Aquaculture Stocks Research Articles

Inoculation Experiments to Understand Mass Mortalities in Sea Scallop, Placopecten magellanicus

Abstract In 1993, sea scallop, Placopecten magellanicus, populations from the Jacques Cartier Bay on the North Shore of the Gulf of St-Lawrence of Canada, experienced masse mortality episodes with mortality rates reaching 80%. Both natural beds and aquaculture stocks were affected. Experiments were undertaken to determine if an unknown or unidentified pathogen could be responsible for the disease and if that disease was transmissible. Three experiments, in which scallops were inoculated with homogenate extracted from moribund and healthy scallop tissue, were carried followed by histopathological analysis. The results demonstrated that the scallops from the Lower North Shore were more vulnerable to external factors such as manipulations and injections than the scallops from other regions, like Magdalen Islands and Gaspesie. The histopathological analysis did not permit to identify the causal pathogenic agent but our results suggested transmission of infection. The exact cause of the mass mortality episodes...

INFLUENCE OF HOST GENETIC ORIGIN AND GEOGRAPHIC LOCATION ON QPX DISEASE IN NORTHERN QUAHOGS (=HARD CLAMS), MERCENARIA MERCENARIA

QPX (Quahog Parasite Unknown) a protistan pathogen of northern quahogs (=hard clams), Mercenaria mercenaria, has caused disease outbreaks in maritime Canada, and in Massachusetts, New York, New Jersey, and Virginia, USA. Although epizootics have occurred in wild hard clam populations, the parasite has most seriously affected cultured hard clams, suggesting that aquaculture practices may promote or predispose clams to the disease. In this investigation the influence of clam genetic origin and the geographic location at where they are grown on QPX disease susceptibility was examined in a common garden experiment. Aquaculture stocks were acquired from hatcheries in Massachusetts, New Jersey, Virginia, South Carolina, and Florida and spawned at a single hatchery in Virginia. All stocks were originally, although not exclusively, derived from wild hard clam populations from each state. The seed clams were deployed at two sites, New Jersey and Virginia, and evaluated during the subsequent 2.5 y for growth, survival, and QPX disease. At both sites, South Carolina- and Florida-derived clam stocks exhibited significantly higher QPX prevalence and lower survival than New Jersey and Massachusetts clam stocks. Levels in the Virginia stock were intermediate. In Virginia, mortality at the termination of the experiment was 78%, 52%, 36%, 33%, and 20% in the Florida, South Carolina, Virginia, Massachusetts, and New Jersey hard clam stocks, respectively. Mortality was significantly correlated with QPX prevalence. Maximum QPX prevalence in the South Carolina and Florida stocks ranged from 19% to 21% and 27% to 29%, respectively, whereas in the Virginia, New Jersey, and Massachusetts stocks prevalence was 10% or less. Similar trends were observed in New Jersey where mortality at the termination of the experiment was estimated to be 53%, 40%, 20%, 6%, and 4% in the Florida, South Carolina, Virginia, Massachusetts, and New Jersey clam stocks, respectively. QPX prevalence peaked at 18% in the Florida stock, 38% in the South Carolina, 18% in the Virginia, and 5% in the New Jersey and Massachusetts stocks. These results suggest that host genotype is an important determinant in susceptibility to QPX disease. As such, hard clam culturist should consider the genetic origin of clam seed stocks an important component of their QPX disease avoidance/management strategies.

An improved enzyme preparation for rapid mass production of protoplasts as seed stock for aquaculture of macrophytic marine green algae

Preparation of protoplasts and their subsequent applications for both basic and applied research of marine macroalgae remains largely under developed due to lack of development of reliable methods with consistent yields of viable protoplasts. An improved enzyme preparation with a single commercial enzyme, e.g. 2% Cellulase Onozuka R-10 in 1% NaCl solution, was developed to produce protoplasts rapidly from different green algal genera of Ulva, Enteromorpha and Monostroma. The simple dissolution of enzyme powder in 1% NaCl resulted in exclusion of 2% Macerozyme R-10 from the mixture consisting of 2% Cellulase Onozuka R-10 with 3% NaCl earlier reported as superior for the same algae. Optimal conditions for the isolation of maximum yields of viable protoplasts were found to be with 2% Cellulase Onozuka R-10 incubated at 20 °C for 2 h in 1% NaCl solution with 0.8 M mannitol adjusted to pH 6.0. The protoplast yield with optimized enzyme mixture was as high as 102.8 × 10 6 cells g − 1 f. wt for M. oxyspermum while it was in the range of 74.4–88.6 × 10 6 cells g − 1 f. wt thallus for seven species of Ulva, and 82.5–95.4 × 10 6 cells g − 1 f. wt for three species of Enteromorpha. The regeneration rate of protoplasts isolated using this method ranged from 89 to 92% with normal morphogenesis. The seeding of nylon threads with isolated protoplasts of M. oxyspermum was successful and after 3–4 weeks the entire frame with nylon threads became thick green in color with tiny germlings in laboratory culture. Thus, the method described in the present study allow for rapid mass production of viable protoplasts that could be potentially used as a source for seed material for mariculture and for other applied phycological research.

