As guppyal84 and blacina have mentioned, clear poop can be a sign of internal infection. B. lacina's link offers a great explanation as to why the droppings might be clear.

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If these are fairly recent purchases, you may indeed have done nothing wrong. The problem is that a lot of commercial fishes have been exposed (often before even getting to you local pet shops) to a number of diseases and parasites.

Some of the Helminthes (worms) may not show themselves for a couple of months. But they will show themselves if they are there and you will have to deal with them. :(
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By the way, I was startled to discover how many of these worms, especially Capillaria, but even Camallanus can infest PEOPLE if they eat raw or undercooked fish!!!!

Reason # 37 for not eating suchi. ;)

Also, one doesn't want to feed wormy culls to other fishes.
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Furan-2 and Maracyn-Maracyn2 are antibiotics, which should be effective against bacteria. If the problems persist, consider other possible culprits.

Another parasitic nominee is Hexamita and related beasties if those feces are white and the fish are getting emaciated. They have proven vulnerable to metroniadazole and di-metroniadazole which come in several brand names.

My concern is that your fish might have some sort of internal worm. Could the bulking up and slimming be related to the release of larval worms into the tank?

Antibiotics are rarely effective against them, although the antibiotics could limit secondary infections within the fish.

You mentioned that you had not seen anything protruding from the fish's vent. While Camallanus only does that when reproducing, it is possible that your fish could be afflicted by one of several species of Capillaria or even tapeworms, which virtually never are seen! Capillaria has a lot on it because not only can it continue through generations within a fish, but should the fish be consumer by birds or humans (who undercook the fish) they can also be parasitized by the worms and even pass it on through their waste products.

But no intermediate hosts are necessary for one fish to infect another.

A number of Anthelmintics are suggested for Capillaria. My sources mention levamisole or Piperazine. Burgess, Bailey and Excell also suggest isolating the fish for treatment. However since these beasties rarely show themselves and may also infest fry (in an early stage), I'd treat the tank. Those medicines are not hard on plants and even leave snails alone if the medicine is removed after a week. Also tank treatment targets the entire decor and accessories in the tank as well as the fish.

If you want to see what the relatively small Capillaria look like, do a google or AltaVista image search. They are another nematode. Also check out their eggs.

It is possible to I.D. their fairly distinctive eggs - taken from the feces - under a microscope, if you are experienced with that tool.

In a general sense, you will find even more info searching under HELMINTH or HELMINTH (parasitic worm related) diseases. Most treatments aimed at one will take out the others. So if you are treating for Capillaria, you are also treating for tapeworms, Camallanus, and flukes. The Anthelmintics may also be effective against Hexamita.

Flubendazol is one of the more water soluble Anthelmintics and may be especially useful because sick fish may not eat any food with a medication in it. Guppies, with the help of an Australian vet found a word de-wormer which was effective. Phry discovered that Discomed from Aquatronics (pink package) contains an anthelmintic.

On the Guppylog site, please also take a look at

Friday January 9th · More on the Camallanus Curse

Camallanus treatment By gupppies Sun Jan 4th, 2004 at 16:40:02 CST

Aerelynn- Camallanus update?  By Phry  Mon Dec 22nd, 2003 at 20:38:11 CST

Something is deffinatly wrong here..  
By Aerelynn  Mon Dec 8th, 2003 at 14:30:16 CST