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While invertebrates in the freshwater aquarium are, for the time being, nowhere near as numerous or diverse as those in the marine aquarium, several species of invertebrate are kept intentionally in freshwater aquaria alongside our fishes. While musing over the possibilities afforded by exapanding this diversity, and seeking out possible creatures that could be kept with our fishes, I alighted upon one group of organisms that should be avoided, certainly if more than one is kept in an aquarium and they are allowed to reproduce.

Snails (gastropods) are the principal molluscs found in freshwater aquaria, and frequently, are present as accidental introductions. Sometimes, they are introduced deliberately, but for many aquarists, snails are a 'nuisance organism'. They have their uses, homing in (albeit slowly) upon uneaten fish food and helping to reduce pollution by food decomposition, but in a breeding aquarium for egg-laying fishes, they are most definitely unwanted, as they will eat the developing eggs.

However, snails are not the only molluscs!

It was while searching for some 'different' freshwater invertebrates that my infamous TFH back numbers delivered a warning. The Mail Call letters page on pages 85 & 86 contained a letter from a Canadian correspondent (one Bryce Dixon), enquiring about freshwater clams that he had found living in streams near his home, and the magazine's response.

Freshwater clams are unusual molluscs, and quite active: several Genera are known to inhabit North American waters, and doubtless there are similar organisms originating from the home waters of several of our popular aquarium fishes. However, leaving aside the usual problems associated with keeping bivalve molluscs in an aquarium (such as the huge ammonia spike that results if one dies, because many bivalves look much the same when alive or dead!), these freshwater clams are problematic for another reason.

When they reproduce, the female clam houses hundreds of larval offspring within her shell, until they reach the point where they are free-swimming. At this point, they are expelled into the water. At this stage in the life cycle, a larval clam is known as a Glochidium (plural Glochidia). They remain in this state for several weeks, before settling down and growing a shell: however, during this stage, they are parasitic upon fishes!

Glochidia attach themselves to the fins, and sometimes the gills, of passing fishes. There they feed for several weeks, presumably from the bloodstream of the host. When viewed under the microscope at even relatively low magnification, a Glochidium displays a pair of very nasty-looking serrated hooks, which it uses to attach itself to a host (it will also attach itself to an amphibian such as a salamander - its choice of host is exceedingly wide-ranging). Not only do these serrated hooks leave unsightly scars when the Glochidium finally detaches itself, but a heavy infestation can weaken a fish to the point where other, fatal diseases such as White Spot can take a hold. One or two Glochidia clinging to a fish's fins may not be a major cause for concern, but in the confines of an aquarium, the number of offspring from a female clam would rapidly overwhelm any fish occupants.

Among the fishes that are preferentially selected as hosts by various Glochidia include: Poeciliid livebearers such as Guppies and Mollies, larger Labyrinth fishes (after reading the letter and the answer, lo and behold, a batch of Pearl Gouramis arrived at my LFS bearing a collection of these things!) and certain Cichlid species (it should come as no surprise to learn that Angel Fishes and Discus come in for particular attention from Glochidia). In a pond, they can be a serious problem with Koi if they make their appearance, and of course anyone specialising in less mainstream fish species such as Native Americans should be on the lookout for them.

They do not constitute a full-blown disease per se, except in large numbers, but even the odd one or two can be unsightly, and, the neophyte aquarist can be forgiven for confusing these organisms with a White Spot outbreak if he or she has never encountered either before. The key differences are these: White Spot forms well-defined small rounded cysts, that can appear on any part of the body or fins of a fish, including over the eye (eeew). Glochidia generally attach themselves to the edges of fins, or the gills, and in appearance look more like tiny pieces of cotton wool, contrasting with the 'miniature billiard ball' appearance of White Spot cysts. They are an unwanted pest in show Betta rearing aquaria, as the puncture sites from the serrated hooks adversely affect fin development in juvenile Bettas, but are susceptible to copper-based medication. It is also possible, though I have not seen this documented, that Malachite Green could be effective against them. The instructions for use with Myxazin, Protozin and the rest of the range make no mention of Glochidia, but it is possible that any of these remedies that is effective against larger parasites such as Anchor Worm will also deal with a Glochidia infestation.

The message that should be derived from all of the above is this. If considering freshwater invertebrates in an aquarium, be on the alert for possible adverse side-effects such as the aforementioned, if said invertebrates are kept with fishes. Many will coexist harmlessly with our fishes, but the life cycle of freshwater clam species includes a parasitic larval stage, and similar parasitic life cycle stages affecting fishes may be a feature of the life cycles of other freshwater invertebrates too. Once again (I'm on that old chestnut again), it pays to do the research!

However, I wouldn't want this to put anyone off being a little more adventurous. Being adventurous sometimes pays dividends. While the struggle might have seemed like scaling the north face of the Eiger in a blizzard wearing nothing but a cheerleader's outfit and pom-poms, keeping marine fishes, and then marine invertebrates, is something we can now enjoy without the heartache suffered by the pioneers. One of the results of that pioneering has been a greater emphasis on preparation beforehand. So, to those tempted to branch out into unusual freshwater invertebrates, one little tip that should save much anguish later is this: try the new acquisition out in a species aquarium first, and find out the conditions it needs to keep it alive, then ask about integrating it with fishes. The old 'divide and rule' adage applies to aquaria of all kinds: isolating potential problem issues and solving them separately, then adding complications incrementally, generally results in greater success than trying to juggle multiple unknowns in one go. So, the advice I'll dispense here is, after that above lengthy preamble, as follows: don't be afraid to be experimental, but do so while alerted to unwelcome possibilities such as that cited above.

Incidentally, I'm still waiting for someone here to announce that they're starting a Neothauma Rift Lake snail farm so that they can sell all those shells at a handsome profit to Neolamprologus Cichlid keepers



Panda Catfish fan and keeper/breeder since Christmas 2002

Nicely done It's a good read for people wanting to try out some invertebrates but haven't done their homework.

apple snails also make great companions for shell dwellers. not only do they eat uneaten foods and clean algae. when they die you can use there shell.

However, the ultimate snail to get of course is Neothauma. And try as I might, I can't find anyone who claims to be cultivating them. However, I did find an advert - online classifed - from someone about 70 miles from my home who will pay a good price for genuine Neothauma shells for his Tanganyikan shell dwellers, so there's a market opportunity for anyone who can get a Neothauma tanganyicensis farm up and running!

If I had the starting capital I'd do it tomorrow ...

Panda Catfish fan and keeper/breeder since Christmas 2002