Different Colour Fish

Hi all,

I know that there is a minimum number of fish of a particular type that should be kept and I know that normally the ideal number is greater than the minimum.
However how do different colours work?

EG I have about 20 dalmation / black mollies and I want to introduce some white mollies I have seen at my LFS.
In theory could I just get 1?

And going a stage further I have 9 black phantom tetras.
Could I add a couple of red phantom tetra's?

Any help appreciated.

This is two very different issues, I'll try to explain.

First, the easy one, the Black and Red Phantom Tetras. These are distinct species, the Black is Hyphessobrycon megalopterus, and the Red is Hyphessobrycon sweglesi. A species is a very distinct clade, and they communicate not only visually but with chemicals called pheromones that fish in that species can read. These also happen to be shoaling species, meaning they have a strong need to live in groups of their own species, and most shoaling species seem to do well with 10 or more (there are some exceptions we need not get into). Taking this a step further, the fact that these two species are in the same genus, Hyphessobrycon, tells us that the two species share a number of inherent traits, be it physiology, pattern, behaviour, and so forth. But they are distinct within their species and that is the primary need that must be met in order for the fish to be healthy (less stress). We now understand that keeping a shoaling species in less than adequate numbers is in fact inhumane because it is denying the fish something it considers to be absolutely essential to its well-being, and there are detrimental consequences.

Mollies are livebearers, in the genus Poecilia. There are 40 valid species according to Fishbase of which several are "mollies" while others are guppies and endlers. Most of the varieties seen in stores are selectively bred from the same natural species (I'm being very general) so they are not necessarily distinct species. But more to the point, they are not shoaling species. The absolute inherent requirement/expectation for a large group does not exist like it does in a shoaling species.

To answer your specific questions with the above in mind...keep the group of Black Phantoms at 9 or more. Do not add Red Phantoms unless you have space for a group of 10 or more of this species as well. As for the mollies, numbers do not matter aside from what the aquarium can biologically manage of course. And here, they may well hybridize as most of them are the same biological species.

Edit to include the GH issue which @Naughts spotted and which I ran past previously. Mollies must have moderately hard or harder water, or they will inevitably develop health issues. The Phantoms will fare much better in very soft water.

sparkypenguin said:

Any help appreciated.

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I would like to add that you need to ensure you meet the water hardness requirements for the fish. Mollies need very hard water and I suspect in County Durham your source water is soft? Phantom tetra need soft water.

Hi,

@Byron - Thanks for the clear information regarding species and shoaling considerations. I will add certainly take this into consideration for all future purchases.

@Naughts - Thanks for the additional water condition info.
My tanks water does vary a bit, my general results are....
PH 7.2 to 7.8 average 7.5
KH 4 to 9 average 5 dKH
GH 10 to 15 average 13 dGH
I did have a couple of months where my tank PH, KH and GH went up to 7.8, 10 and 20 respectively and after testing my tap water I suspect it may have been a change to this, however I never got to the bottom of why as despite numerous phone calls, and promises on their behalf, the local water authority never got back to me.

It can sound incredibly complex. It isn't.
Dogs and wolves are related and maybe an alien would think they were the same. In its dogquarium, they might put packs of pekinese and timber wolves together, then maybe add some coyotes so they'd have friends.
Yeah...

The problem with species, breeds and fishes matters. Breeds are created by human actions, through selectively choosing individuals from a species. That's what your different pet store mollies are - human colour and shape form creations through a process of hybridization and selection. The original fish hang together in loose groups, but don't shoal.

The tetras are distinct species, created by conditions in nature. They can look very similar but be genetically quite different. I am less hardline about numbers than @Byron is, but if I have six H sweglesi, I really have one unit of fish. They need each other to thrive. I have a recently arrived large group of cardinal tetras in quarantine, and to me, each set of 30 is basically one adult angelfish exploded into 30 functioning pieces, as far as an aquarium goes. I was hoping for 90 but got 50, and they are one big fish to me.

If we go with colours, I could get neons, or green neons. It wouldn't work. The fish would know. Plus the different but similar fish come from different conditions in the wild.

You might be thinking that this old guy aquarist talks too much and goes on (you're right), but species, even related species, have a lot more to them than what we see colour-wise. Our perspective is influenced by dogs, where my retriever is the same species as the guy next door's spaniel. In many cases, similar tetras will shoal together, and may be able to thrive. There are species in nature that are always found together, and sometimes, they even resemble each other. One of the dwarf Corys has an equal sized tetra with the same colours that it shoals with. It's really fascinating.

