Surface water is a key factor in the transmission of pancreas disease in salmon

Original article available at: Norwegian school of veterinary science

Anne Stene’s PhD thesis explains how environmental factors affect the outbreak and transmission of pancreas disease (PD) in farmed salmon.

Both infected and dead salmon can shed the salmonid pancreas disease virus into the sea and the virus particles can be spread by the wind and ocean currents from one fish farm to the next along the coast.

Pancreas disease (PD) is currently the most serious of the viral infections affecting Norwegian farmed salmon. The disease leads to increased mortality, weight loss and low fish product quality. It therefore has a significant influence on fish welfare and on profitability in the aquaculture industry.

Coastal currents are a key factor in disease transmission
The PD virus can survive for long periods of time outside the salmon host in cold, clean seawater and it therefore has a strong infective potential along the Norwegian coast. Using a hydrodynamic model developed by SINTEF (http://www.sintef.no/home/), Stene was able to demonstrate that the transmission of the disease between fish farms at different locations is primarily caused by the direction of ocean currents near the surface of the water. Her findings also show that fish farms located in close proximity to infected/diseased salmon and fish farms owned by companies with many other infected farms have an increased risk of their stocks becoming infected with PD.

In addition to identifying risk factors for the transmission of PD, Stene focused on risk factors for outbreaks of the disease. Her doctoral project, which was carried out at the Norwegian Veterinary Institute, shows that salmon become infected with PD when the sea’s temperature rises over a period of time. The reason for this may be that the increase in water temperature leads to a state of chronic stress in the fish, which in turn has a negative effect on their immune defence system. An outbreak of the disease usually occurs when there is a high concentration of the virus in the fish. This can result in extensive shedding of the virus, which in turn leads to a high infection pressure in the sea.

An important finding in Stene’s study is that fat from infected and dead fish at the bottom of the cages also contains the virus. Some of this fat will float to the surface and can potentially infect salmon that come into contact with it. This floating layer of fat can spread to other fish farms by means of ocean currents near the surface. This underlines the need to remove dead fish as quickly and efficiently as possible.

Important knowledge to prevent infection
Stene’s thesis shows that the virus does not pose a problem during the smoltification of salmon in fresh water. Rather, the most important factor is the transmission of infection during the growth phase in salt water. If it is possible to slaughter infected fish before the temperature rises, outbreaks of PD can be limited and this will reduce concentrations of the virus in the sea. And when fewer viruses are carried by the currents, the risk of infection will decrease. Knowledge about water-born transmission and the risk of outbreaks is an important tool in when it comes to production planning with a view to preventing infection.

Stene’s research therefore provides fish farmers with new information, when they are considering locations for releasing young salmon, as regards the direction of predominant surface currents in relation to farms containing infected fish. Similarly, the slaughter of fish can be planned in relation to the location’s infection status, outbreak risk and the probability of disease transmission to neighbouring farms with fresh fish. Such measures must of course be weighed up against concerns regarding commercial viability for the individual farm and for the industry as a whole in each area. The costs can be high in the short term but must also be appraised in a more long-term perspective.

Anne Stene defended her doctoral research on 23rd October 2013 at the Norwegian School of Veterinary Science with a thesis entitled “Transmission of Pancreas Disease in marine salmon farming in Norway”.

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A new species of the fish pathogenic bacterium Edwardsiella

The original article available at: Norwegian school of veterinary science

Takele Abayneh Tefera’s doctoral research project has uncovered a genetic divergence between the fish pathogen Edwardsiella tarda and Edwardsiella tarda type strain.

He has also identified phenotypic markers that distinguish one from the other. The fish pathogenic strain is now classified as a separate species: Edwardsiella piscicida.

Edwardsiella tarda is a bacterium that can infect a number of animal species and also humans. Edwardsiellosis is one of the most serious systemic bacterial diseases in fish, resulting in substantial losses in the fish farming industry all over the world.

Takele Abayneh Tefera has developed effective molecular tools for the identification and characterization of different strains of Edwardsiella. He developed a new TaqMan real-time and conventional PCR analysis for this purpose and then evaluated it in relation to the Loop Mediated Isothermal Amplification (LAMP) analysis. For the first time, he also used the Multi-locus Sequence Analysis (MLSA) for the typing and characterization of E. tarda, isolated from different sources. This is a useful tool for detecting sources of infection and for understanding the epidemiological relationship between isolates from the environment, fish, livestock and humans.

The MLSA analysis showed that there exist geographic and host-specific genotypes of the species E. tarda. Bacterial strains from fish were found to be only distantly related to E. tarda type strain and other strains from humans. Furthermore, genetic and phenotypic analyses also confirmed a genetic divergence between these strains of bacteria.

The findings of this study indicate that the fish pathogenic strain has been wrongly classified as E. tarda. Phenotypic characterization by means of a number of biochemical tests and pathogenity studies on zebra fish identified phenotypic markers which also differentiate fish pathogenic strains from the reference bacterium.

Based on genetic and phenotypic differences, Tefera and his colleagues have proposed that fish pathogenic Edwardsiella strains previously classified as Edwardsiella tarda should now be classified as a new species: Edwardsiella piscicida. The new species has now been approved and incorporated into prokaryotic nomenclature.

Tefera’s work also led to the introduction of a new Multi-locus Variable Number Tandem Repeat Analysis (MLVA) for the further typing of different isolates of the new species of bacteria Edwardsiella piscicida. Employing this method proved to be more sensitive than the MLSA-analysis when it came to investigating outbreaks of E. piscicida.

