Japanese authorities said Tuesday they had discovered for the first time fish swimming off the country's Pacific coast carrying high levels of radioactive materials. The finding, the latest blow from the nuclear crisis, is stoking concerns about environmental damage to local marine life, the safety of the nation's food supply, and the viability of Japan's iconic seafood industry, which was already struggling following the tsunami.

The two separate samples of tiny fish were caught before Tokyo Electric Power Co. , the operator of the crippled Fukushima Daiichi reactors, began the process Monday night of dumping 11,500 tons of contaminated water into the sea, raising fears that the problem could spread significantly in coming days. Tepco has said that, before the authorized unloading of water, there was an uncontrolled leak of an uncertain quantity of highly radioactive water from the reactors into the sea.

Efforts to end the release of more highly radioactive water at the Fukushima Daiichi plant finally met with some success Tuesday, Tepco said, as the injection of what it called "liquid glass" gel around a damaged pipe managed to reduce the toxic flow by half. Workers poured 3,000 liters, or 780 gallons, of gel-like sodium silicate onto the rocks supporting the pipe. Authorities said the substance would continue to harden over time and could continue to slow the flow of water.

Workers have tried a variety of methods to reduce the flow since it was discovered Saturday. The water is thought to be from the highly damaged No. 2 reactor. A water sample taken just outside the water intake for the No. 2 unit showed the level of radioactive iodine-131 at 7.5 million times the allowable limit, the most dangerous level of radiation so far detected.

Separately, South Korea said Tuesday it would seek more information from Japan's Foreign Ministry about the decision to allow Tepco to dump the 11,500 tons of low-level radioactive water into the ocean. The water is being discharged to free up storage space for much more toxic water. "We regret having caused concern to other countries because of the discharge of the radioactive water," said Hidehiko Nishiyama, deputy director general of the Nuclear and Industrial Safety Agency, the industry regulator. "We will try to avoid further dumping of contaminated water as much as possible."