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Following are abstracts of papers presented at the workshop "Probiotic Solutions: Alternative Disease Control Methods in Aquaculture" held December 9-10, 1999, at Malaspina University-College, Nanaimo, British Columbia, Canada. Bacterial diseases have a significant negative impact on production efficiency in aquaculture operations. Traditionally, this impact has been controlled or diminished through the use of chemical agents such as antibiotics. In recent years, however, there has been a growing interest in overcoming these problems through the use of alternative husbandry methods. One method that is providing encouraging results is "probiotics", the use of antagonistic bacterial strains to control populations of potential pathogens through competitive exclusion. Examples of this technology already exist in land-based agriculture, where probiotics as an alternative to antibiotics is becoming well established and commercialized probiotic products are now available. The workshop was organized to increase the awareness of the aquaculture community to the potential benefits afforded by probiotics. "Probiotic Solutions" was the third workshop in a successful series, which includes "Live Feed" and "The Perfect Egg". During this two-day workshop, international experts from the aquaculture and agriculture industries shared their probiotics-related experiences and reviewed the most recent information on microbial control. The workshop ended with recommendations for the development and application of techniques to obtain control of the microbial environment in aquaculture systems. The Organizing Committee gratefully acknowledges the support of: Mid-Island Science, Technology & Innovation Council National Research Council of Canada Aquaculture Association of Canada Status of Bacterial Disease, Diagnoses and Control Efforts in Aquaculture Dr. Brian Austin, Department of Biological Sciences, Heriot-Watt University, Riccarton, Edinburgh, EH14 4AS, Scotland Over the last 20 years, there has been a dramatic increase in the range of taxa associated with disease in aquaculture. In part, this increase may reflect developments in bacterial taxonomy, a greater attention to meaningful diagnoses, and/or the emergence of a greater range of pathogens. For example, there has been a steady increase in the number of Vibrio species associated with disease in fish and shellfish. Recent additions include V. fischeri, V. furnissii, V. ichthyoenteri, V. pelagius, V. trachuri and V. viscosus. It is personal experience that as many of 25% of diagnoses may be erroneous. For example, workers have great difficulty identifying bona fide isolates of V. splendidus. In this respect, the conventional approach of using phenotypic tests for identification purposes is not necessarily appropriate. Some commercial systems, which have been designed for medical bacteria, are not strictly appropriate for use with fish isolates. Alternative approaches of serology may be commendable providing laboratories have access to monospecific antisera. For the future, molecular techniques offer hope for rapid specific and sensitive diagnoses, but it is difficult to foresee a period when they will used away from the specialized laboratory. Emphasis has been placed on the development of effective disease control strategies. The reliance on chemotherapy with antibiotics is gradually losing favour in Europe and North America. Vaccines are more commonly used for finfish and even for some invertebrates even though the mechanism of action is improperly understood. Nutritional supplements/non-specific immunostimulants and probiotics are rapidly entering the armory of disease control mechanisms.
Dr. Ralph Elston, AquaTechnics, PO Box 687, Sequim, WA, 98324, USA World mollusc production continues to increase, exceeding 15 million metric tons of shellfish in 1997 (FAO 1999). Research to support intensive cultivation of molluscs to fit a traditional agricultural model, including brood stock selection and maintenance, control and optimization of reproduction, and intensive culture of larvae and seed appears in the scientific literature in the 1950's (e.g. Davis and Chanley 1956, Walne 1958). Even these early reports referenced the problem of pathogenic bacteria (Walne 1958). Commercial production scale bivalve mollusc culture of early life stages (larvae and seed production) began in earnest in the 1970's and continues to grow. Vibriosis is the most commonly recognized and occurring bacterial disease of shellfish larvae and seed and may, in reality, result from a variety of described as well as poorly studied pathogenic bacteria. Although improved hygienic practices have dramatically reduced the impact of this disease for oyster larvae, vibriosis remains a significant problem in juvenile (seed) production and persists in other more susceptible larval species such as scallops and geoduck clams. Intracellular rickettsia-like infections are also known to seriously affect juvenile abalone in culture and are also commonly found in bivalves. Hinge ligament disease, caused by gliding or Cytophaga-like bacteria, is a commonly occurring and important limitation to intensive culture productivity for juvenile bivalves up to about 1-cm shell dimension. There are also two known viral diseases of intensively cultured bivalves as well as several parasitic diseases. Operation of an intensive culture system requires that practices be in place to limit the entry of bacteria and other microbial contaminants from the three primary sources, namely the brood stock, algal food cultures and the sea water source. In addition, pathogenic bacteria must be managed within the culture system. Such bacteria may be found on system surfaces and recolonize such surfaces rapidly after disinfection. Although hygienic practices are essential and effective to some extent, they are often not sufficient to prevent the occurrence of infectious diseases in the hatchery and nursery systems. Even the earliest reports of bivalve larval culture referenced the use of antibiotics to improve survival. While purified antibiotics added to cultures may improve survival, their use has three primary drawbacks. These are high cost, problems associated with the formation of resistant strains of bacteria and the fact that few antibiotics are registered for legal use for application in bivalve cultures. As a result, antibiotics are not widely used in bivalve mollusc intensive culture. Displacement of pathogenic bacteria in culture systems with beneficial bacteria has been proposed for bivalve culture systems. At present, limited results from such applications do not appear to be reproducible between different culture sites or applications although there are isolated reports of the utility of this approach. Systematic investigative research and documentation appears to be necessary before this method can be successfully applied, including evaluation of different mechanisms of displacement of pathogenic by benign bacteria.
