Australian Aquaculture Research Articles

Effects of trout farms on stream macroinvertebrates: linking farm-scale disturbance to ecological impact

Trout farms are a significant component of the Australian aquaculture industry, but there have been no studies on the ecological impacts of Australian trout farms. I analysed biolog- ical monitoring data from 5 trout farms in the Goulburn Valley, Victoria, Australia. Using multi- variate ordination and a Bayesian hierarchical model, I compared macroinvertebrate assemblages from upstream of the farms to those downstream, and related upstreamdownstream differences in invertebrate assemblage condition to 5 farm-scale indices of disturbance. I found clear, but small, ecological impacts of individual farms (i.e. upstream to downstream differences in inverte- brates), with between-farm variation in impacts largely explained by the indices of disturbance. The greatest impacts were seen for farms with high production intensity that utilise a high propor- tion of stream discharge, export a high relative load of nitrogen to the stream and are in areas of good biological condition. Recent research has explored operational and engineering solutions that reduce the downstream ecological impacts of trout farms. Adoption of such practices may help such farms to minimise impacts on streams.

Ultraviolet irradiation is an effective alternative to ozonation as a sea water treatment to prevent Kudoa neurophila (Myxozoa: Myxosporea) infection of striped trumpeter, Latris lineata (Forster)

Myxozoan parasites are known pathogens of cultured finfish. Kudoa neurophila n. comb. (Grossel, Dyková, Handlinger & Munday) has historically infected hatchery-produced striped trumpeter, Latris lineata (Forster in Bloch and Schneider), a candidate species for seacage aquaculture in Australia. We examined the efficacy of four water treatment methods to prevent K. neurophila infection in post-larval (paperfish) and juvenile striped trumpeter. Treatments included dose-controlled ultraviolet irradiation [hydro-optic disinfection (HOD)], ozone with conventional UV (ozone), mechanical filtration at 25 μm and then foam fractionation (primary filtration), and 50-μm-filtered sea water (control). In post-larvae (initially 10.3 ± 2.7 g, mean ± SD, 259 days post-hatching, dph), the infection prevalence (PCR test) after 51 days was 93 ± 12% in the control, 100 ± 0% in primary filtration and 0 ± 0% in both ozone and HOD. Likewise, in juveniles (initially 114 ± 18 g, 428 dph), prevalence was 100 ± 0% in the control and primary filtration treatments with no infection detected in ozone and HOD. Concurrently, there was a 50-100% reduction in heterotrophic bacteria and 100% reduction in presumptive Vibrio sp. in sea water HOD and ozone treatments. HOD with a dose of ≥44 mJ cm(-2) UV was as effective as ozonation at >700 mV ORP for 10 min, in preventing K. neurophila infection.

Resistance Determinants of Pseudomonas Species from Aquaculture in Australia

There is limited information on antibiotic resistance determinants present in bacteria of aquaculture origin in Australia. The presence of integron and other resistance determinants was investigated in 129 Pseudomonasisolates derived from nine freshwater trout farms in Victoria (Australia). Polymerase chain reaction (PCR) was carried out for the detection of integrase genes Int1, Int2 and Int3, gene cassette array, integron-associated aadA, beta-lactamase resistance genes blaTEM and blaSHV. Genes coding for efflux pump mexA, mexB and oprM were also investigated as well as cadA and czr which are known to mediate resistance to cadmium. Class 1 integrons were detected in 30/129 (23 %) isolates while class 2 and class 3 was not detected in any of the isolates. aadA gene was detected in 28 of the 59 integrase positive isolates which are also resistant to streptomycin. The strA-strB, blaTEM or blaSHV genes were not detected in any of the strains. mexB was detected in 85/129 isolates and cadA gene in 59/92 isolates tested. The sequence analysis mexB from this study demonstrated similarity to the RND multidrug efflux transporter mexB and its homologue TtgB which in addition to multidrug efflux also transports toluene out of the cell. The sequence analysis of cadA confirms similarities to the cadmium translocating P-type ATPases, cadA of various Pseudomonas spp. Pseudomonas spp. carrying integrons, efflux gene and cadmium resistance genes are present in farm-raised fish and sediments even though no antibiotics were licensed for use in Australian aquaculture at the time of the study.

