Small Numbers Of More Species V.s. Large Numbers Of Fewer Species

There is a wide range of advice on things like minimum tank size and fish numbers across sites and various fish stores. Sometimes stores also have deals on certain numbers of fish, but I find it unlikely that it is to encourage people to have larger groups for the sake of the sense of security of the fish 
I'm not sure what camp I fall into on this discussion. I have a few species only tanks (one for dwarf puffers and one for tiger barbs), and most of the other tanks I have are larger numbers of fewer species. However, I like lots of different fish, but have got around the issue by having lots of tanks.
Perhaps if I hadn't made so much space available for tanks I would have smaller numbers of more species in the tanks that I did have. 

The majority of smaller fish we keep are shoaling species, in the wild they will live in shoals of thousands or more. There are a few such as bettas and cichlids that aren't but they are the minority. The CC gives the absolute minimum of one species you should keep, that's not necessarily the optimum. If you want to keep more variety, then make sure you have at least this minimum, preferably with a few more. Many species of similar size and temperament will more or less shoal together e.g. many species of tetra and corydoras. I tend more towards the fewer species/more individuals approach these days, mainly because a large group of identical small fish look better than a smorgasbord of mixed colours and sizes. I liken it to a garden, the average person will plant one of this and one of that, while the designer will plant broad sweeps of one plant, the first will look like random chaos, the second will be much more harmonious.
Whatever, I feel the most important is to make sure you have fish of similar temperament , don't mix boisterous fish with timid. I don't worry too much about water hardness and pH, the majority (but not all) fish these days have been commercially bred and are much more tolerant than the wild caught ones on which much of the data is based.

When I first got tropical fish about 18 years ago (after a year with my children's faiground goldfish) I was definitely in the 'as many species as possible' camp in a 60 litre tank. We didn't have the internet back then, and my only source of information was the very out-dated books in the library. I don't remember even considering shoal size when I started, I just bough fish according to the shops saying so much per fish or a bit less for 5, which still seems a typical way that fish are sold. Once we got broadband I began reading and discovered about shoaling fish and their needs.

It is only in recent years that I have come to prefer larger shoals of fewer species. I got a 125 litre tank in addition to the 60; then replaced the leaking 60 with a 50 litre; then replaced the 125 with a 180 litre. Each time I got a bigger tank I moved the existing fish and bought a few more. I soon had tanks with less than the ideal numbers as older fish started dying of old age, and of course that freed up space for another species.

Then two things happened.

Three years ago, I bought some fish that brought camallanus worms into the tank. I lost a lot of fish to that so when I came to restock I decided on bigger but fewer shoals, though I still had smaller shoals of survivors.
This spring I bought a pair of apistogrammas which were carrying the very medication-resistant form of whitespot. They were the only fish that didn't come down with it. Two months of continual treatment took its toll on the fish; I lost over half of them and the rest were still covered with spots. In the end I put them down and had an empty tank for 3 months during the summer to allow the whitespot (or probably 'import' spot) to die out.
This gave me the opportunity to start again. You will find threads on here about deciding which fish to go for.  My signature contains the result of that three months thinking.
I bought 18 Hengel's rasboras, Trigonostigma hengeli (but 3 died leaving 15); 18 Daisy's rice fish, Oryzias woworae; 5 peacock gudgeons, Tateurndia ocellicauda and 6 stiphodons, species unknown but sold as Indie blue gobies. The Boraras and cories were in my 50 litre tank but I had to close that due to alterations to the kitchen and nowhere to move it too.
The rasboras and rice fish are shoaling fish, the gudgeons and stiphodons aren't shoaling fish as such but need company of their own kind.

That's how I came to change from minimum numbers of lots of species to lots of each of fewer species.



I agree with fcmf, I certainly found that when I started I wanted lots of fish as there were just so many to choose from.
And I also think that the way fish are sold is a factor. So many shops sell shoaling fish as so much for one fish but if you buy 5 you pay less than five times the single price. This encourages people to buy 5 of lots of different fish; to get more than 5 of any species you'd have to buy 10 or 15 to get the discounted price. My favourite shop is different. Their fish are priced at so much each but 10% off if you buy at least 5 of the same. You can buy 6 or 7 fish and get the same discount as other shops only charge for multiples of 5. Or even 18 if that's what you want 




Watching the behaviour of bigger groups is now part of the attraction for me. My rice fish swim all over the tank, they take no notice of each other except for males chasing females. They are inquisitive fish, which makes water changes interesting - they are attracted like magnets to the siphon tube  The rasboras are not just shoaling, they are schooling. They do everything as a group. Now they are getting bigger, they are spending less time schooling but individuals are never far away from the group.



I need to say that all this applies only to shoaling fish. It does not apply to territorial fish.

In your other thread, I suggested that if you got honey gouramis to get just one male with two or three females. Male gouramis are territorial. Multiple males should only be kept in a tank which is big enough for multiple territories. Years ago I bought a trio of honey gouramis - 1 male 2 female - and after a couple of weeks one female changed colour overnight and I got up to find 2 males, 1 female in my 60 litre tank. One bullied the other constantly and the weaker one died soon after. After that I made sure I knew how to tell the difference and never had more than one male at a time.
Dwarf south American cichlids are also territorial, both males and females. In some species, females have small territories while males have larger ones which include several female territories. With other species, the fish form pairs which hold a territory together.
Male peacock gudgeons are territorial which is why I have 2 males, 3 females in a tank with a 107 x 45 cm footprint.




As for stress related disease, I have found that all the fish get sick regardless of species. Admittedly my fish have only had whitespot on a few occasions over the years and one case of camallanus worms, but those diseases were not species specific, they all caught the disease.
There are certain species which must have hard or soft water. Putting these fish in the wrong water would result in just that species becoming sick. Mixing aggressive and timid fish will result in the timid fish becoming sick. Researching before buying will flag up problems.