Zebra Danio bullies

[El from AZ]

Hi everyone I'm new to asking questions on this site so bear with me please. For many years I enjoyed owning tiger Oscars but a couple years ago after my last Old Man Died I decided to get a 30 gallon tank and put some colorful tropical fish in there. Now I live in a pretty pitiful place to buy fish, and admittedly I did absolutely no research before I went and bought some fish figuring this sales person must know what they're talking about LOL. I came home with for beautiful GloFish tetras which by the way I still have after 2 years but a fish called a painted glass fish they look pretty enough to me so I get home and I start researching and I cannot believe that they put dye in those glass fish I still have one believe it or not but they all got growths on them and what not the idiots salesperson also sold me some fiddler crabs which really are not supposed to stay under water all the time I was pretty pissed off and I gave them to a friend. This is what brings me to this forum about 6 months ago I got six zebra Danio and 5 sunset platys I am down to three danios and one platy and realize I have a Danio in there that is a total jerk because I was seeing blood marks on all of these dead fish. it's a good thing goes danios are fast because if I could have caught the right one he would probably be down swimming in the sewer I was really upset It was like a two-week period The Jerk doesn't bother my tetras. And they're not even that pretty LOL I'm afraid to put more fish in there has anybody else had this problem?

 

[Curiosity101]

Just because the dead fish have bloody marks on them doesn't definitely mean that they were attacked to death by a Danio (unless you specifically saw it happen?).

Danios are quite fast, nippy (as in biting) fish. They do tend to fair better being kept with a good number of their own kind cause then they tend to all chase and nip eachother which is fine.

What fish do you have in the tank at the moment?

What are the dimensions?

And do you happen to have some recent water test results to hand? I'm wondering if water quality could be a factor.

 

[El from AZ]

Just because the dead fish have bloody marks on them doesn't definitely mean that they were attacked to death by a Danio (unless you specifically saw it happen?).

Danios are quite fast, nippy (as in biting) fish. They do tend to fair better being kept with a good number of their own kind cause then they tend to all chase and nip eachother which is fine.

What fish do you have in the tank at the moment?

What are the dimensions?

And do you happen to have some recent water test results to hand? I'm wondering if water quality could be a factor.

the tank is a 30-gallon tank 30 in Long 18 inches high and 12 inches deep it has regular water changes and tested regularly for ammonia GH KH pH no.2 + no.3 the only thing is I do have hard water and there's nothing I can do about that. Anyway yes I did see one particular zebra Danio chasing others around relentlessly and the next thing you know they would have a red bloody spot toward the end of their tail. My tank is hardly overstocked with four Tetra and 3 zebra Danio and one lonely Sunset platy left because he tortured them too and I don't think they could take it I had them for probably 6 months before everything started to go to hell my tetras have been there for 2 years. I am just wondering what I should do because I really would like to get a few more fish and I don't know if I want to get anymore of those zebra danios. In the past week or so things seem to have settled down and there is no more chasing around. Now I have never bred fish and never plan to but do male fish get aggressive with females?

 

[Curiosity101]

tested regularly for ammonia GH KH pH no.2 + no.3

Do you happen to have the latest readings to hand?

I am just wondering what I should do because I really would like to get a few more fish and I don't know if I want to get anymore of those zebra danios.

If I were you it really depends on whether you like the Zebra Danios or not. If you do, then they're likely to be a lot better behaved if you get more of them cause they'll bicker amongst themselves rather than with other fish. And bickering / chasing in Danios is normal behaviour.

However if you're not a big fan of Zebra Danios and they're causing issues then I'd probably just ask my local shop if they'll take them, and/or put an ad on line to give them away for free. Then you'll be free to replace them with something a bit more friendly.

Now I have never bred fish and never plan to but do male fish get aggressive with females?

Some do. It could be males getting boisterous, but it could just be Danios being Danios.
This isn't the best article on breeding Danios but has a couple of pictures that may help as a guide to sexing them.
http://thefishdoctor.co.uk/breeding-zebrafish-zebra-danios/

 

[El from AZ]

Just because the dead fish have bloody marks on them doesn't definitely mean that they were attacked to death by a Danio (unless you specifically saw it happen?).

Danios are quite fast, nippy (as in biting) fish. They do tend to fair better being kept with a good number of their own kind cause then they tend to all chase and nip eachother which is fine.

What fish do you have in the tank at the moment?

What are the dimensions?

And do you happen to have some recent water test results to hand? I'm wondering if water quality could be a factor.