Incidence of class 1 integron and other antibiotic resistance determinants in Aeromonas spp. from rainbow trout farms in Australia

There is limited information on antibiotic resistance determinants present in bacteria of aquaculture origin in Australia. The presence of integron and other resistance determinants was investigated in 90 Aeromonas isolates derived from nine freshwater trout farms in Victoria (Australia). Polymerase chain reaction was carried out for the detection of integrase genes Int1, Int2 and Int3, gene cassette array, integron-associated aadA, sul1 and qac1 genes, streptomycin resistance genes strA-strB, β-lactamase resistance genes bla(TEM) and bla(SHV) , and tetracycline resistance genes tetA-E and tetM. Clonal analysis was performed by pulsed-field gel electrophoresis (PFGE). Class 1 integrons were detected in 28/90 (31%) and class 2 and class 3 in none of the strains, aadA gene in 19/27 (70%) streptomycin-resistant strains, sul1 in 13/15 (86.7%) sulphonamide-resistant strains and qac1 gene in 8/28 (28.6%) integron-bearing strains. Five strains from two different farms carried gene cassettes of 1000 bp each containing the aadA2 gene and PFGE analysis revealed genetic relatedness. tetC was detected in all and tetA in 9/18 (50%) tetracycline-resistant strains. The strA-strB, bla(TEM) or bla(SHV) genes were not detected in any of the strains. Aeromonas spp. carrying integrons and other resistance genes are present in farm-raised fish and sediments even though no antibiotics were licensed for use in Australian aquaculture at the time of the study.

Opinion 2212 (Case 3267) Cherax tenuimanus Smith, 1912 (Crustacea, Decapoda, parastacidae): proposed designation of neotype not accepted and usage not conserved

An application to conserve the specific name Cherax tenuimanus Smith, 1912 by designation of neotypes for this species and for Cherax cainii Austin in Austin & Ryan, 2002, two species of freshwater crayfish or ‘marron’ important in the Australian aquaculture industry, was not approved. Type fixations for Cherax tenuimanus Smith, 1912 and Cherax cainii Austin in Austin & Ryan, 2002 are maintained.

The effects of pre-harvest stress and harvest method on the stress response, rigor onset, muscle pH and drip loss in barramundi ( Lates calcarifer)

Barramundi ( Lates calcarifer) farming is a significant sector of the Australian aquaculture industry with production technology rivalling that found in the salmonid or kingfish species. It is evident however that one area of production, the final harvest stage, still has room for improvement to maintain the optimum quality of the farmed domestic product. There is considerable literature that suggests harvest methods involving stress and excessive exercise contribute significantly to final flesh quality in fish. In this study the effect of harvest method on the final flesh quality was evaluated in barramundi. Harvest size barramundi were exposed to either a rested harvest technique (utilising the aquatic anaesthetic AQUI-S), or an alternative technique which aimed to simulate the harvest conditions commonly observed on Australian barramundi farms (involving air exposure and exercise prior to slaughter). Results show that time to full rigor onset was significantly delayed (12 h) in rested fish compared to the simulated harvest treatment (3 h). Flesh pH was also significantly higher and remained this way until 18 h post-harvest in rested fish. There was no difference in drip loss from flesh samples obtained from each of the two harvest methods over 4 days storage at 2–4 °C. Furthermore, in additional barramundi exposed to the simulated conventional harvest technique and not killed, but allowed to recover, significant elevations in plasma cortisol, glucose and lactate were observed. To our knowledge, this investigation presents the first information on the stress response and the effects of stress at harvest on flesh quality in barramundi. These preliminary results validate the use of rested harvest as an alternative method of improving barramundi quality and thereby further differentiating Australian product from foreign imports.

