Treatment

While I was very optimistic about fenbendazole as a treatment option, I'm a little more worried now. After two days of treatment, I don't see fewer Camallanus worms hanging out of the fish. I am very concerned about whether the fish are ingesting enough of the drug, especially the smallest female Macropodus, which also seems to be the worst infected. I have soaked a mixture of foods in a fenbendazole suspension, and I'm hopeful that they are getting enough of it, but the only way I have of monitoring the treatment is by looking at the worms hanging out of the fish. They still appear red and healthy, which isn't a good sign. This is the final day of the treatment course, so I was hoping for some visible results. "TheGreatBlueDiscus" had visible results after 36 hours, but since he was treating his fish twice a day, that amounts to three treatments.

Since I won't be able to continue the treatment over Christmas, I'm seriously considering euthanising the Macropodus. Not something I would want to do, but I can't afford dead fish floating around the tank for several days (there's only so much my plague of snails can handle).

Timeline of infection

A parasitic nematode like Camallanus needs to get into the aquarium from somewhere. I've been thinking about possible paths of infection. According to Levsen and Berland (2001) Camallanus cotti takes 11 days to fully develop in its copeopd host, and then another 34-42 days to develop after it is ingested by a fish host. Presumably the adult feeds for at least a few days before it extrudes from the anus of the fish and starts releasing larvae of its own. Levsen (2001) found that it took a minimum of 62 days and a maximum of 110 days for visible signs of the parasite in a system with monoxeny - direct (fish to fish) infection. Since I first saw signs on the worms in mid-December, they became infected somewhere between early September and early November. That said, I first noticed the worms last weekend, and once I looked there were worming hanging out of several Macropodus.

In that time period I bought (and didn't adequately quarantine) quite a few fish. The fighter is an unlikely culprit - not only did we buy him too recently, he also shows no signs of infection. The pygmy corys are also unlikely, since they have never been in the main tank. On the other hand, the plant tank has a population of copepods, so I would only have to introduce the copepods, not actually any fish. It's reasonable that Camallanus was introduced with infected copepods that came with the Java moss. The timeline is reasonable - about 55 days. I also transferred a couple larger corys from the plant tank to the main tank, and an Otocinclus. They are also potential sources of infection.

There are, of course, other possibilities. I bought three batches of neon tetras this Fall, and had remarkably high mortality. I also bought some ghost shrimp. The ghost shrimp themselves are unlikely vectors - I have not read about Camallanus infecting shrimp, although there's a slight chance that they were using them as secondary hosts. The neons, on the other hand, are another story.

I bought my first batch of neons back in early September. Four of the five died within two days, and that was followed by a wave of mortality: a fighter, two Angels, two platies and a couple Macropodus. It seems pretty obvious that they weren't the ""cleanest" of fish. The extra burden of Camallanus infection could be blamed for the death of the neons (if you're already feeding parasitic worms, you have fewer resources with which to handle stress), it seems unlikely that transmission of the Camallanus larvae could have resulted in such rapid mortality among the other fish.

While I initially blamed the pet store, the deaths of the other fish led me to wonder whether something had gone wrong with my water, and that the timing might have been coincidental. Anyway, the sole survivor remained in the tank, seemingly healthy, but with a shrunken abdomen (which was always a cause for concern). He died a couple months later, after I bought some more neons to keep him company.

I'm most inclined to blame the neons (or more specifically, the one neon). And while I could do a lot to improve my quarantine procedures, segregating new fish for 2 to 4 months just isn't something I can do at present. While I hate the idea of medicating new fish as a precautionary measure, I can see why people would do it.

1. Levsen, A. (2001). Transmission Ecology and Larval Behaviour of Camallanus cotti (Nematoda, Camallanidae) Under Aquarium Conditions . Aquarium Sciences and Conservation, 3(4), 315-325. DOI: 10.1023/A:1013137801600
2. Levsen, A., Berland, B. (2002). The development and morphogenesis of Camallanus cotti Fujita, 1927 (Nematoda: Camallanidae), with notes on its phylogeny and definitive host range. Systematic Parasitology, 53(1), 29-37. DOI: 10.1023/A:1019955917509

First casualties?

While the Camallanus still appear well (there are still red worms hanging out of most of the Macropodus), one of the male Macropodus died. Was it worm-related, meds-related or just coincidence? I'm inclined to think it's something other than coincidence. After all, the only visibly infected fish are the Macropodus, so I'm guessing that they are more susceptible to the Camallanus.

It makes me wonder whether there's a stress component. The Macropodus are likely to be the most stressed fish in the tank, since their struggles for dominance consume a lot of their energy. Interesting thought.

Camallanus biology

One of the challenges of home diagnoses is "getting it right". Based on the University of Florida IFAS Extension document (Yangong 2006) on nematode infections in fish, a diagnosis of Camallanus infection seems reasonable. But, like any biologist, my first question is: what species? Is there only one species that you tend to find in freshwater aquaria, or are there many?

According to Yanong, Camallanus requires a secondary host, usually a copepod. I suppose a moderately planted tank with driftwood has lots of room for copepods, even if I can't see them. There are enough hiding spots for them in there. So I'm guessing that control of secondary hosts really isn't an option.

"The dreaded Camallanus worm"

On Sunday I noticed something red and spiky protruding from the anus of one of my female Macropodus in the main tank. When I looked at them carefully, I saw something similar on one of the males. While I had never seen anything of the sort before, it was easy enough to recognise based on the descriptions I had read online - my tank was infected with "the dreaded Camallanus worm". A quick Google search reveals two things - one, that aquarists dread this worm (a genus of parasitic nematodes), and two, that there are two fairly well-established treatments: fenbendazole and levamisole. Fenbendazole is a common dog dewormer, and levamisole is apparently used for pigs. Fenbendazole was available at the pet store locally, so I went with that. However, levamisole is probably easier to use, since it can be applied to the water, and is usually effective with a single treatment. Fenbendazole needs to to ingested by the fish, and involves a three-day treatment cycle, followed by another treatment two weeks later. Since the fish have to ingest the drug, the issue of dosage becomes very complicated. On the other hand, the more powerful a drug, the more suspicious of it I am. I was reassured by the low level of warning on the fenbendazole package as well.

Based on what I could find online, I decided to make a solution (or suspension) of the fenbendazole and soak bloodworms in it. For good measure, I also added some sinking pellets to the mix. The fish at both quite happily, so it does not seem like the drug made the food unappealing (either that, or it didn't soak in well enough, which is a concern of mine).

Like everything else in the world of fishkeeping, the major source of information out there is the bulletin boards. And like everything else, I'm hesitant to trust them. I'm glad I came across this University of Florida IFAS Extension document. It was also nice to find this essay at PetFish.net - most people use levamisole, so it's nice to have something against which to compare my own experience.