1,721,029 research outputs found
Inland saline aquaculture: overcoming biological and technical constraints towards the development of an industry
Get PDFSecondary salinisation has rendered over 100 million hectares of land throughout the world, and over 5 million hectares in Australia, unsuitable for conventional agriculture. The utilization of salinised land and its associated water resources for mariculture is an adaptive approach to this environmental problem with many potential economic, social and environmental benefits. Despite this, inland mariculture is yet to develop into an industrial-scale, rural enterprise. The main aim of this study was therefore to identify and address some of the technical and biological limitations to the development of an inland finfish mariculture industry.
Three technical aspects essential to the development of an Australian inland mariculture industry were reviewed; potential sources of water, the species suitable for culture in these water sources and the production systems available to produce them. Based on factors such as their quantity, quality and proximity to infrastructure, the most appropriate water sources were deemed to be groundwater obtained from interception schemes and waters from operational or disused mines. In terms of species, mulloway (Argyrosomus japonicus) were identified as having many positive attributes for inland mariculture, including being temperate and therefore having the ability to be cultured year-round in the regions where the majority of secondary salinity occurs. Seasonal production of barramundi (Lates calcarifer) in ponds in the temperate climatic zones has potential, but may be more appropriate for those salinised water sources located in the warmer parts of the country. Rainbow trout (Oncorhynchus mykiss) were also identified as having excellent potential provided water temperature can be maintained below the upper lethal limit and also have potential for seasonal production, perhaps in rotation with barramundi. In terms of production systems, pond-based culture methods were found to have many advantages specific to inland mariculture. Static ponds enable culture in areas with low groundwater yield and more cost-effective potassium supplementation compared with flow through ponds. Static ponds also largely overcome the issues associated with the disposal of salt-laden and eutrophied waste water; however yields from static ponds are typically low and limited by the nutrient input into the pond.
In response to the yield constraints of static pond culture, a new culture technology known as the Semi-Intensive Floating Tank System (SIFTS) was designed, patented and constructed in collaboration with the aquaculture industry and tested in a static inland saline pond in the wheatbelt of Western Australia. This technology was designed to reduce nutrient input into ponds by the collection of settleable wastes and to provide large volumes of well-oxygenated water to the target species, to ameliorate the loss of fish from low dissolved oxygen during strong microalgal blooms. The three species identified above has having excellent potential for inland mariculture (mulloway, rainbow trout, and barramundi) were grown in SIFTS held within a 0.13 ha static, inland saline water body (salinity 14 ppt) over a period of 292 days, yielding the equivalent of 26 tonnes/ha/year (total for all three species). Rainbow trout were grown with an FCR of 0.97 from 83 to 697 grams over 111 days (SGR, 1.91%/day) between June and September, when average daily water temperatures ranged from 12.3 degrees C to 18.2 degrees C. Over the same time period, mulloway grew only from 100 to 116 grams, however, once temperatures increased to approximately 21 degrees C in October, feed intake increased and mulloway grew to an average size of 384 grams over 174 days with an SGR and FCR of 0.68 %/day and 1.39, respectively. Barramundi stocked in November with an average weight of 40 grams increased to 435 grams in 138 days (SGR 1.73%/day) with an FCR of 0.90. The SIFTS significantly reduced nutrient input into the pond by removing settleable wastes as a thick sludge with a dry matter content of 5 to 10%. The total quantity of dry waste removed over the 292 day culture period was 527 kg (5 tonnes/ha/yr), which was calculated to contain 15 kg of nitrogen (144 kg/ha/yr) and 16 kg of phosphorus (153 kg/ha/yr). The release of soluble nutrients into the pond resulted in blooms of macro- and micro- algae which caused large and potentially lethal diurnal fluctuations in dissolved oxygen within the pond, however, comparatively stable levels of dissolved oxygen were maintained within each SIFT through the use of air lift pumps.
It is well documented that saline groundwater is deficient in potassium which, depending on the extent of the deficiency, can negatively impact on the performance of marine species, including fish. The physiological effects of this deficiency on fish, however, have not been previously described. As such, I conducted a bioassay investigating the physiological effects of a hypersaline (45 ppt) groundwater source containing 25% of the potassium found in equivalent salinity seawater (i.e. 25% K-equivalence) on juvenile barramundi. Histopathological examination of moribund fish revealed severe degeneration and necrosis of skeletal muscles, marked hyperplasia of branchial chloride cells and renal tubular necrosis. Clinical chemistry findings included hypernatraemia and hyperchloridaemia of the blood plasma and lowered muscle potassium levels. It was concluded from this study that the principal cause of death of these barramundi was skeletal myopathy induced by unsustainable buffering of blood plasma potassium levels from the muscle. Although such hypokalaemic muscle myopathies have been previously described in mammals and birds, this was the first description of such myopathies in fish.