Genetic variability amongst Streptococcus iniae isolates from Australia

Journal of Fish DiseasesVolume 31, Issue 4 p. 305-309 Genetic variability amongst Streptococcus iniae isolates from Australia R A Nawawi, R A Nawawi Aquatic Animal Health Laboratory, Centre for Marine Studies, University of Queensland, Brisbane, Queensland, AustraliaSearch for more papers by this authorJ Baiano, J Baiano Aquatic Animal Health Laboratory, Centre for Marine Studies, University of Queensland, Brisbane, Queensland, AustraliaSearch for more papers by this authorA C Barnes, A C Barnes Aquatic Animal Health Laboratory, Centre for Marine Studies, University of Queensland, Brisbane, Queensland, AustraliaSearch for more papers by this author R A Nawawi, R A Nawawi Aquatic Animal Health Laboratory, Centre for Marine Studies, University of Queensland, Brisbane, Queensland, AustraliaSearch for more papers by this authorJ Baiano, J Baiano Aquatic Animal Health Laboratory, Centre for Marine Studies, University of Queensland, Brisbane, Queensland, AustraliaSearch for more papers by this authorA C Barnes, A C Barnes Aquatic Animal Health Laboratory, Centre for Marine Studies, University of Queensland, Brisbane, Queensland, AustraliaSearch for more papers by this author First published: 18 March 2008 https://doi.org/10.1111/j.1365-2761.2007.00880.xCitations: 23 Dr Andy Barnes, Aquatic Animal Health Laboratory, Centre for Marine Studies, University of Queensland, Brisbane, Queensland 4072, Australia(e-mail: a.barnes@uq.edu.au) Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume31, Issue4April 2008Pages 305-309 RelatedInformation

The impact of diet on the growth and proximate composition of juvenile whelks, Dicathais orbita (Gastropoda: Mollusca)

Dicathais orbita is a predatory marine whelk of interest as a new source of protein for potential production in aquaculture. Establishment of a successful aquaculture industry based on this species will require optimisation of their diet for fast growth and survival, whilst maintaining a good proximate composition in the flesh. Here we compare the effects of four diets fed to juvenile D. orbita over a 12 week period, to evaluate consumption, feed conversion, growth rates, mortalities and proximate composition. It was found that diet impacts significantly on the growth and survival rates of this whelk, with bivalve feeds resulting in significantly higher consumption (P<0.0001) and growth rates (P<0.0001) compared to artificial pellets, despite similar feed conversion ratios (P=0.359). The artificial pellets were found to have significantly less moisture, but higher protein, glycogen and lipid content than the bivalve feeds (P<0.05) and resulted in whelk flesh with significantly higher energy and ash content (P<0.05). D. orbita showed a preference for scavenging frozen bivalves over predation on live molluscs in captivity, which could reflect an optimal foraging strategy to minimise the energy required to subdue prey. Overall, juvenile D. orbita display similar growth (up to 0.8 g/month) and high survival (>90%) compared to other gastropods in culture. Their flesh has a high calorific value (∼19 kJ/g), with significantly higher protein (>26 mg/g) and glycogen (>35 mg/g) content than their bivalve prey (P<0.05). Consequently, this species has a promising future as a new species for molluscan aquaculture in Australia.

