水产养殖专业英语阅读材料

1. Microalgae contain large amounts of useful carbohydrates, proteins, lipids and antioxidants. This makes them an essential food source in the rearing of all stages of marine bivalve molluscs (clams, oysters, scallops), the larval stages of some marine gastropods (abalone, conch), larvae of several marine fish species and penaeid shrimp, and zooplankton.
2.Shrimp are infected by more than 20 virus-caused diseases, these viruses being classified within more than 10 families that are quite diverse in their genetic material, infection cycles, geographic distribution, host range and pathogenesis. The emergence and spread of these pathogenic agents have led to considerable economic losses, threatening the economic viability and long-term sustainability of the shrimp aquaculture industry worldwide. For some countries, the economic and social impacts of these pandemics have been sometimes so important that shrimp production has never fully recovered. As a consequence, the need for better control and understanding of viral diseases has prompted an increasing interest in the study of the shrimp immune system, and significant advances into the molecular bases for antiviral immunity in these animals have been gained in the last years.
3.The effects of recent global climate change have devastated some commercial aquatic organisms, which has resulted in considerable economic losses. Temperature is one of the most important environmental factors to consider when growing organisms in aquaculture. Temperature affects many chemical and biological processes including: the amount of dissolved oxygen in the water, chemical reactions, photosynthesis and aerobic respiration, the mobility and metabolism of organisms as well as their sensitivity to toxic substances, parasites and disease. Any change in the culture water temperature can have a dramatic effect on the growth and survival of aquatic organisms, and low temperature stress has deleterious effects on many aquatic animals. For example, fish farming in southern China has been adversely affected by winter mortality for several decades, especially in 2008.
4. Accumulating evidences indicate that low temperature can induce oxidative stress in aquatic organisms. When cells are exposed to low temperature, the rate of enzymatic reactions falls down, leading to a decrease in the demand for ATP and accumulation of electrons in certain points of the respiratory chain. The situation promotes a sudden increase in the production of a number of ROS which remove the burden of excess reducing potential. ROS are continuously generated by aerobic metabolism or oxidative stress and can damage important biomolecules, such as DNA, proteins and lipids. Due to the potentially serious effects of ROS, organisms have evolved defense mechanisms that act at various levels and can prevent, ameliorate or repair the damage caused by ROS.Water temperature is one of the most important environmental factors which directly affect the survival, growth, and metabolism of shrimp. Shrimp farming in southern China has been adversely affected by winter mortality for several decades, especially in 2008. Recent studies of shrimp have shown that acute low temperature stress would induce reactive oxygen species (ROS) production and hemocyte apoptosis, increase caspase-3 transcription and activity levels, cause DNA damage and lipid peroxidation, reduce the immune functions and resistance against pathogen infection. These studies conducted acute low temperature
stress experiment by transferring rapidly from a suitable temperature to a low temperature. However, in the natural environment, water temperature fluctuation is more complicated, and shrimp may suffer in the process of water temperature decrease. So far, only few study focus on the effects of temperature decrease on shrimp.
5. Hemocytes play an essential role in physiology and immune defense of shrimp. Loss and damage of circulating hemocytes would depress the immune ability, increase the susceptibility against pathogens, and even endanger the survival. Rapid low temperature transfer has been reported to cause total hemocyte count (THC) reduction which resulted from increased apoptotic hemocytes.
6. Streptococcosis has become a major problem for tilapia farmers and there is still no effective commercial vaccine available that can be used to prevent streptococcosis in tilapia. Tilapia growers must therefore focus on prevention and treatment of the disease. Streptococcosis can cause mass death in tilapia farms, and unlike many other tilapia diseases it will affect even large and otherwise healthy fish. Fish weighing at least 100 grams are actually more susceptible to streptococcosis than small fish. Streptococcosis outbreaks are known to take place primarily when the fish has been subjected to some form a stress, e.g. due to overcrowding, improper water chemistry or changing water temperatures.
7.Streptococcosis can be acute or chronic. Acute streptococcosis normally occurs during the warm season when the water temperature is high and will typically result in peaks of mortality that goes on for 2-3 weeks. Chronic streptococcosis occurs when the water temperature is lower and does not cause any peaks of mortality. The mortality rate will be low but the amount of dead fish will become high in the long run since the mortality level tends to be really persistent.
In farmed tilapia, the major cause of streptococcosis is Streptococcus agalactiae. The closely related bacterium Streptococcus iniae can also cause streptococcosis in tilapia, but is normally not as lethal as Streptococcus agalactiae. All species of Streptococcus are gram-positive, non-acid fast, non-motile, oxidase-positive, catalase-negative cocci.
