| Driven by Pacific white shrimp Litopenaeus vannamei's rapid growth rate, higher firmness of meat, it is recognized in the world as an excellent type of shrimp aquaculture. Species was introduced in China since the late 1990s. To carry out intensive breeding and artificial breeding techniques, shrimp production has reached 80 % to 90 % in China.This thesis aims at assessment the reproductive performance and offspring quality of tank-reared (TR) L. vannamei and compare it with pond-reared (PR) broodstock, estimate the heritabilities and the genetics for weight at age of domesticated L. vannamei at three consecutive ages (120,150,180 days-old) when reared in standard commercial culture conditions. L. vannamei were reared in standard commercial pond conditions over two generations with full pedigree information, and quantifying the response to selection, heritability and genetic correlations of growth in L. vannamei at about five months of age.1. Assessment of broodstock reproductive performance and offspring quality from different sourcesThis chapter presents results of an experiment that was carried out to evaluate the reproductive performance and offspring quality of domesticated L. vannamei was compared when farmed on two different rearing conditions: earthen pond or pond-reared (PR) and concrete tank or tank-reared (TR). The experimental period started one day after eyestalk ablation of the females and lasted for 60 days. Artificial inseminations were performed whereby each of the two spermatophores from a single male was used to inseminate two different females to produce paternal half-sib families. Ovarian developments, moulting, and spawning events were monitored regularly. Furthermore, the numbers of eggs and larval quality parameters were determined. There was no significant difference in the spawning frequency, fecundity, egg spawning success rate, numbers of eggs per spawning, and egg hatchability between the TR and PR females (P > 0.05). However, PR females matured and spawned more rapidly after ablation and more often than TR females. Significant variations in the offspring quality of the broodstock from the two sources (TR and PR) were found. The larval stage index (LSI) at ZⅢ, MⅢand 5 days post metamorphosis from mysis to postlarval stage 1 (PL5) was very different (P < 0.05) between the treatments, it showed that larval development of progeny from the PR sources was significantly faster than for larvae of the TR sources. Nevertheless, the group of PR breeders resulted in significantly shorter postlarval stage periods (7 days) than the group of TR breeders (9 days) (P < 0.05). The survival percentage up to 15 days post metamorphosis from mysis to postlarval stage 1 (PL15) stage of the PR breeders was significantly higher (74 %) than for the TR (56 %) sources (P < 0.05). In general, the PR broodstock resulted in better offspring quality than the TR broodstock. The results suggest the potential to selectively breed stocks with improved characteristics adapted to the local culture environment.2. Analysis on heritability and genetic correlations of weight and age in L. vannameiA common goal of shrimp stock breeding programs is to improve weight at age. Weight at age is a strong driver of economic returns in most shrimp stock industries; is relatively easy and inexpensive to measure; and commonly has a moderate heritability. The heritabilities and the genetics for weight at age of domesticated L. vannamei at three consecutive ages when reared in standard commercial culture conditions were assessed. L. vannamei were reared in standard commercial pond conditions over two generations with full pedigree information. 29 half-sib and 124 full-sib families of L. vannamei were obtained by artificial assistant fertilization of two to four females by single male. From the families originally obtained, only 21 half-sib and 47 full-sib families had high numbers at pond stocking and high survival rates and therefore the analyses were done on a random sample of 60 shrimp from each family. Weights, heritabilities, phenotypic and genetic correlations of animals were measured at 120, 150 and 180 days of age. The normality of weights at different ages data was evaluated with natural log transformation. Shrimp had mean weights with standard errors of 16.44±5.57 g, 30.90±9.64 g and 39.70±12.38 g for females; and 14.14±4.88 g, 19.30±7.54 g and 24.26±8.23 g for males respectively at 120, 150 and 180 days of age. The mean growth rate was 0.39±0.11 g d-1 for females and 0.17±0.05 g d-1 for males. The estimates of heritability with standard errors at 120, 150 and 180 days were 0.45±0.11, 0.32±0.13 and 0.32±0.13 respectively. Genetic correlation between weight 120 and weight 150 was 0.94±0.03; and correlation between weight 120 and weight 180 was 0.93±0.02. Genetic correlation between weight 150 and later measure was 0.93±0.02. The phenotypic and genetic correlations between weights at different ages decreased as time increased, with the genetic correlations always being lower than the phenotypic correlations. The results from the current study suggest that improvements in harvest weight should be yielded by weight-based selections between 120 and 150 days. The propitious period between stocking and harvest was between 120 and 150 days, with a final survival commonly between 71 % and 84 %, and harvest weights of 15.29 g– 25.10 g. 3. Response to selection, heritability and genetic correlations of growth in L. vannameiTo quantify the response to selection, heritability and genetic correlations between weight and size of L. vannamei, the body weight (BW), total length (TL), body length (BL), first abdominal segment depth (FASD), third abdominal segment depth (TASD), first abdominal segment width (FASW), and partial carapace length (PCL) of 5-month-old parents and of offspring were measured by calculating seven body measurings of offspring produced by a nested mating design. Seventeen half-sib families and 42 full-sib families of L. vannamei were produced using artificial fertilization from 2–4 dams by each sire, and measured at around five months post-metamorphosis. The results show that heritabilities among various traits were all high: 0.515±0.030 for body weight (BW), 0.394±0.030 for total length (TL), 0.409±0.020 for body length (BL), 0.412±0.020 for first abdominal segment depth (FASD), 0.422±0.020 for third abdominal segment depth (TASD), 0.429±0.020 for first abdominal segment width (FASW) and 0.415±0.020 for partial carapace length (PCL). After one generation of selection, the selection response was 10.70 % for offspring growth. The realized heritability for weight at around five months of age was 0.30. The genetic correlations between body weight and body size were significantly different from zero (P < 0.01) and very high: 0.85, 0.84, 0.66, 0.67, 0.77 and -0.08 respectively. However, partial carapace length (PCL) presented a negative correlation with the body weight. Most of the traits were positively correlated, which indicates that they can be improved simultaneously while the negatively related ones show that improving one will be at the detriment of the other. PCL also presented the lowest correlation with the other variables. Several morphological measures are identified as potential selection criteria and discussed with regard to the handling necessary to make each measurement and the correlation between these measurements and body weight.In conclusion, several factors need to be addressed in order to optimize the husbandry practices of L. vannamei and to enhance harvest growth. High genetic variability is crucial in the breeding program because it is critical for both the short term and long term limits of response. Therefore, strategies to maintain the variability through generations of selection should be part of the breeding program. This knowledge may also add to the development of improved hatchery protocols and help sustainable development of L. vannamei culture industries in the future. Then, external morphological parameters can be applied during breeder selection for enhancing the growth without sacrificing animals for determining the body size and breed ability; and selective breeding can be improved significantly with increased production simultaneously. |
PDF Full Text Request