Green Spotted Puffer sick?

Hi and welcome to the forum

How long have you had the fish for?
How long has the fish been looking skinning?
What does the fish's poop look like?
What do you feed the fish and how often do you feed it?

How long has the tank been set up for?
How often do you do water changes and how much do you change?
Do you dechlorinate the new water before adding it to the tank?
Do you gravel clean the substrate when you do a water change?

What is the ammonia, nitrite, nitrate, and pH of the tank water?​

What sort of filter do you have?
What filter media/ materials are in the filter?
How often and how do you clean the filter?

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Poor water quality can cause clamped fins.
If the fish is eating well but losing weight, then it probably has intestinal worms.​

Do a 75% water change and gravel clean the substrate every day for a couple of weeks or until the problem is identified or resolved.
Make sure any new water is free of chlorine/ chloramine before it's added to the tank.

 

I really need more information about the fish. If you could answer the questions I asked above, it would rule out possible water quality issues causing this or even starvation if the fish is not being fed enough or being fed the wrong food.

If you don't want to answer them, that is up to you and the following information is used for deworming fish. However, without the above information, intestinal worms is just a guess.

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You can use Praziquantel to treat tapeworm and gill flukes. And Levamisole to treat thread/ round worms. If you can't find these medications, look for Flubendazole.

Remove carbon from filters before treatment and increase aeration/ surface turbulence to maximise oxygen levels in the water.

You treat the fish once a week for 4 weeks. The first treatment will kill any worms in the fish. The second, third and forth treatments kill any baby worms that hatch from eggs inside the fish's digestive tract.

You do a 75% water change and complete gravel clean 24-48 hours after treatment. Clean the filter 24 hours after treatment too.

Treat every fish tank in the house at the same time.

Do not use the 2 medications together. If you want to treat both medications in a short space of time, use Praziquantel on day one. Do a 75% water change and gravel clean the substrate on day 2 & 3. Treat the tank with Levamisole on day 4 and do a 75% water change and gravel clean on day 5, 6 & 7 and then start with Praziquantel again on day 8.

The water changes will remove most of the medication so you don't overdose the fish. The gravel cleaning will suck out any worms and eggs that have been expelled by the fish. Repeating the treatment for 3-4 doses at weekly intervals will kill any worms that hatch from eggs. At the end of the treatment you will have healthier fish.