River guardian

Various years ago, Coatzacoalcos river was filled of a big variety of fishes; but after the introduction of tilapia in Veracruz's rivers, the variety decreased a lot.
Birds are new guardians of the river, controlling populations of Plecostomus an Oreochromys, but the tortoises and predator (and originals from the site) fishes, need to be reintroduced in to renew the variety of life in the river...