So I don't think you need 10 of each, if the fish click. But at least 5-6, in case they don't. As many as you can have is best for them. It can be expensive for us, but once you get into fish...

@GaryE
Thanks very much for your help,, you make good points and I especially like your analogy of multiple small = 1 large fish.
I too have Corys, mine are Pandas, and sometimes they will swim about with the Black Phantom Tetra's but to be honest I think Pandas are so chilled that they would shoal with sharks!

I've got 9 of the Black Phantoms, 4 female and 5 male, they so shoal at times but a lot of the time they just swim about in small groups or by themselves. I think this is because they feel quite secure. The males often spar off against each other which is really fascinating to watch.
If I do go for some Red Phantoms I will get a similar number.

And by the way I appreciate the fact that you go into detail as it helps my understanding, and note I'm not that young myself

It is clear to me that something extremely important is not being understood, no disrespect to anyone, in the last couple of posts. Numbers are crucial to the health of shoaling fish as I will explain (I hope). But first, some explanation to correct a possible misunderstanding of 'shoaling" in post #6.

With freshwater fish, shoaling refers to a species that always lives in a usually very large group. This is not the same as schooling when this term is applied to marine fish that not only remain in huge groups but hunt their prey as a unit. Freshwater fish, not even piranha, school in the technical sense. But they are shoaling fish (all characins are, as are all cyprinids, many catfish like cories, etc.). The need for a large number is programmed into their DNA, part of their genetic blueprint as a species. The fish "expect" to be in a group of their own, and there are some very serious detriments to the fish when this expectation is not provided by the aquarist.

A study [link below] of four species that were maintained in groups of 3, 5 and 10 clearly demonstrated that the fish in the smaller groups, both of them, had more severe stress permanently. They displayed increased aggressive behaviours in consequence, due to the stress. A species like the neon tetra that is normally peaceful became noticeably aggressive in the groups of five and three (there was little if any difference in the two smaller groups, both were negative on the fish). But perhaps even more telling, the fish in the smaller groups always demonstrated a latency to feed. When a fish is so stressed and affected by something that it no longer is emboldened to eat, you know it is serious to the fish.

In some species this is greatly heightened. The Tiger Barb was another of the species studied, and the fish of this species that were placed in the groups of three and five began to tear into each other so much that the scientists removed them from the study by the end of their first day. They said it would have been inhumane to keep these fish together. They also noted that this observation concurred with the findings in the hobby that this species needs larger groups.

So, it is extremely important to your Black and Red Phantom Tetras to each be in a group of 10+ of their own species, compared to five or six or, heaven forbid, even fewer. When such numbers cannot be managed due to tank size or other fish, then do not get that species. It is clearly cruel and inhumane to force a shoaling fish into smaller groups.

Panda cories swimming with tetras was mentioned...this is not the same thing at all. The cory species Corydoras hastatus regularly swims in the upper water column and usually in company with a shoal of a small characin. I've seen all sorts of cories swim with upper fish over the years. The critical factor for all of these cories however was having a decent-sized group of their own, in order to provide a need these fish have and which must be met assuming we care about their well-being.

@Byron

Thanks for that and I'm sure it's not that complicated but just to be sure that I am understanding correctly...
Freshwater fish are categorised into distinct species.
Each species will be either shoaling or not and this distinction is very important.
Shoaling fish have an in built need to, and must, be kept in minimum numbers of their own distinct species.

A few questions...

Non shoaling fish....
1. Have they any requirement to be kept in a group of their own species?
2. Can they be kept as a single fish in a community tank?
3. Can they be kept as a single fish in a tank by themselves?

Shoaling fish....
1. If a shoaling fish has a minimum requirement to be kept in a group of 10, and is being kept in a group of 10, and then 1 dies, then surely the only option is to either buy at least another 1, or to give the fish away to someone who already has some?
2. Is there a reliable source of data that provides minimum numbers for each distinct species?

This is a good debate for us, and I hope someone other than the three of us reads it!

There are fish whose lifestyle is solitary. They hold territories, hate all visitors and only connect with their own species for breeding. They are awful aquarium residents, unless you want one fish in a large tank. Usually, they inhabit caves or lie low. The only really popular ones are the red tailed and rainbow 'sharks'.

There are station keepers. Betta splendens comes to mind. They hold a spot , feed there, and hope to nest there. They'll fight off fish that intrude. Wild Bettas live in wild population densities, with males eyeing each other but carefully avoiding challenges.

Schooling tends to be a fear response. A threatened fish seeks cover in its own, to confuse predators. If you wonder why you don't see schooling in your tanks, it's because your fish don't live in fear.

