My Harlequin Rasbora Keep Dying One By One, What Could Be The Cause?

[Mark2320]

Little over 2 weeks ago I added 8 harlequin rasboras to my tank. In the beginning they were schooling and doing fine. However, since a few days they are dropping one by one. It starts out with one fish not schooling and hiding in a corner. Then a few hours later it is gasping for air at the surface and it's dead in half a day. I tested my water several times and it has 0 ammonia, 0 nitrite and around 0 nitrate. Does anyone have an idea what I'm doing wrong. At the moment another one is gasping for air it seems like.

 

[JJfishes]

When did you set the tank up? 0 Nitrite, 0 Nitrate, and 0 Ammonia looks like an uncycled tank to me or you just have a lot of plants...

Gasping for air could mean there's not enough air in the water and they're getting suffocated.

 

[Mark2320]

Some extra info:
My tank is 20G.

8 harlequin rasbora atm (I bought 4 new ones yesterday)
4 amano shrimp
3 corydoras julii
3 otocinclus

When did you set the tank up? 0 Nitrite, 0 Nitrate, and 0 Ammonia looks like an uncycled tank to me or you just have a lot of plants...

Gasping for air could mean there's not enough air in the water and they're getting suffocated.

I have a lot of plants, I added a picture. I cycled the tank for a few weeks and added beneficial bacteria.

 

[JJfishes]

Are any of the other fish gasping or just the Rasboras? Do you have an air pump for surface exchange (more oxygen in the water).

 

[Mark2320]

Are any of the other fish gasping or just the Rasboras? Do you have an air pump for surface exchange (more oxygen in the water).

It's just the Rasboras. I have no air pump but my filter does move the water (at the surface) a bit. If there would be a lack of oxygen you would say that all of them should be gasping for air right? And not one by one.

 

[SeanyBaggs123]

How many have died?
Do you notice the change overnight?

 

[Mark2320]

4 have died so far, I did not specifically notice the change overnight.

 

[SeanyBaggs123]

What I'm wondering, since its only the raspboras... is if there is some aggression/hunting at night rather than disease.

 

[Mark2320]

There is some aggression but I read that it is completely normal and that they are establishing some sort of pecking order. Now that I'm thinking off it, yesterday two of them seem to be fighting.

 

[SeanyBaggs123]

Just my opinion, but if you aren't seeing any other symptoms and the other fish seem fine..... Probably due to stress of some sort (Whether it be water paramaters, aggression, the don't like the way one of the leaves sway haha seriously anything).

Could add more cover with another (larger) plant or rearrange that beautiful aquascape to break up the line of sight. Additionally, with schooling fish like that, the more the better. I have seven and they get along famously. Hope that helps.

 

[Mark2320]

Just my opinion, but if you aren't seeing any other symptoms and the other fish seem fine..... Probably due to stress of some sort (Whether it be water paramaters, aggression, the don't like the way one of the leaves sway haha seriously anything).

Could add more cover with another (larger) plant or rearrange that beautiful aquascape to break up the line of sight. Additionally, with schooling fish like that, the more the better. I have seven and they get along famously. Hope that helps.

Thanks for the advice, what do you mean with "break up the line of sight"?

 

[Truckjohn]

Add an airstone and see if things don't perk up.

I ran into the same thing with Danios... Added an air stone and everybody was happy.

 

[JamieLu]

Break up line of sight means but plants and other visual barriers up so the fish can't always see eachother and have places to hide if they need

 

[SeanyBaggs123]

Break up line of sight means but plants and other visual barriers up so the fish can't always see eachother and have places to hide if they need

^What she said. Air stone couldn't hurt either.

 

[ColmC]

Aw I love harlies, have 11 in my tank

I would do a water change and add an air stone .

 

[Mark2320]

Another one is gasping for air now... This one seems to have a white bump on his head, his eye almost seams to pop
Is something else going on? Some kind of disease among my fish?

 

[SeanyBaggs123]

Fish Pop-Eye Disease

I would read that over.

We must be missing some info here though.

Can we go over how you cycled your tank and what test kit you used to establish the parameters you quoted above?
Have you been testing PH as well?
Is it possible you're overfeeding? How often and how much?

It is possible that it's some sort of infection (likely bacterial), but I think the more probable cause is still either aggression or water parameters (especially if it's still only the Raspboras)

I still think a 50% water change a small airstone (just in case there isn't enough dissolved oxygen) is a good idea... Pending your answers to the above questions.

