SAPPORO -- The former president of a fish processing firm in Hokkaido was arrested Tuesday on suspicion of having knowingly sold salmon roe tainted with E. coli bacteria, which sickened dozens of people nationwide, police officials said.The arrest reportedly marks the first time a food company manager has been held criminally liable for poisoning caused by the 0-157 strain of the E. coli bacteria.Toru Ise, 42, former owner of Notsuke Bussan in Bekkai, eastern Hokkaido, was arrested on suspicion of professional negligence resulting in injury. His firm is now undergoing liquidation.Police consider Ise's culpability to be grave because he allegedly shipped the roe despite knowing they were tainted.According to police, Notsuke Bussan sold about 6 tons of soy sauce-seasoned salmon roe to a Tokyo food company in October 1997. The firm shipped back 5.1 tons, however, claiming the products had a bad taste. Tests carried out by the firm show the roe were infected with large amounts of various germs.But police say Ise failed to conduct independent hygiene tests on the returned product, instead shipping 3.6 tons of tainted roe to a different food company in Tokyo during April and May. The roe was then sent on to several sushi shops and other eateries in seven prefectures, sickening about 31 people aged 2 to 44. Some will require up to two years to recover.In 1996, food contaminated with the O-157 strain of E. coli, which causes diarrhea and cramps, claimed 12 lives and sickened more than 10,000 people in Japan. Most were children and elderly people, who have a lower ability to resist such bacterial infections.