Deciding on fish numbers

Most aquarium fish can be classed into one of three living preferences:

Schooling and shoaling:
These fish, depending on the species, live in groups that range form a few hundred to a few million individuals. Home aquariums are most often not able to hold groups that large, but the bigger the group the better it is. I usually recommend that one should aim to keep 10 – 15+ individuals per schooling species as there is no excuse to not do so if stocking a new aquarium. Unfortunately, some people find out that they have only a few individuals from a schooling species after the aquarium is fully stocked, in which case it is best to try and increase the numbers to at least 6 individuals per species or to find them a new home. In some way, fish are aware of individuals up to a point, at which the individuals become “many”. I think that 6 individuals is this point for many species. One of the most important functions of schooling is to protect the individual fish from predators, either by letting the weaker fish in the group be picked off first (as easier prey) or appearing as one larger fish. The main difference between schooling and shoaling fish is that shoaling fish will normally only swim in a tight formation when threatened, usually going about their own business (for example, Trigonostigma heteromorpha). On the other hand, schooling fish (such as Paracheirodon innesi) will spend most of their time swimming close together, even to the point of facing the same way. The group includes fish like tetras, rasboras, danios, barbs, many loaches and rainbows. One unusual member of this group is Neolamprologus brichardi, a shoaling cichlid.
Small groups:
There are a few different variations of small groups which can be found. These include small groups of social fish, which do not have much social structure (such as livebearers) or which have a specific social structure (for example, cichlids); closely knit family groups; pairs of breeding male and female couples; harem groups of one male and a number of females (often seen in many Apistogramma species), or quite rarely, one female with some males. As with schooling fish, small groups provide security for individuals. For some mildly aggressive species, such as Pterophyllum scalare, it may even be possible to keep them peacefully only individually, in proven breeding pairs or in small groups of more than 6 individuals because the dominant fish can then spread the aggression over multiple individuals, instead concentrate it on a single one.
Some of these fish are too aggressive to keep with any others of their own kind, and in some cases, even with other fish which would occupy the same area inside the aquarium, while others simply do not interact with one another on a regular basis. This group includes some loaches, cichlids and gouramis.

It is quite important to try and keep the fish in appropriately sized groups as some may otherwise display odd or aggressive behaviour. The easiest way to find out appropriate stocking numbers is to research the conditions in which the species is found in the wild.

Some basic research showed me that Danio margaritatus and Yunnanilus sp. ‘rosy’ is a peaceful, mid-water schooling fish, which automatically means that I should be considering 10 individuals per species. This is a good number to start with, and there is always the option of adding more later.

Pseudosphromenus dayi, on the other hand, is a solitary fish which breeds in pairs. Males may occasionally be persistent, so I decided that it is better to have 1 male and 2 females, to give the females a bit of a break in case of uninvited attention.

So for my first “final stocking”, I will be aiming at the following:

  • 10 × D. margaritatus
  • 3 (1m 2f) × P. dayi
  • 10 × Y. sp. ‘rosy’

It is very common for final stock to evolve with time, which is why I am referring to this as my first one. As for how I decided on the total number of fish? That is rather difficult to explain as there are no set rules, nor have I seen any good guidelines. I chose the number based on my experience and I always base my decisions on adult size. The stocking numbers are also affected by the amount of plants in the aquarium as they will use up ammonium. For an aquarium which is 60 × 30 × 30 cm in size, I would normally expect to stock between 6 individuals of the larger species I list and 25 individuals of the smaller species. I would also stock conservatively if I pick female livebearers because they will drop fry and it is best to reduce chances of overstocking.

The best advice I can offer on stocking is to not stock more than one feels comfortable with, even if others say that the aquarium will take more fish, and if one is being advised to stock less than one plans to, to try the lower stock first.

Picking plants…

60 litre plant layout planSince I have already decided to stock Asian fish, I am going to try aiming for the same from the plants. I used Tropica’s index of plants by origin as a starting place. My first attempt at creating a layout ended up with a few non-Asian plants which I liked the look of, but this was created long before I even had the aquarium itself.

60 litre plant layout planOn my second pass, I reduced the numbers of species and removed the most demanding ones from my list. I also removed the non-Asian plants, which left me with eight species in total.

For the background, I picked Cardamine lyrata, Cryptocoryne wendtii ‘Mi Oya’, Lindernia rotundifolia and Rotala rotundifolia as these all have the potential to grow very tall; mid-ground, I want Cryptocoryne wendtii ‘Tropica’ and Hydrocotyle sibthorpioides; the foreground plants will be Cryptocoryne parva, which I have never had much success with, and Pogostemon helferi, which I already have.

While I agree with supporting retailers, my LFS charges approximately € 7 – 10 per pot, which is relatively expensive. My usual online retailer is more reasonable, charging € 3 – 5 per pot or bunch of these plants, but because the set-up has already cost almost € 200 and because I want to heavily plant it from the start, I have been looking for these plants from fellow fish-keepers, mostly though forums and suchlike, but also via online advertisements. While I do have some plants to offer for trade, which is the usual etiquette, I will make an effort to pay for them in cash, same as any beginner would be doing.

