FAQs on the Zebra Danios
Related Articles: Barbs, Danios &
Barbed Response; Wrongly maligned for being fin-nippers, barbs
are in fact some of the best fish for the home aquarium by
Related FAQs: Zebra Danios 1, Zebra Danios 2, & FAQs on: Zebra Danios Identification, Zebra Danios Behavior, Zebra Danios Compatibility, Zebra Danios Systems, Zebra Danios Feeding, Zebra Danios Health, Zebra Danios Reproduction, & Barbs, Danios, Rasboras 1, Barbs, Danios, Rasboras 2, B,D,R Identification, B,D,R Behavior, B,D,R Compatibility, B,D,R Selection, B,D,R Systems, B,D,R Feeding, B,D,R Disease,
Stocking microdevarios to avoid aggression
This is my third time or so writing in. I love your site and you guys
give great advice. So here I go again, and forgive me if this is a bit
long of a write up.
So, I have a planted nano tank aka "bucket", capacity of just
over 8 US gallons.
<A small tank indeed.>
After cycling it, I purchased a group of 10 Microdevario kubotai for the
tank. Fish colored up and seemed to be doing well for a long while --
about 2 months. I did notice that they chased each other and nipped each
other's fins, with one or two of them always having small bites in their
<Not uncommon among Danios to be honest. Adding more help. It's the
males, presumably, that fight, but sexing them isn't easy/possible
depending on the species.>
Filter is a (sadly not manufactured anymore) Marineland Duetto 50, which
is kind of like a mini canister filter rated up to 10 gallons.
<Have a similar "Duetto" filter in one of my aquaria. Not the most
reliable filter out there (have replaced motorised part at least twice
already) but as you say, it's small and fits into nano tanks nicely.>
I keep it at maximum flow, because I read that these fish need strong
<Somewhat, but more running water habitats than torrential hillstream
habitats, so don't go crazy.>
I also have the outflow agitate the surface so as to provide more oxygen
dissolution (no CO2 in this tank). There were also a few cherry shrimp
in there as tankmates. All ammonia, nitrite tests I did turned up 0,
with 5-10 ppm nitrate.
Well, about two weeks ago, I made a very bad decision. A friend in my
local fish club gave me eight wild caught Otocinclus, which are actually
either peppered Otos or small Hisonotus catfish. They are a bit longer
than typical Otos. So I put 4 of the new Otos in the nano and the other
4 in my main tank, as both tanks had decent amounts of green algae and
diatoms. The Otos did a great job on the diatoms and green algae in the
nano, but I started testing the water in the nano two days after adding
them, and started detecting ammonia. Then all but one of the shrimp
suddenly died -- not good.
<Indeed, but one dead shrimp does not a massacre make...>
So, after about a week of no reduction in the ammonia readings (was
waiting to see if the biofilter could grow enough new bacteria to pick
up the load), I moved the Otos into my main tank, where they could join
their brethren. That was a few days ago.
<And then what happened...>
Today I was looking in the nano, and noticed a sad sight. The
most-picked-on Kubotai has very ragged fins, and he had what looked like
a white film on one side of his body. He is swimming ok, but was
noticeably thinner than the other Kubotai. His stomach isn't concave,
but neither is it convex. The next-most-bullied fish wasn't looking so
great either, with a small white patch on his caudal fin, but not his
body. So, I immediately dosed Nitrofurazone and have my fingers crossed.
It could be the illness making him thin, or he could just be bullied so
badly that he can't get enough to eat, which of course made him more
susceptible to illness along with the ammonia spike.
So here is my question-- if he (guessing it is the weakest male) dies,
which he very well might -- or, for that matter, even if he
lives--should I replace him with one or more Kubotai?
I'm afraid that if he dies, the next weakest one will get then picked on
and/or starved to death. And so on and so on.
I wonder if getting, say, 2 or 3 more M. Kubotai for that tank, the
aggression will be better dispersed so as not to result in more bullied
or sick or nearly starved fish. I know that danios are very social. But
also do not want to overstock the nano (again).
<Indeed so. But in this case, I think you'd be fine with, say, a dozen
specimens or more in a tank this size, assuming good filtration and
Please let me know what your thoughts are, and thanks so much.
