dead fishes in fish pond

My 1st task in my new company that i joined as project assistant manager is to start up a fish pond that is left not taken care by the previous owner,

on 8th February 2012,

about tilapia...

is the common name for nearly a hundred species of cichlid fish from the tilapiine cichlid tribe. Tilapia inhabit a variety of fresh water habitats, including shallow streams, ponds, rivers and lakes. Historically, they have been of major importance in artisan fishing in Africa and the Levant, and are of increasing importance in aquaculture. Tilapia can become problematic invasive species in new warm-water habitats, whether deliberately or accidentally introduced, but generally not in temperate climates due to their inability to survive in cool waters, generally below 60 °F (16 °C)