It was hypothesized from the results described above that the physiological effects of potassium deficiency are dependent on salinity and that they would be ameliorated by potassium supplementation. These predictions were tested in a subsequent study which measured the effects of potassium supplementation between 25% and 100% K-equivalence on the growth, survival and physiological response of juvenile barramundi at hyperosmotic (45 ppt), near-isosmotic (15 ppt) and hyposmotic (5 ppt) salinities. Unlike those juvenile barramundi reared at 45 ppt and 25% K-equivalence in the previous study, those reared in 50% K-equivalence water at 45 ppt in this study survived for four weeks but lost weight; whereas at 75% and 100% K-equivalences fish both survived and gained weight. Homeostasis of blood plasma potassium was maintained by buffering from skeletal muscle. Fish reared in 50% K-equivalence at this salinity exhibited muscle dehydration, increased branchial, renal and intestinal (Na+-K+)ATPase activity and elevated blood sodium and chloride, suggesting they were experiencing osmotic stress. At 15 ppt, equal rates of growth were obtained between all K-equivalence treatments. Buffering of plasma potassium by muscle also occurred but appeared to be in a state of equilibrium. Barramundi at 5 ppt displayed equal growth among treatments. At this salinity, buffering of plasma potassium from muscle did not occur and at 25% K-equivalence blood potassium was significantly lower than at all other K-equivalence treatments but with no apparent effect on growth, survival or (Na+-K+)ATPase activities. These data confirmed the hypothesis that proportionally more potassium is required at hyperosmotic salinities compared to iso- and hypo- osmotic salinities and also demonstrated that barramundi have a lower requirement for potassium than other marine and estuarine species being investigated for culture in inland saline groundwater.
In addition to ongrowing fish, saline groundwater has potential for hatchery production. Specific advantages include the vertical integration of inland saline farms and the production of disease-free certified stock through isolation from the pathogens and parasites found naturally in coastal water. To determine the potential of utilizing inland saline groundwater for hatchery production, barramundi larvae were reared from 2 to 25 days post hatch in 14 ppt saline groundwater with either no potassium supplementation (38% K-equivalence) or full potassium supplementation (100% K-equivalence). Growth, survival and swimbladder inflation of these larvae were compared against those grown in control treatments of seawater (32 ppt) and seawater diluted to 14 ppt. Those reared in saline groundwater with 38% K-equivalence exhibited complete mortality within 2 days, whilst those held in groundwater with full supplementation survived at a rate equal to both control treatments (pooled average 51.1 plus-minus 0.5%). At 25 days post hatch, there was no significant difference in larval length or dry weight between those grown in the 14 ppt control treatment and those in the saline groundwater with full potassium supplementation. There were no significant differences in swim bladder inflation between any of the surviving treatments (average 93.3 plus-minus 2.5%). This is the first description of rearing barramundi larvae both in low salinity seawater and in saline groundwater, and demonstrates that the requirement for potassium by larval barramundi is higher than for juveniles of the same species.
In addition to a deficiency in potassium, saline groundwater in Western Australia often contains an elevated concentration of manganese relative to seawater as a result of anaerobic reduction of manganese oxides or the pedogenic weathering of manganese-bearing rock. The effects of elevated manganese on marine or estuarine fish have not been described and a study was therefore conducted to determine if manganese, at a concentration typical of that found in saline groundwater, has any impact on fish. The effects of 5 mg/L of dissolved manganese on juvenile mulloway at salinities of 5, 15 and 45 ppt were determined by comparing the survival, growth and blood and organ chemistry with those grown at the same salinities without manganese addition. Survival of mulloway at 45 ppt in the presence of 5 mg/L of manganese (73 plus-minus 13%) was significantly lower than all other treatments, which achieved 100% survival. Those fish grown in seawater without manganese exhibited rapid growth, which was not affected by salinity (SGR = 4.05 plus-minus 0.29%/day). Those fish grown at 5 ppt and 45 ppt in the presence of manganese lost weight over the two week trial (SGR 0.17 plus-minus 0.42 and -0.44 plus-minus 0.83%/day, respectively), whilst those at 15 ppt gained only a small amount of weight (SGR 1.70 plus-minus 0.20%/day). Growth was therefore affected by manganese and by the interaction of manganese and salinity, but not salinity alone. Manganese was found to accumulate in the gills, liver and muscle of the fish. No gill epithelial damage or other significant histological findings were found, however, significant differences in blood chemistry were observed. Blood sodium and chloride of manganese exposed fish were significantly elevated in hyperosmotic salinity (45 ppt) and depressed at hyposmotic salinity (5 ppt) compared with unexposed fish; consistent with manganese causing apoptosis or necrosis to chloride cells. Blood potassium was significantly elevated and liver potassium significantly reduced at all salinities in the presence of manganese. These findings are consistent with manganese interfering with carbohydrate metabolism. There were no differences in blood sodium, chloride or potassium across salinities in fish not exposed to manganese, demonstrating mulloway are capable of efficient osmoregulation across this salinity range
Phenotypic characteristics of differing genetic groups of Giardia duodenalis and their implication for species identification
No full textAlthough it has long been acknowledged that the Giardia duodenalis group of isolates is very diverse and heterogeneous, we still lack comprehensive studies which compare groups of isolates from a selected geographical area on the basis of both genotypic and phenotypic characteristics. In the present study, twelve isolates (eleven from Western Australia, one from the USA) were selected based on the genetic diversity they exhibited upon isoenzyme analysis. Prior to any characterisation, the isolates were all cloned and a cloned cell line was subsequently selected at random for further characterisation. RAPD-PCR verified their distinctive groupings and showed that both parent and clone retained their basic classification and that none of the cloned cell lines had become cross contaminated despite more than three years of continuous in vitro cultivation.
