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FAQs on the Rainbowfishes Behavior

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 Compatibility, Rainbow Selection, Rainbow Systems, Rainbow Feeding, Rainbow Disease, Rainbow Reproduction,


Turquoise or Lake Kutubu Rainbowfish behavior      4/23/14
I was at the LFS today and there were some beautiful Turquoise rainbow fish there. There were only two left. The guy who works there said that if I did not have the emperor tetras in the 75 gallon that they would go well with the two angels. Is it true that these rainbow fish are really aggressive?
<Male Rainbowfish can be very feisty, yes. Keep in mixed sex groups, partly for behaviour and partly for better colours; ideally 6 or more, though one male and two females can work well enough.>
The males are the beautiful ones and I read they love to dominate and will bully or kill anything in the tank if it can.
<That's overstating the case a bit, but males will try to throw their weight around with any other similar-looking fish, typically other Rainbows. Generally peaceful towards everything else.>
They look big enough to eat most tetras or swordtails and maybe aggressive enough to stress to death a couple of larger angels who are non-aggressive.
<Rainbows can make excellent Angel companions, but do bear in mind Lake Kubutu Rainbows need hard, alkaline water. They will eat bite-sized fish (anything up to, say, small male Guppies) but aren't predators beyond that.
Good with similar sized barbs, characins, etc.>
Thank you
<Most welcome, Neale.>

Re: Boesemani rainbows struggling, repro. beh. obs.  12/24/10
Comment on FAQ link:

"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."
Thinking this is perfectly natural part of mating. My males all do this, while intensifying their colors and displaying a big orange stripe down their head. Then they chase the females as such, lowering their nose to the ground tail up to "show" the lady his big orange stripe and attract her interest (though most of my males are harshly rejected lol) They do it most during times where the tank light is off, but the room is lit (dusk/dawn lighting effect)
<Ahh, thank you for this input. Bob Fenner>

Boesemanni Rainbowfish finnage tipped/edged in Black is this normal?   5/30/2010
I've spend a lot of time searching the web, can't seem to find the answer to my question . I've had this fish for about 3 years seems healthy in everyway. except the bottom dorsal fin is edged in black instead of white.
the anal fin too. Is something wrong with him? I had not noticed this before. I recently lost to rainbows they were elderly past there life-span.
could this be stress because he lost he's buddies? Please help as I would hate to lose this guy.
<Hello Karyn. If what you're seeing are simply continuous black fringes to the anal and dorsal fins, them yes, these are probably normal. Melanotaenia boesemani has a lifespan of more than 5 years, and is generally a very hardy species, but like most Rainbowfish it dislikes acidic conditions, so check the pH isn't below 7.0, and that the water isn't too soft, around 10 degrees dH is about right. Black marks can sometimes indicate ammonia burns or very rarely protozoan infections, but I don't think that's the case here; in those situations, the dark marks are irregular blotches on the fins and skin. Cheers, Neale.> 
Re: Boesemanni Rainbowfish finnage tipped/edged in Black is this normal?
Hi Neale,
Thank you soooo much for getting back to me I really appreciate it. I can relax now!
The water here in (east bay area, ca) is soft
<Not ideal for this species.>
The water has a high ph when it comes out of tap-fish stores have tested my water and have said my ph is low-those readings have to be wrong I contacted Kordon who's here in Hayward and he gets water report weekly .said it is impossible to do a water change and have a low ph using Hayward water.
<Do read here:
You might find it helpful to use the cheap, easy to make Rift Valley salt mix [Epsom salt, baking soda and marine salt mix] at one-quarter to one-half the recommended dose. This Rainbowfish species comes from a Lake where the water is basic and moderately hard, and it's life will be quite short in soft water. Aim for pH 7.5-8.5, 10 degrees dH.>
I will support your wonderful site that I recently discovered. Thanks again-Karyn
<Glad to help. Cheers, Neale.>

