Significance and Impact of the Study: White spot syndrome, caused by white spot syndrome virus (WSSV), is the major disease threatening the shrimp aquaculture industry and leads to tens of billion dollars of economic losses in the world each year. This study established a CPA-based method for detecting WSSV, which is rapid, sensitive and specific. It is anticipated that this novel assay will be instrumental for diagnosis and surveillance of WSSV. Abstract White spot syndrome virus (WSSV) is one of the main pathogens seriously threatening penaeid shrimp farming in the world. This study designed and synthesized five specific primers based on the conserved sequences of WSSV genome, optimized the reaction system and conditions, and finally established a cross-priming amplification (CPA)-based detection method for WSSV (WSSV-CPA). The results indicated that the optimized reaction temperature and time of WSSV-CPA were 63°C and 60 min, respectively. The detection limit of the WSSV-CPA assay was as low as 10 copies ll À1 and shared same sensitivity with the WSSV-qPCR assay. Due to dispensing with expensive thermal cycler, timeand cost-saving, and ease of use in field, it is anticipated that the WSSV-CPA method developed in this study will be instrumental for the diagnosis and surveillance of WSSV.

The objective of this study was to estimate genetic parameters for three traits based on 28 Cynoglossus semilaevis families approximately 6 months of age (at least 5 cm total length), including trait_1 (survival of 26 families, 3434 individuals in total subjected to challenge tests with Edwardsiella tarda), trait_2 (survival of 20 families, 2016 individuals in total subjected to challenge tests with Vibrio anguillarum) and trait_3 (survival of 27 families, 9340 individuals tagged at circa 180 days of age and reared in indoor ponds for circa another 5 months). The result showed that there were large differences in the survival of the families after challenge (11.11-65.31% for E. tarda and 9.18-70.54% for V. anguillarum). Additionally, the survival of families reared in indoor ponds was also different, varying from 21.00% to 73.67%. Heritabilities of the three traits varied from 0.14 to 0.26, as estimated by the linear model (LM) and the threshold model (TM). The trait_1 heritabilities (0.26 and 0.19 estimated by LM and TM) were higher than those of the others (0.20 and 0.23 estimated by LM, 0.14 and 0.19 estimated by TM). The estimates of heritabilities using LM were consistently higher than those of TM in this study. There were significant medium genetic correlations of 0.44 and 0.42 between trait_1 and trait_2 obtained from LM and TM (P < 0.05). However, very low and non-significant genetic correlations of trait_1 and trait_3 (À0.10 for LM, À0.05 for TM), as well as those of trait_2 and trait_3 (0.05 for LM, 0.04 for TM) were obtained. Therefore, indirect selection for trait_1 and trait_2 was effective, but almost ineffectual for trait_1 and trait_3 as well as trait_2 and trait_3. Otherwise, there was no significant difference in the predictive abilities of LM and TM. Two families resistant to both Edwardsiella tarda and Vibrio anguillarum were selected plus one family resistant to both Vibrio anguillarum and naturally infected by unknown pathogens through family selection. As there was very low and non-significant genetic correlation of trait_3 and trait_1 as well as trait_2, superior strains are anticipated with the ability to resist two or more kinds of diseases, through the crossing of families selected for the three traits described above. The results support the hypothesis that genetic variation exists for disease survival, which could be used to design a breeding program for selecting strains of Cynoglossus semilaevis with high disease resistance.

Genetic parameters of growth traits at different growing stages of Paralichthys olivaceus (Temminck and Schlegel, 1846) were estimated using 30 families. The estimates of heritability for body weight at four developmental stages viz., 210, 450, 720 and 830 days of age, varied from 0.12 to 0.37. The heritability at 720 days of age was the lowest and that of 450 days was the highest. The maternal effect was 0.08 at 210 days, 0.03 at 450 days and almost zero (8.89 E-8 and 2.40 E-7) at 720 and 830 days. Correlation coefficients of the estimated breeding value (EBV) and phenotypic value (PV) of body weight at different developmental stages were 0.470 -0.803, which were highly significant (p<0.01). Correlation of estimated breeding value (EBV) and phenotypic value (PV) was the highest at 210 days of age and the lowest at 720 days. Genetic correlation among the four stages showed large variation (0.339-0.811), which were highly significant except that of 210 and 830 days. The value and accuracy of estimating genetic parameters for growth traits at different stages was different. Therefore, the growth stage should be taken into account when designing a breeding program for growth traits in P. olivaceus.