Nutritional diseases

Nutritional diseases of fish may develop as a result of deficiency (undernutrition), excess (overnutrition), or imbalance (malnutrition) of nutrients present in their food. The disease usually develops gradually because animals have body reserves that make up for nutritional deficiency up to a certain extent. Disease signs develop only when supply of any diet component falls below critical level. When there is too much food, the excess that is converted to fat and deposited in fish tissues and organs, may severely affect physiological functions of the fish

Nutritional diseases

Diagnosis of nutritional diseases is difficult because many signs exhibited by fish are non-specific and most nutritional deficiencies are hard to define. A compilation of data on feed composition and feeding management, as well as husbandry practices, are needed to define a case. Most of data on fish and shrimp nutritional diseases were gathered under experimental conditions. Under farm conditions, most of that definition would be clouded with errors in husbandry practices or secondary infection. Therefore, attempts to diagnose nutritional diseases should be carefully done using every available technique to define the case

Healthy and wholesome aquaculture.

The concept of healthy and wholesome aquaculture as a holistic approach to sustainable food-fish production has gained more relevance since it was discussed in a similar SEAFDEC forum almost a decade ago. Similar concepts to optimize yield from various production systems with least impact on the environment include Best Management and Good Aquaculture Practices. The three prioritized areas of disease control, food safety and environmental integrity that were identified during the first Fish for the People Conference in 2001 guided the research and development strategies for the past decade. The dynamic nature of aquaculture, however, also paved the way for major species introductions that changed the regional production scenario altogether. An important component of effective disease prevention and control is the development of diagnostic techniques. In response to recommendations made in 200I during the first Fish for the People Conference, diagnostic procedures have been harmonized, classified according to levels of complexity, and a few have been translated into techniques for pond-side application. Disease surveillance and reporting have been enhanced in most countries and the awareness about transboundary diseases has been heightened. The region, however, still has a lot to learn about bringing in new and exotic species and their accompanying threat of disease introduction. The past decade has seen the replacement of Penaeus monodon by P. vannamei as the major shrimp species in culture that has resulted in the introduction of major viral diseases like infectious myonecrosis virus (lMNV) and taura syndrome virus (TSV). The first outbreak of koi herpes virus (KHV) occurred in Indonesia in 2002 and Japan in 2003, and the disease continues to affect the koi and common carp industry in some countries in Asia (Lavilla-Pitogo & Nagasawa 2004). Various parasites have become major threats to sustainable marine fish production. Thus, controlling the spread of important pathogens through the introduction of exotic fish species, or the transfer of infected fish to another facility or to wild habitat remains a major problem. The development of specific-pathogen-free stocks and the corresponding implementation of biosecurity measures are the most significant advancements to control viral diseases each a prerequisite of the other to guarantee successful production. The vastness of land-based aquaculture systems, however, makes the cost of implementing biosecurity prohibitive, thus, there remains the need for additional health implements to boost fish health like vaccines, immunostimulants, probiotics, chemotherapeutics and disinfectants. Although major research efforts have been devoted to develop such products, satisfactory field test results are wanting for most of them. The issue on unwanted residues in marketable fish products and the fate of antimicrobials and chemicals in the environment are the major deterrents for their widespread application in aquaculture. Furthermore, the lack of fish health professionals that are qualified to prescribe drugs and chemotherapeutants in aquaculture is an issue that needs urgent action in the region. The clamor for aquaculture to reduce its dependence on fish meal as the source of protein in artificial feeds has led to numerous studies about fishmeal substitutes. The search for suitable alternative fish feed ingredients may now require a combination of biochemical engineering and manufacturing to enhance the nutritional composition of non-traditional protein sources. Fishmeal substitutes and other feed ingredients that will not compromise fish health and drastically alter carcass composition needs to be developed. Since proper feed management is a key component for farm profitability and sustainability as well as in the reduction of environmental pollution, extension and technology transfer should continue so that various stakeholders will be informed of their responsibility. Efforts to improve fish feed development should continue keeping in mind that feed is a key determinant of fish health. For aquaculture to meet the target production to supply the protein requirements of a burgeoning global population, production systems should further emphasize the key components of keeping diseases under control, producing fish that pass food safety standards, and maintaining the integrity of the culture system and its environment. In various countries, supportive efforts are in the form of certification, accreditation and compliance of aquaculture facilities with standards. However, aquaculture, being a relatively new sector in the food production industry, needs to harmonize its efforts with other common resource users

Will microbial manipulation sustain the ecological balance in shrimp (Penaeus monodon) hatcheries?

