Environmental watchdogs accused a Mexico-based startup Thursday of violating international trade law by selling a health supplement made from endangered totoaba fish to several countries including the U.S. and China. Advocates told The Associated Press they also have concerns that the company, The Blue Formula, could be selling fish that is illegally caught in the wild. The product, which the company describes as “nature’s best kept secret,” is a small sachet of powder containing collagen taken from the fish that is designed to be mixed into a drink. Under the Convention on International Trade in Endangered Species of Wild Fauna and Flora, to which Mexico and the U.S. are both signatories, any export for sale of totoaba fish is illegal, unless bred in captivity with a particular permit. As a listed protected species, commercial import is also illegal under U.S. trade law. The environmental watchdog group Cetacean Action Treasury first …