Dr. Martin Kalmokoff, Bureau of Microbial Hazards, Food Directorate, Health Protection Branch, Health Canada, Ottawa, Ontario, Canada A wide variety of commercial probiotics are available for use in both humans and in animal production systems. The majority of these consist of either single cultures or mixtures of lactic acid bacteria (LAB), Bifidobacteria spp., as well as a variety of fungi. Health claims for these products include alterations to the ecology of the gut microflora, resulting in the suppression of pathogens, and stimulation of host immune system through mechanisms involving colonization of the gastro-intestinal tract, competitive exclusion, and the production of acids and bacteriocins. Although some positive effects have been reported under certain conditions, evidence supporting the beneficial effects of these products in healthy humans remains scarce. Experimentally, ruminants have represented a very good model for the study of probiotics. Positive effects on productivity resulting from alterations to the endogenous microbial flora have been demonstrated (e.g. detoxification, rumen protozoa, phage therapy) and recently, examples of the competitive exclusion of Escherichia coli O157:H7 from the rumen of calves, and the use of a genetically-modified rumen anaerobe for detoxification of a plant toxin in sheep, have been reported. In contrast to animal probiotics, live bacterial cultures (primarily LAB) are widely used in the production and preservation of many fermented food products. LAB and other bacteria produce a wide range of antimicrobial agents including bacteriocins, phage, and antibiotics. Increasing consumer demands for both minimally processed and ready-to-eat foods have renewed interest in the application of these cultures for both the extension of shelf life and the creation of additional barriers to the growth of pathogens.
Dr. Abayomi Alabi, Island Scallops Limited, 5552 West Island Highway, Qualicum Beach, BC, V9K 2C8, Canada One of the difficulties encountered in commercial invertebrate hatcheries has been poor larval survival attributed to attack by opportunistic bacteria. A wide range of methods is therefore employed to limit and reduce the number of bacteria occurring in hatchery water supplies and rearing systems. Chemotherapeutants depend on a host having a higher tolerance threshold level to the substance than the target organism. However, these differences are often marginal and depend on the physiological state of the larvae. Bacterial resistance has also been reported in response to widespread and indiscriminate use of antibiotics. Other pre-treatment methods frequently used are filtration, ultra-violet (UV) light irradiation and ozonation. All these methods aim to reduce or eliminate bacteria in the water. However, disinfection or partial sterilization of seawater appears to encourage the selective development of bacterial communities that differ from those found in natural seawater. The onset of bacterial diseases has usually been attributed to environmental changes which favour the development of excessive levels of a particular pathogen. Obtaining control of the microbial environment of larval rearing systems should therefore permit increased manipulations of the bacterial flora and lead to increased larval survival. Such control may be obtained by maintenance of balanced populations of bacteria and by the use of defined probiotics. This study details results obtained in the successful commercial scale production of crustaceans, bivalves and echinoderms using these techniques. Potential shortcomings in the use of these methods are also discussed.
