Six men who had already received suspended prison sentences for illegal fishing of rare species appeared in a Shanghai court on Tuesday - World Oceans Day - to face public interest civil litigation for their wrongdoing.

It was the first civil litigation case regarding public interest in the field of environmental protection heard by the Shanghai Maritime Court since China"s Yangtze River Protection Law came into force in March.

Prosecutors from the No 3 Branch of the Shanghai People"s Procuratorate asked the court to order monetary compensation for environmental damage totaling 810,000 yuan ($126,700) and demanded the men make public apologies.

The prosecutors said that between May 4 and May 10 last year, two of the defendants, surnamed Jiang and Zhou, organized three others to drive a boat in key areas of the Yangtze River and near Shanghai"s Chongming Island and put down several deepwater nets.

The three caught as much as 1.4 metric tons of rare fish species - daoyu and fengweiyu - from the areas, where fishing is banned. Jiang and Zhou then sold the fish. They hired another man to transport the fish to a food market and he also helped sell them.

After receiving reports from the public, police caught the three men on May 10 in the act of catching fish. In December, the six men were sentenced to prison terms ranging from one year and three months to two years by a Shanghai court after being found guilty of illegal fishing and then put on probation.

Daoyu, also known as knife fish by locals, is a seasonal delicacy in China but its population has been severely threatened by overfishing. At the beginning of 2019, the country imposed a complete fishing ban in key areas along the Yangtze River.