FAQs on the Rainbowfishes
Related Articles: Rainbowfishes, Fishes at the rainbow's
end; An introduction to the Atheriniformes, the
rainbowfish and silversides by Neale Monks
Related FAQs: Rainbowfishes 1, Rainbowfishes 2, & FAQs on: Rainbow Identification, Rainbow Behavior, Rainbow Compatibility, Rainbow Selection, Rainbow Feeding, Rainbow Disease, Rainbow Reproduction,
|"Water changes. Rainbowfish REALLY like water changes. I
typically perform 50% water changes on my fish (weekly suggested
but at least 1x every 2 weeks) and they really enjoy this. 10-20%
weekly changes really just doesn't get the job done. Hardness,
pH On the GH side anywhere between 100 ppm - 250 is fine for them.
Harder is ok too but they get tougher to breed and the eggs
sometimes don't hatch at the higher hardness values. On the KH
end I feel that it is extremely important to get at least 3-4
degrees of carbonate hardness here. If you have softer water
supplement it by adding baking soda, sodium bicarbonate. In my
water a tablespoon in ~ 55 gallons increases by about 1 degree KH.
pH bounce is something that really stresses Rainbowfish and if
present can cause them to get TB. Most of the Rainbowfish people
have pretty well discounted the other wasting diseases. TB is not
easy to test for but when it has been done - skin ulcers, mouth
ulcers, bloating (shot kidneys) and wasting have all been positive
for TB." Excerpted from a note in by Gary Lange
community tank- 8/20/11
Hope you are well. I greatly appreciate the hard work you put into
maintaining WWM as a great resource to both novice and experienced
<Thanks for the kind words.>
I have a question involving stocking, planning for future growth of
juvenile fish and the actual projected adult size of my fish. I have a
75 gallon, heavily planted freshwater community aquarium with EI dosing
and DIY CO2. My temperature is 76, PH at 7-7.2, KH is 10 and GH of
In February of this year (2011), I purchased some Boesemanni Rainbow
fish from a breeder via the internet-I purchased 10 and received
The plan was for them to join my; yellow Gourami, 5 Brochis Splendens
(best fish ever!),
<Agree; charming, underrated fish, perhaps even better than
Corydoras for medium-sized community tanks.>
5 Giant Danios, 7 Otos, 100 or so red cherry shrimp and 2 Amano shrimp
which they did. It was winter when I purchased them, so I ordered 10
assuming I would get 8 or 9 after shipping casualties (had never
purchased fish in that manner before, and read that casualties should
be planned for).
<Actually, less of an issue than many expect. Most of the fish we
buy are air-freighted, and provided the seller knows what they're
doing, and you don't choose species that ship poorly, you should do
well with this approach.>
The seller shipped an extra 3 and they all survived, putting me +5
When I got them, they were but a few months old, still unsexed and
bland in color.
<Absolutely standard with Rainbows.>
It looks like they are 3 females and 10 males (not the ratio I was
hoping for) and there is a bit of a size difference between the largest
and the smallest.
The rainbows are starting to get a bit larger, the largest being 2.5
inches or so but most in the 2 inch range.
Currently I am not having any issues-all my fish are getting along and
my water quality is top notch. What is the actual adult size I can
expect for the Rainbows-the information on the web isn't very
<Oh, realistically a good 10 cm/4 inches, but occasional specimens
do get bigger. Wild-caught specimens tend to be bigger and more
colourful than farmed ones. I have seen some nearer 12 cm/5
Likewise, my giant Danios and Gourami have not really lived up to
maximum sizes listed on most sites-they are all about 3-3.5 inches and
I have had them for nearly 2 years. I have seen estimates on max size
for all 3 (Danio, rainbow and Gourami) species maxing out at 6
<Six-inch Giant Danios are really very uncommon. Farms tend to breed
from specimens that reach sexual maturity quickly, and these are often
smaller than average specimens. So over the generations, farmed fish
tend to be smaller than wild specimens. In the wild, only the biggest
specimens have the strongest genes, and so they're the ones that
breed the most. So you get the opposite thing there, selection in
favour of big, strong specimens rather than small but precocious ones.
There are some exceptions here, notably among the Mbuna cichlids that
live longer and eat better in captivity than in the wild, so
they're often bigger than in the wild. But almost everything else
is smaller in captivity once it's been farmed for a few
What are your thoughts on the eventual growth I can expect from my
fish, specifically the rainbows, and do you have any recommendations on
how I should adjust my stocking for future success?
