Heterosis and combining ability evaluation for growth traits of blunt snout bream(Megalobrama amblycephala)when crossbreeding three strains

The blunt snout bream(Megalobrama amblycephala)is a major aquaculture species in the Chinese freshwater polyculture system.In this study,complete diallel crossing of three strains(i.e.,Liangzi[LZ],Poyang[PY]and Yuni[YN])was used to evaluate the combining ability and heterosis effect of intraspecific crossbreeding on the growth performance(i.e.,body weight,total length,body length,body height,and Fulton’s coefficient of condition).The offspring produced from the three strains were reared in a communal pond for 20 months,and nine microsatellites were used to assess their pedigree.Of the749 offspring,708(94.53%)could be assigned directly to a single parental pair.Significant differences were observed in body weight(BW)among the different combinations,indicating that the combining ability of BW from each strain was significantly different.The general combining ability(GCA)of BW from the sire was much higher than that from the dam.The GCA for the dam and sire of the LZ and YN were the largest and the smallest,respectively.The special combining ability of YN$9 PY#was the largest,and YN$9 PY#showed significantly positive heterosis effects on all F1growth traits,except for Fulton’s condition coefficient(K)(P\0.05).In addition,significant positive linear correlations were found between the mean BW of corresponding progeny and the H E of the parental generation(y=600.7x-29.472,r=0.8651,P=0.0026),H O(y=1206.9x-518.14,r=0.7436,P=0.0216),and the polymorphism information content(y=1021.3x-331.31,r=0.8245,P=0.0063)as determined by a correlative test.The findings obtained from the study will be important for future considerations of M.amblycephala stock improvement programs.

The blunt snout bream （Megalobrama ambly- cephala） is a major aquaculture species in the Chinese freshwater polyculture system. In this study, complete diallel crossing of three strains （i.e., Liangzi [LZ], Poyang [PY] and Yuni [YN]） was used to evaluate the combining ability and heterosis effect of intraspecific crossbreeding on the growth performance （i.e., body weight, total length, body length, body height, and Fulton＇s coefficient of con- dition）. The offspring produced from the three strains were reared in a communal pond for 20 months, and nine microsatellites were used to assess their pedigree. Of the 749 offspring, 708 （94.53 %） could be assigned directly to a single parental pair. Significant differences were observed in body weight （BW） among the different com- binations, indicating that the combining ability of BW from each strain was significantly different. The general com- bining ability （GCA） of BW from the sire was much higher than that from the dam. The GCA for the dam and sire of the LZ and YN were the largest and the smallest, respec- tively. The special combining ability of YN♀ ×PY♂ was the largest, and YN♀ × PY♂ showed significantly positive heterosis effects on all F1 growth traits, except for Fulton＇scondition coefficient （K） （P 〈 0.05）. In addition, signifi- cant positive linear correlations were found between the mean BW of corresponding progeny and the HE of the parental generation （y = 600.7x - 29.472, r = 0.8651, P = 0.0026）, Ho （y = 1206.9x - 518.14, r = 0.7436, P = 0.0216）, and the polymorphism information content （y = 1021.3x - 331.31, r = 0.8245, P = 0.0063） as determined by a correlative test. The findings obtained from the study will be important for future considerations of M. amblycephala stock improvement programs.