Dr. Gidon Minkoff, Island Scallops Limited, 5552 West Island Highway, Qualicum Beach, BC, V9K 2C8, Canada Repeated mortalities of turbot larvae in a commercial hatchery, at particular time intervals within any production cycle (day 13 to 18 from first feeding), were attributed to bacterial (mainly Vibrio spp.) infections. Histological analysis revealed enteritis, coinciding with bacterial proliferation in the intestinal lumen, as the main pathology in moribund larvae. Systematic analysis of the bacterial flora in the live food systems, the larval rearing tank water as well as the larvae, indicated that the live food played a central role in transmitting the bacteria to the larvae. Following this observation attempts were made to clean the live food as well as the tank water. Using simple bacteriological methods in which bacterial populations from the larval tank water and the live food were assessed using TCBS and TSA agar, protocols for turbot larval rearing were developed. In these protocols daily exchange rates of larval tank water were adjusted to the magnitude of the bacterial population. Furthermore, chemicals other than antibiotics were used for reducing bacterial proliferation in the tank water. Control of bacteria in the live food was evaluated through changes in the enrichment procedures. Finally, procedures for manipulating the bacteria associated with the live food were investigated.
Ms. Ingrid Salvesen, SINTEF Fisheries and Aquaculture, Brattora Research Centre, N-7465 Trondheim, Norway A strategy for microbial management in marine larviculture is presented. The strategy is based on three different elements that include non-selective reduction of bacteria, selective control of bacterial composition and enhancement of the ability of larvae to sustain bacteria in the environment. Presented experiments demonstrate the possible benefits of applying the different elements in larval rearing. A combination of the different elements in an overall strategy can substantially improve average survival, growth and reproducibility between replicates. Limitations of the strategy are discussed
Dr. Jan A. Olafsen. University of Tromsø, Norwegian College of Fishery Science, Department of Marine Biotechnology, N-9037 Tromsø, Norway Marine organisms live in intimate relationships with the microflora. Various forms of interactions between bacteria and biological surfaces occur at egg, larval and adult stages, and may result in the formation of an indigenous microflora - or be the first step in an infective process. Such interactions require a better understanding of the microbes colonizing factors and host natural. In aquaculture eggs are kept in incubators with a microflora that differ in numbers and characteristics from that in the sea, and become overgrown with bacteria within hours after fertilization. Members of the adherent microflora may damage eggs, whereas we do not know whether a natural egg epiflora may bestow some protection. The factors that may protect eggs from bacterial invasion are not yet understood. Marine fish larvae ingest bacteria and are thus primed with antigens before active feeding commences. At present we know little about the establishment, composition and role of the normal microflora of fish. Uptake and sequestering of intact bacterial antigens by newly hatched larvae may result in immune tolerance, but we have scarce information about acquired tolerance of fish to the microflora. A number of marine bacteria adhere to fish mucus, and pathogenic vibrios may colonize the gastrointestinal brush border of fish larvae and result in extensive microvilli damage. However, little is known about adhesins, receptors or other colonization factors. Marine filter-feeding invertebrates are also exposed to a dense microflora harboring multiple pathogens. Whereas the body fluids of warm-blooded animals are normally sterile, hemolymph of healthy bivalves may contain bacteria, and thus they may act as vectors for the spreading of fish pathogens. Thus the commensal microflora of larvae in aquaculture may be affected by microorganisms in the water, on the eggs and in resident invertebrates of the farm. Lectins in invertebrate hemolymph are constitutive proteins whose activities may be augmented following invasion of bacteria, and thus act as opsonins. Recently we have demonstrated that bivalve lectins may react with the LPS of marine bacteria, and that part of the lectin molecule may also exhibit antibacterial activity. Thus, there is a complex relationship between host defenses and the natural microflora. Successful aquaculture will depend on extensive knowledge of the complex interactions between the cultured organisms and the bacterial communities that develop on mucosal surfaces and in the rearing systems. The use of probiotics has proven advantageous in domestic animal production, and such modulations of the microflora may also have a potential in aquaculture. For halibut (Hippoglossus hippoglossus) the numbers of mucous (saccular) cells increase following addition of bacteria to incubators. Survival of the halibut larvae is affected by incubation with commensal, non-pathogenic bacteria, such as Lactobacillus plantarum or apathogenic strains of Vibrio salmonicida and Vibrio iliopiscarius sp. nov., isolated from fish. Higher survival rates were obtained when V. salmonicida and L. plantarum were added to the incubation water, whereas V. iliopiscarius reduced survival in the first critical two weeks of the yolk-sac stage. Thus incubation of halibut larvae with commensal bacteria may increase survival, depending on the strain used.
