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Hornwort - A Plant For All Seasons?

NOTE: I posted a topic on this plant a little while back. This is a sort of refresher topic, or a new one for those that missed the old one

I've recently acquired some Hornwort (Ceratophyllum demersum), a plant which I've mentioned before has numerous advantages for the aquarist, particularly one interested in raising fry, but which has some disadvantages too. I'll cover the disadvantages first, then mention some reasons why, despite its minus points, it should form part of every aquarist's collection of tools. Yes, I did mean that, and you'll see why soon!

The biggest disadvantage of Hornwort is that it is brittle. Amazingly so. You only have to look at it and bits snap off. It does not develop any roots, which means that anchoring it to a substrate requires a certain amount of ingenuity and a willingness to get one's hads very wet indeed, and while doing so, green bits flake off it, seemingly purpose-designed to clog filters. However, this means that it absorbs its nutrients directly through its stems and leaves, which is one of the reasons I've described it as a 'tool' - again, all will be revealed in due course!

If you want to cultivate this plant, don't worry unduly over specialised requirements. All it needs is a reasonable amount of light, water with nutrients in (such as those produced by any collection of fishes), and an absence of those fishes that will make a snack of it, such as Tinfoil Barbs or Silver Dollars. Under these conditions, it will thrive. Indeed, if you happen to want to produce it in industrial batch quantities, this isn't too difficult either, if my recent introductions are a reliable indication - I have stems in the main Characin/Panda Cory aquarium that are growing at the rate of - wait for it - three inches per day. At this rate of growth, you'll soon have a whopping surplus to sell back to the LFS! Even in a coldwater aquarium, it will grow vigorously, but in a tropical aquarium, it literally grows like stink. It will produce offshoots at a speed that makes a mockery of much more tender plants such as Cabomba, and in a tropical aquarium, one can expect to be harversting the surplus at a sufficient rate to become a weekly supplier to aquatic plant nurseries everywhere. This growth rate can be embarrassing when it isn't wanted, but when it is, you'll be glad of it! I cannot help but think, however, that only an idiot would let this plant loose into a wild waterway in a tropical climate, because under those conditions, it would make the Water Hyacinth plagues in some places look like a famine. As a corollary, anyone who keeps Pacus will find this plant is actually capable of keeping up with the appetites of even fairly large specimens if grown in a separate aquarium for the purpose of feeding herbivores - an indication of just how prodigious its growth rate can be!

However, this plant has several plus points. First, aesthetics. It looks like a more stringy version of Myriophyllum, but loses nothing because of this, and gains quite a few brownie points when it displays the lush deep green shade under aquarium lighting that makes it a favourite of aquarium photographers. Innes in his venerable tome remarked that fish photographers never seem to tire of it even in his day, and in the right setting, it's not difficult to see why. The shade of green varies according to angle of light, depth of water, orientation of stem, etc., but always seems to be absolutely perfect for setting off all manner of different fish species when photographing them. Plus, a wall of Hornwort at the back of a special photography aquarium goes a long way toward eliminating the 'nuclear bomb flare' effect of flash bouncing off the rear glass. MkCube will discover that this is probably THE plant for setting off Lemon Tetras to advantage, and it helps to bring out the best in my Cardinals and Pencil Fishes too, to the point of asking myself if there is a Ceratophyllum species native to the waters in which many South American Characins live, because I can't think of a single Characin species that would not look utterly superb with this plant as a backdrop. Lemon Tetras in particular, however, seem to look extra special when swimming alongside Hornwort, and if MkCube wants to try using it as a foil for his own Lemons, I guarantee he won't be disappointed! In fact, my Lemons seem to enjoy hanging around it, which makes me suspect that there is something growing in the native waters of the Lemon Tetra that looks a lot like it, and that they use it for cover and possibly for spawning.