8. The fish gut microbiota contributes to digestion and can affect the nutrition, growth, reproduction, overall population dynamics and vulnerability of the host fish to disease; therefore, this microbial community is highly relevant for aquaculture practice. Recent advances in DNA sequencing technologies and bioinformatic analysis have allowed us to develop a broader understanding of the complex microbial communities associated with various habitats, including the fish gut microbiota. These recent advances have substantially improved our knowledge of bacterial community profiles in the fish intestinal microbiota in response to a variety of factors affecting the host, including variations in temperature, salinity, developmental stage, digestive physiology and feeding strategy.
9.The immune system in fish is customary divided into innate (non-specific) and acquired (specific) system. Superoxide anion production and lysozyme activity are widely used as non-specific immune parameters in fish. Several reactive oxygen species (ROS) are produced by fish phagocytes during the respiratory burst. Once
bacteria or fungi are engulfed by leucocytes, the host’s NADPH-oxidase is activated, which in turn increases oxygen consumption and subsequently produces ROS such as superoxide anion (O2−). The release of superoxide anion is known as the respiratory burst, and together its derivates are bactericidal.
10.Tilapia is widely cultured in tropical and subtropical regions of the world. The production of tilapia has increased from 332,186 MT in 1990 to 4,080,898 MT in 2012 (FAO, 2014) and has been recognized by FAO as the most potent culture fish species in supplying human protein source of the Century. Feed is the most expensive cost item in aquaculture industry, often ranging from 50 to 60% of the total variable expenses. Fish meal is the major dietary protein source, comprising between 20 and 60% of fish diet in general. Due to increasing demand, limited supply, and the dramatic increase in fish meal price, efforts to replace fish meal by other plant protein source such as soybean meal have been increasing in aquafeed.
11. As aquaculture becomes more important for feeding the growing world population, so too do the required natural resources needed to produce aquaculture feed. While there is potential to replace fish meal and fish oil with terrestrial feed ingredients, it is important to understand both the positive and negative implications of such a development. The use of feed with a large proportion of terrestrial feed may reduce the pressure on fisheries to provide feed for fish, but at the same time it may significantly increase the pressure on freshwater resources, due to water consumption and pollution in crop production for aquafeed.
12. Mediterranean marine aquaculture has been dominated by two leading species, gilthead sea bream (Sparus aurata) and European sea bass (Dicentrarchus labrax). However, risk of market saturation and reduced prices led to consider species diversification as a priority. Meagre (Argyrosomus regius) presents a very good potential for large scale farming in Mediterranean countries. Meagre adapts easily to captivity, exhibits high growth rates reaching 1.2 kg in less than 2 years in cages, and tolerates wide temperature (2–38 °C) and salinity (5–39‰) variations. Meagre has good market characteristics, namely an attractive body shape for selling as whole-fish, good processing yield and nutritional values, low fat content, excellent taste and firm texture. Currently, meagre is produced in small scale with a global aquaculture production of 10,221 tons in 2012, and it is sold at high prices in niches. Countries like Spain, France, Greece, Italy, and Egypt, stand out as main juvenile producers. Due to its recent introduction in the aquaculture industry, little data is available about nutritional requirements, and potential of feed ingredients for the species. In fact, diets currently used for feeding meagre are similar to those used for European sea bass and gilthead sea bream
13.Fish meal (FM) has been the main protein source in feeds for carnivorous species such as meagre. However, the increasing demand, high price and supply fluctuations, makes it a priority to replace dietary FM by alternative protein sources. Soybean meal (SBM) is by far the most used plant protein source in fish diets, followed by other oleaginous such as rapeseed and sunflower meal. Leguminous seeds are also good dietary protein sources, particularly if they are locally produced, contributing to the sustainability and cost-effectiveness of fish-farming.Among leguminous seeds,
soybean, peas and lupines are the most widely used in aquafeeds.
14. Many different terrestrial protein and oil sources have been evaluated for potential fish meal replacements in aquaculture diets.The soybean (Glycine max), when processed, produces a high quality source of protein with a balanced amino acid profile and can replace fish meal as an economically and nutritious alternative.In some species such as tilapia, soybean meal can replace a majority of the fish meal in a diet with no adverse impacts on growth or health.However, in most commonly farmed carnivorous species such as Atlantic salmon, coho salmon, and Japanese flounder, soybean meal can only be incorporated into diets at much less than 50% due to the presence of antinutritional factors in soybean meal that cause enteritis and significant negative health implications and reductions in growth. However, replacing fish meal with soy protein has shown promising results for many species of flatfish, such as Japanese flounder (Paralichthys olivaceus), Egyptian sole (Solea aegyptiaca), and Atlantic halibut (Hippoglossus hippoglossus). Soy protein concentrate is a refined soy product in which many of the antinutritional factors have been removed; therefore it can replace the majority or all of the fish meal in diets for carnivorous species.
