Hybridization(interspecific hybrid)has been used in numerous species to increase growth rate,manipulate sex ratios,produce sterile animals,improve flesh quality,increase disease resistance,improve environmental tolerance and improve a variety of other desirable traits to make aquaculture more profitable.GIFT(Genetically Improved Farmed Tilapia)strain Nile tilapia is the main kind of cultured tilapia,which has many advantages such as rapid growth rate and high fillet yield.However,GIFT tilapia has poor disease resistance capability to Streptococcus iniae infection,which may be related to too much inbreeding.Breed improvement by interspecific hybrid may enhance disease resistance capability in tilapia.A complete diallel mating system between GIFT tilapia and O.aureus and additive-dominant genetic model were used to analyze heterosis of 8 growth-related traits,genetic effect and correlation of traits.At the time of day 100 over the experiment,the results indicated that:(1)Heterosis of growth related traits in F₁ hybrid varied from 0.129 4 to 0.368 4,and population heterosis over parent mean(H_pm)of these growths related traits were all positive in F₁.In addition to caudal peduncle length(CPL),other growth related traits have negative or insignificant positive population heterosis over parent better(Hpb);(2)The general heritability in the broad sense(H_B)with 0.714 2-0.995 3 indicated that genetic variations of all 8 traits were significantly influenced by additive effect and dominance effect(P<0.01),whereas,the narrow sense of growth-related traits except CPL varied from 0.469 4 to 0.737 9,and indicated additive effect controlled the genetic variation of output value;(3)The phenotypic correlations 0.776 6-0.999 7 and genetic correlations 0.994 1-1.000 0 between body weight,body length,total length,body width,body height,head length,caudal peduncle length and caudal peduncle height,were all highly statistically significant(P<0.01).Furthermore,after sampling,experimental fish were infected with 3.95×10⁶ CFU/mL S.iniae through abdominal cavity.F₁ generation of GIFT tilapia purebred combination died 12 h later,whereas F₁ generation of Aureus tilapia purebred combination died 192 h later.384 h after infection,mortality of F₁ for GIFT purebred combination was 40%,while mortality of the reciprocal cross combinations was 20% and 23.3% respectively.The lowest mortality(6.67%)was found in F₁ for Aureus purebred combination.Overall,the results indicate that,except CPL,other growth related traits have no heterosis; however,hybridization can improve the disease resistance of breeding offspring.