In the literature  its said that blackfish are aggressive this is not right, in the video below you can see five or maybe six fish are excited but they are not aggressive instead I would say they are cautions and excited.

[wpvideo Lzk4g9Kz]

On the upside the fish look healthy not overly fat but that would be that they are just beginning to put on weight after a long winter, the pond there in is in great shape ,lots of weeds an over hanging tree branches , as yet I have not seen any blackfish young but there is still time.