Roundworms (Nematodes)
Part 3
21-04-99
By Jim E. Quarles.

Before introducing you to your worst nightmare, let me state, that following this part of the articles on fish diseases, I will outline some of the medications that are used in the vain hope that some hobbyist will realize the actual harm they are causing in nature by the methods they employ to treat their sick fish. This has reached the point of endangering treatment of human diseases.

Roundworms

The roundworms are related to radiferous, but two look totally different. The horsehair worms are also related. Most nematodes are free-living in rock, soil, freshwater and marine water, mud, debris, and decaying sludge, leaf litter, and animal waste. They are found everywhere, even in Arctic Ice, and they are the most abundant animals on earth.

They are also parasites or mimmensals in plants and animals where they may be harmless or indeed very harmful. Some are agricultural pests, such as root knot, and others are major parasites involved with humans. Hookworm, ascaris, pinworm and trichinosis, in the temperate zone and blindness, loa loa, guinea worm, filariasis, and elphantisis in tropical countries. All of the above are caused by nematode infections.

Some are useful, micro worms and vinegar eels are both cultured as food for baby fishes. The micro worms were discovered from a bar in soggy mats under beer mugs, vinegar eels in apple cider. Many are essential to natural decomposition of organic matter. Also, many free living ones feed on diatoms or algae, while others are carnivorous. Nematodes live inside all invertebrates and vertebrates, including fishes. Only a few kinds have been reported as parasites inside aquarium fishes, mostly in hatcheries, but that undoubtedly because they've not been sufficiently studied. Not long ago anisakine worms were discovered in raw fish and shellfish, the discovery was made when sushi and sashimi were popularized in Hawaii. Anisakine worms are big worms and wander about through tissues of people sometimes coming out the nose. They normally live in sea lions and seals and never to quite find a comfortable resting-place in people maybe we just don't taste good to them!

These parasites become a real problem for aquarists. You may ask why don't we just zap them with formalin or copper? The problem has been unusual structure and metabolism and resistance to our standard drugs. We only now understand their physiology and so that we can develop a drug that will interfere with the nematode function what will not at the same time interfere with a fish function. Most truly effective preparations are not on the shelves of aquarium shops nor are they released to the pet trade as over the counter products. However you will find them in dog, cat and horse foods.

So just what is some of the biological factors of Nematodes that make them so successful in nature? One thing to notice is that they are rounded in cross sections, thin, elongated, and in most cases pointed at both ends but coiled as just one. They have tough skin, which is called cuticle, and it's as difficult to get through as the cuticle of your fingernails. This enables them to go anywhere, through anything, and resist heat, drying, chemicals, digestive juices, and lots of predators. And if that was not enough protection, below the cuticle, is an equally tough muscle that is mostly longitudinal and this is why then tend to coil up like a watch spring.

The sexes are separate, with males and females often of different sizes and shapes. Most lay eggs but others are live bearers. In explaining their life cycle it must be noted that they pass through several larval developmental stages, and like many parasites this occurs in different hosts, but some only require a single host to complete its life cycle.

Nematode Parasites of fishes

When considering fish parasites, here, I am only referring to those most commonly found in tropical fish kept by the hobbyist either as a hatchery product or simply for personal enjoyment.

This of course is a little known or studied subject, and we are learning more about these parasites all the time. More is known about Nematode parasites in marine game fish than the fish normally found in the hobby trade.

Nematodes in aquarium fish are most often discovered when they encyst on the flank, causing a huge boil that can be lanced. They also infest the intestinal tracts of guppies and other live bearers.

I first became interested in the parasites while developing my discus fish hatchery. Tapeworm and other forms of roundworms can be said to be common in all wild caught discus and angelfish.

In most cases I have found that while all fishes have parasitic worms in their intestinal tract, only rarely will they cause illness. Out breaks are more often a consequence of crowding, resulting in constant reunification. The adage: "A clean tank is a healthy tank" has never been truer than in the case of parasites.