Microalgae aquaculture feeds

Microalgae feeds are currently used in relatively small amounts in aquaculture, mainly for the production of larvae and juvenile shell- and finfish, as well as for raising the zooplankton required for feeding of juvenile animals. The blue-green algaSpirulina is used in substantial amounts (over 100 t y^–1) as a fish and shrimp feed, and even larger markets can be projected if production costs could be reduced. Another potential large-scale application of microalgae is the cultivation ofHaematococcus for the production of the carotenoid astaxanthin, which gives salmon flesh its reddish color. In the long-term microalgae biomass high in lipids (omega-3 fatty acids) may be developed as substitutes for fish oil-based aquaculture feeds. In shrimp ponds the indigenous algal blooms supply a part of the dietary requirements of the animals, but it is difficult to maximize algal productivities. A separate algal production system could feed the shrimps and minimize the need for added feed. Bivalves feed essentially exclusively on marine microalgae throughout their life cycle. The development of cultivation technologies for such microalgae would allow the onshore production of these animals, with greatly improved product quality and safety.This paper was presented at the Symposium on Applied Phycology at the Fourth International Phycological Congress, Duke University.     

Antipodean aquaculture agents

Parallel features exist among diseases in Antipodean hosts when compared with those in other tropical and temperate regions. These features can be associated between infections in fish and prawns and between infections in freshwater and saltwater systems. Both fish and prawns are prone to physical stress, to behavioural stress, and to both introduced and native disease agents, agents that are limiting factors in several established aquaculture ventures. Both types of hosts are reared in a variety of facilities, each allowing for a different dynamic predisposition for disease. These diseases include those caused by native freshwater, estuarine and marine agents in both introduced and native hosts, and by introduced agents in those hosts. Some infections reflect unexpected or unidentifiable agents and host responses. Much can be learned in Australia and New Zealand from the infections, successes, failures and innovative methodologies experienced or used in the rest of the world. Potential in the Antipodes for production of unique and abundant fishery products is immense for both local and export markets. Approaches, however, should remain cautious regarding introductions and persistent regarding the investigation of potential diseases, host responses, diagnostic methods and management techniques.     

Virus diseases in aquaculture

World Journal of Microbiology and Biotechnology -     

Microalgal feeds for aquaculture

The concurrent trends of increasing consumption of seafood and decreasing natural harvests will dictate that a larger portion of seafood must be derived from aquaculture in the 21st century. The difficulty of producing economically large quantities of microalgal feeds is currently one of the major impediments to the further development of the aquaculture industry. Traditional methods, which rely on photosynthetic growth in outdoor ponds or indoors under artificial lights, suffer from the phenomenon of light-limitation of biomass density. Certain species of microalgae are capable of heterotrophic growth to high density utilizing sugars or other organic compounds for energy and cell carbon. This paper reviews work with strains of heterotrophic algae that have demonstrated potential as both nutritional feeds and for economical production by fermentation.     

