Short answer: a few.
In September, I received 80 Blue Israeli Tilapia fingerlings for use as janitors in six different hardy water lily tanks at about 1500G total. I choose to experiment with acclimating 10 tilapia fingerlings to full salt by adding 1G of mature display tank water to 30G glass tank outdoors. Included with tilapia were 6 mosquito fish. Sometime during the next month, the water in 30G tank of tilapia turned dark green with phytoplankton. Due to neglect on my part, salinity got > 40ppt: one tilapia and 3 mosquito fish survived and were put in 40G Rubbermaid tub with established live rock & ornamental sponges. I don’t know how fish are doing as the whole point of the experiment was to develop temperature hardy janitors in mariculture tanks to eat nuisance algae, so I don’t feed the fish. However, a 30G continuous culture of phytoplankton is more valuable to me than janitor fish.
Shortly, I will add 150G Rubbermaid tub that is counter sunk in ground for geothermal passive temperature control. Heater low temperature setting at 65 degrees falling. Today with 60 degree high air temperature, full sun increased 55G tank water temperature to 77 degrees at which point I removed glass lid to allow evaporative cooling.
Except for 150G Rubbermaid tub, tanks on top of ground will be shut down in April, due to Texas heat for 6 months.