<See above. Danionins are hierarchical and often squabble. Big groups
Run the tank for at least a week before adding any new fish. Maybe
overfeed -- very slightly -- for a few days to see if the filter is in
good condition before adding new fish. Sometimes medications knock the
filter bacteria back a bit, and it can take a while for them to settle
Odd number of danios -- why? 8/7/14
I also worry that if he dies, the aggression will get more concentrated
among the 9 remaining. But then I read on your site that it's better to
stock zebra danios and the like in odd numbers. Why is that?
<<Defuses aggression best: "Odd man out" sort of theory... while pairs
are antagonizing/challenging each other... the "spare" has a chance to
escape, rest up. RMF>>
<No idea. I'm skeptical. Bob F's a fan. Whether it's true or not I can't
say and I've no idea if there's any science behind it. Can fish count?
Do they understand odd numbers? What is definitely true is that the
bigger the group, the harder for the bully to harass any one fish all
the time. The more fish, the smaller the (theoretical) amount of time
directed at any one weaker fish. In practise this doesn't always hold
true -- bullies sometimes target one particular fish, ignoring the
Will having 9 M. kubotais be better than having 10?
<11 would be better than 10, but 9 less good.>
After reading about the odd-number recommendation, I'm wondering now if
I ought to humanely euthanize this fish if he doesn't improve from
whatever illness is attacking him.
<A personal decision, but if the fish clearly has no chance of recovery,
then yes, euthanasia (e.g., via Clove Oil) makes sense.>
Even before my water quality issues, he typically had bites taken out of
his caudal fin and sometimes dorsal fin.
<Indeed. But as in your previous email, this doesn't preclude the next
smallest/weakest becoming the target. Cheers, Neale.>
Re: Stocking microdevarios to avoid aggression
Oh my, I had no idea that message went through. My cat pawed my iPad
just as I was finishing it. I guess he must have sent it! Sorry, I sent
a briefer e-mail this morning (American East Coast Time) that asks about
the same problem. Please forgive the duplicate submission.
<Not a problem. Have answered both. Cheers, Neale.>
Re: Stocking microdevarios to avoid aggression
Well, I have a sad update. I had to euthanize the poor little M. Kubotai
this morning. I woke up to find him near the top, struggling to swim,
and with bloody streaks on his abdomen. He had been improving after I
started treating with Nitrofurazone -- the film on his body disappeared,
though his fins still had white edges where they had been bitten. I
wonder if the abdominal bloodiness was due to the illness or just him
getting attacked by the others?
<A little from column A, a little from column B. By this I mean that
systemic bacterial infections (even the notorious Mycobacteriosis) are
often latent in aquaria, but become problems only when fish are stressed
(or, as a medic might say, their immune system no longer works
Teleost fish have a remarkable immune system, different to ours in
important ways (less adaptive, but with stronger non-specific responses)
that explain how fish can heal themselves from wounds with no help from
us -- when they're healthy, at least. But if you think about it, they're
swimming about in a Petri dish -- warm, wet conditions with lots of
bacteria. So as good as their immune system is when they're healthy, if
their immune system shuts down because of physical stress, poor diet,
wrong environmental conditions, then they're quickly invaded and
overwhelmed by pathogens floating about in the water.>
Fingers crossed that the remaining 9 do OK until I can get 3 more.
So, one question for you -- do I continue with the antibiotic treatment
even though none of the other fish is obviously ill? I'm thinking yes,
just because I don't want to risk increasing antibiotic resistance.
<Exactly. On principle, unless you're a medic or a vet, you should
always complete any/all courses of medication. An exception would be
made where there's a "contraindication" -- i.e., the medicine is making
the fish sicker than they are. But otherwise yes, finish the drugs. This
is a good idea for humans, too!>
All the other fish look pretty good...for now at least.
