Rotifers have the ability of retaining nutrients and are fed certain species of algae , so that when they are fed to the larval fish, they transfer the nutrients in the larvae in to the fish. Rotenone A naturally occurring substance found in the roots and stems of several tropical plants. Very potent biocide , used in some countries to kill off larvae and predatory fish prior to introducing parent fish for natural spawning or newly hatched fry. Also used in some areas for fishing, where it is added to the water course and the fish collected as they float to the surface. Round Tanks Type of holding unit.
Round tanks have the advantage of a naturally self cleaning action.
As the water swirls around the tank, solids are drawn towards the middle, where the outlet is situated. Many species prefer the consistent current of a round tank to other more static systems. See also screening , d-ended tanks and raceways Rs232 Communications language used by computers to talk to devices such as mouse, printers, keyboards etc. Limited to one device per cable. Rs485 Communications language used by computers to talk to multiple devices such as monitors and controllers over distances of up to 1km.