Shoalers take many forms. My killies can live in large groups, as long as I never have only 2 males together. My cardinals are lost in small groups. It varies. Every species has evolved differently. We want to simplify it, but.

Here's one of our real oversimplifications - African Cichlids. In one lake, Lake Malawi, in the vast and rich continent of Africa, there is a lineage of Cichlids that have evolved a need to live in crowds. In the many other lakes and rivers of the continent, fish hold large territories, often in pairs or pairs with juveniles around and would be in abject misery crowded. So what does the hobby do? They're from Africa. Crowd them.

The number issue is a problem. With understanding, the numbers we need keep growing. It was 6. Now we see problems with 6, as @Byron has detailed. So 10 has become an arbitrary number. One of my friends has described cardinal tetra and Corydoras migrations to me. The cardinals were in the millions. The Corys in the tens of thousands. But when the Corys get to their destinations, there are sources galore that say they break up into little groups of 6 to 8. They forage in manageable groups, but may group together at night. Not a lot of divers go in at night to find out.

I think 10 is a number we have pulled out of our... well, we decided just like that. I'll risk sounding cruel and say the best number is the most you can get and care for. I seem to be buying 4 Corydoras arcuatus tomorrow, because that's all the seller has left. A low number? Yup. So I will do my best to breed them, and get a decent shoal going for them. I can't conjure them up. With a lot of other fish, I can't afford big groups.

But if I lack space for a big group, I don't buy. I may have to build a population, but I try to never crowd one.

Naughts said:

I would like to add that you need to ensure you meet the water hardness requirements for the fish. Mollies need very hard water and I suspect in County Durham your source water is soft? Phantom tetra need soft water.

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I wouldn’t be so sure about Co Durham water being soft. I was dragged up just a few hundred yards from the Co Durham border and ours was very hard.
A regular poster in iirc the Peterlee area mentioned they live in an insanely hard water area surrounded by soft water. Also mentioned their local Asda sells more kettles than any other in the U.K. due to the speed of furring up brought about by water hardness.
I keep forgetting to take my test kit up there when I “go home” as water hardness may play a part in my retirement as I’ve never lived in a soft water area in my life.

sparkypenguin said:

Non shoaling fish....
1. Have they any requirement to be kept in a group of their own species?

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This would depend upon the species, there is no "one size fits all" here. The aquarium size also impacts numbers. The important thing that must be understood is that a shoaling species must have a decent-sized group. Anyone observing a shoaling species in their habitat will readily see how they "shoal," compared to a non-shoaling species in their habitat.

sparkypenguin said:

2. Can they be kept as a single fish in a community tank?

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Depends upon the species.

sparkypenguin said:

3. Can they be kept as a single fish in a tank by themselves?

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Depends upon the species.

sparkypenguin said:

Shoaling fish....
1. If a shoaling fish has a minimum requirement to be kept in a group of 10, and is being kept in a group of 10, and then 1 dies, then surely the only option is to either buy at least another 1, or to give the fish away to someone who already has some?

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You cannot take numbers so rigorously. Scientific studies have clearly proven without any doubt whatsoever that a group of ten will be in better health/condition/well-being than a group of five or three. This does not mean that a group of nine or eight will not be OK. But clearly the inference is that the more in the group the better. This hobby has always wanted numbers--"how many fish can I keep in my 10g tank?" is a question asked by I don't know how many beginning aquarists. What must be understood is that what really matters to the health and well-being of any fish is to have what the fish "expects." If species "x" needs a group, and the tank will only accommodate four or five fish, then obviously species "x" is not suited to that tank.

In my 30 years of fish keeping I have many times had a group of say 12 or 15 of species "x" and after maybe eight or nine years they begin to die of old age. I may not want to continue with that species for whatever reason, so I am not going to buy more. But this is vastly different from acquiring a few fish of the species and forcing them to exist contrary to their nature. The crucial importance of the group may or may not still be influencing the fish after eight or more years. I have seen examples where is did not appear to be an issue, and the lone remaining fish of that species lived on for another year or more. Of course, there is no way whatsoever for me to know whether or not the fish was impacted somehow, I can only judge from its behaviours going forward. If it continues to swim normally, feed, behave itself...I will allow it to live out its days in the tank it has become accustomed to over the years. But if this lone fish begins to bully other fish--and I have had this occur with some species--it must be removed for the health of the entire tank. One disruptive fish can stress out a whole tank of fish...I've seen this with a 1-inch fish in a 90g tank. Euthanizing the lone fish is the kindest action in such cases. The fish has without any question been impacted by the loss of the shoal, and this is not something you can reverse no matter what you do. The fish has been stressed acutely and it responds the only way it can--wanton aggression.

