Photo/Illutration The fish in the tank on the right supply feces to the vegetables on the left, at Sunshine Aquarium in Tokyo’s Toshima Ward on May 29. (Harufumi Mori)

There’s a use for fish poo, the problem that afflicts all aquarists--from salmon farmers to a child with a bedroom aquarium.

Nutrient-rich feces can be reused by vegetable farmers, as illustrated by a pair of projects in Tokyo.

“I saw for myself the exceptional power of nature,” said Hideo Yamabe, an assistant manager at Sunshine Enterprise Co., which operates Sunshine Aquarium in Tokyo’s Ikebukuro district.

At the aquarium complex, lettuce and mint are growing beside a tank that contains three fish species including a rosy tetra.

A sign reads: “Veggies are growing with fish excrement.”

A reporter saw families looking impressed during a visit to the aquarium in an Ikebukuro skyscraper in late May.

Aquaponics is the merging of aquaculture with hydroponics. Microbes decompose feces, releasing nutrients for plants and clean water is returned to the fish tank. The nutrients allow vegetables to be grown without soil.

The concept is timely. Growing awareness of the need to recycle should interest people in this type of reuse. A pavilion showcasing the concept is planned for the 2025 Osaka Kansai Expo.

Sunshine Aquarium experts began researching aquaponics as a way to promote fish. But they soon found that whereas they knew all about aquatic species, they lacked knowledge of vegetables.

The aquarium operator spoke to Iwakura Experience, a group that has revitalized communities in the mountainous Iwakura district in Ome, western Tokyo. Onsen and farming are project areas it has helped residents with.

Two years ago, Iwakura Experience set up a aquaponics program to tap into tourism related to sustainable agriculture.

It had a local farmer among its members, so the vegetables side was assured. But it had little knowledge about fish.

A common acquaintance served as matchmaker in bringing Sunshine Aquarium and Iwakura Experience together.

“We received a lot of help from the aquarium before we succeeded in our project,” said Daisuke Motohashi, 44, head of Iwakura Experience.

The hardest task for Iwakura Experience was deciding which fish species to keep. It tried the silver shark, a visually attractive tropical species. But the fish died when temperatures rose in summer.

Sunshine Aquarium recommended that the group try temperature-resistance Pangasius, native to Southeast Asia, and Metynnis from South America. The aquarium also gave advice on how to keep the fish healthy.

Iwakura Experience filled a 60-square-meter greenhouse with pots containing 20 different vegetables and other plants.

It repeated trial and error about some issues, including the balance between the number of fish and that of seedlings.

And then it reached harvest time. Baby leaves were shipped to a nearby farmers' market for the first time in May this year.

In the meantime, Sunshine Aquarium had its own failures. It tried growing Japanese mustard spinach and lettuce but the crops failed. So, it asked Iwakura Experience about the right temperature and how to keep plants photosynthesizing indoors.

These secrets and more are revealed in a display at the site where lettuces are now growing contentedly for visitors to see.

In the future, Sunshine Aquarium hopes to use its aquaponic crops as food for its fish and tortoises to bring about some self-sufficiency to the facility.

And Iwakura Experience reports a growing interest in aquaponics. Several programs are under way across Japan including in Iwate, Niigata, Kanagawa and Gifu prefectures. 

Related News