Morten Rye

White spot syndrome virus (WSSV) causes major worldwide losses in shrimp aquaculture. The development of resistant shrimp populations is an attractive option for management of the disease. However, heritability for WSSV resistance is generally low and genetic improvement by conventional selection has been slow. This study was designed to determine the power and accuracy of genomic selection to improve WSSV resistance in Litopenaeus vannamei. Shrimp were experimentally challenged with WSSV and resistance was evaluated as dead or alive (DOA) 23 days after infestation. All shrimp in the challenge test were genotyped for 18,643 single nucleotide polymorphisms. Breeding candidates (G0) were ranked on genomic breeding values for WSSV resistance. Two G1 populations were produced, one from G0 breeders with high and the other with low estimated breeding values. A third population was produced from “random” mating of parent stock. The average survival was 25% in the low, 38% in the random and...

The shrimp industry is now largely based on Litopenaeus vannamei. Current strategies for disease management in Asia emphasizing exclusion and eradication with strict quarantine and importation protocols have not been effective in controlling disease epidemics. New diseases have been introduced on illegal importations; commercial shrimp populations are derived from imported SPF stocks susceptible to endemic diseases; and local breeding programmes are based on populations not resistant to a range of diseases. Broodstock are largely poorly adapted to local conditions and repeated disease epidemics occur. Strategies for disease management should concentrate on: (i) minimizing the risk of introducing new diseases to the region; (ii) development of populations more resistant to endemic diseases; and (iii) better management practices that minimize the likelihood of serious epidemics and delay infection, but do not depend on attempts to eradicate diseases already present. This can be implemented by building on the better management practices already established in the region and in addition: (i) applying strict quarantine procedures for diseases not reported in the region whilst making the processes sufficiently agile to reduce illegal introductions; (ii) eliminating standard rigid importation protocols and tailoring protocols in accordance with the disease situation of both the country of origin and destination; (iii) increasing genetic variation available within Asia by public sector support for programmes to enlarge the pool of genetic variation and encouraging collaboration with breeding programmes that encompass a broad genetic base; (iv) establishing selection programmes that permit reincorporation of animals exposed to disease into the breeding nucleus; and (v) establishing propagation systems that provide growers with high health status stocks without requiring overly strict SPF certification of facilities.

The high yields obtained in agriculture rely heavily on the use of domesticated and genetically improved breeds and varieties. Until quite recently this has not been the case for most farmed aquaculture species that, in the genetic sense, are still much closer to the wild state than are the major terrestrial animals and food crops. Less than 10 % of the total world aquaculture production is based on improved strains. Due to a growing human population and a decline in production from capture fisheries, there is therefore a great disparity between the need for increased aquaculture production and the genetic quality of the strains available to meet that need. Moreover, full benefits of investments in management improvements (feed and feeding practices, control of diseases, etc.) can only be obtained through the use of genetically improved animals.

ABSTRACT Establishing procedures for monitoring and quantifying genetic changes in a breeding program is not required in order to obtain response to selection, but is essential for several other reasons. Foremost, effective monitoring of the genetic changes that result from the selection process serve as an invaluable tool for assessment of the efficiency of the breeding work, and enables the breeder to make proper adjustments if the realized gains do not meet the theoretical expectations for the current scheme. Valid documentation of genetic progress for key traits of economic importance is also increasingly important for marketing purposes, as providers of eggs, fry or fingerlings often face strong competition in their main markets as aquaculture industries mature. Implementation of effective protocols for measuring genetic change in breeding programs is not as straightforward as it may intuitively seem. The complexity arises from the fact that changes in the phenotype measured over time are the sum effect of all genetic and environmental changes that occur during the period of interest, and are also affected by possible genotype by environment interaction effects. In this context environmental changes comprise any change of non-genetic nature, and thus are inevitable in any applied breeding program and even in most well controlled selection experiments. Thus, the task of accurately quantifying how much of the change in the animals phenotypic expression that is resulting solely from the selection process often becomes very complex. Moreover, even with valid response estimates at hand, interpretation of short term responses are further complicated by the fact that initial responses in small populations may fluctuate substantially due to random genetic drift, sampling error, variable selection differentials as well as variable environmental effects (Falconer and MacKay, 1996). Consequently, accurate and reliable estimates of selection response can only be drawn after several cycles of selection. Estimation of genetic gains in selection programs therefore requires carefully designed protocols in order to provide valid results. An excellent account of alternative approaches with emphasis on application to aquaculture species is given by Gall et al. (1993). In the following, four alternative methods are discussed: the use of an unselected control line, use of divergent selection, repeated matings and genetic trend analysis. A method to quantify the relative selection response originating from the male and female side under a phenotypic selection scheme is also briefly described.

For four sub-populations of Atlantic salmon (Salmo salar) in Norway, additive, dominance and additive by additive genetic variances and inbreeding depression were estimated for body weight at slaughter after two years in sea-water. The data used were from a hierarchical mating design, in which each sire was mated with two to seven dams. In each generation, 104 to 206 full-sib

... oped methodologies for quantifying values of, eg, environmental services and animal welfare, where subjective opinions may be strong and vary considerably among individuals and cultures (Braden and Kolstad 1991; Freeman 1993; Smith 1993; Bennett 1996). Olesen et al. ...

Selection for disease resistance in fish may be performed directly on basis of survival data obtained in controlled challenge trials, or indirectly using information from immunological or molecular markers linked to differential survival. In the present study, several key innate immune parameters were measured in aeromoniasis resistant and susceptible lines of rohu Labeo rohita to assess their suitability as immune markers for use in indirect selection for increased resistance. Experimental infection with Aeromonas hydrophila (9.55 × 10(6) cfu g(-1) fish) through the intraperitoneal route produced higher survival in the resistant line (73.33%) as compared to the susceptible line (16.67%). Blood and liver tissue samples from both lines were collected to study some of the innate immune parameters and immune-related gene expression. The respiratory burst activity of blood phagocytes, serum myeloperoxidase activity and ceruloplasmin level were significantly (p < 0.05) higher in the resistant line compared to the susceptible line. Lower level of blood glucose and serum natural haemolysin titre were marked in the resistant line as compared to the susceptible line. No significant difference was measured in total serum protein concentration, antiprotease activity and bacterial agglutinin level between two lines, while the expression of transferrin, complement factor C3 and TLR 22-like transcripts were significantly (P < 0.05) higher in liver samples of the susceptible line. However, no such difference was found in β(2)-microglobulin and lysozyme gene expression between lines. The study demonstrated the possibility of using some of the investigated innate immune parameters as indirect marker traits for selection for improved resistance to aeromoniasis in rohu.