Tasmanian Strain Research Articles

Characterization of smoltification in the Tasmanian strain of Atlantic salmon (Salmo salar) in recirculation and flow-through systems

This study examined morphological, physiological and molecular indicators of smoltification in Atlantic salmon (Salmo salar) juveniles in a flow-through (FT) and recirculating aquaculture system (RAS). Fish were exposed to 24-h light to initiate smoltification, for 5 (FT) and 7 (RAS) weeks prior to transfer from freshwater (FW) to seawater (SW) and were sampled weekly preceding and following SW transfer. Mass, length, condition factor, plasma chloride, gill Na+/K+-ATPase (NKA) activity and expression of salinity-specific isoforms of NKA mRNA transcripts were monitored. Fish raised in FT had significantly lower specific growth rate (SGR) in FW than in SW and showed a significant 5-6-fold increase in gill NKA activity, and high plasma chloride levels after transfer to SW. These fish also exhibited no significant reduction in relative mRNA expression of NKAα1a in FW but a sharp significant downregulation post-SW transfer. No significant increase in NKAα1b was seen until week 8 (3 weeks post-SW transfer). The log2 ratio of NKAα1b to NKAα1a showed a significant 8-fold increase throughout the study. Fish raised in the RAS had significantly higher SGR in FW than SW, and showed significantly higher plasma chloride in saltwater challenged fish compared to the freshwater control at all weeks during the FW phase. Fish had a 50% higher initial NKA activity than in FT, increasing significantly 2-3-fold and showed an immediate down-regulation of NKAα1a after exposure to 24-hr light in FW, and a further reduction after SW-transfer. There was no significant increase in NKAα1b in the RAS-raised fish for the duration of the study, and there was a significant 8-fold increase in log2 ratio of NKAα1b to NKAα1a. Whilst there were too many varying factors to statistically compare hatchery type in this study, it's evident that there are potentially system-related effects worthy of future investigation.

Preliminary characterization of Tasmanian aquareovirus (TSRV) isolates.

In an attempt to determine whether or not genetic variants of the Tasmanian strain of Atlantic salmon aquareovirus (TSRV) exist, 14 isolates of TSRV, originating from various locations in Tasmania, covering a 20-year period (1990-2010), obtained from various host species and tissues, and isolated on different cell lines, were selected for this study. Two categories, termed "typical" and "atypical", of variants of TSRV were identified based on preliminary genotypic and phenotypic characterization carried out on these 14 different isolates. In addition, electron microscopic examination indicated the existence of at least three variants based on viral particle size. Finally, this study demonstrated the existence of at least one new variant of TSRV isolates, other than the more commonly isolated typical TSRV isolates, in farmed Tasmanian Atlantic salmon.

A reinvestigation of saxitoxin production and sxtA in the ‘non-toxic’Alexandrium tamarense Group V clade

The three Alexandrium species A. tamarense, A. fundyense and A. catenella include strains that can be potent producers of the neurotoxin saxitoxin (STX) and its analogues, the causative agents of paralytic shellfish poisoning (PSP). These three species are morphologically highly similar, differing from each other only in the possession of a ventral pore, or in the ability to form chains. The appropriateness of these morphological characters for species delimitation has been extensively debated. A distinctive clade of this species complex, Group V, Tasmanian clade, is found in southern Australia, and occasionally occurs in bloom proportions. This clade has been considered non-toxic, and no PSP toxins have been found in shellfish following blooms of this species. In the present study, we report on a Tasmanian strain of A. tamarense, Group V that produces STX and possesses the gene, sxtA that is putatively involved in STX production. The toxin profile was determined and is unusual, including a high proportion of GTX5 and a small amount of STX, and differs from that of co-occurring A. catenella (Group IV). A putative bloom of A. tamarense that occurred in October 2010, and the subsequent finding of STX in Sydney Rock Oysters (Saccostrea glomerata), may suggest that some naturally occurring strains of this species could produce STX.

Physical characterisation of Tenacibaculum maritimum for vaccine development

Tenacibaculum maritimum is a well known fish pathogen worldwide, affecting many fish species including Atlantic salmon in Tasmania, Australia. The aim of this study was to characterise and understand the similarities and differences between the isolates in order to select isolates for later pathogenicity and vaccination trials. Several physical characterisation tests were carried out: whole cell protein profiles, lipopolysaccharide profiles (LPS), extracellular product profiles (ECP), indirect immunofluorescent antibody test (IFAT) and hydrophobicity. The Tasmanian strains of T. maritimum appear relatively homogeneous physically, but antigenically different. All isolates were hydrophobic and produce a variety of ECP profiles. There were two isolates that stand out in all assays (89/4747 and 01/0356-7) and showed great variation from the other isolates. All isolates have been confirmed as T. maritimum. Based on the tests carried out three isolates were chosen for in vivo trials: 89/4747, 89/4762, 00/3280. This is the first study to characterise T. maritimum isolates from Tasmanian waters. The opportunity to develop vaccines for the Tasmanian salmonid aquaculture industry is enhanced by a greater understanding of the physical characteristics of pathogens.

