Danio too thin

Question
QUESTION: Hi,
I have a 20 gallon tank water is healthy and stable. I do a 20-30% water change every week.  I have 3 Zebra Danios and I noticed about a week ago that one started to lose weight.  His weight rapidly declined and now he is extremely skinny.  Seems to be eating, swimming, and hanging out with the others as usual.  The other Danios are not showing any problems as of yet.  What are the possible causes of this rapid weight loss AND should I be concerned about something spreading to the my other fish.  (the tank also has some Rasboras, tetras, shrimp, and 1 Betta)

Thanks!

ANSWER: Hi L,

Separate your Danio and put him in a hospital tank.

That tank should include a heater, water, and an aquarium filter.

He will require a dose of something with Prazquantel in it.  He probably has a parasite inside of him, which is preventing his body from absorbing food as it's eaten.  

When dogs and cats get worms, they lose weight.  The worms eat their nutrition, and likewise, the fish is losing his nutrition the same way.

Often, Danios can perish before it's noticed, so it's good you saw this ahead of time.

You might consider dosing your whole aquarium, but if you have invertebrates, you should remove the fish and treat him in a hospital environment.  Watch the other fish.  Sometimes, with internal parasites, it's only one swimming fish who gets it, but all the bottom-feeders will catch it from eating his waste.

I would not treat the fish with the shrimp in the water, either.  Shrimp are highly sensative to medications.

I recommend using this product:

Prazipro - it works and it's not harmful to most delicate species of fish.  Tetra being one of them.

http://www.rockymountaindiscus.com/prazipro.htm

I would be concerned about spreading.  You may consider treating the entire tank, but the shrimp will have to be removed.

I hope you remember to rate my expert advice.  I do this because I truly love animals, fish and people.  What a better way to help people learn?  :)

Happy fish-keeping!

Renee

---------- FOLLOW-UP ----------

QUESTION: 1.  In case I have an infestation, I think you are saying I should treat the entire tank.  Is this correct?
2.  If I am treating the entire tank, do I still need to isolate the currently affected Danio?
3.  If I move the shrimp to another tank during treatment, how long should I keep them out, and since they may be infected would I not be reinfecting the tank when I return them to the community?
Thanks again for you help.

Answer
Hello L,

The shrimp can't be in the water after the Prazipro is used, until the water is changed.  This means if you move the shrimp from that tank, then you must completely clean the other tank before returning the shrimp.  The Prazquantel in the treatment will kill him.

My recommendation is to remove the shrimp, put him in a tank, and then treat your entire aquarium.

After you run the course of treatment as per the directions on the box, then the water in your tank needs to be changed out before the shrimp can come home.  

The first day after treatment, change 50% of the water.

Then, every 3 days afterwards, another 10% for the next 2 weeks.

Once the water has circulated out, you can return the shrimp.

There is another method...right now you can treat the main tank's fish and gravel with the prazipro, and then you can clean the entire tank when done, and start it new.  Some of the live bacteria will still be in the gravel, so when it's returned, you won't have a huge cycle if you use the same gravel and you only wash it out (don't boil it or anything, it will kill the bacteria) instead of sterilizing it.  Just do 10% water changes on weekends for a month and it should recycle just fine.

Most fish parasites do not infect shrimp. He is probably fine.

:)

I hope this helps and is clearer on how to go about this.

Renee