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Genetic parameters and genotype by rearing density interactions for growth traits and survival were investigated in Litopenaeus vannamei. A total of 3626 shrimps from 40 families in two densities (low density, 80 shrimps m−2; high density, 160 shrimps m−2) were measured for four growth traits, body length, body weight, cephalothorax length and abdominal segment length. Variance components and genetic parameters for growth and survival were estimated using a two-trait animal model or a threshold (probit) sire and dam model. The common environment effect was excluded because it could not be partitioned effectively, likely because of high heritability. The heritability for growth traits varied from 0.21 to 0.44, indicating a moderate level. For survival, the back-transformed heritability ( [ABSTRACT FROM AUTHOR]

The aim of this study was to estimate heterosis and heritability for harvest body weight of the Pacific white shrimp ( Litopenaeus vannamei) measured at commercial farm conditions. Heterosis and heritability were estimated using a base population from diallel crosses of eight introduced strains. The base population included 9936 shrimp from 207 families that were produced with 188 sires and 172 dams using a nested mating design by artificial insemination. Heterosis was calculated basing on the least squares means ( LSM) of harvest body weight. The results showed that most of the hybrids (75%) have positive heterosis for harvest body weight, which ranged from −13.36% ( UA2 × UA5) to 13.80% ( UA6 × UA5) with a mean of 2.41%. The high amount of heterosis manifested in the hybrids indicated the usefulness of these hybrids for improving the growth. Variance components and heritability for harvest body weight were estimated using an animal model. The heritability estimate for harvest body weight was 0.092 ± 0.082 ( h2) when genetic groups were excluded from the pedigree, but it was decreased when genetic groups were included in the pedigree ( [ABSTRACT FROM AUTHOR]

Genetic parameters and response to selection were estimated for the harvest body weight of Litopenaeus vannamei. The data consisted of 24 072 progeny from 178 sires and 171 dams in two generations (G0 and G1) with a nested mating structure. All families were randomly divided into two groups and then cultured in two farms at different locations (Huanghua and Qingdao). The heritability estimates from G0 and G1 were 0.278 ± 0.136 and 0.423 ± 0.065 respectively. Over two generations, the heritability estimate was 0.335 ± 0.087, and the common environmental effect was 0.084 ± 0.031. A bivariate animal model was used to estimate variance and covariance components, whereby the body weight in the two farms was treated as a genetically distinct trait. Genetic correlation was close to unity (0.943 ± 0.066), indicating that a genotype by environmental interaction for harvest body weight was small. The response to selection in harvest body weight was estimated using two methods (the realized and predicted responses). The realized response was estimated from the difference in the least squares means of body weight for the selection and control populations. The predicted response was obtained from the difference in the mean estimated breeding values between generations. The realized response was 2.30%, while the predicted responses were 2.00% and 1.37% for within- and across-generation datasets using two sets of genetic parameters respectively. The results would provide crucial information in pacific white shrimp breeding programs in China. [ABSTRACT FROM AUTHOR]

The inability of Penaeus vannamei to tolerate low temperatures is of major economic concern in temperate climates, as it reduces their growing season and leads to over-winter mortality. In this study, the heritability of body weight and survival under two grow-out temperature conditions, genotype by environment interaction for body weight and survival at different grow-out temperatures, and the heritability of cold tolerance traits of P. vannamei were investigated and estimated. The heritability estimates for body weight in normal controls (CK) and low-temperature groups (LTT) were, respectively, moderate (0.3191 ± 0.0622) and low (0.1368 ± 0.0889), and those for survival were all low (0.1094 ± 0.0265 and 0.0598 ± 0.0229, respectively). The genetic correlations between the CK and LTT groups for body weight and survival were 0.4788 ± 0.2073 and 0.2968 ± 0.2284 respectively, and both of them showed significant differences from unity ( P < 0.05). Furthermore, their K -values were all higher than 0.50, which indicated that the genotype-by-environment interaction effect was substantial in both growth and survival at different temperatures. The cold tolerance heritability estimated from a cold temperature challenge (18 °C to 8 °C) using cooling degree hours for each individual (CDH) and survival rate of each family at half lethal time (SR 50 ) were low (0.0258 ± 0.0205 and 0.0211 ± 0.0196 respectively), and negative genetic correlations between these cold tolerance traits and body weight (− 0.7702 ± 0.4583 and − 0.8253 ± 0.4553 respectively) were also estimated from the cold challenge. However, they showed no statistically significant differences from zero. Thus, more research needs to be conducted on the more accurate heritability of cold tolerance trait and genetic correlations between traits in P. vannamei to further improve the achievement of breeding goals. [ABSTRACT FROM AUTHOR]

Genetic parameters and predicted and realized selection responses were estimated for harvest body weight of Chinese shrimp ( Fenneropenaeus chinensis ) after five generations of multi-trait selection. The body weights of 15,201 tagged shrimp representing 460 full-sib families in 6 generations were recorded at harvest. Heritability estimates for body weight showed large variation in magnitude (0.00 ± 0.00-0.36 ± 0.07) when analyzing data from each generation separately. When data from all generations (G 0 -G 5 ) were included in analysis, the heritability estimate for body weight was 0.18. While, G 0 was more affected by environmental conditions than the other generation in this study, when data from G 0 was excluded, the heritability was 0.21. The common environment effect estimate was 0.08 when all data included and 0.06 when G 1 -G 5 included. The females were significantly larger than the males at harvest ( P < 0.05). The genetic correlation of the harvest body weight between sexes was similar within and across generations, indicating that body weight in male and female shrimp is likely controlled by the same genes. Breeding candidates in the base population (G 0 ) were selected according to their individual breeding values for growth. In later generations (G 1 -G 5 ), candidates were selected according to a selection index including breeding values for growth, survival time after WSSV infection and pond survival. The response to selection for harvest body weight was estimated by two methods (the realized and predicted responses). The realized response was estimated from the differences in the least square means of body weight between the selection and control populations. The predicted response was obtained from the differences in the mean breeding values between generations. The accumulated realized response was 18.60% after performing five selections. The accumulated predicted responses estimated using two sets of genetic parameters obtained from within and across generation datasets were 6.43% and 6.50%, respectively. The results are discussed in a practical context of developing selective breeding programs for Chinese shrimp, and it is indicated that the selective breeding program has generated effective genetic improvement after five generations of selection. The future direction of the genetic improvement program is discussed. Statement of relevance Chinese shrimp, Fenneropenaeus chinensis , is one of the most valuable mariculture species in China. The Yellow Sea Fisheries Research Institute (Qingdao, China) initiated a multi-trait selective breeding program for Chinese shrimp in 2004, based on a combined family and within (inter) family selection scheme to improve growth, survival time after WSSV infection and pond survival. A new selected breed named “Huanghai No. 2” (registration no. GS01-002-2008) was approved in 2008. This program provided significant economic and social benefits. However, only limited results regarding this program have been reported, which involved genetic parameters of harvest body weight and genetic correlations among different traits using only one year data, a smaller subset of the current study. Growth is one of the most desirable economic traits in aquaculture. Good growth is important for efficient production and contributes to more profitable and sustainable development. Currently, the selective breeding program for F. chinensis is ongoing and the breeding nucleus was divided into different lines after performing five selections. In this paper, we will focus on the results related to genetic evaluation for the harvest body weights from G 0 to G 5 . We will present more reliable estimates of phenotypic and genetic parameters, calculate the response to selection after performing five selections and discuss the longer term implications of the findings from a genetic improvement viewpoint. [ABSTRACT FROM AUTHOR]