Isolates were first verified as being members of the duodenalis morphological group on the basis of Filice’s (1952) system which used the shape of the median body, to order isolates as belonging to one of three morphological groups. The usefulness of Filice’s (1952) system in further subdividing the duodenalis morphological group was also tested. Although his system holds true in differentiating between the three morphological groups of G. duodenalis, G. agilis and G. muris, it failed to resolve the complex of isolates constituting G. duodenalis any further.
Morphological variation at the ultrastructural level has recently been reintroduced as a taxonomic tool in Giardia research and caudal flagellar and total trophozoite length were used to characterise the isolates chosen for the present study. Intraspecific variation within the G. duodenalis group was found to extend into the morphological characters tested here. Trophozoite length varied from 13.5|im (PIcl0) to 18.4|im (BAH 12cl4) and caudal flagellar length ranged from 4.6|im (PlclO) to 16.1pm (BAH 33c7). UPGMA analysis grouped isolates similarly to previously obtained isoenzyme electrophoretic data.
Prior analysis of growth dynamics in isolates of G. duodenalis had shown significant differences between two genetically distinct isolates (Binz etal, 1992) and these results were confirmed and extended during the present study. Mean generation times obtained for the twelve isolates studied varied from 6.6 hours (PlclO) to 24.5 hours (BAH 33c7). Scheffe’s post hoc test identified four distinct groups among the isolates examined. These results have implications not only for the epidemiology of infection but also for the suggested artificial laboratory induced selection of some genotypes over others by the currently used in vitro culture system.
At the commencement of this study only tentative data were available on the characteristics of the dual nuclei of Giardia trophozoites, and the DNA content of individual nuclei. Again, significant intraspecific variation was demonstrated among the isolates studied and DNA content was found to vary from 0.060pg per trophozoite (BAH 33c7) to 0.165pg per trophozoite (BAH 39c9), representing a 2.75 fold difference. Scheffe’s post hoc test identified six distinct groups. Although the data in context with previously published information permitted speculation about ploidy levels in G. duodenalis, the question of genome size could not be resolved.
The extensive heterogeneity demonstrated across the characters examined in the present study reflected that observed in most previous studies on G. duodenalis. Isoenzyme electrophoretic data in particular led Meloni etal. (1988a) and Andrews et al. (1989) to speculate about the presence of a complex of cryptic species within the duodenalis morphological group. However, no study to date has addressed the problem of species identification within this heterogeneous assemblage of isolates, nor has any attempted to collect data to solve the question of how many species there are.
The identification of species is a multi-step process and in the first instance requires the selection of an appropriate species concept and a case for the adoption of the evolutionary species concept was made. The delimitation of species within this framework requires organisms first to be grouped phylogenetically, preferably using DNA sequence or isoenzyme data, and these groups must then be ranked into the same or different species, measuring genetic differences in biologically meaningful characters. Taking into consideration all the data generated during the present study, the value of these genotypic and phenotypic characters in the identification of species within the G. duodenalis morphological group was examined. Growth dynamics and DNA content were found to be more useful in distinguishing groups of isolates than both trophozoite and caudal flagellar length. Although no species could be identified using the current set of characters, the study did demonstrate that some characters were more appropriate for delimiting species than others. Should the evolutionary species concept be adopted for the delimitation of species within the G. duodenalis morphological group, then there is a definite need to design studies in such a way that the data can be applied to the problem of species identification within the group, and biological characters of medical importance may provide the kind of data needed to rank groups of genetically differentiated isolates into species
The ecological impacts of secondary salinisation on halo-tolerant fishes in south-western Australia
Get PDFSecondary salinisation is a anthropogenic process that is increasingly disrupting the health of freshwater ecosystems in Australia. In a continent where supplying future water resources for a growing population is challenging, secondary salinisation not only makes freshwater ecosystems unsuitable for human use, but may also have substantial negative impacts on aquatic biota. A large body of research in Australia and overseas has found that increasing salinisation is associated with a loss of biodiversity in freshwater ecosystems. However, most of these studies are based on salinity tolerance tests conducted in the laboratory, which determine physiological effects of salinity without considering the synergistic impacts of other existing stressors in the system.