15.Apoptosis is involved in all fundamental processes in the immune system of animals. It is a mechanism to regulate the course of an immune response and to establish immunological memory as well as central and peripheral tolerance. The host immune system and viral anti-immune strategies during virus infection have evolved to create a suitable environment for virus replication in vertebrates. The cellular perturbation caused by virus infection can inadvertently trigger any one of many diverse cellular detectors to initiate an innate apoptotic response. In many cases, apoptosis has an adverse effect on virus replication, and, in these situations, viruses frequently express proteins that block the death response of hosts. It is revealed that the antiviral immune response of invertebrates requires the participation of immune system. The p53-dependent apoptosis may take great effects on the immune responses of invertebrates.
16.One of the most important aspects in aquaculture is the nutrition, as for optimum development of organisms, it is essential to have all the necessary nutrients, in terms both of quantity and quality. Nutrients are important for species in culture to stay alive, be healthy and to grow. Even though nutritional principles are similar for all animals, the required level of nutrients varies between species. Animals in production systems need a diet that is properly balanced for the specific requirements of species; however it must also be considered that nutritional requirements are affected by the growth rate, growing conditions, and environmental factors. Knowledge of these allows the formulation of well-balanced and cost-effective feeds.
17.The identification, evaluation, and development of ingredients is a key step in the development of effective formulation strategies for all aquaculture feeds. Traditionally there has been much reliance on the use of fish meal and fish oil in aquaculture diets and because of this intensive aquaculture has been perceived as a net fish user rather than producer. However, in addition to alleviating concerns about the reliability of aquaculture as a food provider, and also the long-term sustainability of aquaculture as an industry, the use of alternative ingredients also empowers the formulator with
additional options. These options include improving the technical qualities of pellets and also introducing certain nutrients and nutraceuticals to increase the value of the resultant compound diet in which the ingredients are included.
18.The concept of functional aquafeeds represents an evolving concept for fish and crustaceans diets. In the design of functional feeds, a wide range of feed additives can be used to extend beyond the satisfying basic nutritional requirements of the target species to improve growth and feed utilization, but also to support the health and stress resistance of the animals. The nature and characteristics of these feed additives is quite diverse, and their application into diet formulations targets a specific purpose. Some additives, such as acidifiers, exogenous enzymes, are used to improve the an imals’ performance by providing enhanced digestibility of the feed materials, or counteracting the negative effects of antinutrients. Other additives, such as probiotics, prebiotics, phytogenics, and immune-stimulants target the improvement of intestinal health, stress, and disease resistance.
19. Shrimp farming was introduced to Sri Lanka in 1985. By the early 90s the industry was booming with production rates of up to 9000 kg/ha/year. High export volumes contributed significantly (48–70%) to the total foreign exchange earnings during this period. However, in 1993 the first outbreak of the White Spot Syndrome Virus (WSSV) dealt a heavy blow to many farmers. The industry revived, but a second disease outbreak in 1998 caused severe economic losses to all shrimp farmers in Sri Lanka. The final and most devastating outbreak came in 2004 and caused a permanent reduction in the productivity of the industry. Production reduced to under 4000 kg/ha/year and export of shrimps in 2012 (volume and value) dropped by more than 65% compared to 1999. Currently, an estimated 90% of the shrimp farms are abandoned, leaving the coast dotted with areas that are unsuitable for other forms of agricultural/aquaculture production, mainly due to changes in the hydrology and polluted residual matter.
20. The environmental costs that accompanied the establishment of shrimp farming in Sri Lanka are significant. For the establishment of shrimp farms in Puttalam District, over 50% of healthy mangrove forest in the area was removed. With the loss of mangroves, an important buffer zone and habitat for marine life has disappeared. The construction of shrimp farms also led to the removal of above and below ground carbon, along with the potential for future carbon sequestration. Other impacts include pollution of surface and ground water, in addition to the depletion of wild stocks and healthy broodstocks for coastal fisheries. As a result, rather than providing permanent economic benefits, the establishment of shrimp farms has led to unstable livelihoods and has increased the vulnerability of coastal populations to climate change impacts.。