mainichi - Foreign species of fish including angelfish and piranhas are being found in large numbers in the Tama River between Tokyo and Kanagawa prefectures, resulting in some dubbing it the "Tamazon River" after South America's Amazon.
People are apparently releasing fish that have become too difficult to look after into the river, and the fish are surviving winter near water treatment areas, where the water temperature is higher.
To combat the problem of foreign species of fish being dumped in the river, local residents have set up a drop-off area for unwanted fish. Mitsuaki Yamasaki, 51, the head of a local river fish association, established the "fish postbox" in part of the association's fish preserve in Inada Park, Kawasaki, in 2005.
The "postbox" measures 7 meters by 4 meters. Reaching his hand into a container, Yamasaki pulls out a long-nosed fish measuring about 1 meter, which thrashes against the surface of the water. It is a longnose garpike. One longnose garpike was caught in a net in February, and another one was left by a visitor. The fish's sharp teeth can easily bite through a nylon net.
"The Tama River is like a department store for foreign species of fish. People sometimes called it the 'Tamazon,' after the Amazon River," Yamasaki says.
During Japan's period of rapid growth, home wastewater was discharged directly into the Tama River, polluting it. After water treatment facilities were set up, the quality of the water improved, and from about 10 years ago, sweetfish have been observed making their way upstream. At the same time, tropical fish and other foreign species have also been spotted in the river. Most treated water in the river was originally warm water discharged from homes, and it has raised the river's overall temperature.
Yamasaki has caught some 200 species of foreign fish in the Tama River, ranging from typical aquarium fish such as guppies and angelfish to piranhas and arowanas. Some of them have bred, and it is believed they pass the winter near water treatment facilities, where the water is warmer.
The fish postbox at Inada Park receives about 10,000 fish a year. Yamasaki temporarily looks after fish at his home, then has postbox members or schools take care of them.
Still, cases of people releasing fish into the river continue. A pair of garpikes was spotted swimming in the river and sweetfish were found inside them. Diseases that had been rare in Japan are also being detected.
"I'm worried that gars will start breeding in large numbers," Yamasaki says.
In the Machiya district of Tokyo's Arakawa Ward stands Tropiland, one of the biggest shops for aquarium fish in Tokyo with several hundred varieties imported from all over the world. Inside one tank at the shop is a pair of alligator garpikes priced at 1,980 yen. Now the fish are only about 10 centimeters long, but a label warns that they will get bigger: "These fish easily grow larger than one meter, so please allow room for them and keep them in a large tank," the sign says.
A 35-year-old worker says the store tells customers that some fish are difficult to keep, but he adds that customers often don't have a strong sense of responsibility.
"Many people think of the fish as part of their home interior or as accessories. They're like paintings," he says, shrugging.
So what happens when people give up on keeping their fish? People with experience in the business say that some are flushed down the toilet, and others are thrown out with raw garbage, but some owners secretly release them into rivers.
But this is not always the case. Around 7 p.m. on May 8, Yamasaki's mobile phone rings.
"I've got a fish I can't look after any more -- can you take it?" the caller asks. About three hours later, Yamasaki arrives at a station in Kawasaki to meet the caller. The young man, who looks like a student, is carrying a polystyrene box. Inside is a foreign species of catfish measuring about 30 centimeters in length.
"My fish tank is too small for it, and I have to move to a new place," he says, his voice trailing off.
"Don't worry," Yamasaki says in a friendly tone, as tears well up in the owner's eyes.
Yamasaki says that recently, more people are using the fish postbox in Kawasaki after being forced to move homes amid harsh economic conditions that sometimes are accompanied by lay-offs.
"Even though people might be feeling sorry for their pets, releasing them into the river is an example of ignorant good intentions," Yamasaki says. The 51-year-old played in the Tama River as a child, and is happy to see sweetfish swimming upstream again.
The fish drop-off spot is free to use, but tropical fish can die if they are dropped straight in, so Yamasaki advises people to phone in advance.
A boom in tropical fish was seen in Japan in the 1990s, and interest was sparked further by the 2003 hit animation "Finding Nemo." Recently children have started buying tropical fish with money they traditionally receive at New Year's, say workers in the industry.
The Japan Aquarium Fish Association started accepting discarded fish in 2007, but it has not received full cooperation from fish retailers. And since commercial aquarium fish are not designated as "invasive alien species" which can damage the environment, there are no legal restrictions on keeping them or releasing them. The Ministry of the Environment has not conducted surveys on aquarium fish in rivers on the grounds that there have been "hardly any reports of actual harm" caused by the fish.
Takashi Maruyama, an assistant professor at Tokyo University of Marine Science and Technology who is familiar with the issue, criticizes the release of such fish.
"Keeping fish requires ethical responsibility, but now people who never before had any interest in living things have joined the aquarium fish boom," he says. "Releasing such fish is just a way of evading reality."
Maruyama says a system is needed to improve the situation.
"There is no binding power in the work companies are doing to collect such fish, and the system isn't working. We need to establish a system with cooperation from administrative bodies."
Tokyo's Tropical Fish Dilemma in 'Tamazon River'
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