Effects of fish oil substitution with a mix blend vegetable oil on nutrient digestibility in Murray cod, Maccullochella peelii peelii

The replacement of fish oil with vegetable based oils is a strategy which is increasingly being adopted by the aquafeed industry as an essential component to reduce the reliance on a limited supply of a natural resource, which in turn also provides cost benefits. The aim of the present investigation was to evaluate the lipid and fatty acid digestibility of a mix blend vegetable oil in juvenile Murray cod; an emerging species of increasing interest in the Australian aquaculture sector. Five semi purified experimental diets were formulated with 17% lipid originating from fish oil (FO) which was substituted in 25% increments by blended vegetable oil (VO), formulated using olive oil (12%), palm oil (43%) and linseed oil (45%) to match the major fatty acid classes of the FO. Significant differences between the dietary treatments with regard to the lipid and individual fatty acid digestibility were recorded. This study clearly demonstrated that in Murray cod fatty acid digestibility decreases with chain length, and inversely increases relative to the degree of unsaturation. The combination of chain length, degree of unsaturation and the melting point of individual fatty acids resulted in the digestibility of PUFA > MUFA > SFA and short chain > longer chain fatty acids. Therefore, the inclusion of a mixed blend vegetable oil resulted in significantly reduced lipid digestibility in juvenile Murray cod.

Antibiotic and heavy metal resistance in motile aeromonads and pseudomonads from rainbow trout ( Oncorhynchus mykiss) farms in Australia

A total of 129 Pseudomonas spp. and 90 Aeromonas spp. were isolated from nine rainbow trout ( Oncorhynchus mykiss) farms in Australia. All the isolates were tested for sensitivity to 15 antibiotics and the multiresistant strains were tested for sensitivity to seven heavy metals. Minimal inhibitory concentrations (MICs) were determined by the agar dilution method. In Pseudomonas spp., resistance to amoxicillin, cefalothin, ceftiofur, ticarcillin, chloramphenicol, florfenicol, streptomycin, nitrofurantoin and trimethoprim was widespread, whereas resistance to cefotaxime and oxolinic acid was less common and only single isolates were resistant to tetracycline and sulfamethoxazole; all isolates were sensitive to ciprofloxacin and gentamicin. In Aeromonas spp., resistance to amoxicillin and cefalothin was widespread, resistance to ticarcillin, tetracycline and streptomycin was common, whilst resistance to ceftiofur, florfenicol and sulfamethoxazole was less common. Single isolates were resistant to chloramphenicol, nitrofurantoin and trimethoprim, and all isolates were sensitive to cefotaxime, oxolinic acid, ciprofloxacin and gentamicin. Multiple resistance was also observed. Most isolates were tolerant to different concentrations of various heavy metals, as evidenced by their MICs ranging from 6.25 μg/mL to >3200 μg/mL. These results confirm our previous findings that bacteria resistant to antibiotics are present in fish and sediments from aquaculture in Australia. In addition, we have found resistance to heavy metals in fish and sediment isolates. Much of the antibiotic resistance detected is likely to be intrinsic, although resistance to oxytetracycline, streptomycin and sulfonamides suggests either contamination from run-off from farms or perhaps off-label use of antibiotics in a situation where no antibiotics are licensed for use in aquaculture.

Risk assessment for metazoan parasites of yellowtail kingfish Seriola lalandi (Perciformes: Carangidae) in South Australian sea-cage aquaculture

Metazoan parasites can threaten the sustainability and profitability of finfish sea-cage aquaculture. It is critical, therefore, to identify local parasite species and determine which are potentially harmful. Although several studies have documented parasite species on wild and farmed fish from aquaculture sites, few have used qualitative risk analyses to determine the likelihood and consequence of parasite transfer from locally found wild fish to farmed fish. Indeed, most risk assessments for marine fish farming identify hazards from diseases reported in other, often distant, countries. The usefulness of this approach is limited if an endemic parasite with potential to cause serious disease is undetected before the establishment of aquaculture. This study performs a qualitative risk assessment for 57 metazoan parasite species found to infect wild yellowtail kingfish ( Seriola lalandi) and Samson fish ( S. hippos) in southern Australia to determine real risks to local sea-cage aquaculture of S. lalandi in South Australia and for industry expansion elswhere. Risk was estimated by considering the likelihood and consequence of parasite establishment and proliferation in S. lalandi sea-cage farming. Benedenia seriolae and Zeuxapta seriolae (Monogenea) were considered extremely likely to establish and proliferate. B. seriolae is currently recorded as the highest potential negative consequence for cost-effective sea-cage farming of S. lalandi in Australia, should the industry expand elsewhere. However, B. seriolae infections can be managed by bathing fish in either hydrogen peroxide or fresh water. Absence of potential treatment methods for Paradeontacylix spp. (Digenea), Kudoa sp. and Unicapsula seriolae (Myxozoa) suggests that these species may present the highest negative consequences for S. lalandi aquaculture in Australia. However, the presence of myxozoan infection in the flesh of wild South Australian Seriola spp. needs confirmation to determine whether these parasite species present an immediate risk to farmed S. lalandi in South Australia.