Disease in marine aquaculture

It has become almost a truism that success in intensive production of animals must be based in part on development of methods for disease diagnosis and control. Excellent progress has been made in methods of diagnosis for major pathogens of cultivated fish, crustacean and molluscan species. In many instances these have proved to be facultative pathogens, able to exert severe effects in populations of animals under other stresses (marginal physical or chemical conditions; overcrowding). The concept of stress management as a critical prophylactic measure is not new, but its significance is being demonstrated repeatedly. The particular relationship of water quality and facultative pathogens such asVibrio, Pseudomonas andAeromonas species has been especially apparent. Virus diseases of marine vertebrates and invertebrates — little known two decades ago — are now recognized to be of significance to aquaculture. Virus infections of oysters, clams, shrimps and crabs have been described, and mortalities have been attributed to them. Several virus diseases of fish have also been recognized as potential or actual problems in culture. In some instances, the pathogens seem to be latent in natural populations, and may be provoked into patency by stresses of artificial environments. One of the most promising approaches to disease prophylaxis is through immunization. Fish respond well to various vaccination procedures, and new non-stressing methods have been developed. Vibriosis — probably the most severe disease of ocean-reared salmon — has been controlled to a great extent through use of a polyvalent bacterin, which can be modified as new pathogenic strains are isolated. Prophylactic immunization for other bacterial diseases of cultivated fish has been attempted, especially in Japan, with some success. There is also some evidence that the larger crustaceans may be immunologically responsive, and that at least short-term protection may be afforded to cultured populations. Some progress has been made in marine disease control through chemical treatment in intensive culture systems, principally through application and modification of methods developed for freshwater aquaculture. Major constraints to use of chemicals are restrictions due to public health concerns about food contamination, and the negative effects of some chemicals on biological filters and on algal food production. There is a continuing need, however, for development of specific treatments for acute disease episodes — such as the nitrofurans, developed in Japan, which are effective for some bacterial diseases. The history of aquaculture — freshwater as well as marine — has been characterized by transfers and introductions of species to waters beyond their present ranges. The process continues, and carries with it the possibility of transfers of pathogens to native species and to the recipient culture environments. International groups are attempting to define codes of practice to govern such mass movements, but examples of introductions of real or potential pathogens already exist. The most recent and the most dramatic is the world wide transfer of a virus pathogen of penaeid shrimps. Earlier examples include the introduction of a protozoan pathogen of salmonids to the western hemisphere, and the introduction of a parasitic copepod from the Far East to the west coast of North America and to France. The conclusion is inevitable — diseases are substantial deterrents to aquaculture production. Diagnostic and control procedures are and will be important components of emerging aquaculture technology.     

Developing Porphyra/salmon integrated aquaculture for bioremediation and diversification of the aquaculture industry

For rapid growth and appropriate pigmentation,Porphyra requires the constant availability of nutrients, especially in summer when temperate waters are generally nutrient depleted. Cultivation near salmon cages allows the alleviation of this seasonal depletion by using the significant loading of fishf arms, which is then valued (wastes become fertilisers) and managed (competition for nutrients between desirable algal crops and problem species associated with severe disturbances). Porphyra,being an extremely efficient nutrient pump, is an excellent candidate for integrated aquaculture for bioremediation and economic diversification. Frequent harvesting provides for constant removal of significant quantities of nutrients from coastal waters, and for production of seaweeds of commercial value. The production of P. yezoensis being limited in the Gulf of Maine, an assessment of the potential of seven native north-west Atlantic Porphyra species is presently in progress. To enable the production of conchospores for net seeding, the phenology of these species and the conditions for their vegetative conchocelis exponential growth, conchosporangium induction, and conchospore maturation were determined. The development of integrated aquaculture systems is a positive initiative for optimising the efficiency of aquaculture operations, while maintaining the health of coastal waters. This revised version was published online in August 2006 with corrections to the Cover Date.     

Biotechnology and aquaculture of rotifers

Biotechnology can be defined as any technology that involves living organisms or their derivatives. In applying this definition to rotifers, we focus on their contribution in culturing of early larval stages of marine fish. After almost four decades of marine fish culture in captivity, the success of this worldwide industry is still quite dependent on mass culture of the species Brachionus plicatilis and B. rotundiformis. In mass culture, the rotifers are continuously driven to reproduce at high rates, in relatively extreme environmental conditions of high population density and high loads of organic matter. Therefore, the success of mass cultures and future improvements in these systems relies on a close interaction between basic and applied studies of rotifers. In the present review, we will attempt to analyze why rotifers are suitable for early life stages of fish and to describe, in general, methodologies that have been devised for reliable supply of rotifers in large quantities. Problems associated with rotifer production, nutritional quality and effect on fish health and nutrition, will be discussed. Research on B. plicatilis and B. rotundiformis has increased enormously during the past three decades and these two species are the best-studied rotifers so far. While much of the research on these species is directed or devoted to the needs of aquaculture industry, they are also used as models for addressing basic biological questions, due to the relative ease of culture and their availability. Studies on feeding, pheromones, speciation in rotifers, the occurrence and putative hormones involved in sexual and asexual reproduction and production of resting eggs, are few examples of such studies. Rotifers will probably maintain their role as food organism for fish larvae, in spite of attempts to replace them with more accessible formulated food. Development of new culture methods that will improve the nutritional quality and production efficiency of rotifers may result in more diversified and flexible tasks for these organisms in aquaculture.     

