In this case, twice the number of brood fish are needed, but more fry would be produced. Replace broodstock at least once a year. Brood fish should be changed more frequently if good quality food is not available. This should be done when the number of fry collected drops constantly with each subsequent collection. Male tilapia are aggressive and can injure unresponsive females while attempting to mate.
Dense phytoplankton reduces visibility in water and reduces aggressive behavior.
The following illustrations show how this is done. Small breeding hapas are easily inspected for fry. Objects inside the hapa should be removed to avoid injuring fish. Non-floating crowding bars require two people to move the bar and may require an additional person to remove fry with a dip net. The following figure illustrates the inspection procedure using a non-floating crowding bar which slides over the hapa support frame.