<Oh, I think you have good ideas already. The Rainbowfish/Gourami
combination works well, and I've seen things like Lace Gouramis and
Moonlight Gouramis work particularly well. Is there any particular type
of fish you'd like to keep?>
My original plan was to add a school of 4f and 4m rainbows to my
existing livestock, but I am now 5 fish richer then I planned for. I
doubt upgrading to a 90 gallon tank would provide much benefit, and I
don't think I am in a position to start from scratch and spend all
of the money that would come with upgrading all of my lighting, stand
etc to get a 6ft long tank. Thanks much for your help!
P.S. here is a link to full details on my tank with pics:
Re: Boesemanni rainbow community tank- 8/20/11
Thanks Neale. I have no intention of adding any additional fish-just
don't want to end up too crowded with the fish in there right now.
I figured that I would be pushing the bio-load limit a bit, but I am
glad to know I
will be within reason at adult sizes. I appreciate your analysis and
<I see. I don't think you're overstocked yet. Good luck!
Boesemani Rainbowfish in sg
1.003 tank? 11/15/10
This is my second question in a week. I don't want to abuse this
wonderful resource, but I do have another question.
I have a Rainbowfish that looks to be a Lake Kutubu Rainbowfish (my
knowledge of Rainbowfish is pretty limited, though I have read your
articles on the WWM site). Its other Rainbowfish "friends"
died over the
past year; I'm pretty sure the deaths were from Columnaris.
He is in a tank that has softer water and a lower ph than I now know
Could he thrive in a 90 gallon, low-end brackish tank, sg 1.003, ph 7.8
with an Archer (Toxotes jaculatrix) and a spiny eel (tyre track)?
If so, I would want to buy more of his species and create a proper
school for him.
Thanks for your thoughts on this.
<Hello Laura. As a very general rule, Melanotaenia species from
hard, alkaline water environments will do well at low specific
gravities, even if they don't naturally come from brackish water
habitats -- off the top of my head, the only Melanotaenia species that
I can recall coming from brackish water in the wild is M.
nigrofasciata. In any case, Melanotaenia lacustris and Melanotaenia
boesemani need hard, basic water anyway, and the addition of very small
amounts of salt should do them no harm at all. I'd be keeping
the tank at 10% seawater salinity, i.e., 3.5 grammes/litre, or about SG
1.002. My guess would be that your Rainbowfish will thrive kept in such
conditions. Archerfish aren't fussy about salinity at all, and
Spiny Eels need fairly low salinity conditions, so reducing the
salinity shouldn't cause problems. Cheers, Neale.>
Re: Boesemani Rainbowfish in sg 1.003 tank?
Thanks, Neale--that's great news.
By the way, I saw your book on brackish fish at my favorite fish store
in Manhattan over the weekend.
<Ah, and if you look in the Australian Fish chapter, you'll see
quite a bit about Rainbowfish in brackish water systems!>
It took me by surprise and I nearly squealed in delight when I saw your
name. I told the manager that I had had a back-and-forth with you
through the WWM website. I don't know if he quite grasped the
importance of the moment (!), but I was impressed. Anyway, I know that
book is going to be on my Christmas list!
<God bless Santa Claus!>
Re: Boesemani Rainbowfish in sg 1.003 tank?
I had to give you an update on my Blue Rainbowfish.
Since I put him in the 90 gallon low-brackish tank he's a different
His color is so intense and beautiful and he has a bright neon band of
yellow (I have never seen this before) on his dorsal line (don't
know the technical term but that's as good as I can do).
I got him some Rainbowfish friends (6) and he immediately (and I mean
didn't skip a beat) started courting all the females. In fact, I
think all but one is a female because he's very aggressive with
only one of the fish.
The tank is big and I have it heavily planted but the fish that he is
attacking doesn't try to hide. If the fish was suffering would it
The most amazing thing just happened--I went to take a photo of my
beautiful fish to attach to this email. I had turned out the lights
about a half an hour ago. When I turned on the light I couldn't
find him, then I
saw him: pitch black!!!! Absolutely black as night! I didn't know
they changed color like that. Wow--that is so cool!
<Glad your fish have responded so well to the slightly brackish
While not essential by any means, many aquarists have found that under
home aquarium conditions the addition of small amounts of marine salt
mix is beneficial to Rainbowfish. Anyway, yes, males are aggressive
towards one another, though rarely to the point of causing harm unless
the tank is too small. Having lots of females causes male Rainbowfish
to exhibit extremely bright colours, and when people buy just males
they lose out on some of the best colours you'll see on male
rainbows. And yes, rainbows change colour at night. Many other fish do,
too, so it's worth keeping an eye out for.
Pencilfish are famous for this, as are neon tetras. Cheers,
Australian rainbow fish, hlth.,
I am writing concerning one of my rainbows. I have 55 gal. freshwater
aquarium with 15 fish 6 of which are rainbows.