Next, water chemistry management. If agricultural runoff into reservoir supplies creates an unpleasant nitrate problem, then Hornwort will happily mop up the nitrates, and thank you very nicely for feeding it into the bargain. Even if nitrate contamination of the tapwater supply is not a problem, nitrate generation by the biological filter will, if allowed to continue unchecked, become a problem, and this plant is a superb weapon in the campaign to keep nitrates down. Not having roots, it absorbs its nutrients throughout its entire surface area, which, thanks to its structure, is immense in comparison with the actual volume of space occupied by its tissues. With a supply of nitrates from the biological filter to absorb, it will set about converting them into foot-long strands of itself, and more, with a vigour that has to be seen to be believed. And, of course, as a pond plant, it is tough enough to withstand winter conditions here in the UK, being a native member of our aquatic flora, so ponds icing over won't be an undue worry with this species, as it has adapted to survive such extremes. Not only will it survive temperature extremes, but its water chemistry requirements are so undemanding that it will be capable of acting as a nitrate manager in a refugium for anything from a blackwater Discus breeding aquarium with a pH down as low as 5.0, up to a Rift Lake aquarium. Salt tolerance, however, is likely to be low, but along comes a relative to the rescue - Ceratophyllum submersum, another British native, is naturally found in brackish estuaries, so those aquarists keeping Scats, Puffers and Bumblebee Gobies can use this related plant in a refugium in a similar manner.

Next, fry protection. Not only is this plant an excellent refuge for tiny egglayer fry (and for that matter, even big livebearer fry like Mollies will probably appreciate it also), with a network of whorls of fine leaves that should make even the shyest fry feel safe and well, but, thanks to the nitrate absorption qualities outlined above, it is a valuable tool in the nursery aquarium where an undergravel filter might be unsafe to use. Some fish fry are notoriously delicate, and need their water changes to be implemented gradually, which means that for some species, the nursery aquarium can take on the character of an intensive care unit! Indeed, some Angelfish breeders have conducted experiments, and proven that fry mortality is considerably reduced when the nursery aquarium is furnished with Hornwort. Chances are it will have a similar beneficial effect upon other fry species too, which is why the big Panda Cory breeding aquarium that's about to go live in my home will have a LOT of Hornwort in it to help keep those delicate Panda fry happy, while reducing the need for major water changes, allowing me to rig up a trickle system happy in the knowledge that whatever the output from any future crop of Panda babies, the Hornwort will keep it manageable. My current nursery aquarium is doubtless benefitting from being used as a Hornwort cultivation pond in miniature ready for the 'rollout' of the big breeding aquarium, and the current occupants (Big Junior and friends) seem to appreciate this latest addition too!

In a previous post on this plant, I described it as something of a 'rough diamond'. However, I'm learning to live with its minus points, and enjoy the many plus points of a plant that will hopefully improve my fry survival rates among my Panda Corys in the future, and which also makes a truly stunning photographic backdrop if arranged with a little thought prior to loosing off several rolls of film (yes, I'm still using 35mm film because I can't afford a digital camera yet - hopefully future crops of Panda fry will cure that!).

And, speaking of possible future fry, the Pandas are spawning again as I write this. Guess what? It isn't just the Java Moss that gets a lookover as an egg repository - the Pandas have discovered the Hornwort! They still prefer the Java Moss, but now they have a choice, and Mata Hari seems suitably grateful to me for not only providing an alternative repository for yet more of her eggs, but a place to hide when the males get too frisky and boisterous even for her!

So, I look forward to reporting in future, that the Hornwort has delivered the goods, and helped me raise a nice numerous batch of Panda fry ... watch this space



Panda Catfish fan and keeper/breeder since Christmas 2002

I love your plant articles. They're wonderfully written with lots of details! Bravo!

Calilasseia - you seem to be very knowledgable when it comes to hornwort. tell me, is there any way to remove brown algae from it? are there any fish or critters that will do this for me? i have a number of stems growing in my recently planted tank and though they're growing at a very fast pace, they seem to be covered in brown algae, which obviously inhibits them from demonstrating the deep green color you write of in your piece. any help would be greatly appreciated here. thanks!

Rich

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Back in the saddle!

My Otocinclus do the job quite nicely. Mind you, as a result, because they now seem to prefer the Hornwort to the Java Moss, some of the Java Moss is starting to look a bit tatty

Panda Catfish fan and keeper/breeder since Christmas 2002

thanks! i was thinking about getting a few ottos for my tank, but now i've been leaning towards a bristlenose. do you think it would do the job as well?

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Back in the saddle!

My hornwort used to grow really fast like you described, but it seems to have slowed considerably. Any ideas why? I know there are no roots, but how do you keep yours planted? I feel like I'm constantly replanting mine. Every other day I find it floating on the top. Thanks

Difficult keeping it anchored to the bottom - I find I'm using lead weights that are at least five times bigger than normal to do the job because the plant is so bouyant, especially if it has multiple branches!

Panda Catfish fan and keeper/breeder since Christmas 2002