Native self sustaining aquarium

[Lepisosteus]

there’s some formula that pond designers use to calculate the amount of natural food (minnows) required to feed pond fish assuming that the bait fish reproduce. If I remember the ratio is something ridiculous like 100:1 increasing by a factor of 10 for every level of the food pyramid. To feed just the one bluegill in your tank you would need about 100 minnows. Then to feed those 100 minnows you would need 100000 Scuds/mosquito larvae etc. simply put, it’s not possible to have a self sustaining ecosystem with a top consumer in an aquarium.

I had roughly a million gallon pond a few years back. Before adding any top predators the pond was full of goldfish/carp hybrid and fathead minnows. Some evenings you could look out over the water and see a lake of gold from the amount of goldfish in the pond. You could take a minnow trap or dip net and catch hundreds of fatheads with ease.

I then put a single northern pike, 20 or so massive largemouth bass along with crappie, bluegills, perch, and rock bass. Within a year you couldn’t find a goldfish under 12”. all fatheads were gone. The largemouth would spawn every year but I had to restock the system with thousands of shiners twice a year to sustain them. Its been years since I went back but from what I hear there are no bass remaining.

the perch and crappie reached incredible sizes. Borderline provincial records I’d bet but still it was not self sustaining.

 

[jjohnwm]

I think the ratio would probably be much higher than a mere 100:1. If you stop and think about it, if the bluegill eats one minnow per day...and you know darn well he is going to eat more than that!...then it would take only a wee bit over three months for him to finish them all. Even if they had bred, any survivors would still be very small at that point, and would be eaten at a much higher rate, so...no, it just doesn't work.

The idea of a balanced system, in which small fish miraculously find the millions of tiny food items they need and then even more miraculously reproduce at a rate high enough to feed a larger predator, which also miraculously has the self-control to curb its appetite to low enough levels for the whole scheme to work...keeps coming up over and over again.

It's a pipe dream.