<All one species, I hope. Australian Rainbowfish are not only
schooling fish, but also prone to bullying one another if insufficient
numbers. Keep at least six of each species, and don't mix species
of radically different sizes. Make sure there are equal numbers of
females and males (or better yet, more females than males).>
My perimeters are Ph-7.0-7.2, Ammon.-0, No2-0 and No3-10, with weekly
<Fine. But what about water hardness? Rainbowfish on the whole come
from either soft water habitats or hard water habitats depending on the
A good all-around option would be medium hard water (~10 degrees dH)
and neutral to slightly basic pH (7 to 7.5).>
Two days ago I noticed one the rainbows swimming almost vertical with
head down and tail up. He is also using his whole body in a wiggly
motion as he swims. There are no spots or marks on him and he is eating
fine. At times
he looks like he doesn't know where he is swimming to because he
almost bumps into other fish.
<Doesn't sound good. Review water chemistry and water quality.
Check for potential sources of poisons: insect sprays, paint fumes,
children doing stupid stuff like putting soda pop into the aquarium
(happens). Make sure
the food you are offering is adequate. Flake, pellet and freeze-dried
foods are fine up to a point, but they tend to cause constipation if
used on their own, and in some cases this can lead to swimming problems
(I guess the extra weight inside them messes up their buoyancy). A mix
of quality flake with wet-frozen bloodworms and mosquito larvae, plus
live brine shrimp and daphnia would be a good balanced diet. Live brine
shrimp and daphnia are laxatives, so highly recommended for all small
fish now and again.>
Is this cause for concern-something internal---parasite-etc.
<Most likely caused by the environment (i.e., the aquarium) rather
than a mystery parasite; while there are Whirling Disease parasites,
they have complex life cycles that can't be completed in aquaria,
so usually affect only pond fish. Live tubifex can introduce them
though, but I don't think anyone uses live tubifex anymore.>
Need for quarantine?
<Would likely kill a schooling fish like a Rainbowfish. Much better
to identify the possible source of problems, and fix the aquarium. Even
though you have zero ammonia and nitrite, be open minded about this
aspect, and think about whether there could be other problems like
unstable pH or inadequate oxygen distribution throughout the tank that
could be to blame.>
I would appreciate any info you can give me.
Thank you for your time,
Rainbow fish.. Sys. -- 6/17/09
I was just reading this article
Neale about rainbow fishes, because I've been investigating setting
up a brackish system with some Melanotaenia boesemanni. I know some
rainbows do well in brackish and some do not, and was wondering about
<They'll do fine in slightly saline conditions, up to around
1.003 at 25 degrees C. They aren't brackish water specialists
though; of the traded species, only Melanotaenia nigrans is a true
brackish water specialist, and
it certainly does well to around 1.005 at 25 degrees C.>
Also, I was going to set the system up in a 29G tall tank, but read
they might need more swimming room than that, and wanted to get an
opinion from the experts.
<Certainly these medium- to large-sized rainbows will need a tank
upwards of 1 metre/36 inches in length.>
Thanks for everything.
Neale re: threadfins (Rainbows)
4/24/08 Hello again Neale, <Hello Aileen,> I have been fish
keeping almost a year now and it amazes me how much I learn every time
I look through pages of this site. Sometimes too much and the
information gets all jumbled in my head (could be age too) and other
times I learn enough to lead me to ask more questions.. it really is a
wonder resource. <Thank you!> You mentioned some time ago that if
I wanted threadfins I should consider another tank. I thought you were
nuts at the time but...I am going to look at a used 40g tomorrow.
Actually somebody had a 100g I can have but I think two monster tanks
might be a bit much. My thinking is leading me to include in this tank:
threadfin rainbows, wrestling halfbeaks, Corydoras and then I was
wondering about bumblebee gobies or something with some colour. I was
reading on WWM that most bumblebee gobies are considered brackish
except one species, which may or may not, tolerate fresh water better?
<BBGs are complicated: you cannot possibly identify species; even
scientists have trouble doing this under a microscope, let alone with
live fish! Most BBG species seem to be found in a variety of habitats,
from blackwater streams to brackish water. But in aquaria they are
temperamental, and slightly brackish water does seem optimal. This is a
lot like Mollies for example, which may be freshwater fish in the wild,
but unquestionably are easier to keep in brackish. Because BBGs are
very difficult to keep well fed, I'd not keep them in a community
tank.> My water is liquid rock. What are your thoughts on this
community and any numbers you may think appropriate? Are there any
other species you might include instead? <Almost anything that
doesn't explicitly need soft water should thrive. pH stability is
more important than pH value in most cases, and people routinely keep
all sorts of things in hard water conditions. With Threadfin Rainbows,
I'd be looking at Corydoras (and their relatives, like Aspidoras
and Dianema) in terms of bottom dwellers. Kuhli loaches and small
Loricariidae such as Whiptail Catfish would also be appropriate. You
might also opt for some surface fish like Halfbeaks. Tetras and Barbs
are best avoided because of potential problems with fin nipping, but
Rasboras and other small Rainbowfish are certainly an option.