Production of all-male stock by neofemale technology of the Thai strain of freshwater prawn, Macrobrachium rosenbergii

The giant freshwater prawn, Macrobrachium rosenbergii is commercially cultured in many tropical countries. Males of this species grow much faster than females so that, obviously, culture of an all-male population produces significantly higher yield than an all-female or mixed-sex culture. Although sex of M. rosenbergii is determined by genetics, sex reversal from males to females can be triggered by the removal of androgenic glands at an early stage. The empirical information obtained from two families showed that almost all offsprings of the neofemales were male. Therefore we conducted this study to explore the result of such mating with sufficient number of crosses in the Thai strain of M. rosenbergii. The histology of the gonads during the threshold period of sex determination was also studied. The results showed that the gonadal differentiation of M. rosenbergii did not occur until the stage that both gonopore complexes and appendix masculinae appeared in males. The bilateral removal of androgenic glands of a total of 87 postlarvae at stage I (presence of the gonopore complexes but not the appendix masculinae) resulted in 80.4% survival. Among the survivors 30% developed as female and 27.14% eventually matured. Mating of 12 neofemales with normal males resulted in all-male offspring in eight crosses; 88–99.49% males in two crosses. The remaining two crosses produced offspring with 1:1 sex ratio and hence were attributed to mislabeling of the normal female as neofemales. The 10 control crosses (normal male × normal female) produced varying offspring sex ratios from 1:1 (six crosses) to 1.72♀:1♂ (pooled data from four crosses). Fecundity of the neofemales was not different from that of the normal females. Our results suggest that the application of the neofemale technology to produce all-male stock for aquaculture is promising.

Use of molecular tools for research and improvement of aquaculture stocks

Development of molecular genetic markers provides aquaculture with tools for a number of research and practical applications. Genetic marking of experimental groups allows their evalu- ation in the same rearing units, increasing statistical power within limited research infrastructure. Parentage can be inferred for individuals in mixed-progeny groups, quantifying the contributions of individual parents and supporting the estimation of sire and dam effects. Building upon parent- age assignment, walk-back selection entails retention of the best members of each family as broodstock for the next generation. Molecular markers can be used to detect the segregation of quantitative trait loci (QTL) and knowledge of such linkages can be used for marker-assisted selection. Gene expression profiling can identify genes affecting traits of interest, providing can- didates for QTL or functional analysis. Purposeful genetic marking can be used to identify pro- prietary stocks, marketed products, and fish out-planted or escaping into natural ecosystems. Although each application has been demonstrated, genetic markers are not routinely used in commercial aquaculture. The limited practical application can be explained by the limited devel- opment of broodstocks for most aquaculture species, the small size and limited scope of most aquaculture operations, and the costs of genetic screening.

RFLP analysis of the mtDNA control region in white shrimp (Litopenaeus vannamei) populations from the eastern Pacific

White shrimp (Litopenaeusvannamei) population genetic structure from the eastern Pacific was determined by restriction fragment length polymorphism analysis of the mitochondrial DNA control region. Four localities were surveyed with four endonucleases (Alu I, Taq I, Spe I, Ssp I) yielding 48 composite haplotypes. White shrimp showed high average within-locality haplotype (0.823) and nucleotide (5.41%) diversities and also high average nucleotide divergence between all pairs of localities (0.73%). A mismatch analysis of pairwise differences between haplotypes indicated that white shrimp does not fit the sudden population expansion model. An analysis of molecular variance showed significant geographic variation in the frequencies of haplotypes (ΦST=0.1382, P<0.0001). Population differentiation may be maintained by a combination of physical, oceanographic, and biological factors acting as barriers to gene flow among localities. Because of its high polymorphism, the control region might be useful as a genetic marker for monitoring genetic diversity in aquaculture stocks.

