Induction of triploidy and tetraploidy in Nile tilapia, Oreochromis niloticus (L.)

Induction of triploidy and tetraploidy in Nile tilapia, Oreochromis nilotic us, was investigated by heat shock, cold shock, hydrostatic pressure, and/o r chemicals (cytochalasin A, B, and D). Additionally, efficacy of combined protocols was determined. Heat shock 10 min after fertilization induced tri ploidy when incubation temperature was 24 C but not when incubation tempera ture was 31 C. Heat shock of 40-41 C at 4-6 min after fertilization was eff ective in inducing up to 100% triploidy with hatchability similar to contro ls. Cold shock at 13 C for 45 min five min after fertilization induced 85-1 00% triploids. Heat shock and multiple heat shocking were the most effectiv e treatments for the induction of tetraploidy. Two heat treatments of 41 C applied at 65 and 80 min after fertilization for 5 min each produced approx imately 80% tetraploidy in hatched fry. Immersion of fertilized eggs in cyt ochalasin A, B, or D at concentrations up to 10 mu g/L applied at various t imes and durations was ineffective in inducing triploidy or tetraploidy.