Rotifers as food in aquaculture

The rotifer Brachionus plicatilis (O.F. Muller) can be mass cultivated in large quantities and is an important live feed in aquaculture. This rotifer is commonly offered to larvae during the first 7–30 days of exogenous feeding. Variation in prey density affects larval fish feeding rates, rations, activity, evacuation time, growth rates and growth efficiencies. B. plicatilis can be supplied at the food concentrations required for meeting larval metabolic demands and yielding high survival rates. Live food may enhance the digestive processes of larval predators. A large range of genetically distinct B. plicatilis strains with a wide range of body size permit larval rearing of many fish species. Larvae are first fed on a small strain of rotifers, and as larvae increase in size, a larger strain of rotifers is introduced. Rotifers are regarded as living food capsules for transferring nutrients to fish larvae. These nutrients include highly unsaturated fatty acids (mainly 20: 5 n–3 and 22: 6 n–3) essential for survival of marine fish larvae. In addition, rotifers treated with antibiotics may promote higher survival rates. The possibility of preserving live rotifers at low temperatures or through their resting eggs has been investigated.     

Gene transfer technology in aquaculture

The gene transfer technique, transgenesis, has permitted the transfer of genes from one organism to another to create new lineages of organisms with improvement in traits important to aquaculture. Genetically modified organisms (GMOs), therefore, hold promise for producing genetic improvements, such as enhanced growth rate, increased production and efficiency, disease resistance and expanded ecological ranges. The basic procedure to generate transgenic fish for aquaculture includes: (1) design and construction of transgenic DNA; (2) transfer of the gene construct into fish germ cells; (3) screening for transgenic fish; (4) determination of transgene expression and phenotype; (5) study of inheritance; and (6) selection of stable lines of transgenics.GMOs offer economic benefits, but also pose environmental threats. Optimising the mix of benefits and risks is of fundamental importance. The potential economic benefits of transgenic technology to aquaculture are obvious. Transgenic fish production has the goal of producing food for human consumption; thus the design of genetic constructs must take into consideration the potential risks to consumer health, as well as marketing strategies and product acceptance in the market.     

Sewage-fed aquaculture: The Calcutta model

Wastes have been rightly referred to as resources out of place. Since household wastewater often intermixes with effluents from industries and agricultural runoff, multidimensional approaches have been made towards maximizing protein production through rational exploitation of available resources. Sewage-fed aquaculture is a unique system and has manifold advantages in developing tropical countries acting as a major source of nutrients for crop farming and aquaculture, economical for sustainable production and helps to combat environmental pollution. The use of municipal wastewater fed to fertilize ponds began in Calcutta in the 1930s; the city now has perhaps the largest wastewater-fed aquaculture system in the world. A large number of people derive their livelihood from the sewage-fed aquaculture using the principles of systems ecology and applying it through ecological engineering. The subject of sewage-fed aquaculture is reviewed in terms of source, chemical nature, diversity pattern, recycling practices, production potential of aquaculture, environmental issues and safety measures for ecofriendly sustainable environmental management strategies.     

水产养殖中益生菌研究进展

益生菌在水产养殖中能够净化水质、预防疾病、促进生长且安全、环保、无抗性,是抗生素的理想替代品,具有重要的研究价值和广阔的应用前景。本文主要从益生菌制剂的定义概述、作用机理及特性进行阐述,分析益生菌制剂存在的问题,探讨水产养殖用益生菌制剂的研究方向。