Risk Perceptions, Aquaculture, and Issues of Trust: Lessons From Australia

Aquaculture is heralded as a way of helping to feed a growing global population by supplementing supplies of wild–sourced seafood. Australian aquaculture has the potential to become a $1 billion per year industry and to provide employment needed in some rural areas. However, concerns about aquaculture have led to disputes about the industry's access to highly valued marine and coastal environments. The lack of research on this topic has confounded efforts to build a more socially acceptable and sustainable aquaculture industry. This research used key stakeholder interviews and a household mail survey to reveal differences in perceptions of aquaculture risks. Community groups (particularly conservation), ecotourism industries, researchers, some state and local government staff, and informed members of the general public were more likely to focus on aquaculture's risks, and seek improvements in aquaculture planning and management to substantially reduce those risks and make the industry more acceptable to diverse interests.

A new parasite that infects eggs of the mud crab, Scylla serrata, in Australia

The mud crab, Scylla serrata, is currently being evaluated for its feasibility for mass aquaculture in Australia. As part of the evaluation process, pathogens that can affect this species need to be identified. This research note describes a possible new parasite that infects the eggs of S. serrata. The parasite was discovered in two separate cases (three months apart) in a broodstock research program and appears to cause 100% egg mortality. The parasite consists of a cluster of cells with rhizoids that appear to function as an anchorage and a feeding organ. The individual cells range from 3 to 6 μm with a single nucleus. The parasite could not be classified to a phylum by morphology alone. However, BLAST analysis of the DNA sequence from a PCR amplicon generated using universal 18S ribosomal RNA gene primers indicated similarity to pathogenic thraustochytrids, Dermocystidium sp. and Rhinosporidium seeberi. All except R. seeberi are protistan parasites of fish and crustaceans. A neighbour-joining phylogenetic tree confirmed the homology with the thraustochytrids; however, further molecular techniques need to be exploited for absolute classification of this new parasite.

Antimicrobial resistance in bacteria isolated from aquaculture sources in Australia

To carry out a preliminary assessment of the occurrence of resistance to antimicrobials in bacteria that has been isolated from a variety of aquaculture species and environments in Australia. A total of 100 Gram-negative (Vibrio spp. and Aeromonas spp. predominantly) and four Gram-positive bacteria isolated from farmed fish, crustaceans and water from crab larval rearing tanks were obtained from diagnostic laboratories from different parts of Australia. All the isolates were tested for sensitivity to 19 antibiotics and Minimal Inhibitory Concentrations were determined by the agar dilution method. Plasmid DNA was isolated by the alkali lysis method. Resistance to ampicillin, amoxycillin, cephalexin and erythromycin was widespread; resistance to oxytetracycline, tetracycline, nalidixic acid and sulfonamides was common but resistance to chloramphenicol, florfenicol, ceftiofur, cephalothin, cefoperazone, oxolinic acid, gentamicin, kanamycin and trimethoprim was less common. All strains were susceptible to ciprofloxacin. Multiple resistance was also observed and 74.4% of resistant isolates had between one and ten plasmids with sizes ranging 2-51 kbp. No antibiotics are registered for use in aquaculture in Australia but these results suggest that there has been significant off-label use. Transfer of antibiotic resistant bacteria to humans via the food chain is a significant health concern. In comparison with studies on terrestrial food producing animals, there are fewer studies on antibiotic resistance in bacteria from aquaculture enterprises and this study provides further support to the view that there is the risk of transfer of resistant bacteria to humans from consumption of aquaculture products. From the Australian perspective, although there are no products registered for use in aquaculture, antimicrobial resistance is present in isolates from aquaculture and aquaculture environments.