Dr. Steve Griffiths, Group Leader Molecular Group RPC, Fredericton, NB, Canada Traditionally, hatchery bacteriology has involved the use of culture methods to provide a viable cell count. The rationale is to identify any increases in bacterial loading that might enable corrective action. During our initial involvement with a program to monitor haddock and halibut hatcheries, culture methods provided little useful information: water samples were characterized as hosting between 103 and 105 colony forming units (cfus) per ml, regardless of larval status, and live feed cultures of Artemia and rotifers were generally highly contaminated (frequently greater than 108 cfus per ml). The only point at which culture methods were found to be useful was in the appraisal of sterilization methods as a means of reducing bacterial load in source water. The culture method is time consuming, provides little information on culturable species without further biochemical testing and may be prone to overgrowth by particular species of bacteria or fungi. For the past two years we have used bacterial DNA profiling to provide more qualitative information. The profiling methods are based on the identification of short ribosomal DNA (rDNA) sequences that are shared by all bacteria. Universal sequences, which flank more variable regions of rDNA, are then used as primers in the polymerase chain reaction (PCR). Equally sized pieces of DNA are amplified from the most predominant bacteria in the sample. Individual species of bacteria are then identified by running the mixed products on a gel that contains a linear gradient of denaturant. The variation in DNA sequence between the universal primers is further reflected by the concentration of denaturant required to split or melt the double stranded DNA; a less stable piece representative of one species may melt and become fixed at a lower concentration of denaturant near the top of the gel, while another may be more stable and require a higher concentration allowing it to move further into the gel. The end result is a community profile or fingerprint of the predominant bacterial species present in a sample. Individual bands can then be removed from the gel for DNA sequencing and identification by sequence comparison. Most of the work involves the monitoring of predominant species of bacteria that may indicate poor water and feed quality or the proliferation of opportunistic pathogens. Conventional wisdom is that a healthy profile consists of many bands of equal intensity reflecting a balanced bacterial community. In contrast, the appearance of one or two intense DNA bands would indicate an imbalance in the community with a limited number of species becoming predominant. Previous studies have indicated that if a species represents 1% of the total population it will be represented by a discrete band within the profile. Sample preparation for water algae and live feed is a relatively simple procedure consisting of the sedimentation of particulate matter onto a 0.7 cm glass fibre disc in a microcentrifuge tube and a one step DNA extraction method. For finfish larvae, material is first homogenized prior to extraction. The sensitivity threshold is approximately 1,000 cfus per ml of seawater. As such the assay has a built in quality control: if amplification does not occur, the sample may be considered to be within acceptable bacterial load for water samples. The DNA primers we have chosen for the bacterial work are able to amplify DNA from all bacterial species. In addition the technique has the added advantage of identifying rDNA sequences carried by the plastids of some algal species (e.g. Isochrysis), thus providing a rapid method to determine the balance between alga and contaminating bacteria. Thus far, the method has enabled us to make some important observations. At one hatchery mass mortality of larvae was preceded for three years running by the predominance of an unknown unculturable species with sequence homology to Roseobacter. The same species has also been found in another geographically separate haddock hatchery also suffering from high larval mortality (0.05% survival). A bacterium that is often singularly predominant in Artemia can be found at four geographically separate hatcheries implying that an indigenous marine species monopolizes the cultures or that the bacterium is a common contaminant of commercially available preparations. The latter possibility is currently favoured. Even though this same bacterium was found to establish itself in the larvae on first feeding, no connection could be made with increasing mortality of larvae receiving the live feed. At another hatchery, decrease in appetite and increase in larval mortality coincided with the predominance of a coldwater Vibrio species, which was detected in the larval extracts before appreciable losses, occurred beyond early mortality. Treatment with antibiotics appeared to bring the fish back on feed and subsequent samples are being monitored for the proliferation of the same Vibrio species. In summary, the DNA profiling method to provides a rapid appraisal of qualitative and quantitative aspects of environmental bacteriology with the potential for corrective management. The technique may be applied to any situation where bacterial community profiling is required and may also be used to monitor bacterial population changes following the administration of a probiotic.
