Killer Cardinal Tetras??

[Rosey]

Hi
I think I am going to give up on Cardinal Tetras. After cycling the 15 gallon tank 3 months ago water readings are now:

Ammonia - 0
Nitrite 0
Nitrate 15e
PH 7.4

Added four cardinals when water had cycled - one week later added four more cardinals from a local store (after acclimatisation) and overnight all four were dead. One week later added 2 more cardinals and overnight those two were dead as well - (I still have the original 4 cardinals as the other additions were smaller so I can tell from size). I bought another four cardinals yesterday (once again acclimatising them slowly) - I watched the tank last night for some time and the pushing, chasing, bullying by the slightly larger cardinals was worrying!!) Overnight all four of the new cardinals were dead with their rear fins completely missing. So I still have only the four original cardinals left.

I thought these fish were supposed to be passive fish???

I am not sure what to do now as I would like a total of eight but should I just give up??

There is nothing else in the tank so it is the cardinals that are the killers.

 

[Byron]

This is odd to say the least. But it is one reason why shoaling fish should always be acquired together, the entire number, if at all possible. Having said that, I would not expect aggression with this species, but it is something that can occur generally when new fish are added to an existing group. A study a few years back confirmed that shoaling fish in numbers lower than five developed significant increased aggression, and normally peaceful fish developed aggressive behaviours, solely from the numbers.

However, I would look further afield. A 15g is not large, but should be adequate for cardinal tetra at this stage anyway. Do you have plants? Chunks of wood? I am asking about the aquascape because these fish do not like open water tanks; in their habitats they are found around branches or under surface vegetation/aquatic plants. Stress from the absence of adequate covering can cause serious aggression. And as there were only four in the initial group, this can be amplified.

The other issue is acclimatization. Can you explain what you did? And do you know the water parameters of the store (bag) water for comparison?

Byron.

 

[Rosey]

Hello, thank you for your comments.
Yes, I did wonder if it was because I had added to a group of four each time although I felt adding more than four initially would have put too much load on the filter as it had only just finished it's cycle.

Yes, it is a small tank (not like my previous larger tanks which I had years ago) and due to it's size this is why I have taken it very slowly, I would like to add pygmy corys and some shrimps. Also an algae snail.

The tank is planted, sword plant on wood fills right hand side, individual plants on left with half coconut covered in moss, also mopani wood and a piece of grey slate at the front and three moss balls.

I buy from a local fish store and I am always assured that the PH is the same as mine although I still acclimatise new fish by rolling the bag down and leaving it floating in the tank for at least two hours. I then add small amounts of the tank water over the two hours until I feel I have doubled the water content of the bag. I then add to the tank with the light off for at leas one hour. The one fish only lasted 10 minutes when added to the tank and then died with its rear fin completely gone!!!

 

[Byron]

How do you confirm the store water is the same as your tank?

Leaving that for the moment, one thing about your acclimation (which is otherwise very good)...never add water from the bag into the tank. Net the fish out after you have mixed the water as described. I know this can still add undesirables with the fish, but the water can contain all sorts of pathogens, ammonia, etc. that you do not want entering your tank.

I'm not sure what else to suggest at this point. I am still wondering about the water parameter differences. Have you spent a considerable time sitting in view of the tank without moving? For up to half an hour or longer, without moving? This may seem silly, but when the fish know you are there, they may well not behave normally, not because they are trying to fool you, just because your presence is suggestive to them of food, etc. Sitting motionless for a period of time often allows us to see things we wouldn't otherwise notice, like an aggressive fish in the group. I had this very thing with Emperor Tetras once, and once I saw it, I separated the fish.

Byron.

 

[Rosey]

OK, yes, will do, net the new fish into the tank without the water.

Yes, when I put these four new ones in yesterday, the tank is directly in front of me and because of all the problems I have had I moved slightly closer and sat there for at least half an hour and watched the shoving, chasing and what appeared to be aggression from one of the original cardinals but I didn't think that one culprit would kill all four of the new ones. I removed the dead fish (only found three of them so far) today and there tail fins had completely gone.

I should have removed the culprit then as these four left seem quite OK together. My problem is that is four enough to just leave them and not try to add any more to the group.

 

[Byron]

OK, yes, will do, net the new fish into the tank without the water.

Yes, when I put these four new ones in yesterday, the tank is directly in front of me and because of all the problems I have had I moved slightly closer and sat there for at least half an hour and watched the shoving, chasing and what appeared to be aggression from one of the original cardinals but I didn't think that one culprit would kill all four of the new ones. I removed the dead fish (only found three of them so far) today and there tail fins had completely gone.

I should have removed the culprit then as these four left seem quite OK together. My problem is that is four enough to just leave them and not try to add any more to the group.

If you feel you have identified an aggressive cardinal, it would be wise to remove him from the tank. If you have another tank to house him even temporarily, good. If not, will the store take it back if you explain things and buy another five or six?

Even a temporary net in the tank might work, one of those mesh breeding nets. Add five-six new fish, and if all is well, you will have identified the problem.

Byron.

 

[Rosey]

Good Idea, I do have a mesh breeding net - I think I will go to the same fish place and watch them and if it is only one causing the problems I will remove it. I have two pygmy corys on hold at the same place and really don't want to add them until this is sorted out just in case it is something wrong with the tank.

Thank you for your help - I really didn't think that cardinals were going to cause such a problem!!