sparkypenguin said:

2. Is there a reliable source of data that provides minimum numbers for each distinct species?

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No. There are some species where we know that even 10 is insufficient. The study I cited previously makes it very clear that in general terms, the more there are in the shoal/group the better for the fish. As I said earlier, everyone wants numbers. The long-standing six of a shoaling species was based on no scientific data whatsoever. We used to be told that water changes were dangerous and old tank water was best. No scientific data behind that. But we now know from scientific data that the concept was way off the mark. With shoaling fish we now have clear evidence that the difference between 5/6 and 10 is like night and day. Aiming for a group around ten will without any question provide a better environment for a shoaling fish. I always aimed for 12-15, and if for some reason I felt that number would not manage in the tank, then I did not acquire the fish. We aquarists are solely responsible for the health and well-being of every fish we acquire. Knowing/learning its needs from studying the habitat and then doing our best to meet those as much as is reasonably possible is the mark of a good caring aquarist.

ClownLurch said:

I wouldn’t be so sure about Co Durham water being soft. I was dragged up just a few hundred yards from the Co Durham border and ours was very hard.
A regular poster in iirc the Peterlee area mentioned they live in an insanely hard water area surrounded by soft water. Also mentioned their local Asda sells more kettles than any other in the U.K. due to the speed of furring up brought about by water hardness.
I keep forgetting to take my test kit up there when I “go home” as water hardness may play a part in my retirement as I’ve never lived in a soft water area in my life.

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I wasn't sure, hence the word suspect and the question mark. The OP gave their hardness as 10-15dGH in post #4. It's not really suitable for phantom tetras OR mollies.

Naughts said:

I wasn't sure, hence the word suspect and the question mark. The OP gave their hardness as 10-15dGH in post #4. It's not really suitable for phantom tetras OR mollies.

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Sorry.

Byron said:

Mollies are livebearers, in the genus Poecilia. There are 40 valid species according to Fishbase of which several are "mollies" while others are guppies and endlers.

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Oh, Fishbase should update their info. For there are way more than just 40 species within the genus "Poecilia". And I'm not even considering mollies, guppies and endler for that matter...

GaryE said:

They can look very similar but be genetically quite different.

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That's my motto about fish: Phenotypically does not mean that it's genotypically the same...

GaryE said:

but species, even related species, have a lot more to them than what we see colour-wise.

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That's totally correct...!

Byron said:

With freshwater fish, shoaling refers to a species that always lives in a usually very large group.

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The problem with the terms "schooling fish" and "shoaling fish" is that the commercial trade had let go of the term "shoaling" and used the term "schooling" instead, for decades... So, just that misused term has been copied over the years and people took that for granted. There are way more things that can be told about fish that are incorrect which info we are so used to hold on to all those years while it's incorrect info.

GaryE said:

This is a good debate for us, and I hope someone other than the three of us reads it!

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Check ! It's indeed a good debate to all of us...

@Byron @GaryE @emeraldking

Sorry for my delayed reply, I did have another reply partly typed but got called away and this is the first chance I have had to read the more recent posts. So here are my updated thoughts...

Byron said:

The study I cited previously

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I could not get the link to work on the study

GaryE said:

This is a good debate for us, and I hope someone other than the three of us reads it!

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Although I feel under educated compared to both of you I also think that you are correct when you say that it's much more complicated than it's generally made out.

So what I take from the above is that it appears that there is no reliable source of information where a fish keeper can find the number of fish that should be kept of a particular species. Whilst I totally understand that the number can change as we learn new information but surely based on current knowledge there should be some form of industry figure? If not then how are "beginners" and even "experts" supposed to know?

Are we just to read multiple articles and ask on forums or do we just buy a number and watch them to see if we think they are happy? We certainly cannot ask the LFS as from my experience they cannot be 100% honest due to the fact that they rely on sales. Where did the number 6 or 10 actually come from, surely they must have been based on some actual facts? How do we know that 10 or 15 is enough when it appears that the more the merrier for certain species, who is to say that it should not be 100 minimum? Are we as individuals really able to tell from the behaviour of a fish if it is happy, after all my mollies, platies and phantom tetras all seem very happy but within this post I have been told that my water is not suitable?

I find it very difficult to believe that there could not be some form of figure based on what is known, after all I have already been told on this post figures for certain species so surely it is just a case of going through on a species to species basis? Is it because the industry does not want to do this as it would stop the sales of many fish due to the majority of people not having sufficiently large tanks for the numbers required?