Welcome, I think one of the first things you should do is decide how many bgill you would like to or expect to harvest per year. We can help you with figuring out this number, but remember it has to be a reasonable or realistic number. The higher the number the more management will be involved in reaching the goal.
Theo mentioned that you could use channel catfish to thin bluegills in your small pond. I would not do that for at least two reasons. 1. Catfish in your small pond will tend to make it murkier or cloudier than if they were not there. Adult bluegills and bottom invertebrates will feed and grow best in water with visibilities of 2ft to 3ft. Catfish could easily spawn and young add new catfish to your small pond � not a good thing if you are interested in lower suspended sediments.
A pond 30x30 is small, 900 sq ft. Without it being a flow thorough system, I think it will be difficult for you to manage and properly control a reproducing population of bgill in such a small pond unless you pull a seine through it twice a year � spring and fall. This will allow you to keep good and proper numbers of bgill in the pond for proper �balance� which will result in optimum growth. As "ewest" points out, a reproducing population of bgill will result in less than the best growth rates due to several factors.
I am thinking that maybe the best way to achive your goal is to use single sex fish in this very small pond where you expect an annual harvest of fish. I think you could grow an 8.5" - 9" BG in southern MI in 4yrs and if optimum conditions maybe 3 yrs. Yr 1=3.0", yr 2=6.0", yr 3=8"-9".
1. Where or how did you get your bgill for stocking?
2. How many bgill would you like to get out of this pond per year?
3. What is acceptable harvest cleanable size of BG for you?