The south of Western Australia is a biodiversity hot spot, but has been severely impacted on by secondary salinisation. Only 44% of flow in the 30 largest rivers in the Southwest Coast Drainage Division is fresh and more than half of the rivers in the region can be classified as brackish or saline. Among these rivers, the Blackwood River is the second largest in the region, has the highest discharge and contains all eight native riverine fish species which are endemic to the south-west. More than 85% of the river catchment has been cleared and salinity has an annual upward trend throughout the upper catchment and in the main channel of the lower catchment, while lower catchment tributaries remain fresh. In this study, I have used a combination of field and laboratory studies to investigate the impacts of increasing salinity on the biological performance of native and exotic freshwater fishes in different parts of the Blackwood River.
Eleven species of fish were captured in the Blackwood River during the study; Galaxias occidentalis, Gambusia holbrooki, Leptatherina wallacei, Pseudogobius olorum, Edelia vittata, Tandanus bostocki, Nannatherina balstoni, Bostockia porosa, Afurcagobius suppositus, Galaxiella munda and Oncorhynchus mykiss. The greatest diversity of fish species (G. occidentalis, G. holbrooki, L. wallacei, P. olorum, E. vittata, T. bostocki, N. balstoni, B. porosa and A. suppositus) was found in the main channel of the lower catchment, where salinity typically varies between 2 and 5 ppt. Eight species (B. porosa, E. vittata, G. occidentalis, N. balstoni, T. bostocki, A. suppositus, G. munda and O. mykiss) were found in freshwater tributaries of the lower catchment, where salinity is always less than 0.5 ppt. In the upper catchment, where salinity varied from 7 ppt to over 31 ppt, only four species of fish were captured; the native riverine species G. occidentalis, the introduced G. holbrooki and the euryhaline species L. wallacei and P. olorum.
For the four species of fish that were distributed throughout the Blackwood River (G. occidentalis, G. holbrooki, L. wallacei and P. olorum), I investigated the size, morphology, life-cycle, diet and rate of parasitism between populations in the upper and lower catchment. All four fish species have relatively short life spans and this was more evident in the case of G. holbrooki and P. olorum in which 100% (n = 558) and 98% (n = 163), respectively, were classified as 0+. Forty-five percent of L. wallacei (n=788) and 41% of G. occidentalis (n=942) were classified as 0+. Significant numbers of G. occidentalis (46%) and L. wallacei (43%) were found in their second year of life, while this number was only 2% for P. olorum. No L. wallacei (n = 776) older than three years were captured in this study, while 1% (n = 937) of G. occidentalis were recorded as four years old.
Spawning of L. wallacei in the upper catchment peaked by mid spring, while fish in the lower catchment delayed spawning until early summer. There were no significant differences between spawning time of G. occidentalis and P. olorum populations in the upper and lower catchments of the Blackwood River, although biannual spawning of P. olorum was only recorded in upper catchment sites. The breeding season of G. holbrooki in both the upper and lower catchments of the Blackwood River lasted for a period of at least six months (from October to beyond March).
Dietary analyses of all four fish species from the upper and lower catchments of the Blackwood River revealed their opportunistic feeding behaviour. Overall, the highest diversity of invertebrate fauna was recorded in the diet of L. wallacei, while the lowest diversity was recorded in P. olorum. Crustaceans including Amphipoda, Copepoda, Cladocera and Ostracoda, made up a greater proportion of the diet of all four fish species in the salt affected upper catchment than in the lower catchment. There were significant differences between the dietary compositions of all fish species in both upper and lower catchments. The eggs or larvae of native fishes were not commonly found in the diet of G. holbrooki, although dietary analysis showed that this species is clearly in competition with native fish fauna.
Over all, five species of macroparasites, including nematodes, trematodes and cestodes, were found in association with the four fish species studied. The highest prevalence of parasite infections were recorded in the native species G. occidentalis (5.9%), P. olorum (5.7%) and L. wallacei (2.8%) with the lowest prevalence in the introduced G. holbrooki (0.2%), despite G. holbrooki making up approximately 77% of the fish population in the river. This reduced parasite diversity in introduced species, compared with native hosts, has also been reported in a wide range of other taxa, and may contribute to the competitive advantage of introduced pest species. There was a correlation between the distribution of one species of parasite, Diplostomum sp., and position of its fish intermediate host in the catchment. This trematode, which has a complex life-cycle involving a number of different hosts, was mainly restricted to the freshwater tributaries, occurred rarely in the main channel of the lower catchment where the salinity was relatively low and was never found in the salinised upper catchment.
Despite the circumstantial evidence from field studies that the current pattern of fish distributions in the Blackwood River has been influenced by secondary salinisation, salinity tolerances of native freshwater fishes have not previously been measured under controlled laboratory conditions. The acute salinity tolerance of populations of G. occidentalis from the upper and lower catchments of the Blackwood River was studied experimentally, and compared with the tolerance of two other native fish species; E. vittata which is found in the main channel of the lower catchment, but not in the upper catchment; and N. balstoni which is restricted to a single small, freshwater tributary of the lower catchment. Nannatherina balstoni was found to have the lowest salinity tolerance with EC50 = 8.2 ppt and EC95 = 9.3 ppt. This confirms that the upper catchment of the Blackwood River, where the salinity was significantly higher than this range throughout most of the year, is unsuitable for this species and this may explain its absence from most of the catchment. The salinity tolerance of both E. vittata (EC50 = 14.5 and EC95=15.6) and G. occidentalis (EC50 = 14.6 ppt and EC95 = 15.8 ppt) was considerably higher than that of N. balstoni (LC50 = 8.2 ppt and LC95 = 9.2 ppt). It is possible that the eggs, larvae or juvenile stages of E. vittata are more sensitive to salinity than adults and this prevents this species from establishing its life-cycle in the upper catchment of the Blackwood River. Additionally, the greater dispersal capabilities of G. occidentalis may enable it to maintain its life-cycle in the upper catchment by moving into refuge areas as salinity increases.