 

[Byron]

Good Idea, I do have a mesh breeding net - I think I will go to the same fish place and watch them and if it is only one causing the problems I will remove it. I have two pygmy corys on hold at the same place and really don't want to add them until this is sorted out just in case it is something wrong with the tank.

Thank you for your help - I really didn't think that cardinals were going to cause such a problem!!

You're welcome.

So I understand, you will put the likely offender in the net, and add 5-6 more new cardinals. If all is well after a few days, maybe the store will take the offender? It will need to go somewhere.

Re the pygmy cories, make sure you get a group, not just two; at least 7, preferably 9-10. At the same time. This is a very delicate cory, and they always settle in better the more there are. It also needs more than the larger species. And it needs sand as a substrate. Last point, cooler water, with 75-76F max.

Byron.

 

[Rosey]

I need to do some research as to how many will be ok in a 15gallon tank. I was looking to get two of each of the three different pygmy corys that are available in the UK, adding two at a time?? My tank isn't large enough for any more. Is an odd number better than an even number or does it make any difference.

I will get some more cardinals before bringing the corys home - the fish place may be able to get me the six I would like and keep them for me until ready.

The fish place (the reason I don't call it a shop is because it is just up the road from me in the country and he stocks coldwater pond equipment/fish and has a small shed with his tropical and marine fish. He has been going for years and is well respected in the community.

My tank is at 78 degrees and I understand that corys will adjust to this, I could drop it a bit.

 

[Rosey]

I forgot to say, they will take the 'offender' if I can sort it out. When I gave up my tanks some years ago now, I gave them all my beautiful tropical fish, plecos, corys, etc. I think they owe me!!!

I do have small gravel in my tank and although sand is recommended for corydoras, I have kept them before in tanks with small gravel and they have not had problems with their barbels wearing away/damage and they have lived for years. I think this is open to debate!!

 

[Byron]

I forgot to say, they will take the 'offender' if I can sort it out. When I gave up my tanks some years ago now, I gave them all my beautiful tropical fish, plecos, corys, etc. I think they owe me!!!

I do have small gravel in my tank and although sand is recommended for corydoras, I have kept them before in tanks with small gravel and they have not had problems with their barbels wearing away/damage and they have lived for years. I think this is open to debate!!

Yes. All cories should be over sand or mud or a mix; to my knowledge, none occur in watercourses with gravel. Obviously we don't want mud in an aquarium, so sand is the best option. The reason this is important is the behaviour of the cory. It picks up a mouthful of the substrate, sifts it around looking for tidbits of food, then expels the substrate out through the gill slits. It can't do this with gravel. This is also why the substrate sharpness/smoothness is important, to prevent harm to the delicate gill filaments as well as the barbels, mouth and fish underbelly which is not covered in scutes.

Larger cories can "manage" with fine gravel, but I prefer not making my fish manage when I can provide better. I used fine gravel for many, many years. I finally tried sand in one tank six years ago, and liked it so much I changed over all my tanks in the intervening couple of years. It is difficult to put into words how one knows, but the fish do have a better time over sand. It is comical to see a cory upended, head half buried in the sand, and then sand flying out the gills.

It isn't that much of a job to change a 15g...imagine my work when I changed over my 90g two years ago, and the even larger 115g a year before that. But I'm glad I did, not only for the cories. I like happy fish.

 

[Rosey]

Oh, I see, you learn something everyday. When I set up the tank I started off with aquatic granule for the plants and then the gravel. I must admit that I don't relish the idea of changing it to sand - but if it is better for corys then I may change it. My corys used to play in the filter flow output - just like children - all at the top of the tank being swept along and then going back for more - taking it turns - amazing to watch. These were all large pandas, sterbai, peppered etc. They are such wonderful fish.

 

[Byron]

Oh, I see, you learn something everyday. When I set up the tank I started off with aquatic granule for the plants and then the gravel. I must admit that I don't relish the idea of changing it to sand - but if it is better for corys then I may change it. My corys used to play in the filter flow output - just like children - all at the top of the tank being swept along and then going back for more - taking it turns - amazing to watch. These were all large pandas, sterbai, peppered etc. They are such wonderful fish.

Yes, I have always had cories throughout my 25 years of fish keeping. I presently have a 10g with Corydoras pygmaeus that spawn regularly; I have 30 or so from the original 7 now. The other cories, some 50 representing 12 different species, all wild caught, are in my 70g flooded Amazon tank. They spawn often, but the eggs get eaten with so many other fish, and the few fry I manage to grow up are rescuees from the canister filter when cleaned.

What are the plant granules? These can be problematic for cories, depending.

 

[Rosey]

Oh, how wonderful - the two I have put by are Pygmy hasbrosus and the next two I would like are the pygmeaus with the black stripe.

I would love to have large tanks again although i really don't think I have time for the maintenance at the moment - I used to have free weekends which were taken up with maintenance on the tanks and Eheim filters. Getting too old for it now although I do miss the enjoyment they gave me. I am also a pleco lover.

 

[Byron]

Oh, how wonderful - the two I have put by are Pygmy hasbrosus and the next two I would like are the pygmeaus with the black stripe.

I would love to have large tanks again although i really don't think I have time for the maintenance at the moment - I used to have free weekends which were taken up with maintenance on the tanks and Eheim filters. Getting too old for it now although I do miss the enjoyment they gave me. I am also a pleco lover.

You need more than just two of a species. At least 6, preferably more, of either C. pygmaeus or C. habrosus. I've had the latter a couple times, not at present. You can keep them together, but please have more of each species, and acquire them at the same time (the species I mean) so they will settle in much faster and safer.