There's really only four fundamental bass/bluegill pond situations.
1) Balanced-bass & bluegill several size classes, good relative weights;
2) bass overcrowded-not enough forage;
3) bluegill overcrowded-not enough predators; 4)everything else-transitional fisheries...
1) Balanced. Everyone strives for this...good size ranges of bass, plenty young of the year and intermediate size fish, both bluegill and bass. Relative weights are average to above average for all fish.
2) Overcrowded bass-not enough forage--the most common scenario I come across. Out of 100 unmanaged lakes I come across, probably 90 are in this category.
3) Bluegill overcrowded--not enough predators--This probably occurs 1 or 2 times out of a hundred. Yes, I have seen it, and when you do, it's pretty obvious. What you will see is this--lots of full grown adult bluegill, relative weights from 60-80%, often laden with parasites, with too few intermediate size bass, also 60-80% relative weights, no large bass. What happens? Bluegill become the dominant species (maybe because a bass fishery is overharvested early in the pond's life). When bluegill dominate, several things happen. First, they over-compete in their own food chain. They over-compete for nesting sites. There's just enough bass to eradicate young bluegill off the nest. Also, bluegill reproduction is hindered in overcrowded situations. Nature has a way to signal overcrowded fish to slow their reproduction. Overcrowded bluegill produce fewer eggs, and viability is affected because nutrition is affected. A consequence is also minimal reproduction of those intermediate size adult bass. Too many mouths, overall, between bluegill and bass, and the food chain stops mid-stream. Leave that fishery as is for several years, expect the same fish to lose weight, and the food chain to be prematurely eradicated each spring. The solution is this...cull bluegill in conjunction with improving the pond's ability to produce more fish. Increase production, reduce numbers, remaining fish compensate by spawning. New fish, a change of dynamics, improved food chain, and you see a big difference. Feeding, fertilization, and adjusting fish numbers is the best answer for this scenario.
Another way to attempt to correct overcrowded bluegill populations is to use large bass. Know the average size of your bluegill, and stock large bass, big enough to eat the dominant size range of bluegill.
4) Everything else--transitional fisheries. The only time I see this type fishery is after a major drought or a flood, or a fish kill. Fish are resilient, and will always attempt a come back. When their numbers are adjusted by some rapid change of nature's pulse, fish respond by spawning and growing. Here's an example..a sampling of fish shows only young of the year bass with intermediate bluegill in an established lake. Further sampling reveals two adult bass, underweight, with six adult bluegill, fat and healthy. This is a transitional fishery, headed toward one of the three above scenarios.
If the above overcrowded bluegill situation was bass overcrowded, you wouldn't see the 10-20 bluegill to 1 bass ratio. Overcrowded bass almost always dominate the ratio, sometimes 20 bass per adult bluegill. Look at ratios, and body condition. That tells the true tale.
Fishman, the biggest key (next to ratios and body condition) is how large the bluegill are compared to how large the predators are. In a healthy bass/bluegill population, only the largest bluegill can't be eaten by the largest bass. All other fish are fair game for big bass. As long as you have a variety of sizes of bluegill to go with your managed predator numbers, you're right, you can't have too many bluegill.
And, Cecil, there are more signs than just adult bluegill.
It's learning this kind of stuff that keeps me doing it. Just when I thought everything made sense, something else shows up. The most fun thing, about pond management, to me, is trying to figure out all the factors, water quality, chemistry, fish species, populations, dynamics, communities, micro, macro, vegetation, silt. It's like a huge puzzle, and the more pieces you find, the better the picture looks.
Fun, huh?