This study has provided valuable insight into the impact of secondary salinisation on the biological performance of freshwater fishes in south-western Australia. These impacts are likely to be further exacerbated by continued increases in salinisation and reduced rainfall due to climate change
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
The prevalence of Cryptosporidium and Giardia in Western Australian freshwater and marine fish species, and Australian cultured fingerlings
No full textThis study aimed to examine the prevalence of protozoan parasites, Giardia and Cryptosporidium in fish hosts. Three different subgroups of fish: cultured species, wild freshwater species and wild marine/estuarine species were all screened for Cryptosporidium and Giardia by PCR amplification at the small subunit (SSU) rRNA locus. With all positives sequenced at second locus, actin for Cryptosporidium and gdh for Giardia.
Two hundred and twenty seven fingerlings (juvenile fishes) were collected from commercial aquaculture hatcheries within Australia, with 8 different fish species represented. From the Canning/Swan River and Blackwood River systems in Western Australia sampling of freshwater fish produced 227 samples, again 8 different fish species were sampled. Five species of marine fish were obtained from commercial fishers, in total 255 fish were collected.
A low prevalence of both parasites was recorded in fish hosts, 0.8% (6/709) for Cryptosporidium and 3.8% (27/709) for Giardia. This study provides the first recording of Giardia species, G. duodenalis assemblage A, B and E, Giardia microti, C. parvum, C. bovis and the pig genotype II in piscine hosts and identify a genetically distinct genotype of Cryptosporidium in Mugil cephalus, which is distinct from all currently acknowledged species of Cryptosporidium. This study provides initial investigation into the prevalence and geographical distribution of these parasites within fish. The presence of zoonotic species of both parasites draws attention to the public health importance of investigating parasites within piscine host species
Genetic variation in Giardia duodenalis and the molecular epidemiology of giardiasis
No full textIn this study the nature and extent of genetic variation in Giardia was investigated to obtain fundamental knowledge on its mode of reproduction, population structure and zoonotic potential, all of which are important in order to fully understand the epidemiology of giardiasis and the taxonomy of the causative agent. Previous studies have contributed little information to these areas due to the comparison of relatively few isolates. Therefore, the major aims of my work were to characterise isolates of Giardia in order to investigate genetic variation and its significance to the epidemiology of giardiasis. Isolates of Giardia. from throughout Australia and overseas, were obtained from humans, cats, cattle, sheep, dogs, goat, beaver and rats and examined using one or more of the following techniques: in vitro cultivation; restriction fragment length polymorphism (RFLP) analysis; enzyme electrophoresis; and amplification of repetitive DNA sequences using the polymerase chain reaction (PCR).
In vitro cultivation of Giardia distinguished intraspecific variants based on observed differences in growth between isolates. Human, cat, goat and sheep isolates of Giardia could be established in vitro while isolates of Giardia from dogs and rats failed to establish. Differences in growth behaviour were also observed between isolates of Giardia from the same host species, namely humans and cats. The observed differences in growth during in vitro cultivation in isolates of Giardia from the same and different host species was usually reflected in genetic differences detected by enzyme electrophoresis.
Enzyme electrophoresis and RFLP analysis produced very similar groupings of isolates of Giardia with identical banding patterns for all zymodemes and schizodemes, including isolates from restricted geographical areas of Western Australia. The significant correlation between the two techniques suggests that the genetic groups identified by enzyme and DNA analyses consist of natural clones of genetically identical organisms and that Giardia has a clonal population structure. This was supported by the finding of widely distributed common genotypes identified by enzyme electrophoresis throughout Australia and overseas.
Electrophoresis banding patterns were of two distinct types. Most isolates produced single-handed enzyme patterns for all the enzymes examined while other isolates produced multiple-banded patterns for a number of enzymes. The observed patterns were interpreted to suggest: (i) that different isolates vary in their ploidy levels with some isolates being functionally haploid and others diploid (or polyploid); and (ii) the possibility of occasional genetic exchange in Giardia. Attempts were made to induce genetic exchange by mixing isolates in vitro and in vivo, but no recombinant genotypes were detected.