<Good luck, Neale.>
Re: A couple of newbie questions for
clarification... Zebra Danio... stkg. - 9/20/11
One more follow up question (then I'll stop bugging you -
I've been reading through the site more and am learning so much
more every day. But I have a few questions about my schooling fish I
couldn't find answers for. So I bought 3 more Danios over the
weekend to keep the old 3 happier, but they're not schooling
<Are they the same species? Zebra Danios and "GloFish" are
the same species and should school together. But Pearl Danios are a
The older 3 hang out at the bottom of the tank largely ignoring the new
three, who school together as surface dwellers. Half the time they go
off on their own and don't even bother schooling. Is this
<Yes and no. Like new kids at school, they may not want to mix with
the older kids just yet, but give it time.>
Do they need to have a 'getting to know you' period, or are
they still going to be nervous in their groups of three? When I first
put the Danios in there I also temporarily had 6 white clouds that we
got to cycle my housemate's new cold water tank (I know I should
quarantine, but I'm living off my carefully rationed scholarship
while I finish off my Masters degree so I can't really afford
another setup now - will invest in a QT tank in future). They stayed
there until we got the new tank set up, and in the interim the Danios
were schooling with the white clouds.
<Curious; often Danios bully WCMM.>
So I'm wondering if the new guys have more of a desire to be with
surface dwellers than the bottom dwellers my older Danios have become?
Or were they just doing this because it was a new environment and they
wanted safety in numbers?
<Would just wait and give this time. Should eventually school
Secondly, I also bought another clown loach. It's a lot smaller
than my other two (it's only about 3cm) as they didn't have any
of the 7cm loaches they usually have there. I figured it would be
lovely to watch it grow and soon enough it would catch up to the other
two. Since its introduction I've noticed a marked change in one of
my loaches (the smaller or the two bigger ones: we'll call them big
loach [the dominant, faster growing of the two bigger loaches], middle
loach and baby loach to avoid confusion). Middle loach used to come out
from their rock tunnels during the day more so than the big loach, but
now he's out a lot of the time. Particularly in the morning,
whenever he sees me near the tank he (or she, I wouldn't know - I
tend to refer to them as he until I know otherwise) will swim over to
He actually only does this with me and no one else (are they
intelligent enough to differentiate between individuals?) He's now
taken to feeding at the surface with all the other diurnal fish (I feed
them once in the morning, then give them bottom feeder food at night
for the loaches and the Bristlenose). He'll even eat dried
blackworms right out of my hand now.
Which is lovely and very cute, but I am not sure if I should be
concerned about the sudden change in foraging behaviour? Is he just
emboldened by not being the smallest loach in the tank now?
<Likely so. Clown Loaches do become more confident the more of them
there are. Also, so-called "dither fish" that swim at the
surface encourage bottom dwellers to swim about in the open. The theory
is that bottom dwellers watch surface fish, and if the surface swimming
fish look happy, the bottom dwellers can assume there aren't any
The biggest loach, on the other hand, will stay in his rock during the
day and will rarely leave. The middle loach will often nudge big loach
during feeding time and they will leave to eat, but big loach will dash
out and grab a piece of food and take it into his tunnel to eat. As I
type this, big loach just swum out to join middle loach who is happily
foraging among the stones for more food, but then soon dashed back. He
seems much more shy and cautious.
And then baby loach, on the other hand, is different again. He's
not concerned with hiding at all. He spends all day swimming around
playing and foraging and will rarely join the other two in their
tunneled rock - he actually loves schooling with the guppies (who are
of the same size as him) and joins them as they dash back and forth
through the bubbles (their favourite game).
Is it normal to see such varied differences in clown loach personality?
Or is having so few messing with their social structure?
<Yes, Clowns vary, and yes, having a very small group means that
what you observe is less likely to be "normal" compared to
when they're kept in big groups. I've seen Clowns in groups of
50 adults, quite something let me tell you, and they school together
<You are doing the right things, so should simply wait and watch for
Good luck, Neale.>
"Glofish" ID... Zebra Danio care...
I have recently seen a fish called a "Glofish" - a relative
of the zebra, yet genetically enhanced to exhibit colors -
<Not "a relative" of the Zebra Danio (Danio rerio) but the
same species, just with an extra gene. Maintenance is identical, though
they're likely to be somewhat delicate by comparison to standard
Zebra Danios thanks to inbreeding and less genetic variation.>
I thought they would make an interesting addition to my tank - What
size tank do they require?