A shift in preferred methods employed to contain bacterial diseases in the hatchery phase of shrimp culture has resulted largely from the unsuccessful control by and deleterious effects of chemotherapy. Manipulation of hatchery microbial ecology has gained popularity, but for successful implementation, this niche-filling approach requires a thorough understanding of the epidemiology of bacterial diseases in the hatchery. This study examined the responses of Vibrio harveyi populations, (associated with luminescent vibriosis in shrimp larvae) to various physico-chemical factors and various hatchery components. Results showed that V. harveyi had a wider range of tolerance to environmental parameters than larvae of Penaeus monodon, such that control measures based on manipulation of these parameters might not be feasible. However, it was evident from the results that there were components in the shrimp hatchery environment that could be manipulated to control high populations of V. harveyi. The natural microflora of seawater, as well as the microbial flora associated with the diatoms Skeletonema costatum and Chaetoceros calcitrans negatively affected the survival of V. harveyi in experimental mixed cultures. The successful manipulation of such benign microbial components to compete with and exclude potential pathogens is necessary to sustain ecological balance in the shrimp hatchery environment.We thank the International Development Research Centre (IDRC) of Canada for funding the research under Project 3-P-88-1053-02. Sheila Mae Buen provided excellent help with the graphs

Occurrence of Vibrio sp. infection in grouper, Epinephelus suillus

Vibrio sp., was consistently isolated from grouper, Epinephelus suillus, with bacterial infection. Fingerlings, which were challenged with the bacterium by injection, were highly susceptible. Immersion challenge resulted in 100% mortality within 48 hrs in fish subjected to combination of injury and exposure to the bacterium. Mortality in uninjured fish was observed in the long bath subgroup, but not in the short bath subgroup. These results are correlated with the present practices in the grouper fingerling industry in the Philippines

Enhancing disease monitoring in shrimp through a geographical information system (GIS) application

Abstract only.SEAFDEC Aquaculture Department (AQD) pioneered fish disease work in the Philippines and developed diagnostic tools through research. Its Diagnostic Service Laboratory was established in the late 1970s to serve the budding aquaculture industry. Through the assistance of SEAFDEC AQD, this service has been replicated by both private and government agencies involved in shrimp aquaculture, thus, data on disease occurrence and prevalence are already available in databases in various forms. Laboratory analysis of hatchery-reared shrimp postlarvae has become an important tool for marketing using both physical and health attributes as gauges for acceptance or rejection of specific batches. Through the years, the diagnostic tools have evolved from mere wet mount microscopy to molecular diagnostic techniques by means of polymerase chain reaction (PCR) to detect viruses. Despite this development, however, disease information is still patchy and difficult to use as decision-support tools because it remains in highly technical and in difficult to visualize information spreadsheets and tables. GIS is a tool that translates complex data in tables and spreadsheets into maps that provide visual displays of information in both spatial and temporal forms. It shows disease trends that are not presently seen and understood by all stakeholders. This paper will highlight the evolution of shrimp health monitoring as a marketing tool in the Philippines and how the application of GIS has helped in understanding disease patterns in the shrimp industry

Antimicrobial susceptibility of Aeromonas spp., Vibrio spp. and Plesiomonas shigelloides isolated in the Philippines and Thailand

Aeromonas spp., non-cholera vibrios (NCVs) and Plesiomonas shigelloides belong to the expanding group of water and food-borne pathogens. They are widely distributed in aquatic environments and are increasingly regarded as important pathogens of aquatic animals, causing significant economic losses in the aquaculture industry worldwide. In addition, these bacteria have been implicated as opportunistic pathogens, mainly causing gastroenteritis in humans. The occurrence and isolation of these bacteria from different sources has been reported in Asia, including the Philippines and Thailand. However, information on antimicrobial susceptibility of these isolates, especially those recovered from aquaculture and aquatic environments is scarce. The aim of this study was to acquire data on the occurrence of antimicrobial resistance among 38 strains of Aeromonas spp., NCVs and P. shigelloides isolated from different sources in the Philippines and Thailand. In addition, the production of extended-spectrum ß-lactamases (ESBLs) by selected strains was determined

Occurrence, characterisation and detection of potential virulence determinants of emerging aquatic bacterial pathogens from the Philippines and Thailand

Strains of Aeromonas spp., 'non-cholera vibrios' (NCVs) and Plesiomonas shigelloides isolated from aquatic environments, fish and human diarrhoeal cases in the Philippines and Thailand were characterised for potential virulence markers. Thus, the production of cytotoxin, cell-associated and cell-free haemolysin and their capacity to adhere to human intestinal (Henle 407) cells in vitro was investigated. In addition, the occurrence of tlh and tdh haemolysin genes and urease activity among V. parahaemolyticus strains was investigated. The results showed that strains recovered from clinical sources (human and fish) produced these virulence factors, whereas these are absent in environmental strains