Enzyme electrophoretic characterisation of isolates of Giardia from different animals and geographical areas, revealed extensive genetic variation with the identification of 47 different zymodemes. The 47 zymodemes could be divided into three main groups: one comprising isolates from humans and a sheep from Western Australia; a second group containing isolates with a worldwide geographical distribution from humans, cats, dogs, sheep, cattle and beaver; and a third group comprising genetically diverse isolates from humans, rats, cat, dog and goat from Australia and overseas. Isolates of Giardia from Aboriginal communities, from within a restricted geographical area, showed a level of genetic diversity similar to that found for isolates characterised from throughout Western Australia. Humans and dogs from these communities were commonly infected with Giardia: PCR analysis of cysts produced similar DNA banding patterns for a number of human and canine faecal samples, which is suggestive of zoonotic transmission.
The results of this study show that isolates of Giardia duodenalis are genetically diverse. The source of this diversity is consistent with a predominantly clonal population structure for Giardia with the possibility of occasional bouts of genetic exchange. Further, the identification of genetically similar isolates of Giardia from humans and other animals using molecular techniques, and the extensive genetic diversity detected in isolates from humans, provides evidence for the zoonotic transmission of this parasite
Selection for faster growing black bream Acanthopagrus butcheri
Get PDFIn Australia, the widespread clearing of native vegetation has resulted in large areas of once-productive agricultural land being affected by rising saline groundwaters. There is considerable interest among farmers and rural landowners throughout Western Australia, in the possibilities that inland saline aquaculture may offer for a potentially productive use of land and water resources that can no longer support traditional agriculture. Black bream (Acanthopagrus butcheri) appear to be an ideal candidate for the developing saline aquaculture industry of inland Western Australia, however their current maximum growth rates are too slow for profitable production. The high productivity of modern breeds of terrestrial livestock species is primarily due to genetic improvement programs utilising selective breeding, and similar gains have also been made where they have been implemented for aquatic species. Before the growth rate of black bream can be genetically improved, however, it is necessary to estimate both the extent of genetic improvement required and the extent of genetic (co)variation in those growth traits which will be subject to, or affected by, selection. The aims of this study were to:
(1) Determine the extent of genetic improvement in growth rate required for black bream to be considered as a profitable aquaculture species.
(2) Estimate the potential for growth rate to be improved through heterosis when different black bream strains are crossbred.
(3) Estimate the additive genetic variation for growth rate, which exists within populations of black bream.
(4) Estimate the genetic (co)variation which exists between growth rate and other production traits.
A partial budget analysis investigated whether enhanced growth rates of black bream would improve profitability and justify a genetic improvement program. It was conducted for two different fish production systems; a commercial operation that incurred more operating expenses due to costs associated with farm initiation (stand-alone farm model) and an existing farm that diversified into aquaculture using the saline water resources of established farm dams (integrated farm model). Sensitivity analyses indicated that a 33% increase in growth rate to at least 200g/annum would allow either production system to return a profit at a farm-gate price of AUS$6/kg whole fish, with fish survival rates of 98% for the stand-alone farm and 65% for the integrated farm model. These results provided a breeding objective, being an improvement in growth rate by at least 33%.
A complete diallel cross of two black bream populations was used to estimate the comparative advantages that might be gained from straight-breeding and crossbreeding. At 90 days of age, the growth traits of standard length, total length and wet weight, varied significantly among all straight-bred and crossbred lines, and among half-sib groups within lines. Differences among half-sib groups explained 6.8% of the total variance in standard length, 8.3% in total length and 7.1% in wet weight, giving estimated heritabilities over all lines of 0.27 plus-minus 0.11 for standard length, 0.33 plus-minus 0.13 for total length and 0.28 plus-minus 0.12 for wet weight. There was no evidence for heterosis in any traits when straight-bred and crossbred lines were compared, and phenotypic (rP = 0.95 - 0.98) and genetic (rG = 0.63 - 0.69) correlations were high among all growth traits.
I used the estimated heritability for wet weight of 0.28 to optimise a factorial mating design from a single population, and to estimate the contribution of additive genetic, nonadditive genetic and maternal effects to variation in growth traits of black bream at 75, 130 and 180 days of age in the hatchery. Maternal genetic and environmental effects were greatest at 75 days of age, accounting for 9.1% of total phenotypic variance in wet weight, 11.4% of variance in standard length and 8.8% of variance in total length. At later ages maternal effects were much reduced, explaining 0.8 - 3.7% of phenotypic variance in growth traits. Additive genetic effects were greatest at 130 days of age, when they accounted for 17.4% of total phenotypic variance in wet weight, 21.4% of variance in standard length and 18.7% of variance in total length. Additive genetic effects were negligible (<1%) at 75 days of age and 4.8 - 5.5% of total phenotypic variance in growth traits at 180 days of age. Non-additive genetic effects (which also included common environmental effects due to families being raised in the same tank) explained 5.8 - 7.3% of total phenotypic variance in growth traits at 75 days of age, but were much smaller at later ages. Variable stocking densities among tanks up to 75 days significantly affected all growth trait measurements below 180 days of age.