<Like Zebra Danios, tank 60 cm/2 feet long is the key thing; these
fish get to about 5-6 cm in length and are highly active. In small
tanks they're less happy and prone to becoming frustrated
Are they a shoaling fish?
<Yes; keep in groups of 6 or more (either 6 Glofish, or a mix of 6
Glofish and standard Zebra Danios, as you prefer).>
Are they compatible with other species of fish?
<Like Zebra Danios in this regard. Community fish, provided not
mixed with anything too slow that might be nipped or otherwise
In general, what is the best way to keep them healthy and happy?
<As Zebra Danios, with due allowance for their preferred cool water
temperature -- 22-25 C is ideal -- and their need for clean water with
a good current and lots of oxygen.>
Also, Do they reproduce in species-only tanks?
<In theory they should be easy to spawn, just like Zebra Danios. But
when you buy these fish, you actually accept a license that prohibits
you from doing so (bizarre as that sounds):
Since these animals aren't sold in the UK, I don't know anyone
who has actually bred them (the European Union has restricted sale of
genetically modified organisms on public safety, animal welfare and
Can't say I'm all that bothered by their absence, and I'd
encourage you to look for some of the naturally occurring Danio species
(like Danio choprae and Danio margaritatus) that are much prettier, in
my opinion, and very definitely legal to breed! Cheers,
GloFish Question Bob, <Yep> Wondering if
we can get your opinion on the GloFish fluorescent zebra
Danios? They look amazing, esp. for freshwater (n fact, even
better than some marine species). Could you
comment? If you haven't heard of them yet, they are at
www.glofish.com and http://www.reuters.co.uk/newsArticle.jhtml?type=scienceNews&storyID=3873977Â§ion=news
has a good article. Thanks! Sandi <Have seen these transgenics... a
whole bunch at last times Aquarama in Singapore... a neat scientific
application... but para mi, "no sale"... too pricey. Bob
Re: GloFish Question Bob, Thanks so much for
your time. I think I'll go with the GloFish even at the
price. They look to cool to pass up. Sandi <They are very
beautiful, and a very interesting "story" to relate re their
"genetic clip-on" technology. Bob Fenner>
The Ethics of Glo-Fish (TM) (6/5/05) Hiya Bob,
<<Howdy. RMF>> I just finished reading the article on
the Glo-fish, and I was wondering if it would be possible to ask the
author if he considers every breed of dog, most breeds of milk and beef
producing cattle, and probably 80% or better of all of the grains and
fruits he eats as also being 'garbage' due to the fact that
they are also man induced 'mutations' (yes, the method may be
different, but the intent and process is the same and similar-one is
just more 'trial and error, after all, no?) For the record, I also
don't like the idea of Glo-fish, or painted chandas, but plenty of
folks hate telescopes, black moors, fancy guppies and swords for just
as legitimate reasons. <Agreed> I can understand a POV of
distaste and dislike, I was just wondering what selective bias the
author uses to determine which of our obvious genetic alterations are
'garbage' and why? ;) (heh, maybe I should write a counter
point article for submission, playing devil's advocate) <All
submissions are welcome for consideration. You will have to use a lot
better grammar than you did in this e-mail. Please capitalize the
proper noun "I" and the first letter of sentences. We post
all e-mails and replies. It's a lot easier for folks to read them
if they are punctuated properly. If you do it then we can spend less
time proofreading and more time answering.> Keep up the good
work-been observing your website for years, all the best! Alan
<Thanks. The author of the article is not a member of the
question-answering crew, so I do not know how to contact him. I do
agree with you on this issue. I have nothing against Glo-Fish (TM)
myself. They were created to serve a utilitarian purpose (pollution
detection). If there is a side benefit of providing pretty fishes that
have not been chemically burned and dyed, that's great from my
perspective. I have no problem with GM foods either. I say you're
right that there is no difference in principle between this and
selective breeding. It's only method and speed. In fact, GM is
better because the planning will lead to fewer bad mutations. It just
needs to be properly regulated. As for the other fish you mention, I
have qualms about some of them. If fish are selectively bred for
appearance, I only have a problem if that creates a deformity that
impairs the fish or causes pain. Some of the fish sold these days
definitely suffer as a result of their selectively-bred appearance.
That's my opinion, for what it's worth. Steve