I had a long discussion with one of the people in charge of the lagoon at Discovery Cove in Orlando, which has about 7000+ saltwater fish in an open lagoon. I asked about fish loss due to people, agression etc...biggest problem was a Blue Heron. Nothing deterred the most aggressive one and they even went so far as to get a federal permit to relocate it. A new one took his place within a few days, and was even worse becasue he would wade out farther than the relocated one. This might end up being the biggest issue. Good luck.