Funny blue-eye behavior - had to share! 11/10/08 Good afternoon to the WWM Crew! I was doing a water change this weekend, and as usual, my tank being in a rather dark corner of the room, I put the lighting strip, still on, on the stand behind the tank, letting it light the tank from behind/below so I can see what I'm doing. I was refilling the tank when I noticed my single remaining blue-eye (Pseudomugil furcatus) swimming on her side... I thought it was really weird and I was slightly worried, until I noticed she was trying to keep her back towards the light. Well, now I know how this species finds the surface of the water! It was quite a strange sight, though, seeing her skim the glass-made vertical "surface" of the water... poor thing... Don't worry, I put her sun back where it belongs ;-) With all my best wishes, and many thanks for the immense service you provide, Audrey <Hi Audrey, good to hear from you! Fish do indeed use a combination of light and gravity to detect "down". It is a familiar experiment in ichthyology to put fish in an aquarium and then rotate the light around it.  Even though the fish can feel, by gravity, which direction is down, it also orients itself so its back (dorsal surface) are pointing towards the light.  At first glance this sounds silly. Why not rely on gravity alone and keep the right up and down orientation? The reason for this "dorsal light reaction" (as it is called) is because fish have camouflage that helps them hide from predators. They have dark dorsal surfaces and light undersides.  From above, the dark dorsal surface matches the deep dark depths, while from underneath the light belly matches the sunlight. If the fish failed to orient itself, it's camouflage would be ruined, and it would become easy prey. So the fish makes the changes it has to, keeping its camouflage working properly. Fish are indeed much cleverer than we sometimes think! Cheers, Neale.>

Mean Dwarf Rainbow Hi there, <Hello Jennifer> I've looked through your FAQ's and can't seem to find anything about this.  I have a 12 Gallon Eclipse system that's been running for about 4 months now. I initially started with 4 dwarf Rainbowfish, 2 male and 2 female, <Mmm, would have been better with one male, three females... and this tank is too small...> at the suggestion of the aquarium store employee (another employee later told me that you shouldn't cycle a tank with rainbows, but that's not the problem here).  Almost immediately we noticed that the largest male was constantly picking on the females, and wouldn't even let the other male swim around the tank (he had to hide in the rocks or behind the filter, poor little guy).  About a month later, one of the females developed a sore on her side and looked like she was going to die, so we returned her to the pet store.  The large male Rainbowfish continued his relentless harassment of the other two fish. Two weeks later, the other female died. And then finally, the smaller male died. Now it's about a month after the small male died, and the large male is still in the tank all by himself and seemingly doing just fine.  Water quality checks out ok, but we do have a bit of a brown algae problem. So, I don't know what to do now. It seems like that fish is just mean and doesn't want to have any tank-mates.  I'm a little miffed at him for killing off the other three fish!  I would really like to have an aquarium with two or three different types of fish, but now I don't know what to do. <I do... trade him in... start with a new livestock plan> If I return him to the pet store, do you have any suggestions for my setup?  (Our water is slightly hard with a slightly high pH). Thanks much for your help. I really love your site. :-) <Ah good... then read it over to make up a list of possible organisms... that stay small, are apparently compatible... and check with us, others re their disposition with each other. Bob Fenner> -Jennifer

Colorless Boesemanni Rainbows   7/8/06 Hello.  I have looked all over and haven't found anything like my question.  About 3 weeks ago I bought 4 Boesemanni Rainbows from a LFS.  All the rainbows in the tank were silver with  only hints of color. <Likely just young... really don't "color up" till are a good two plus inches in length> In a display tank there were 3 or 4 rainbows with beautiful colors, so I knew they were capable of colors.  I specifically asked if the ones in the tank would get color, because they looked nothing like the ones in the display.  The guy that I asked I have talked to before, and he seems to know what he's talking about.  (I've compared his answers with you guys' and others)  He said that they were probably stressed in a small tank with a lot of fish, and with the nets fishing around; they would  get their color when they were  more secure and settled. <This is also a factor>    Another thing he mentioned was that they might not be mature yet. (3 of the 4 that I got are 3 1/2 inches or so, and the 4th is maybe 2 1/2 inches, so I would think that at least the 3 should have decent color.) It sounds good, right? <Yes> It's been 3 weeks and they still are silver, for the most part.  I have seen them  get dark vertical  stripes (but not totally dark blue/purple) and sometimes they have a darker yellow tail, but the color never stays for long.  They've never looked like the pictures I've seen of Boesemanni.  They are in a 75 gallon tank with 5 Congo tetras, 7 longfinned Danios, 2 dwarf Gouramis and a Plecostomus.   The water is within safe parameters on the test strips (even ammonia), and none of the other fish are picking on them.  I can't figure it out.  Would more plants/rocks/hiding places help?  Or do I just give them more time?   Thank you for your time and thoughts. Alicia <Well... there is some hope that these will improve with time, good care and feeding, but there are instances that without good "upbringing" that Rainbows (among other life) are more permanently "decolorized" from poor care... Only time can/will tell. Bob Fenner>

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