جستجوی مقالات مرتبط با کلیدواژه "بهگزینی" در نشریات گروه "شیلات"

In aquaculture industry, genomic selection has a profound potential to improve the genetic programs and production systems. Genomic selection benefits from both the actual relationship between animals and information from genomic markers in strong LD with commercially and biologically important genes. In this paper, technical progresses, practical requirements and commercial applications of genomic selection in aquaculture will be discussed. Using cost-effective genome sequencing, the genotyping capability in all type of organisms even those with no previous genetic knowledge has been provided. Usage of genomic selection proposes advantages more than traditional aquaculture through accurate estimation of polygenic complex traits such as disease resistance, increase the genetic gain, minimizing the inbreeding and negating the limiting effects of genotype by environment interactions. Based on the performed studies, implementation of a genomic selection program can reduce the rates inbreeding up to 81%. At the moment, the genomic selection is now at the position which can be involved in commercial breeding programs to suggest long and/or short term solutions towards reaching the commercial sustainable aquaculture.

The purpose of breeding is to improve the quantity and quality of the desired characteristics in cultured species in the next generations. Individual selection is a simple and practical way to provide a quick response in improving high heritability traits for breeding most species in aquaculture. At first step, in Yasouj cold water fishes breeding research Center, in order to conducting selection program in rainbow trout brood stock as base population and improving food conversion ratio (FCR) in  their offsprings, 150 female and male broods with higher mean weight were  selected, striped in 6 stage and eggs were incubated. One-year produced Fish (45000 pcs.) of the six groups with higher mean weight  in 5 stage were selected (438 pcs.) and remainder was discarded. Before selection, a few fish of six aged-groups as control group were cultured apart. Significant difference (p<0.05) induced between final mean weight of some groups (the selected groups and control group) and significant difference (p<0.05) between mean weight of the control group (717±96 g.) and the selected groups (1007±136 g.) can be a result of genetic improvement of growth rate trait induced of selection process in one generation and most likely because of age difference in them and because of no selection and deletion in control group (don’t throw out small individuals). There were no  significant difference (p>0.05) between FCR of six aged-groups (1.56±  0.16) and control group (1.53±  0.07). The lack of disclosure or promotion of FCR of most of the groups under selection program compared to the control group indicates that the effect of this selection method on the genetic improvement of FCR in one generation is indiscernible and to reveal the improvement of this trait, continuing the selection program to promote growth rate over several generations and, consequently, improve FCR is necessary.

In this study thirty male and female broodstock of rainbow trout (n=30) for generating full sibling collected in Cold-water Fishes Genetic and Breeding Research Center. We generated 13 different families using factorial mating design. Then juveniles were raised at the ponds until 6 months post-hatching. Genome extracted based on standard method and these individuals randomly selected for molecular analysis. Fin clips were cut and specimens were kept at -20̊ C until use. Four specific primers were used for rainbow trout and all the four QTL loci screened in this study were successfully amplified in all families. Statistical analyses including linkage disequilibrium (LD), association between genotypes and two quantitative traits including body weight (BW) and total length (TL) were performed using MapChart 2.1, GDA 1.1. General Linear Model (GLM) was performed with software SPSS 21.0. The results demonstrated the mean observed heterozygosity (Ho) and expected heterozygosity (HE) varied between 0.354 to 0.699 for locus OMM5140 and 0.568 to 0.836 for locus OMM1268, respectively. No significant epistatic interactions were identified between QTL markers. Proportion of phenotypic variation explained by each QTL (PV) for body weight at age 30 and 180 were 18.48 and 31.24, respectively. Hardy-Weinberg departure was observed for most loci from all farms and were disequilibrium (p < 0.05). The four QTL loci variation in rainbow trout is important to gain a better understanding of the genetics of production traits and for transferring genetic information and improved selective breeding program to farms in Iran

Selective breeding programs have great potential to increase the profitability of aquaculture. The first, and one of the most important, steps to be taken when establishing a breeding program is the creation of a population with a broad genetic diversity. This will ensure that rapid inbreeding can be avoided and maximize the likelihood of long-term genetic response. The first step in forming a base population should be to compare productivity in available populations. A base population should combine characteristics of the subpopulations, and the best individuals across different populations should be selected as base population. Traditionally, base populations were created from a number of wild strains by sampling equal numbers from each strain However, for some aquaculture species improved strains are already available and, therefore, mean phenotypic values for economically important traits can be used as a criterion to optimize the sampling when creating base populations. Also, the increasing availability of genome-wide genotype information in aquaculture species could help to refine the estimation of relationships within and between candidate strains and, thus, to optimize the percentage of individuals to be sampled from each strain. In conclusion, marker-based strategies could be used to attempt to maximize variation for disease and meat quality traits, while phenotypic information could be used for traits like growth.

The majority of plants and farm animal production is presently based on genetically improved seeds and stocks. Genetic improvement in aquaculture, however, lags far behind plants and farm animals. It is estimated that at present less than 10% of aquaculture production is based on genetically improved stocks, despite the fact that annual genetic gains reported for aquatic species are substantially higher than that of farm animals. In livestock, genetic gain in growth rate is typically 5 percent per generation, which is 5-6 times less than in aquatic species. The relatively high heritabilities and Large Phenotypic and genetic variation for growth rate and most other traits of economic importance combined with high fecundity and short generation intervals in most species explain the high genetic gains obtained in many aquaculture breeding programs. If genetically improved animals are used, production may be dramatically increased and feed conversion and survival were improved, that leads to better utilization of limited resources such as feed, labour, water, and land. Genetic improvement also reduces production costs as more animals can be grown using the same resources. There could be several reasons why use of selective breeding in aquaculture is far behind plants and terrestrial farm animals, including availability of  fry of wild stock, little knowledge about controlling reproduction of some pieces, lack of knowledge about the economic benefit of breeding programs, lack of knowledge about quantitative genetics and how to start and run breeding programs, substantial investments needed, many aquaculture farmers do not willing to cooperate with researchers, researchers working in the field have not effectively been able to promote the benefits of selective breeding and those extending knowledge to aquaculture lack information and knowledge about the potential of selective breeding.

Family relations between parents are important for inbreeding. Inbreeding depression express the reduction of phenotypic means related to increase of inbreeding coefficient. The effects of inbreeding on growth, survival and resistant to viral disease in Litopenaeus Vannamei have been different. With increasing of inbreeding coefficient, the effect of inbreeding depression was small but significant on growth and had no effect on survival after PL60 stage. The effect of inbreeding depression on resistance to viral diseases was moderate to severe and it was significant only on resistance to TX95 TSV-AG virus. In conclusion, in reproduction and selection programs of western white leg shrimp, selection of growth trait at small to moderate inbreeding coefficients (F