Ram pumps and similar things can't operate in a closed environment.
But there are models, with a separation of the drive pile from delivery pile. So you could pump your water from your aquaponics system in a cycle, driven by a stream nearby. This might even be interesting, if the drive pile water was dirty, or in some other way not suitable to your fish. But usually, if you have that much of water running, it sounds at least as promising, to use the water flow directly to exchange the water in your fish ponds.
According to wikipedia efficiency of a ram pump is as follows:
dh : drive height - the height, you can use to drive the system. E.g. you have a natural fall of 2 feet.
ph : pump height - the height, you want to lift the water to. E.g. you need to pump from sump to fish tank for 5 feet.
vs : volume drive stream - liters of water per time running in your drive stream
vp : volume of pump stream - liters of water per time the ram pump can pump
e: efficiency - energy wise efficiency - might be as high as 0.8, but 0.6 is probably closer to what you actually get.
vp = vs * e * dh/ph
Assuming you have an aquaponics setup with around 15kg of fish in a cubic meter of water, and want to cycle at least once per hour. (
some background data to flow rates)
in the given example this means you need a constant stream of more than 4 tons of water per hour, to keep your system pumped. ( 4000* 0.6 * 2/5 = 960)