About 600,000 kilograms of fish and crabs have been set free into local waterways this spring, up 15 percent year-on-year, local maritime authorities said yesterday.

　　Officers from the Shanghai Marine Supervisory Office released the fish into the Huangpu River, the Yangtze River and Dianshan Lake since early February.

　　The government spent 3.26 million yuan (US$392,771) on the spring fry-release activity last year. The investment for this year will surely exceed that number, though the exact amount isn't available at present, according to city authorities.

　　"These fish can grow up well in the natural water during the period from April 1 to June 30 when fishing is banned," said Chen Weidong, a section chief with the office.

　　"Such an activity can help recover the fishery resources, which were terribly destroyed because of excessive fishing. Meanwhile, it can also help maintain the ecological balance," said the official.

　　The city began releasing small fish into local waterways in 1992. This year, it released 10 types of fish and crabs, including herring, grass carp, silver carp, variegated carp and crucian carp, as well as baby hairy crabs.

　　One principle must be obeyed in the fry-release activity, that is, only native species are allowed to be set free into local rivers. Hybrid and genetically modified species are strictly banned.

　　"The principle aims to protect purebred local marine animals. Otherwise, local species will hybridize with other species, and the purebred species will disappear gradually," Chen said.

　　As a result, all the released fries must come from qualified aquatic fry breeding farms, according to city officials.

　　Before the end of the fishing ban, the maritime authorities will carry out a summer release activity.

　　They plan to set free 27.2 million small fish in local rivers.