent-sized group.

A simple example. If one wants the species Danio margaritatus it requires a group of 20 to be at its best. If the tank were a 10g, this would be too many fish. But the solution is not to have only 10, but none of this species. This is in the best interests of the fish, and that is what absolutely should take precedence.

A 20g long is good space for a number of small-sized species, and the vast majority of such fish are shoaling. This is programed into the species' genetics, and the individual fish "expect" a group. Scientific studies have clearly shown that a group of 10 will be healthier, better adjusted, and live a normal lifespan, all else being equal. As opposed to a group of five or six; these limited groups show increased aggression, and a latency to feed. So numbers do matter, and yes, the more the better in general thinking, but there are no shoaling fish I know of that should ever have fewer than 10-12. If there is no room for a proper-sized shoal, turn to another species. The fish will otherwise be the losers.

I'm fascinated by group behavior in animals. Now, I say this as someone with absolutely no scientific qualifications except having watched a lot of Animal Planet and Discovery.
The reason animals school, flock or herd is mainly a defense against predators. A predator sees a big group and can't focus on any single one in the group.
Another reason is because an individual fish in a school can also think that if the school is attacked by a predator, then the odds are that one of the others will get eaten.
In both cases, it's a numbers game. Neither strategy works with only a few fish. So basically, a fish in an insufficiently sized school or shoal is living in fear of getting eaten all the time. They only feel safe in numbers. This is hard wired into them. When they don't feel safe, they will be under stress and act out as you've pointed out.