Water Sprite and Betta splendens

by Paul Leong, with additional info added by Karlton Lau (03/04/04)

There are many plants suitable for use in a fish aquarium, including several species of water fern commonly referred to as “water sprite”. One of the more common species of this group is Ceratopteris cornuta. (C. cornuta is often identified as Ceratopteris thalictroides, but this is a different species).

Originally from Southeast Asia, C. cornuta has been introduced throughout the tropical zones of the world, and of course, to the aquarium hobby. In the aquarium, it grows very easily, doing best in moderately soft, slightly acidic water with low salt levels and low total dissolved solids. However, it can tolerate a wide range of hardness - anywhere from soft to hard, and pH ranging from 5.0 to 8.5. Limited water movement is also preferred. Some aquarists have even reported success with this plant in tanks with undergravel filtration.

Water sprite is a warm water plant, preferring temperatures that lie within the 73-86F range. In its wild habitat it is found growing in full sun in slowly running water, bogs, and flood areas. To replicate these bright conditions in your aquarium, lighting should be medium to bright (at least ~2 watts of fluorescent lighting per gallon of tank capacity for 8-10 hrs/day) for best growth. Fluorescent or compact fluorescent lighting is recommended because it will give you the most “bang for the buck” in terms of intensity of lighting per watt and will not get as hot.

C. cornuta has bright yellowish green leaves that can be quite decorative. It will readily grow as a floating plant on the water surface, or rooted in gravel. When grown as a floating plant, high humidity is required. Regular weekly to biweekly partial water changes (25 to 40%) and regular weekly applications of fertilizer (use a good aquarium plant fertilizer like Kent Freshwater Plant Supplement or Seachem Flourish) are important for good growth. (Be sure to dilute all fertilizers in about a cup of tank water before pouring it into your tank to avoid burning the water sprite leaves). Good results can also be obtained if C. cornuta is potted in gravel mixed with compost, although as the plant grows larger, it has a tendency to float up. Under good conditions, you’ll be pulling this plant out of your tank by the handful every couple of months!

C. cornuta and other species of water sprite may also produce a spore-bearing form when the leaves reach above water level. When growing well, water sprite will produce buds on the leaf edges, each of which grows into a new plant.

Water sprite grown as a floating plant provides both surface cover to make your fish feel more secure and less “jumpy”, and protective cover for fry among its dangling roots and divided leaves. Infusoria colonies also tend to form around these fine roots, making it a great source of small amounts of naturally occurring fry food. The protective aspect has long made it a favorite of breeders of livebearing species and bubble nest builders such as Betta splendens (bubblenesters).

Fig. 1. Betta fry using water sprite for protective cover.

Adult and juvenile Betta splendens may also use the water sprite as a platform to bask themselves in the warm of your aquarium light, the equivalent of sunbathing by humans, as illustrated in the two pictures below.

Fig. 2. Betta basking on water sprite

Fig. 3. Opaque betta basking on water sprite.

In my experience, Betta splendens also seem to show a preference for using water sprite as a platform for building their bubblenests instead of the Catalpa leaf as shown in the two pictures below.

Fig. 4. Bubblenest formed on water sprite

In Figure 4 above, the male completely ignores the Catalpa leaf and creates his bubblenest on the water sprite instead.

Fig 5. Another instance of a betta preferring water sprite as the platform for its bubble nest.

Figure 5 above shows another instance where the bubblenest was created under the water sprite leaf instead of the Catalpa leaf that was offered (This one is a little harder to see, look at the right side of the photo, near the blue ring of the Ebo Jager heater).

When growing rapidly, C. cornuta and other species of water sprite also help improve aquarium water conditions by extracting the ammonia, nitrates and phosphates produced by your fish as waste byproducts.

All in all, C. cornuta and other species of water sprite are very versatile plants with many uses in a Betta splendens aquarium: as a protective cover (for baby fry and for a spawning female trying to get away from an aggressive male), as a natural platform for encouraging bubblenest building, as a way natural filter for removing waste byproducts, as a platform for infusoria (fry food) to thrive, and last but not the least, as a provider of aesthetic value to your aquarium presentation.