Strange platy behaviour

hi all

Newbie to fish and the forum. I've had a tank for about 4 weeks and all seems fine.
Tonight I noticed my micky mouse platy behaving strangely. He is swimming fine but with one particular rummynose tetra he has started showing his belly and almost standing up on his tail fin.
Anyone know what he's doing please? Thanks

He's very stressed, see how all his fins are clamped tight to his body? That's a sign of a very stressed out fish, potentially very unwell, and the spinning behaviour isn't good I'm afraid... looks like he's on his way out.

Do you have a test kit to check ammonia/nitrites/nitrates? What are the results?

I'm suspecting water quality issues since it's a brand new set up, but if you could copy/paste this template and fill in the answers, people will be able to offer more help if they have a better idea of the set up

Tank size:
tank age:
pH:
ammonia:
nitrite:
nitrate:
kH:
gH:
tank temp:


Fish Symptoms (include full description including lesion, color, location, fish behavior):

Volume and Frequency of water changes:

Chemical Additives or Media in your tank:

Tank inhabitants:

Recent additions to your tank (living or decoration):

Exposure to chemicals:

Digital photo (include if possible):

Thank you. He is eating fine and the other platys look and act as normal. He was perfectly ok until this evening. I have a molly, some rummynose tetras neon tetras glowlight tetras and black widow tetras. Its a 60 litre tank, I will test the water tomorrow

If it's only with another fish could it be postering? Definitely stressed and unusual behaviour.

AilyNC said:

If it's only with another fish could it be postering? Definitely stressed and unusual behaviour.

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Agree. It's not enough space for black skirts, they could be nippy/antsy.

What's "not enough space " ? They've been fine for 4 weeks. It's a 60 litre tank with 3 platys, a molly, 2 black widows and 8 small tetra

That's a 15 gallon tank. I'm going to assume you have a 15 standard which gives us the dimensions of 24″ x 12″ x 12″. Normally this is the minimum for skirt tetras, however with just 2 they do not have anywhere to spread aggression. Also you are mixing hard water fish (mollies and platies) with soft water tetras, which also leads to problems. Do you know your general hardness?

Hello and welcome to the forum, we are here to help give you suggestions to help you and your fish so please do not take it personally. I agree with @HoldenOn skirt tetras should be in groups of 6-8, the more the better. They will fin nip other fish when kept in smaller groups. Rummy nose, neon and glow light tetras should be in shoals of 6 or more. Tetras are schooling fish and become stressed when not in shoals of at least 6. Tetras come from South American jungle streams so they like shade and floating plants. Bright lights can stress them so I would at least try and dim the tank lighting. I have both hard water fish like platys and soft water fish like glow light and neon tetras which I keep in separate tanks. Here is a picture of my soft water tetra tank. You may notice the lights are not bright and I have floating plants. Do you know what type of water do you have? I use RO water to soften my hard water for my tetras.

Thank you for your advice. I am still learning, I read up on the fish before I bought them but am a complete novice. I should point out that the black widows were my partners which have been happily living together for 3 years and are not the problem. The molly was an accident but am loathe to get rid of as she seems happy and has settled well. I understand about water differences and am considering getting a second tank. I have a charcoal and zeolite filters and the temp is 26 degrees.
He is swimming around this morning and his tail fin is spread out again for now. I am beginning to think that he probably is just stressed and not ill. Ill test the water today and try and set up the other tank to move the platys for now.
I appreciate your help

Scoobysnacks said:

Thank you for your advice. I am still learning, I read up on the fish before I bought them but am a complete novice. I should point out that the black widows were my partners which have been happily living together for 3 years and are not the problem. The molly was an accident but am loathe to get rid of as she seems happy and has settled well. I understand about water differences and am considering getting a second tank. I have a charcoal and zeolite filters and the temp is 26 degrees.
He is swimming around this morning and his tail fin is spread out again for now. I am beginning to think that he probably is just stressed and not ill. Ill test the water today and try and set up the other tank to move the platys for now.
I appreciate your help

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I definitely think stress behaviour. Good to check water parameters as it can rule in/out certain causes.

The Molly needs a 90cm/36" length tank to have adequate swimming room, unfortunately your tank is too small.