Dr. Harry Birkbeck, Division of Infection and Immunity, Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow, Scotland In intensive rearing of both turbot and halibut significant losses occur during the transition to first feeding on rotifers or Artemia, and bacteria are considered to play a major role in determining larval survival. The development of the gut flora of larvae has been monitored in a number of hatcheries with different rearing strategies. The bacterial flora that develops in the larval gut is derived from that of the food organisms (Artemia and rotifers) although not necessarily the dominant bacteria associated with these organisms. The properties of bacteria which might colonize the gut, and attempts to colonize the gut with a defined microflora will be discussed. Impact of and Limitations of Vaccines in Bacterial Disease Control Dr. Julian Thornton, Microtek International, Saanichton, British Columbia, Canada There are now many commercial vaccines available for the prevention of disease in finfish aquaculture. These vaccines have historically been either simple bacterins for immersion vaccination of fish, or mixtures of several bacterins formulated with different adjuvants for injection delivery to fish. The adjuvants used have generally been oil (mineral and non-mineral), alum, b(1-3)-glucans, or various combinations of these. The widespread use of vaccines for the prevention of disease outbreaks has been an important contribution to the sustainability of finfish culture. It has lead to a massive reduction in the use of antibiotics, particularly in the culture of salmonids, and in many cases to overall increases in biomass production by generally increasing the health of the stock. Despite the obvious success of various vaccination strategies in aquaculture, there are many situations in finfish culture and in the culture of other aquatic animal species where vaccines are ineffective, or cannot be employed. These situations include, but are certainly not limited to, impaired, or under-developed immune systems, lack of knowledge involving antigens of the pathogens, the lack of a specific immune response, and physical problems associated with vaccine administration. In these situations, alternatives to antibiotic therapy must be sought. These alternatives may include the use of probiotic therapy.
Dr. David J. Nisbet, US Department of Agriculture, Agricultural Research Service, Food Animal Protection Research Laboratory, College Station, Texas, 77845, USA A competitive exclusion culture (PREEMPT™) containing a mixture of twenty-nine different bacterial isolates obtained from the cecae of broiler chickens was developed utilizing continuous-flow culture techniques. Prior to commercialization this CE culture had been referred to in the scientific literature as CF3. This culture has been efficacious in controlling gut colonization by enteropathogens in both experimentally infected broilers and under commercial field conditions. In experiments where day-old broiler chicks were provided PREEMPT™, and then challenged with 10,000 CFU Salmonella typhimurium greater than a 99% reduction in Salmonella cecal colonization levels was observed compared to experimentally infected controls that did not receive the culture. Similarly, PREEMPT™ has also been shown to protect experimentally infected broiler and/or layer chicks from cecal colonization by S. enteritidis (Phage types 4 and 13), S. gallinarum, Listeria monocytogenes, Campylobacter, and Escherichia coli O157:H7. Additionally, groups of chicks provided PREEMPT™ that were experimentally infected with 100,000 CFU S. gallinarum had significantly less mortality compared to groups of chicks not provided PREEMPT™. In a Food and Drug Administration approved, double blinded, pivotal, clinical field trial, all chicks treated with PREEMPT™ and challenged with S. typhimurium were cecal Salmonella negative at end of growout, and this was significantly different than the non PREEMPT™ treated Salmonella challenged controls. Using the same technology a defined CE culture has been developed for the swine industry. This culture has been shown to decrease fecal shedding, gut and organ colonization of salmonellae, and pathogenic E. coli, as well as reduce mortality associated with E. coli in very young pigs. The swine product will be tested in FDA trials and will be available to the swine industry soon. CE products are a novel method of controlling human food pathogens in food-producing animals that can be used as an alternative to antibiotics.