Genetic relationships among members of the Ichthyobodo necator complex: implications for the management of aquaculture stocks

Abstract Ichthyobodo necator (costia) is a common and important flagellate parasite that infests the skin and gills of many freshwater and marine fish. Costia infestations are often fatal and cause significant aquaculture losses worldwide. Recently it has been demonstrated that Ichthyobodo is a multispecies complex with differing host preferences. Knowing if those species have broad or narrow host specificity has important implications for the management of costia. To address the question of host specificity, genomic DNA was isolated from Ichthyobodo trophonts collected from rainbow trout, Oncorhynchus mykiss, koi, Cyprinus carpio, mirror carp, C. carpio, goldfish, Carassius auratus, channel catfish, Ictalurus punctatus, swordtail, Xiphophorus helleri, and Japanese flounder, Paralichthys olivaceus. The small subunit ribosomal RNA (SSU rRNA) gene from each isolate was analysed with previously published Ichthyobodo sequences using Bayesian phylogenetic methods. The internal transcribed spacers (ITS) from six isolates were also PCR-amplified, cloned and sequenced. Both the SSU rRNA phylogenetic analysis and the ITS rRNA sequence data support grouping the 22 Ichthyobodo isolates examined into a complex of nine different species. Many of these species were frequently isolated from multiple hosts, indicating that exchange of infested fish from one region to another has a high potential for spreading the disease. In one instance, the same species was obtained from marine and freshwater fish, further suggesting that certain Ichthyobodo species may not be limited by salinity.

Novel DNA markers for rapid, accurate, and cost-effective discrimination of the continental origin of Atlantic salmon (Salmo salar L.)

AbstractSalmon from geographically representative rivers in North America and Europe were typed for variation at the microsatellite locus SS1 and the mitochondrial DNA ND-1 restriction site 3971, using PCR amplification and agarose-gel electrophoresis. North American salmon showed near-fixation for SS1 alleles between 129 and 135 bp in length and the N mtDNA restriction type, while European salmon near-fixation for SS1 alleles between 183 and 219 bp and the A/D mtDNA type. Based on the observed variant frequencies, using these two markers in combination is predicted to give correct assignment of &gt;99.5% of salmon to continent-of-origin. As both these continental markers can be screened by agarose-gel electrophoresis, their use offers a more rapid, cheaper, and simpler method for accurate assignment of Atlantic salmon to continent-of-origin than do existing methods. These markers can be applied to the identification of salmon in North Atlantic high-seas fisheries, in aquaculture stocks, and in rivers to determine the continent-of-origin of fish-farm escapes.

Comparative analysis of morphometric characters of juvenile sterlet Acipenser ruthenus L. from natural population and aquaculture

A comparative analysis was performed on sixteen morphometric characters, in three different juvenile sterlet Acipenser ruthenus L. populations. Specimens were collected from a wild population in the Serbian part of the Danube River (n = 46), from aquaculture stocks in the Czech Republic originating from Russia (n = 40), and aquaculture stocks in the Slovak Republic originating from Slovakian part of the Danube River (n = 28). Average values for total length were 29·9 ± 3·9 cm, 29·1 ± 3·7 cm and 27·3 ± 7·7 cm for Serbia, Czech Republic and Slovak Republic, respectively. Populations were compared using t‐test and sequential Bonferroni correction for multiple comparisons was applied in order to determine significant differences between them. Results of analysis showed that all three populations differed in prebarbel length, interocular distance and maximum head width. Although all these characters are head‐related, head length itself was very uniform among all populations. The natural population from the Serbian part of the Danube River differed from the populations reared in aquaculture in seven morphometric characters. The two populations reared in aquaculture consistently showed lower morphological variability than the wild population, even though they had different genetic backgrounds (Russia and Slovakia). Future genetic studies will show if this tendency is caused by a reduction in genetic variability.