 

[Mark2320]

I cycled my tank by adding beneficial bacteria. I did that one day 1, 7 and 14. After day 14 I changed a large portion of the water. After two weeks I added 3 otocinclus after I tested my water in the store. I brought the water in a bag and he tested it with his kit (in a suitcase with several little plastic containers for ammonia (0), nitrite(0), nitrate (close to 0) and PH(slightly higher than 7 if I recall correctly). One week after that I bought the Rasboras and one week later I added 4 amano shrimp. Another week later I added the corydoras. I tested my water yesterday and again the values were the same (good). The store owner even recommended to not do a water change for a while perhaps my water was too clean (some nitrate would be good for my plants). I was feeding them once a day and I would feed them so much they can eat in one minute. The store owner thought it was possible I fed them too little so he recommended to feed them some more (I'm feeding them twice a day since yesterday).

This one isn't looking too healthy either, his colour seems "off" compared to the others as well.

Really thanks for trying to help me out btw, it is frustrating to see my fish suffer.

 

[SeanyBaggs123]

Did you have a source of ammonia in the tank when you were adding beneficial bacteria (ie fish, rotting fish food, dosing ammonia yourself)?
When you say you tested your water yesterday, what did you test it with? (be specific. i.e. tetra 5 in 1 test strips or "API Master freshwater test kit" etc...)

The only advice I agree with from the store owner is that some nitrate may be good for your plants. However, I don't think delaying water changes or overfeeding is the way to get there. I personally would feed once a day or even once every other day until you have this sorted, and even after you figure out what happens... I'd go down to once a day.

Are you watching the fish die or discovering them after the fact?

 

[mossman]

What are you feeding and how often? I've had several mysterious fish deaths over the past year and was completely baffled. It turned out I wasn't feeding them enough.

 

[Mark2320]

I did not a source of ammonia in the tank during the cycle. The guy in the store told me that wasn't necessary (I have read several sources that say that you need to add a source by yourself but decided to follow his advice). My water is tested using the kit, I know the strips aren't reliable. One died one hour ago and then I saw the one with the big eye which I put out of his misery myself.

I was feeding them once a day (TetraMin Flakes by Tetra)

 

[SeanyBaggs123]

The ottos, corys, and shrimp all have normal behavior and no symptoms?

Where did you get the raspboras?

 

[Mark2320]

Yes the others are acting completely normal and don't have any symptoms. I bought them in a fish store in The Netherlands. I didn't buy them at the store where I normally go to, since he didn't have them in stock. But he recommended me a different place (same franchise) at the other side of the town.

 

[SeanyBaggs123]

I'm still in the camp that it has something to do with the behavior/aggression (Pecking order) or the fish themselves (source). If the rest of your fish are still fine and only one or two Harlies are getting picked off a day.... Then I doubt it's bacterial infection. Something like columnaris would wipe out your tank in days, and it is not partial to species.

I would still try the large water change and small air stone, and if that didn't work I'd probably return the Raspboras and find a new source for fish.

 

[Mark2320]

I'm still in the camp that it has something to do with the behavior/aggression (Pecking order) or the fish themselves (source). If the rest of your fish are still fine and only one or two Harlies are getting picked off a day.... Then I doubt it's bacterial infection. Something like columnaris would wipe out your tank in days, and it is not partial to species.

I would still try the large water change and small air stone, and if that didn't work I'd probably return the Raspboras and find a new source for fish.

Thanks, did the water change today and changed the direction of the filter slightly. Fish seem to be doing fine, fingers crossed for now..

 

[Mark2320]

So little update: Yesterday I noticed another one being weak compared to the others. Just now I found him "swimming" apart from the others. His colour is completely faded and his head has become darker. Right now there are 3 little ones (seem to be doing fine) 1 bigger one who is kinda chubby and very bright coloured. And this one. I added a video to show you the weaker one. It seems to me that the bigger one is being aggressive/dominant towards the other ones and that is the cause of their death. Do you agree? If that is the case, what should I do? I would like to have a healthy school of at least 6 in my tank.

 

[Elkwatcher]

I'm still in the camp that it has something to do with the behavior/aggression (Pecking order) or the fish themselves (source). If the rest of your fish are still fine and only one or two Harlies are getting picked off a day.... Then I doubt it's bacterial infection. Something like columnaris would wipe out your tank in days, and it is not partial to species.

I would still try the large water change and small air stone, and if that didn't work I'd probably return the Raspboras and find a new source for fish.

If something was going on in the tank with water parameters the Oto's would be the first to show it too. I think you're on to something...

 

[CryoraptorA303]

I'm of the opinion that it's multiple factors. What are your water parameters right now? Since they are only becoming ill and dying after being in a fight, something else is stressing them out, then getting into fights and being injured is pushing them over the edge. From the pictures, they are clearly beginning to suffer from diseases after being injured. I'm wondering whether it's worth getting rid of the biggest guy and getting more smaller ones of around the same size and seeing if the problem disappears. If the big guy is older and more developed, he may be being too rough with the younger ones and injuring them pretty badly, leading to them getting secondary infections and dying.