Adventures in Japanese Ricefish and the Emersed Aquarium

Written by: Chris (@shrimpery)

Recently, after coming over and seeing my seven aquariums, a friend commented that I’m like an old cat lady, except in this case the cats are shrimp. But by my reasoning, there are so many different styles of aquariums- why settle on keeping just one tank? You can see how I’ve almost managed to convince myself that keeping seven tanks is normal. Regardless, out of all the aquariums in my lineup, one stands out as a clear favorite: the ricefish tank on my desk, featuring emersed plants.

Recently I’ve noticed that aquariums featuring both aquatic and terrestrial growth have been increasing in popularity. As evidenced by its relative obscurity (my spell check underlines the word in red),‘emersed’ may be an unfamiliar term to the casual aquarist. For a bit of background, many of the plants commonly used in the aquarium hobby as submerged plants are actually marginals, switching forms in response to seasonal flooding. The idea behind emersed tanks is to feature commonly used plant species that are ostensibly ‘water plants,’ instead showcased in their terrestrial form. You may have even witnessed this phenomenon in your own tank if you’ve ever had a stem plant start to grow out of the water; new leaves exposed to air will have a fundamentally different form and color, better suited for terrestrial living than those that originated below the surface.

I have to give myself some credit for approaching this idea from a different angle than what I’ve typically seen from other emersed plant lovers. Having fallen in love with the Japanese ricefish (Oryzias latipes), aka the ‘medaka,’ I was disappointed by the dearth of english-language reading material on the species. Exploring Japanese hashtags for the fish on Instagram, I stumbled upon the practice of breeding the ricefish in small container ponds, suitable for the confines of urban living. Kept on a patio during the summer and moved indoors during the winter, these tiny ponds often feature simple, easy to keep floating plants, emergent grasses, and dwarf lilies. Although not true biotopes (they feature plants and animals of geographically disparate origins) on Instagram these miniature ponds are nevertheless often called ricefish biotopes, or sometimes, confusingly, ‘biotops’. After scrolling through these hashtags for way too long, I decided to create my own ricefish ‘biotope’ in aquarium form.

Using a UNS 60U aquarium as a canvas, I wanted to create the perfect habitat for ricefish, with the ultimate goal of coaxing them into producing fry. To this end, I did extensive research on plant species that would be suitable for the somewhat dry, drafty confines of my desk/workspace. It was important to choose temperate species: this way I could avoid the obligation to constantly mist them to provide extra humidity. I settled on a variety of “pond plants,” typically chosen for outdoor landscaping use. Happily, many of my choices coincided with the plants used to decorate a medaka “biotope” in Japan.

The plants chosen included a number of semiaquatic grasses, including personal favorite Sphaerocaryum malaccense, Rhynchospora colorata (giant hairgrass), Eriophorum angustifolium (cotton grass), and Eleocharis montevidensis (giant hairgrass). I also used some shrubby accent plants including Oenanthe javanica (water celery), Murdannia sp. ‘red’, and Persicaria (Polygonum) sp. 'Sao Paulo'. In the submerged portion, I used Microsorum pteropus (java fern), Nymphaea nouchali (water lily), Phyllanthus fluitans (red root floater), and Micranthemum tweediei 'Monte Carlo'.

Using a UNS light suspension kit, I suspended a Twinstar S-series RGB LED light above the tank to provide the right spectrum for great plant growth and vibrant colors. I used a massive external canister filter (Eheim 2217) connected to glass lily pipes. Oversized for the tank, it created sufficient water turnover and flow for future livestock success and algae control. By necessity and design, I used twin glass inflow pipes, with an inflow replacing the usual outflow pipe. This was because the tank was only going to be 50% filled with water (and thus needed a longer pipe stem), and to help mitigate the strong flow of the filter while retaining the robust water turnover. To help the plants grow, I injected pressurized carbon dioxide gas by means of a ceramic diffuser, a mini regulator, and a 24oz paintball canister. With all the materials in place, it was time to scape.

Taking advantage of the extra depth in the UNS 60U, I created a buttressing structure of driftwood and moss (Vesicularia montagnei) to hold a steep embankment of enriched aquarium substrate against the back right corner of the tank. The front of the tank was furnished with cosmetic sand and round river rocks, along with a few dried botanicals to promote the growth of biofilms and accompanying infusoria for the livestock to feed upon. When I flooded the tank with water, the raised substrate embankment, taking up approximately a third of the tank, was still submerged by about an inch of water. With no true “dry land,” the plant selection was again critical in ensuring success: many marginal plants cannot withstand having their crowns (the part of the plant where the roots and stem connect) submerged. I purposefully chose plants that thrive in permanently soggy conditions.

To my deep satisfaction, all of my chosen plant species flourished in my setup, and with careful trimming, I soon had dense, bushlike mat grass and shrubs emerging from the water in a very natural fashion. In particular, the Sphaerocaryum malaccense really took off, creating a dense mat of interwoven stems. Countless little nooks and crannies in the bush provided places for ricefish fry (and shrimplets) to hide.

I introduced the ricefish after about a month of cycling. The species is sadly tough to find in the US, so I was excited to find a seller on eBay; I went ahead and purchased twelve fish, keeping them in a separate, temporary setup until the ricefish habitat was fully cycled. Upon their introduction, they immediately started breeding. I now have about three times as many ricefish as I started with, in three separate tanks. I try to remove the fry as I spot them- they look almost like mosquito larvae swimming at the surface- but to my surprise and delight, many of them survived and grew to adulthood inside the tank. I consider this to be an affirmation that I was right in sacrificing water volume for the banked substrate/bush, which provides many opportunities for cover when freshly hatched fry are being chased by hungry adults.

The only other inhabitants of the tank are dwarf shrimp, Neocaridina davidi. I initially started throwing “cull shrimp” (those with unusual or non-standard colors from my other shrimp tanks) into the ricefish tank. Expecting any offspring to be immediately eaten by the ricefish, I was surprised to find numerous tiny shrimp showing up in the tank, unbothered. From around 30 founding individuals, I now have around 200+ shrimp.

The dynamic nature of the plants, fish and shrimp lends the right kind of controlled chaos to an otherwise meticulously planned setup. I got a bit carried away describing this tank, but you can see the thrill I get from the careful execution of an idea like this. As corny as it sounds, it’s true: sitting at my desk working on a stressful day, it’s great to have a little box of nature (one that I created) as a little escape.

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