My first two finds were Cardamine lyrata and a Hydrocotyle cf. tripartita (also known as H. species ‘Japan’ and H. sp. ‘Australia’, sometimes mistakenly identified as H. maritima because it looks similar to H. sibthorpioides) which I bought in a lot of 30 “bunches” for € 30 including delivery, so I will price these at € 1 for the C. lyrata and € 2 for H. cf. tripartita, as they were on the more common side out of the plants I received.

A few days ago, I had another piece of good luck: I received six pots of Lindernia rotundifolia from an unknown source, which I was not expecting. Maybe someone out there likes me, as these are usually € 5 – 10 EUR per pot.

I have also already managed to secure Rotala rotundifolia and Cryptocoryne wendtii ‘Tropica’ from a couple of forum members, once they need trimming again, both for the price of postage.

For the moment, here is how the aquarium looks right now:

Actual 60 litre plant layout

Picking species…

So, I was a little impatient and started looking for plant and fish stock… and of course, I grabbed the plants when I saw them (also made arrangements for more species in a few weeks) which means I should spill my ideas about now. I will be using mainly scientific names because many fish have various common names associated with them and some are common between different species.

Various fish species prefer different areas of the aquarium, so unless one is careful about filling all the levels, soma parts of the aquarium may end up being completely empty, while the fish concentrate in others. There are three main levels to consider:

These are fish which either spend much of their time at the surface because they are surface feeders or breath through labyrinth organs. Most common of these are gouramis, Bettas, hatchetfish and some killifish. These fish often have superior mouths.
Mid-water schooling fish are most common, they are usually found in groups of a few hundred to many thousands, in the wild, which is why they do best if kept in groups of 6 or more, but even better in groups of 10 – 20 or more. Some examples of schooling fish are barbs, danios, rasboras and tetras. Other mid-water fish also include many livebearers and cichlids. These fish usually have anterior mouths.
Bottom and surfaces:
These fish are often grouped together, but make up two quite distinct groups: fish which live towards the bottom of the aquarium and those which live on surfaces and the bottom itself. The first group include earth eating cichlids, some loaches and some Corydoras, while the latter consists mainly of plecos, shrimp, the remaining loaches and Corydoras. The large majority of these have inferior mouths, although some do have anterior ones.

Because the aquarium is only 60 by 30 cm, it restricts me to only the smallest species, as I want my fish to have enough space to turn around and interact with their environment. So, I am restricted to about 30 mm for active schooling fish and 50-75 mm for fish which have low levels of activity. I am going to go for the standard configuration: one group of schooling fish, one group of “bottom feeders” and a couple of centrepiece fish.

First, I need to decide on which fish I wish to focus. As I have not kept loaches in the last five years, they are one of the species I want to look at. Also, living in Germany, has given me access to many unusual species, such as Boraras, so this is starting to look like an Asian themed aquarium. Asian leads me to thinking about gouramis and Bettas, my LFS currently had some Betta channoides, B. strohi, Parosphromenus deissneri, Pseudosphromenus cupanus and P. dayi. So I do a search of all these species, first on Fishbase then read the first ten search results for each, as the internet is not exactly renowned for the accuracy of all information. Average results show me that all species are suitable. I already happen to have a pair of Pseudosphromenus dayi, so they’re going to fill my “centre piece” and “surface feeders” slots.

Now, that leaves me with need for a “bottom feeder” and a “mid-water schooling” species. I start searching through Planet Catfish for small catfish and find Erethistes jerdoni and Erethistes maesotensis, from some experience and conflicting search results, I know that Erethistes and Hara are used interchangeably. I haven’t decided if I really want to go for catfish and loaches, so I’ll just keep these in mind for now.

So now I start looking at loaches, for which, unfortunately, there is no good species resource like Planet Catfish, and come across Yunnanilus cruciatus and an unidentified Y. sp. ‘rosy’ (also known as “Tuberoschistura arakanensis”). After some more searching and enquiries, I decide that Y. cruciatus is on the too large side, and Y. sp. ‘rosy’ is about right. Both of these small loaches are schooling fish, and tend to swim mid-water.

Last, but not least, I looked at the schooling fish.. I was originally planning to go for a Boraras species, but I discovered that Danio margaritatus are from the same location as Y. sp. ‘rosy’. I generally prefer to aim for biotope or at least the same continent or water type, and I have been wanting to keep D. margaritatus for many years now. When this species was first discovered, their habitat was almost destroyed by the greed of fishkeepers everywhere, and the wholesalers falling over themselves trying to collect the species. It has now been a few years, but I will still not buy these fish if they were wild caught, so I am now searching for captive bred specimens. I would also like to mention another interesting species of the same size is Danio erythromicron, it is also very unusual, but an excellent find for a small aquarium.

I will continue with numbers of each species, stocking order and plants in the near future…