Differences in the energetic cost of swimming in turbulent flow between wild, farmed and domesticated juvenile Atlantic salmon Salmo salar

Domestication has been shown to have an effect on morphology and behaviour of Atlantic salmon (Salmo salar). We compared swimming costs of three groups of juvenile Atlantic salmon subject to different levels of domestication: (1) wild fish; (2) first generation farmed fish origination from wild genitors; and (2) seventh generation farmed fish originating from Norwegian aquaculture stocks. We assessed swimming costs under two types of turbulent flow (one mean flow velocity of 23 cm s−1 and two standard deviations of flow velocity of 5 and 8 cm s−1). Respirometry experiments were conducted with fish in a mass range of 5–15 g wet at a water temperature of 15° C. Our results confirm (1) that net swimming costs are affected by different levels of turbulence such that, for a given mean flow velocity, fish spent 1·5‐times more energy as turbulence increased, (2) that domesticated fish differed in their morphology (having deeper bodies and smaller fins) and in their net swimming costs (being up to 30·3% higher than for wild fish) and (3) that swimming cost models developed for farmed fish may be also be applied to wild fish in turbulent environments.

Comparative analysis and characterization of expressed sequence tags in gilthead sea bream ( Sparus aurata) liver and embryos

The gilthead sea bream ( Sparus aurata) is one of the main European aquaculture products and a prospective model species for the Sparidae, which includes several other commercially important species. Future selective breeding of aquaculture stocks will be heavily underpinned by molecular genetic techniques, especially by marker-assisted selection (MAS). Gene marker resources in marine fish species, however, lag behind those of other agricultural animals, and only scanty information exists about the genetic source of phenotypic variation and the identity of quantitative trait loci (QTL). In order to develop molecular resources in gilthead sea bream, complementary DNA libraries were constructed from liver and mixed embryo and larval stages by unidirectional cloning. A long-read expressed sequence tag (EST) database was generated, containing 1394 cDNA clones representing 852 unique cDNA sequence-reads. Tissue-specific patterns of gene expression were determined when grouped using the proposal for characterizing cellular component put forward by the Gene Ontology consortium. Transcripts encoding cytoskeletal proteins were most abundant in the embryonic/larval library, while the most abundant transcripts in the liver library encoded secreted and extracellular proteins. Of both libraries, 505 clones were sequenced in both orientations (5′ and 3′ end sequencing), where 226 clones were determined as full-length sequence reads. Cluster analysis of 3′end-sequenced clones from both libraries revealed that alternative polyadenylation signals were utilized, although no evidence of alternative splicing was found. We report for the first time for gilthead sea bream or any sparid a transcriptional analysis of two tissues and briefly consider the utility of ESTs for characterizing tissue-specific expression profiles.

Behavioral differences among rainbow trout clonal lines.

Salmonid fish show considerable geographical variation in morphology, physiology, and behavior. Understanding the genetic mechanisms underlying this variation could be useful for enhancing aquaculture stocks, identifying unique populations for conservation, and determining the genetic factors underlying natural adaptation and domestication. As a first step toward the genetic dissection of salmonid behavioral diversity, we examined variation in behavior patterns among four clonal lines of rainbow trout ( Oncorhynchus mykiss ) derived from geographically diverse source populations with different domestication histories. Clonal lines were crossed with two outbred (i.e., not homozygous) females, and the resulting progenies were reared and tested under identical conditions. Clonal line had significant genetic effects on mean swim level, hiding, foraging, startle response, and aggression level. Multiple comparisons suggest that domestication history of the source populations had a strong influence on these behavior patterns. Progeny of two clonal lines derived from populations reared in captivity for over 100 years exhibited reductions in predator avoidance behavior patterns and increases in aggression compared to progeny of two clonal lines from more recently domesticated populations. These results will facilitate future investigation of the genetic factors underlying population variation in these behavior patterns influenced by domestication.

Microsatellite markers from a commercially important South‐east Asian cyprinid, the silver barb (Barbodes gonionotus Bleeker)

Abstract Barbodes gonionotus (Puntius gonionotus/javanicus, Bleeker) is a cyprinid fish, endemic to South‐east Asia and is of great importance in both wild fisheries and in aquaculture in the region. It is a common to dominant species in the middle and lower stretches of medium and large rivers. Five highly polymorphic microsatellite loci are described (HO = 0.7–0.9, number of alleles per locus = 10–37), which will be of use both in population genetic studies and for the assessment of true effective breeding population sizes in aquaculture stocks.

