Todd, you're right. Metabolic needs have to be met, the GC has to swim about and run it's various organ systems, immune system, etc. The difference between plant mass and GC mass is dissipated as heat energy. The water becomes a little warmer due to these functions taking place within the fish. My only contention is that even with this taken into account, don't you think that some of your clients have the perception that the GC eat the macrophytes and "poof", they're gone? Energy and mass interact in a closed system. The plant material just doesn't disappear. It becomes fish mass, plus, as you pointed out, heat energy, but then what? If you're lucky your pond moves nutrients out through the overflow, but besides that, you can account for every single calorie into a pond equaling every single calorie out. Which by the way, I guess we need to include fish harvest as an energy outflow. Still, let me be concise about my point. I am ONLY saying the following:
Any nutrients that pass OUT of a grass carp are at least temporarily available for creation of new plants.
I promise you, I am not indicting your use of grass carp in pond management. They work quite well in many circumstances but I would like to make this second statement:
People with ponds often believe that stocking grass carp will solve all of their vegetation problems. Sometimes these people need to be made aware of possible ramifications to this stocking, such as possible increase in simpler plant forms.
I've seen first hand in every single pond that grass carp have been stocked in there has been a decrease in Secchi readings. I have the data, and unless it's been coincidental and happened twenty times in a row, then pond owners should know all the facts.
I really respect Meadowlarks desire to challenge the status quo. Tried and true has application, but every pond is different and almost every pond owner has a slightly different take on what their goals are, so shouldn't the point to this forum be to allow each of us to rethink the things that we believe are hard and true facts? I'll bet that since signing onto Pond Boss forum the first time that I've reassessed a good 1/3 of the things that I believed. There are even a few things that I changed my mind about, then changed it again. That's what makes this so fun!