Huys L.a,c, Rombaut G.b, Dhert P.a, Robles R.a, Sorgeloos P.a, Swings J.c, aLaboratory of Aquaculture & Artemia Reference Center, University of Ghent, Rozier 44, 9000 Gent, Belgium; bLaboratory of Microbial Ecology and Technology, University of Ghent, Coupure Links 653, 9000 Ghent, Belgium; cLaboratory of Microbiology, University of Ghent, Ledeganckstraat 35, 9000 Gent, Belgium Cultivation of marine fish larvae is mostly done under intensive hatchery conditions resulting in unpredictable survival rates and sometimes even mass mortality. Experiments have suggested that these mass mortalities may be due to the proliferation of pathogenic bacteria that prevent the establishment of a normal microflora in the larval intestine. Therefore, it is of utmost importance to develop a strategy able to control the microbial conditions in the culture of marine fish larvae. Colonization of the digestive tract with beneficial or "probiotic" microorganisms is a well-recognized practice in veterinary medicine and this concept may be used in larval rearing. In the present study, the aerobic bacterial flora in the gut of turbot larvae and their influence on larval survival was investigated. The overall goal was to identify beneficial bacterial strains that later on may be used to improve the hatchery output in terms of reproducibility and larval survival rates. In total, 127 bacterial isolates were isolated from first feeding turbot and based on their fatty acid profile obtained by FAME-analysis and using principal component analysis, the isolates were subdivided in 12 major gas chromatographic (GC)-groups or clusters, 11 isolates remained unclustered. Four specific GC-groups (cluster A, B, I and J) were selected as potential beneficial bacteria for turbot larviculture as the majority of the isolates of these clusters derived from rearing tanks with a survival percentage higher than 35%. Representative isolates of these clusters were screened on their ability to enhance the poor reproducibility of larval survival in a small-scale turbot starvation test. Also a Vibrio mediterranei Q40 strain, isolated from sea bream larvae, was included in these small-scale starvation tests. The representative isolates of cluster A and the Vibrio mediterranei Q40 strain showed a distinct and reproducible positive effect on the survival of turbot larvae compared to the untreated control groups. This result implies that the strains representing cluster A and Vibrio mediterranei Q40 could play a role as first colonizers of the gut of larval turbot. Thus the early colonization of the gut by non-opportunistic bacteria may initiate a resident microflora and in that way prevent the proliferation and colonization of the gut of larvae by opportunistic and/or pathogenic bacteria. As several studies demonstrated that once feeding commences, the intestinal microflora was derived from the live feed ingested rather than the bacteria present in the water. Only mass cultivated live food, such as rotifers Brachionus plicatilis, might be the most important source of opportunistic bacteria in first feeding marine fish larvae. This is due to the dense rotifer cultures and their accompanying food that inevitably constitute a high level of organic materials allowing a high growth rate of the bacterial population. Therefore, screening for a potential beneficial bacterial strain for turbot larvae goes together with screening for a potential beneficial bacterial strain able to optimize the rotifer population. The effect of the selected bacterial strains on the rotifer culture was verified under monoxenic conditions. The strains representing cluster A, B, I and Vibrio mediterranei Q40 considerably enhanced the density of the rotifer population. These results indicate that pre-emptive inoculation of the seawater with specific bacteria, namely the inoculation of the water immediately after disinfection of the rotifer resting eggs in order to obtain monoxenic cultures, provides a method to control the bacterial environment. Consequently this is leading to a more predictive rotifer production, which is necessary for the intensive larval fish production. Hence, the possibility of manipulating the bacterial flora of the vector system such as rotifers provides a method for controlled transfer of desirable bacteria to the gut of turbot larvae. However the bacterial development in first feeding turbot larvae is still a complex system and further studies on the interactions between the fish larvae and the bacterial communities of the rearing water and the live food are required.
Dr. Susan M. Bower, Fisheries and Oceans Canada, Pacific Biological Station, Nanaimo, BC, V9R 5K6, Canada The opportunities for the use of probiotics in shellfish culture in British Columbia are recognized. In addition to the standard proposed uses of probiotics to control bacterial disease outbreaks, this technology may have other applications. For example, waters from the Strait of Georgia are known to be periodically unsuitable for the culture of bivalve larvae. Although the specific reason(s) for apparent poor water quality have not been identified, speculation on the cause include the presence of adverse chemicals associated with the Fraser River plume or toxins released from phytoplankton blooms. Preconditioning of water by probiotics may circumvent such problems. Another novel opportunity for probiotic use may arise in conjunction with the proposed culture of abalone in British Columbia. The demise of the only attempt to commercially culture abalone in British Columbia was in part attributed to the protozoan parasite Labyrinthuloides haliotidis. Investigations into methods for preventing or controlling this parasite in a culture facility revealed its resistance to many disinfectants and chemical treatments applicable to the aquaculture industry. However, it was noted that L. haliotidis did not survive in vitro in the presence of bacterial contaminants. Thus, it is speculated that if L. haliotidis should again become a problem for abalone culture, investigations into probiotics could identify useful techniques for managing this disease agent. Although probiotics represent an alternative to the use of chemicals for the control of disease agents in container-based aquaculture operations, implementation must proceed cautiously because the overabundance of even beneficial organisms in a culture system could have unpredictable detrimental effects.
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