Detection and enumeration of Heterosigma akashiwo and Fibrocapsa japonica (Raphidophyceae) using rRNA-targeted oligonucleotide probes

Effective management of fish aquaculture stocks to mitigate the impact of fish-killing phytoplankton requires intensive spatial and temporal sampling to identify and quantify potentially harmful species. so that adequate warning of a harmful algal bloom may be given. Here, we report the development and application of large-subunit rRNA (LSU rRNA)–targeted oligonucleotide probes as tools to aid in the detection and enumeration of the fragile, fish-killing species Heterosigma akashiwo and Fibrocapsa japonica (Raphidophyceae). Oligonucleotides directed toward H. akashiwo and F. japonica were evaluated using fluorescent in situ hybridization (FISH). Probes that labelled those species well in the FISH format were then incorporated into a sandwich hybridization assay (SHA). SHAs were successfully developed for both H. akashiwo and F. japonica. Batch culture experiments showed that the response of the SHA using a constant number of H. akashiwo and F. japonica cells harvested in exponential vs stationary phase of growth varied by a factor of approximately two. Preliminary field trials indicate that the SHA appears to be a faster, more cost-effective, and easier-to-use method for detecting and estimating the abundance of H. akashiwo and F. japonica than is FISH or conventional light microscopy. This is particularly true when large numbers of samples need to be processed routinely and rapidly, and when the organism in question is fragile and subject to lysis or morphological distortion if chemically preserved prior to microscopical observation.

Endocrine sex control strategies for the feminization of teleost fish

In many species of cultured finfish, females exhibit higher growth rates than males and attain larger sizes. In addition, in some species, males mature before reaching marketable size. Together, this results in a larger dispersion of sizes and an overall reduction in production. Therefore, there is great interest from the private sector to produce all-female stocks. This review concentrates on the use of oestrogens for sex control, discussing the advantages of producing monosex female stocks for finfish aquaculture, and pointing out those cases in which hormonal sex reversal technology is worth applying. The biological basis on which hormonal sex manipulation rests, the process of sex differentiation—which, compared to that of other vertebrates, is quite labile in teleost fish—is described in order to understand the effects of treatments. Sex control is typically achieved by exposing sexually undifferentiated fish to exogenous steroids in order to direct the process of sex differentiation towards the desired sex. These treatments finish months or years before marketing and steroid residues disappear in less than a month after the end of treatment. The currently available methods to produce monosex female stocks, the direct and the indirect methods, are explained, comparing their respective advantages and disadvantages. Feminizing treatments are also used to produce all-male stocks in some species. Thus, this review concentrates on the use of oestrogens for sex control, either in the direct method of feminization or in the indirect method of masculinization. So far, oestrogens have been applied to at least 56 different species, using 12 different oestrogenic substances (three natural and nine synthetic). Special attention is given to the method of administration, including immersion and dietary treatment, and to the variables of the hormonal treatment itself: steroids used, dose, timing and duration of treatments. The importance of correct treatment timing in relation to the degree of gonadal development is emphasized and the outcome of the treatment evaluated in terms of survival, gonadal morphology and sex ratios, growth performance and deformities. Next, the current methods to produce all-female or essentially all-female stocks are presented for 35 different species, including eels, salmonids, cyprinids, poecilids, cichlids, gouramies and flatfishes. A section on regulatory issues discusses the advantages of using the indirect method of feminization, when feasible, and emphasizes the convenience of using the natural oestrogen estradiol-17β rather than synthetic oestrogens. A guideline for the development of monosex technology in new species is presented. The overall goal is to emphasize the use of the indirect method, which means that fish that reach the marketplace have never been exposed to steroids. If this method is not feasible, as it happens in many species, an alternative is the use of the direct method, applied in an optimized protocol, to achieve maximum treatment efficiency with minimum exposure to steroids.

Preventing the introduction of zebra mussels during aquaculture and fish stocking activities

Preventing the introduction of zebra mussels during aquaculture and fish stocking activities

Parentage and relatedness determination in farmed Atlantic salmon ( Salmo salar) using microsatellite markers

This study demonstrates how both parentage and relatedness can be determined in a mixed family aquaculture (Atlantic salmon) stock in the absence of physical tags and/or pedigree information. Under a number of different scenarios, both real and simulated, we could use microsatellite markers to assign parentage to offspring with varying degrees of accuracy. The precision of assignment to one correct parental pair depended not only on the number and variability of the microsatellite markers, but also on the number of potential pairings from which to choose, i.e., the more families in the breeding program the more microsatellites required to discriminate between them. Using eight highly variable markers resulted in an assignment of an individual to the correct parental pair of greater than 95% even when the number of possible parent pairs is >12,000. These same microsatellite loci were capable of discriminating between related and unrelated individuals in a situation where no pedigree information is known. Based on these results we conclude that the use of a number of microsatellite markers represents a realistic and cost-effective alternative to physical tagging in a family selection program.