 

[El from AZ]

My water parameters all seems to be okay like I said I do have hard water but everything else is the pH is 7 the nitrates are 20 the nitrites are zero and ammonia perfect yes I have to make a decision what I want to do with these danios thank you for all of your information

 

[King puff]

Danios are not the culprit as these fish do not have true teeth. Definitely not sharp enough to pierce scales. I think it may be ammonia burns. I know you say it is fine but a tank with few fish does not have as much bacteria in it. This means if you add 11 fish at once these bacteria cant keep up and the ammonia builds up. I am not sure when you tested it but the bacteria colonies have probably grown to a reasonable amount to keep up with debris.

Your nitrates are also a bit high. They should be at a maximum of 10.

 

[Curiosity101]

I think it may be ammonia burns. I know you say it is fine but a tank with few fish does not have as much bacteria in it. This means if you add 11 fish at once these bacteria cant keep up and the ammonia builds up.

This was something I was going to suggest next, dissolved tail fins and bloodiness around the end of their body can often be ammonia poisoning (in your case it would have most likely been a spike). And it can happen from large changes in bioload relative to the current bioload. Which also why I was wondering about the overall stock currently.

If you do swap out the danios or add more I'd recommend checking your water every day for a few days as of introducing them, just to be safe

Your nitrates are also a bit high. They should be at a maximum of 10.

This isn't true though. Nitrates can be safe and fine up into 40+ (I can't remember the exact number). And some places would not physically be able to get below 10 unless using RO water cause their local water supply contains much more than 10.

 

[El from AZ]

This was something I was going to suggest next, dissolved tail fins and bloodiness around the end of their body can often be ammonia poisoning (in your case it would have most likely been a spike). And it can happen from large changes in bioload relative to the current bioload. Which also why I was wondering about the overall stock currently.

If you do swap out the danios or add more I'd recommend checking your water every day for a few days as of introducing them, just to be safe



This isn't true though. Nitrates can be safe and fine up into 40+ (I can't remember the exact number). And some places would not physically be able to get below 10 unless using RO water cause their local water supply contains much more than 10.

Thank you for letting me know about the nitrate number I have never had it down to 10 I have always been told and read about it could be up to 40 safely but I will keep my eye on it

 

[Essjay]

Actually, recent research shows that nitrate should be kept below 20 ppm, with some fish species needing lower than that. Nitrate does affect fish and shortens their lives. Byron can probably give you more precise details.

 

[Byron]

Nitrates have not been well understood in the hobby, at least until recently. There are few studies dealing with the effect of nitrate on aquarium fish compared to the studies on commercial hatchery food fish species. But we have learned much in recent years.

Nitrate, like ammonia and nitrite, is toxic to all fish. The effects of poisoning by ammonia or nitrite are more rapid and lethal, but nitrate too is toxic. Tolerance can vary from species to species, and the duration of the exposure also affects how fish are affected. In very general terms, the higher the nitrate, or the longer the fish are exposed, the more detrimental to the fish. Fry have a significantly lower tolerance, which is not really surprising as this is the case with many issues.

We also need to remember than in their respective habitats, no species of fish we maintain in an aquarium is exposed to nitrate, any more than they are to ammonia or nitrite. When nitrate levels have been detected in a very few habitat waters, the level has been very low, seldom (so far as I am aware) reaching even 1 ppm. Considering that the physiology of all freshwater fish species has evolved over thousands of years to function best in a very specific environment, which includes substances in the water, it should be obvious that the closer we can come to those same environmental conditions in the aquarium, the healthier will be the fish.

Nitrates should be as low as possible, and never above 20 ppm. Cichlids are now known to have issues with nitrates above 20 ppm, and it is being suggested as likely causes of problems like Malawi bloat which used to be thought food-related. No reputable ichthyologist will suggest higher nitrate levels.

We have had a couple threads recently on nitrate. One important distinction is the source of the nitrate: nitrates in the source water is one problem, and nitrates occurring from the biological system within the aquarium is another problem, and these two have somewhat differing methods to deal with nitrate. If the source water is zero nitrate, and you are seeing nitrate above 20 ppm in the aquarium, immediate steps can be taken to deal with the cause, which is organic in nature: too many fish, too large fish, too much food being fed, insufficient water changes/filter cleanings/substrate cleaning. Live plants help by using ammonia before thee bacteria get it, which means less nitrite, and thus less nitrate in the end; some plants will also use nitrate though usually only when ammonia is insufficient in balance. Keeping nitrates below 20 ppm is frankly crucial; keeping them even lower is advantageous.

How nitrates affect fish is another area only now being researched. In general terms, fish are simply weakened if they are struggling with high nitrate. This leads to other issues of health, including stress and a weakening of the immune system. Spawning can be affected, and of course growth of fry. So far as is known, fish will not live to their normal lifespan.