Riccia fluitans in the submerged form
Using Riccia as a submerged plant is relatively new within the aquaristics; but as it often happens it turns out that mother nature has know this phenomenon for a long time. In nature, Riccia is often found growing under water where the swirling water of a waterfall or strong turbulence has wedged a piece of thallus in a root or among other water plants. Riccia can also be caught on the mudflats when the water withdraws during the dry season and under such circumstances the plant develops rhizoids, which are used to fasten the plant and to take up water and nutrients from the mud.
The will rarely happen in the aquarium and we will have to help Riccia a bit if we would like it to develop it's beautiful under water form. You can for example fasten Riccia to a piece of rock by spreading out a thin layer of thallus and then subsequently wrapping transparent fishing line around it. Riccia can also be fastened using a nylon hairnet. Regardless of the technique used, Riccia will soon cover the hairnet or nylon line and develop and beautiful turf providing you offer it favourable CO2 and light conditions. After a few hours in light, small bubbles will form on the tips of the thallus resembling shining pearls. This characteristic bubble formation only develops if you use CO2 enrichment of the water together with a light source of high light intensity. However, you can also observe these fancy bubbles when changing the water of the aquarium. The tap water is usually super saturated with CO2 that will stimulate photosynthesis immediately after changing the water; but the bubbles will disappear the day after if you do not continue to add CO2 to the water.
No matter how you fasten Riccia it will never attach to the substrate. Therefore, you have to replant it occasionally because otherwise it will eventually loosen from old parts of the thallus drifting to the surface. You can lengthen the intervals where it is necessary to replant it by occasionally cutting it with a scissor or you can sprinkle gravel on top of it thereby forcing it to remain submerged a little longer.
The submerged form of Riccia can be used in different ways. A single piece of rock with Riccia will look decorative in any aquarium but you can also use more rocks placing them with a few centimetres apart, in groups and formations, and maybe at different levels in the aquarium. After a while the different turfs will merged to a whole. Combining the different techniques with your personal skills and some patience, you can create the fancy under water landscapes which are so beautiful when it is all covered by millions of small bubbles.
Riccia is not a particular demanding plant although it prefers relatively soft water to thrive perfectly. Riccia can grown extremely fast providing you offer it sufficient light and CO2 and under such circumstances it is also necessary to supply micro- and macronutrients. Various types of nutrient deficiencies will almost always result in yellowish or light green thallus and eventually it completely stops growing. Riccia thrives at any temperature between 10 and 28 oC but the higher the temperature the more light, CO2 and nutrients it will require.
Under certain circumstances, Riccia develops a dark green, transparent form that lacks aerenchyma or air filled pores. This form is heavier than water and sinks to the bottom of the aquarium. The heavy, dark green form is though to be a hibernating winter form since it avoids freezing by sinking to the bottom.
Riccia is a cosmopolitan found almost in any part of the world. There is quite a few geographic varieties which differs both in the way they look and in the way they grown in the aquarium. The Japanese variety with relatively long thalli is the most suitable for aquarium use. The other Asian and European forms are much more fragile. They break easily when they are attached to a piece of rock and they cannot create a thick and beautiful turf before they loosen and drift to the surface.
Tropica produces ready-made Riccia stones fastened with hairnet to ceramic stones. Riccia is also sold in small batches leaving it up to you to decide whether you will try to build your own unorthodox under water landscape or you will use it the traditional way as a floating plant where it provide perfect shelter for fry.
By Jan Ole Pedersen, Ole Pedersen and Claus Christensen
Source: www.tropica.com