Takele Abayneh Tefera defended his doctoral research on 26th November 2013 at the Norwegian School of Veterinary Science with a thesis entitled: Fish pathogenic Edwardsiella tarda: Evaluation of molecular identification methods and characterization of a novel species.”

 

ImagePicture: Electronic micrograph of E. Tarda (now E. piscicida) LTB4 strain after negative staining

(Source: Courtesy of Lan et al. 2008)

 

Feeding enzymes to shrimp and fish in Sustainable Aquaculture

Commercial fish feeds usually contain high fish meal as the major protein source, ranging from 30-50 per cent (Hardy, 1995). But now-a-days, fish meal is generally avoided in the feed due to its scarcity and high cost. Hence, aquaculture nutrition have been trying to improve the nutritional value of fish feed by enzyme supplementation, to find suitable alternatives to fish meal, since last decades, stated Prakash Chandra Behera, Technical Manager of AQUA, PVS Group, India.

Feeding enzymes to shrimps and fishes is one of the major nutritional advances in the aquaculture sector since last few years. Exogenous enzymes are now extensively used throughout the world as additives in animal diets. Also, supplementation with enzymes can help to eliminate the effects of antinutritional factors and improve the utilization of dietary energy and amino acids, resulting in improved performance of fish/shrimps (Farhangi and Carter, 2007; Lin et al., 2007; Soltan, 2009).

The primary purpose of enzyme application in feeds is to improve digestion. The digestive processes will work better and result shown in improved feed efficiency by providing an extra dose of enzymes. Further, aquatic animals are lack certain digestive enzymes during early development or throughout their life. In the case of fishes / shrimps lacking certain enzymes even in adulthood, application of these enzymes results in better utilization of nutrient fractions that are digested by the enzymes.

Enzymes:

Enzymes are one of the many types of protein in biological systems. Their primary characteristic is to catalyze the rate of a reaction but is not themselves altered by it. They are involved in all types of anabolic and catabolic pathways of digestion and metabolism. Enzymes tend to be very specific catalysts that act on one or ,at most a limited group of compounds known as substrates. Enzymes provide additional powerful tools that can inactivate anti-nutritional factors and enhance the nutritional value of plant-based protein in feeds. They provide a natural way to transform complex feed components into absorbable nutrients.

The addition of enzymes in feed can improve nutrient utilization , reducing feed cost and the excretion of nutrients into the environment.

Sources of Enzymes:

Enzymes are produced in every living organisms from the higher animals and plants to the simplest unicellular forms of life as they are essential for metabolic process. Microorganisms that generally involved in production of various enzymes are:

Bacteria: Bacillus subtilis, Bacillus lentus, Bacillus amyloliquifaciens and Bacillus stearothermophils.

Fungus: Triochoderma longibrachiatum, Asperigillus oryzae , Asperigillus niger and yeast

Microbial enzymes

In animals, digestion of food is carried out by the animal’s digestive system and by microorganisms that inhabit the intestinal tract. The bacteria present in the gastrointestinal tract of fish/shrimp are potent producers of proteolytic enzymes. They may also produce cellulase moderately. The adding of live microorganisms to diets to produce enzymes is possible in specialty feed applications. Large scale commercial enzyme applications are rely on enzymes produced by microbial fermentation technology.

Anti Nutritional Factors in Aquafeed

Feed ingredients from plants sources contain some compounds that either the shrimp/fish cannot digest or which hinder its digestive system because they cannot produce the require enzymes to degrade .Though the palatability of many plant materials has demerits, anti-nutritional factors are the most serious concern in replacing the fishmeal completely in feed formulations. Anti-nutritional factors have an adverse impact on the digestion of feed and its efficiency. There are many kinds of anti-nutritional factors and they are associated with the most widely used plant materials like trypsin inhibitor proteins, glucosinolates and phytate.

Heat inactivation and water soaking are the two common detoxification methods used to overcome most of the anti-nutritional factors.

Factors contributing to use of Enzymes

  • Increase need for quality food grain for fish/shrimp
  • Increase need for quality animal products /by –products
  • Search for alternate sources of food with better nutritive value
  • Economic margins(reduced cost : benefit cost)
  • Quick realization of profits
  • Rise of environmental awareness

Types of Enzymes available for Fishes / shrimps

Many enzymes have been used in fish/shrimp nutrition over the past several years which includes cellulose, (β-glucanases), xylanases and associated enzymes like; phytase, proteases, lipases and galactosidases. Enzymes in the feed industry have mostly been used for culture animals to neutralize the effects of the viscous, nonstrach polysaccharides in cereals and other food grains.

Action & Benefits of Feed Enzymes:

  • Reduces in digesta viscosity
  • Enhances digestation and absorption of nutrients especially fat & protein.
  • Improves Apparent Metabolizable Energy(AME) value of the diet
  • Increases feed intake, weight gain and feed gain ratio
  • Reduces ammonia production
  • Improves nutrient Digestibility.

Endogenous enzymes found in the fish/shrimp digestive system which help to break down large organic molecules like starch, cellulose and protein into simpler substances.

The carbohydrate digestion improves by using microbial enzymes. Addition of exogenous carbohydrates enzymes to feed increase utilization of unavailable dietary carbohydrates .High levels of non-starch polysaccharides (NSP) such as cellulose, xylans and mannans reduce the nutritive value of many plant ingredients. Intestinal enzymes to digest these carbohydrates are not produced by most animals.

[Read more at thefishsite]