Livebearers are certainly a possibility, though some Goodeidae are fin
nippers so choose with care.> And since I have your attention, I was
reading on here some time ago about separating swordfish fry before the
appearance of the sword to prevent inbreeding. So I immediately set up
another 10 gal to do so. But I realized when I was trying to sex them
that they appear to be all female! Is this a probability? <No. While
the idea that Swordtails change sex is widely held, there are actually
no scientific studies that backs it up. It is much more probable that
aquarists mistake undeveloped males for females. Male livebearers
don't develop their sexual characteristics until a certain age
(usually around 2-3 months depending on the species). Obviously until
the gonopodium is formed they cannot fertilise the females, so you
don't need to separate them until that time.> Or am I missing
something like the triangular fin I am supposed to be seeing on only
the females? Is the differentiation not as great in fry as adults? I
ended up separating by size as it seemed the best alternative at the
time. Since I was having so much trouble purchasing healthy vibrant red
swords I decided to keep the try of a lone surviving, vibrant female.
The batch was small but healthy, I have not lost any and they are about
5 months old. But still, not a sword in the bunch...I was hoping for
some nice deep red males for another long term plan. <If you have
just 5 fry, it is statistically possible, though unlikely, they are all
one sex. But if the fry are less than a couple months old, you
can't sex them anyway.> Thanks in advance for your help Aileen
<Good luck, Neale.>
Rainbow-Killies-Planted Tank set Up
9/12/06 Hi, I'm in the process of planning a FW planted 54g
corner tank (38"x27"x22") and was wondering if I could
get a second opinion on a stocking list. Equipment will be an Eheim
2028 can. filter (275gph output), 300w in line heater, 55w pc light
w/6700k bulb, 15g QT tank and a separate 15g hospital tank. I'm
planning on weekly water changes of approx. 10 gallons, (more if
nitrates rise beyond 20ppm.) Also, the water from my tap tests: 7.2 pH,
3 degrees KH and 6 degrees GH. My current stocking plan is: 1m & 3f
threadfin rainbows, I. werneri 1m & 3f Pacific blue-eyes, P.
signifier 1m & 3f forktail blue-eyes, P. furcatus 1m & 1f
red-lined killifish, A. striatum 1m & 1f rainbow notho, n. rachovi
1m & 3f spotted blue-eyes, p. gertrudae 1m & 1f clown
killifish, a. annulatus 1m & 1f blue notho, n. patrizi My main
questions would be... Too many fish? < Between the filter and the
plants you should be able to handle the nitrate load.> Any obvious
aggression/territoriality problems sure to surface over the weeks??
< Many of the rainbows are in the same genus. I would expect males
not to get along. The rainbows may be too active for the Killies and
out compete them for food.> I'd rather have less fish than more
problems. Also, should all of these guys be okay with my tap water?
< Most of your fish would prefer a pH to be lower than 7, but you
are very close already.> And any suggestion on a temperature that
everyone would be happy with? Thanks in advance for your input and
dedication to helping the hobby, (and hobbyist.) < Go with 77 F and
thanks for your kind words.-Chuck> Enough already? Adding
Melanotaeniids to a largely FW Amazon mix 1/31/07 Hi,
<Hello> Thanks for running such a fantastic site. It
has been a real help with a whole bunch of questions that I have
had. However, I now have one that I am not sure how to work
out the answer to. <We're in the same boat...> I'd really
like to add a few Dwarf Neon Rainbows to my tank (Juwel Rekord 96l /
25g US). Ideally 2 males and 4 females as I read that you
need a 1:2 male female ratio. <Better than "even pairs"
yes> The staff at more than one LFS have said that it would be fine,
but I suspect that I am pretty much up against the carrying capacity of
my set up. As it has been healthy (more or less) for the year or so
since it was set up, I don't want to risk messing things
up. The current inhabitants are: 9 x Neon Tetra 5 X Oto 6 x
Amano Shrimp 3 x Corydoras What do you think? <Mmm, there's room
enough, but the Rainbows do "like" different water quality
than the fishes you presently have... likely some "middling
ground" could/can be found to suit all here though> Enough
already, or should I go for the Rainbows? I guess the
alternative would be to wait until some of my fish die off through
(hopefully) old age. Thanks in advance. Phil <Do take a read on...
WWM, Fishbase.org re the water conditions of all these fish species.