One of the most important of these traits is feed conversion efficiency. Feed conversion efficiency (FCE) is the effectiveness with which feed is converted to saleable fish product. Feed costs are a major input to aquaculture production systems and genetic changes in FCE may therefore have an important influence on profitability. FCE is usually expressed by a composite measure that combines feed intake and growth rate. The two most common measures are feed conversion ratio (feed intake/weight gain over a specified time interval) and its inverse, feed efficiency. Feed conversion ratio and feed efficiency are measures of gross FCE, because they do not distinguish between the separate energy requirements of growth and maintenance. There is abundant evidence of substantial genetic variation in FCE and its component traits in terrestrial livestock species and, although data are few, the same is likely for cultured fish species. The major problems with selecting from this variation to genetically improve FCE in fish species are:
* It appears impractical to measure feed intake on individual fish, so that family mean data must be used.
* We do not know the optimal time period over which to test fish for FCE.
* We do not know the genetic correlations between FCE under apparent satiation or restricted intake conditions, or between FCE at different times in the production cycle.
I measured the relationships between feed intake to apparent satiety and weight gain in replicate half-sib families of black bream at four times over a 56-day test period. After 42 days, I found significant additive genetic variance in both weight gain and feed intake, and a stabilisation in family group variation in both traits. This indicates that 42 days is the minimum test period over which to measure genetic variation for FCE in black bream. There were high, positive phenotypic (and probably genetic) correlations between weight gain and feed intake after 42 days. There was no detectable genetic variation for either feed efficiency (weight gain/feed intake), or residual feed intake, which is the difference between the actual feed intake of an individual and the intake predicted from its body weight and growth rate. I argue that selection for improved FCE might be better achieved not by using a composite measure, but by using a weighted selection index that accounts for the genetic covariance among weight gain, feed intake and other correlated traits
Parasites of native and exotic freshwater fishes in the south-west of Western Australia
Get PDFFewer than 200 fish species are found in freshwater habitats in Australia, of which 144 are confined exclusively to freshwater. At least 22 species of exotic freshwater fish have been introduced into Australia, and 19 of these have established self-sustaining populations. However, the parasite fauna of both native and exotic freshwater fishes in Australia is poorly known. This is particularly the case in the south-west of Western Australia, where there have been no previous comprehensive studies of the parasites of 14 native species and nine or more exotic species of fish found in freshwater habitats.
This study represents a survey of the parasites of freshwater fishes in the South West Coast Drainage Division and reports 44 putative species of parasites in 1429 individual fishes of 18 different species (12 native and six exotic) from 29 locations. Parasites were found in 327 (22.88%) fishes, and of the infected fishes, 200 (61.16%) were infected with only one species of parasite and 127 (38.84%) were infected with two or more species of parasites. For helminth and arthropod parasites, which were more comprehensively surveyed than protozoan and myxozoans, I found 37 species compared to 77 species found in a recent study of fishes from the East Coast Drainage Division.
The present study demonstrated that parasitic infection was significantly more common in native fish species (mean prevalence of infection with any species of parasite = 0.36 ± 0.09) than in exotic fish species (0.01 ± 0.12). Parasites were found in all native fish species, but in only two exotic fish species that were examined. Parasite regional and component community diversity were estimated by species richness (the number of species, S) and by an index of taxonomic diversity (HT). Both parasite species richness and parasite taxonomic diversity were significantly greater in native fish species (mean S = 10.5 ± 2.3; mean HT = 1.19 ± 0.14) than in exotic fish species (mean S = 1.6 ± 3.3; mean HT = 0.27 ± 0.20). These relationships were consistent over all geographic locations that were sampled. The reduced parasite load of exotic species compared to native species has been previous reported across a wide range of taxa. It is thought to arise partly because founding populations of hosts have a low probability of harbouring the species’ total parasite fauna, and partly because parasites that infect introduced exotic species may not be able to maintain their life cycle in the new environment. It has been suggested that a reduced parasite load increases the competitive ability of exotic species compared to native species (the parasite release hypothesis) and this may partly explain the abundance and apparent competitive success of exotic over native species of freshwater fish in the South West Coast Drainage Division.
For native species of fish, there were major differences among species in both prevalence of parasitic infection and parasite community diversity, but this variation was not related to fish size, whether the fish were primarily freshwater or primarily estuarine, or whether they were primarily demersal or pelagic.
In this study, I report two new parasites in south western Australian waters. Both are copepod parasites; Lernaea cyprinacea and a new species of Dermoergasilus. The Dermoergasilus appears to be native to the south-west of Western Australia and has been described as Dermoergasilus westernensis. It differs from previously described species in the genus principally by the armature of the legs. This new species was found on the gills of freshwater cobbler, Tandanus bostocki and western minnow, Galaxias occidentalis in two different river systems.
Lernaea cyprinacea is an introduced parasitic copepod found on the skin and gills of freshwater fishes in many areas of the world. The parasite has not previously been reported in Western Australia. We found infestations of L. cyprinacea on four native fish species (G. occidentalis; Edelia vittata; Bostockia porosa; T. bostocki) and three introduced fish species (Carassius auratus; Gambusia holbrooki; Phalloceros caudimaculatus) at two localities in the Canning River, in the south-west of Western Australia. The parasite has the potential to have serious pathogenic effects on native fish species, although it appears to be currently localised to a small section of the Canning River.