Cannibalism Reduction in Juvenile Barramundi Lates calcarifer by Providing Refuges and Low Light

Cannibalism is a special form of predation to kill and consume the whole of an individual of the same species. Cannibalism has been found in 36 of 410 fish families and can take place at various sizes or ages depending on species and environments (Hecht and Pienaar 1993). The occurrence of cannibalism in larval and juvenile fish is of considerable concern for aquaculture (Smith and Reay 1991). Intracohort cannibalism is one of the most important issues to address in intensive fish aquaculture. Among commonly aquacultured fish species, cannibalism has been reported in catfish Clarias gariepinus (Hecht and Appelbaum 1988). walleye Stizostedion vitreum (Cuff 1980), common carp Cyprinus carpi0 (Damme et al. 1989), Atlantic cod Gadus morhua (Folkvord 199 I) , Perca Jluviatilis (Melard et al. 1996), and many others. Since cannibalistic behavior has been widely found in fish culture, determination of factors influencing cannibalism is important in order to reduce its impact. Factors causing cannibalism fall into two primary categories: genetic and behavioral factors. Within the genetic category the principal cause of cannibalism is size variation within a cohort (Valerio and Barlow 1986). The behavioral category of causative factors is obviously linked to the genome, but environmental factors are closely linked to agonistic behaviors (Fox 1975; Hecht and Appelbaum 1988). Barramundi Lates calcarifer is an important species for aquaculture in Australia and

Managing the development of sustainable shrimp farming in Australia: the role of sedimentation ponds in treatment of farm discharge water

In Australia, the shrimp farming industry operates within strict environmental guidelines applied at national and state government levels. In this paper, we briefly review the current status of the development of an ecologically sustainable shrimp farming industry in Australia and the future research priorities to assist in maintaining sustainable development. The broad objectives of the current regulations governing shrimp aquaculture in Australia are to achieve appropriately sited and operated facilities. However, there are differences amongst the various jurisdictions, and these need to be reconciled. Currently, shrimp farm discharge regulations are based on permissible characteristics of discharge water quality. These parameters are highly variable over short time frames, and this presents a significant barrier to the development of cost-effective sampling strategies that accurately reflect trends in farm discharges. Furthermore, water quality parameters may provide little information about the effect of discharges on the ecology of the receiving waters. We describe more sophisticated indicators of the potential impacts of shrimp pond discharges, including the δ 15N-nitrogen isotopic ratios in marine plants, which integrate the high variability in water quality parameters. In many shrimp-farming countries, including Australia, there is an increasing trend towards the use of sedimentation ponds (=settling ponds, settling basins) for treating pond effluent prior to discharge or recirculation. Despite this trend, the performance of such systems has rarely been studied at farm scale, and therefore their effectiveness is poorly understood. We have examined the nutrient reduction performance of sedimentation ponds on a commercial farm over an entire production season. The results demonstrated that the sedimentation ponds were effective in reducing discharges of suspended particulates, but were less effective in reducing nutrient concentrations. Total suspended solids (TSS) were reduced by 60% with residence time of 0.7 day. The best reductions of total phosphorus (TP) and total nitrogen (TN) (35% and 23%, respectively) were in a sedimentation pond with 2 days residence time. The pond with the longest residence time, 4.6 days, had poorer removal rates for each of the three parameters. Although sedimentation ponds alone are a useful strategy, we advocate that sustainable development of shrimp farming requires an integrated approach involving appropriate planning, regulation and effective monitoring protocols by governments, and reduction of the volume of effluent and mass loadings of nutrients from shrimp farms. The key future challenges are to continue to improve feeds and feed utilization efficiency; reduce water usage through recycling and reduced exchange; and improve treatment of discharge water to remove nutrients.