Reproductive compatibility among four global populations of the toxic dinoflagellate Gymnodinium catenatum (Dinophyceae)

Reproductive compatibility was examined among 21 strains of Gymnodinium catenatum derived from four different populations from across the globe: Tasmania, Australia (15 strains), Japan (2 strains), Spain (2 strains) and Portugal (2 strains). Pairwise crossing of strains demonstrated extensive intrapopulation compatibility (to resting cyst formation) among all four populations. The observations were most consistent with a heterothallic, multiple-group mating system, requiring more than two groups to explain the pairwise crossing data. Despite the ability of strains from different populations to produce resting cysts, the viability of progeny was highly variable among interpopulation crosses. Cysts from all crosses showed a high germination percentage (93–100%) and released a swimming planomeiocyte. Crosses between different Tasmanian strains, and those between Spanish and Japanese strains, showed high post-meiotic viability (65% and 80%, respectively). However, progeny from Tasmanian–Spanish and Tasmanian–Japanese crosses showed very low post-meiotic viability (5–10%), indicating a higher level of somatic incompatibility between these populations. Significant differences in sexual life-history (e.g. rate of gamete formation and cyst dormancy) were also noted between interpopulation crosses, suggesting genetically determined strain- and population-level differences. The crossing data indicate a high level of mating diversity within the Australian population and show that the Japanese and Spanish populations are more closely related to each other than to Australian populations; this is supported by molecular studies. Implications for the proposed global dispersal of G. catenatum and the use of interbreeding to examine population relationships are discussed. New measures are proposed for examining strain (RCs) and population (RCp) levels of reproductive compatibility, respectively, which are calculated as the product of proportion of successful matings (termed the compatibility index) and the number of cysts produced (average vigour) in successful crosses.

Intraspecific variation in the selenium requirement of different geographic strains of the toxic dinoflagellate Gymnodinium catenatum

The requirement for selenium (IV) was assessed in five strains of the toxic dinoflagellate Gymnodinium catenatum Graham, representing three populations from Tasmania (Australia), as well as one each from Japan and Spain. Strains were grown in nutrient-enriched sea water medium with 10–9 M selenium added as selenite (H2SeO3), or with no added selenium, and monitored for growth and cell yield. Strains exhibited different selenium (Se) requirements, as evidenced by (i) a decrease in exponential growth rate (10–20%) and cell yield (up to 80%) (Japanese strain); (ii) a decrease in cell yield only (Tasmania Derwent Estuary 1987, Tasmania Huon Estuary and Spanish strains); and (iii) no decrease in growth or cell yield (Tasmania Derwent Estuary 1993 strain). Variation in the response to Se deficiency was greatest between the two strains isolated from the Derwent Estuary, Tasmania, in different years (1987 and 1993) and less between Tasmanian strains from different localities (Huon and Derwent Estuaries are 50 km apart) or between Tasmanian and Japanese or Spanish strains. Strain variability in micro-nutrient responses such as described here may provide a partial explanation for different bloom patterns exhibited by the same dinoflagellate taxon under apparently similar environmental conditions.

GENETIC VARIATION AMONG STRAINS OF THE TOXIC DINOFLAGELLATE GYMNODINIUM CATENATUM (DINOPHYCEAE)

The toxic dinoflagellate Gymnodinium catenatum Graham has formed recurrent toxic blooms in southeastern Tasmanian waters since its discovery in the area in 1986. Current evidence suggests that this species might have been introduced to Tasmania prior to 1973, possibly in cargo vessel ballast water carried from populations in Japan or Spain, followed by recent dispersal to mainland Australia. To examine this hypothesis, cultured strains from G. catenatum populations in Australia, Spain, Portugal, and Japan were examined using allozymes and randomly amplified polymorphic DNA (RAPD). Allozyme screening detected very limited polymorphism and was not useful for population comparisons; however, Australian, Spanish, Portuguese, and Japanese strains showed considerable RAPD diversity, and all strains examined represented unique genotypes. Multidimensional scaling analysis (MDS) of RAPD genetic distances between strains showed clear separation of strains into three nonoverlapping regional clusters: Australia, Japan, and Spain/Portugal. Analysis of genetic distances between strains from the three regional populations indicated that Australian strains were almost equally related to both the Spanish/Portuguese population and the Japanese population. Analysis of molecular variance (AMOVA) found that genetic variation was partitioned mainly within populations (87%) compared to the variation between the regions (8%) and between populations within regions (5%). The potential source population for Tasmania’s introduced G. catenatum remains equivocal; however, strains from the recently discovered mainland Australian population (Port Lincoln, South Australia, 1996) clustered with Tasmanian strains, supporting the notion of a secondary relocation of Tasmanian G. catenatum populations to the mainland via a shipping vector. Geographic and temporal clustering of strains was evident among the Tasmanian strains, indicating that genetic exchange between neighboring estuaries is limited and that Tasmanian G. catenatum blooms are composed of localized, estuary‐bound subpopulations.

Electrophoretic analysis of genetic variation in Echinococcus granulosus from domestic hosts in Australia

Allozyme variation was examined in 26 isolates of the Australian mainland sheep strain and 13 isolates of the Tasmanian sheep strain of Echinococcus granulosus. One isolate of the British horse strain was examined for comparative purposes. Fifteen enzymes, encoded by 20 presumptive loci, were analysed. Differences in expression of enzymes were found between adult worms, protoscoleces, and fluid and germinal layer from hydatid cysts. Major differences were found at nine enzyme loci between the isolate of the British horse strain and isolates of the Australian mainland and Tasmanian sheep strains. The Australian strains differed in allelic frequencies at two loci, but no diagnostic alleles were found. Allozyme variation was detected within both the Australian strains. The proportion of polymorphic loci (P) was estimated at 0.15 for both strains, while the total gene diversity ( H) was 0.02 for the mainland strain and 0.06 for the Tasmanian strain. The pattern of genetic variation over geographic areas and the absence of multi-locus associations suggested that cross-fertilization was occurring in both strains. However, deficiencies of heterozygotes at some loci provided evidence for self-fertilization. These data are discussed in relation to proposed models of strain variation in E. granulosus.