The fish that were killed had accumulated in their biomass lots of all the nutrients that are necessary for plant and animal growth which is why allowing them to die back into the pond will fertilize the pond with a surge of nutrient fertilizer as the fish decompose. Removing the dead fish actually sets the pond aging process back toward cleaner nutrient conditions which would have been a very BIG benefit to slowing the aging (eutrophication) of the pond. IMO a mistake for not doing it,
For a better idea of how much nitrogen(N) and phosphorus(P) fertility was in 6000 lbs of dead fish according to a prior PBoss thread this amounted to 147lbs of P and 678 lb of N. That is a lot of fertilizer to be putting into a pond of 12 ac ft. Expect to see lots of green growth in the next few years as the pond ecosystem responds to all the released nutrients. It is said that one pound of phosphorus will grow 500lbs of algae thus the 147 lbs of P could produce 73,500 lb of algae = 36.7 tons.
https://forums.pondboss.com/ubbthreads.php?ubb=showflat&Number=540041