Effect of speed on Taiwanese paddlewheel aeration

Aerators are generally used in Australian aquaculture ponds day and night at full speed without regulation. This situation is untenable in view of climate change, as energy conservation becomes an essential issue for all industries, including aquaculture. Variable speed performance curves were developed for the paddlewheel aerators that have been employed on Australian marine aquaculture ponds so that speed may be actively adjusted to match pond water quality requirements. Results show that speed of rotation is a significant factor effecting the performance of a paddlewheel aerator. Of particular note was the observation of backsplashing when kinetic energy (pumping head) was greater than the radius of a paddlewheel. The process of backsplashing is readily identified when whitewater is seen flying above a paddlewheel. It is hypothesised that backsplashing dilutes the oxygen-starved water entering a paddlewheel, thereby degrading the operational efficiency. Backsplash breakpoint speed is related to paddlewheel diameter. Aerator users can reduce backsplash by changing mechanical gearboxes or using a variable frequency drive (VFD inverter).

Genetic improvement in the Australian aquaculture industry

Most aquaculture industries in Australia are at an early stage of development and would benefit from the introduction of genetic improvement programmes. Size at harvest is perceived by industry participants, managers and researchers as the trait that will most influence profitability. Although most current genetic improvement programmes in aquaculture use mass selection, inbreeding is widely regarded as an important problem, which could be overcome by the use of family data in selection decisions. The major research priority is the development of genetic markers to enable accurate pedigree determination. The major constraint upon the implementation of genetic improvement programmes by aquaculture industries is lack of available funds and resources. Industry ownership and national co-ordination of research and development is seen as the best way of addressing this constraint.

Gene pool management of hatchery Barramundi Lates calcarifer for production and stock augmentation programmes

The depletion of Australia's wild Barramundi Lates calcarifer fishery pre-empts two future roles for Barramundi aquaculture in Australia: first, the industry is primarily intended to supply meat upon a sustained basis; and second, it will probably serve as the predominant source of genetic material for the augmentation of those wild populations that have been depleted, and in that sense the process becomes somewhat circular and interdependent. This paper considers this relationship in the context of captive gene pool management and suggests an alternative method of conserving Barramundi genetic resources to be used to provide genetically "compatible" stocks for the two activities in conjunction with genetic improvement for commercial operations.

Viral Diseases of Fish and Shellfish in Australian Mariculture.

Except for table and pearl oyster culture, marine aquaculture in Australia has only a short history. This, together with the less intensive culture methods which are usually employed, probably explains why relatively few viral diseases have been detected and even fewer are of significance. However, we predict that, as more species are brought into aquaculture and management practices intensify, viral diseases of both fin- and shellfish will assume greater significance. The one exception is salmonid mariculture which is based on stocks which are uniquely free of the major, pathogenic salmonid viruses as a result of their effective quarantine from northern hemisphere populations. In Australian finfish mariculture the major pathogen is the nodavirus which causes mass mortality in larval barrumundi (Lates calcarifer). The recent massive mortality of pilchards (Sardinops sagax) is also discussed as are lymphocystis and a number of less important viral diseases. No viruses of commercial significance have been detected in Australian molluscs, although a herpesvirus infecting juvenile clams Katelysia sp. has been a significant impediment to commercialisation of these shellfish. The situation with shrimps is somewhat different as a new syndrome called mid-crop mortality syndrome (MCMS) has caused major losses. This syndrome appears to be a multifactorial disease with at least four viruses being visualised by electronmicoscopy. Of these, two are regarded as the most important; a parvo-like virus (spawner-isolated mortality virus) and a possible rhabdo-like virus (gill-associated virus) which resembles yellowhead virus.