Over all localities from which fishes were sampled in the present study, the proportion of native freshwater fishes with parasitic infections and the component community diversity of the parasite fauna of native fishes were both negatively related to habitat disturbance, in particular to a suite of factors (river regulation, loss of riparian vegetation, eutrophication and presence of exotic fish species) that indicate increased human usage of the river and surrounding environment. The reduced parasite load and diversity in native fishes from south-west rivers with greater human usage was due principally to the loss of a number of species of trematode, cestode and nematode endoparasites which use fishes as intermediate hosts. Other studies have also found that endoparasites with complex life cycles are most likely to be adversely affected by environmental changes, presumably because any environmental changes which impact on either free-living parasite stages or on any of the hosts in the complex train of parasite transmission will reduce parasite population size and may cause local extinction of the parasite species.
The most heavily infected species of native freshwater fish in the South West Coast Drainage Division was T. bostocki with 96% of all individuals containing at least one species of parasite. As with most freshwater fishes of south-west Australia, T. bostocki is limited in its distribution to waterways with relatively low salinity. The degree of parasitism and histopathology of internal and external organs in T. bostocki from the Blackwood River was examined over a period of rapid, seasonal changes in water salinity. As salinity increased, the infracommunity richness and prevalence of ectoparasites on the skin of fishes decreased, while the infracommunity richness and prevalence of endoparasites increased. This was associated with a decrease in histopathological lesion scores in the skin and an increase in histopathological lesion scores in internal organs, particularly the intestine. I hypothesise that the seasonal spike in salinity had two contrasting effects on parasitic infections of T. bostocki. Firstly, it increased the mortality rate of parasites directly exposed to water, leading to a decrease in ectoparasitic infection and associated pathology. Secondly, it suppressed immune function in fish, leading to a decreased mortality rate of parasites not directly exposed to water and a more severe pathological response to endoparasitism
Black spot disease in freshwater fishes of south-western Australia: identification of the parasite, host range and potential as a bioindicator for water quality
Get PDFThe salinisation of freshwater ecosystems by anthropogenic influences is recognised as one of the largest threats to the highly endemic freshwater fish fauna of south-western Australia. There has also been some recent evidence that secondary salinisation is affecting the parasite community of freshwater fishes. A parasitic trematode, which causes black spot disease in the musculature of native fishes, has previously been tentatively identified as Diplostomum galaxiae, a species first described from a galaxiid fish (Galaxias auratus) in Tasmania. The aims of the current study were to confirm this specific identification using genetic analyses; investigate the host and geographic range of the parasite in south-western Australia; and determine whether the parasite could be a suitable bioindicator of secondary salinisation.
Encysted metacercariae were extracted from preserved fishes in the collection of the Freshwater Fish Group & Fish Health Unit, Murdoch University, and from a specimen of Galaxias truttaceus from Tasmania, and a section of the 18S rRNA gene sequenced. All parasites from south-western Australia and Tasmania were genetically identical, but did not group with other species in the Diplostomum genus in phylogenetic analyses. Instead, the Australian parasite aligned more closely to a clade containing Posthodiplostomum spp., and several genera from the Strigeidae family. Reclassification of the parasite causing black spot disease in south-western Australian freshwater fishes is thus recommended, following more extensive comparisons with the parasite throughout Australia. In the interim, the parasite has been designated with the temporary name Dip01.
Historical collections of fishes from the West Australian Museum and from the Freshwater Fish Group & Fish Health Unit, Murdoch University were assessed, to collate records of Dip01 metacercariae. The parasite appears to preferentially infect Galaxias maculatus and Galaxias occidentalis over other species; although it was also found in two percichthyids (a single Nannatherina balstoni and several Bostockia porosa from a single catchment) and has been reported previously from two estuarine fishes (Leptatherina wallacei and Pseudogobius olorum) that have colonised secondarily salinised rivers of the region. The overall prevalence of Dip01 in G. maculatus was 11.7% (95% CI 9.3-14.4%), and in G. occidentalis was 6.1% (4.8-7.7%). The mean intensity of infection in G. maculatus was 3.5 (2.0-7.3) parasites/infected fish, while the mean intensity in G. occidentalis was 7.8 (5.9-10.3) parasites per infected fish. The geographic range of Dip01 closely matches that of the preferred hosts, G. maculatus and G. occidentalis.
Prevalence and intensity data were compared against historical environmental data from the Water Information Reporting database of the Department of Water and Environmental Regulation, where available. There was a significant inverse relationship between parasite prevalence and salinity, with Dip01 only occurring in habitats with a conductivity of less than 1,000 μS/cm. Based on these data, the parasite appears to be a useful bioindicator of salinity, as it is restricted to low salinity waters, even though its preferred galaxiid hosts are tolerant of a wide range of salinities
- …