Genetic improvement of marronCherax tenuimanusSmith and yabbiesCheraxspp. in Western Australia

Marron and yabbies are farmed commercially in Western Australia and are native and introduced species respectively. Genetic improvement of farmed stock for aquaculture can be achieved by choosing particular strains, by selective breeding or by producing hybrids of different strains. Studies into the taxonomy and growth of both marron and yabbies have shown variation between geographically isolated populations. This variation may offer potential for selecting strains that demonstrate desirable traits for aquaculture, such as improved growth rates. In addition to selection of wild strains that demonstrate desirable traits for aquaculture, further advances in production may be achieved by selection of characteristics in captive stock that are heritable. In marron, moderate proportions of the phenotypic variation in growth rate, tail and chelae size have been shown to be heritable (h2 = 0.3–0.6). Recent research into yabby genetics involved assessing growth and reproductive characteristics of geographically isolated populations of yabbies inhabiting a range of ecotypes throughout Australia. Growth rates and size at sexual maturity varied among populations. However, there was no significant difference in the sex ratio between these geographically isolated groups. The main focus of the yabby genetics research has been to develop a method to prevent or reduce reproduction of yabbies. Uncontrolled reproduction in this species results in high densities and smaller animals because growth is density dependent. Preventing reproduction and thereby controlling densities in yabby ponds or dams can be achieved by stocking monosex populations. The stocking of monosex populations results in an estimated 70% increase in gross income. Hybidization of yabby populations was investigated as a method of controlling reproduction. Sterile hybrids were produced by crossing yabbies from geographically isolated populations. These experiments have also revealed a hybrid cross that consistently produces only male progeny. If this all-male hybrid strain performs as well as all-male monosex pond stock, achieved by manual sexing, the production of large, and therefore higher value, yabbies will be increased in the commercial aquaculture industry.

Out-of-Season Spawning of SunfishLepomisspp. in the Laboratory

Abstract Although propagation of sunfish Lepomis spp. has historically been done in earthen ponds, there is interest in producing these fish in the laboratory. The objective of this study was to spawn sunfish out of season by means of temperature and photoperiod manipulation. By manipulating temperature and photoperiod, we were able to spawn bluegills L. machrochirus over a 6-month period (December 1994–May 1995): 41 spawns. averaging 20.000 larvae each, were obtained from 24 females. By manipulation of photoperiod alone, we were able to spawn fish during a 3-month period (October–December 1995): 21 bluegill spawns of about 20.000 larvae each and 7 spawns of hybrid sunfish (female green sunfish L. cyanellus × male bluegills) of about 10,000 larvae each were obtained from 12 female bluegills and 24 female green sunfish, respectively. This protocol allows for production of sunfish larvae, regardless of season and without the use of hormones, for both laboratory studies and aquaculture stocking.

Epizootiology, distribution and the impact on international trade of two penaeid shrimp viruses in the Americas.

Marine penaeid shrimp are effected by approximately twenty viruses, the majority of which were discovered as a result of their negative effects on aquaculture. In the Americas, infectious hypodermal and haematopoietic necrosis (IHHN) virus and Taura syndrome (TS) virus have had a significant negative impact on aquaculture industries and, in one instance, on a commercial fishery. Both viruses have become widely distributed as a consequence of the movement of host stocks for aquaculture. IHHN virus (IHHNV) causes catastrophic losses in cultured and wild Penaeus stylirostris. In marked contrast, P. vannamei is relatively resistant to IHHN but infection results, nonetheless, in poor culture performance. TS virus (TSV) is the 'mirror image' of IHHNV in its effect on P. stylirostris and P. vannamei. TSV causes catastrophic losses in P. vannamei, whereas P. stylirostris is highly resistant to TS. In the less than three years since the discovery of TSV in Ecuador in 1992, the virus has spread rapidly and caused massive production losses in most shrimp-growing countries in the Americas.