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Cotton Shrimp Disease - Microsporidosis of Shrimp and Prawns
Common, generally accepted names of the organism or disease agent
Cotton shrimp disease, Milk shrimp disease, Roe shrimp, Cooked shrimp.
What is cotton disease?
Commonly the muscle degeneration associated with cotton shrimp disease.
The protozoan Microsporidian has generally been recognized by the progressive white opacity associated with the musculature.
Such microsporidian(Agmasoma -Thelohania spp., Amesoma - Nosema spp., Pleistophora - Plistophora spp., and Perezia spp) -infected prawns are known as ‘cotton shrimp’, ‘milky white’ or ‘chalky white’ prawns.The disease can appear as black or blue bands on larger shrimp.
This disease is found in both white and brown shrimp and more common in the white then brown.
Microsporidia invade and replace host tissue such as muscle, heart, go**ds, gills, hepatopancreas, and nerve ganglia, depending on species. May cause low level mortalities. Infection often causes the shrimp to have a whitish colour making the product unmarketable.
Gross Observations: Heavy microsporida infections of the muscle tissues cause the muscle to become opaque and the shrimp appear cooked although they are still alive.
Squash Preparations: Microsporidian spores in muscle (also visible if Giemsa stained). Identification to genus and species is based on spore size, shape and number of spores per sporont.
DNA Probes: The chromosomal DNA regions of the SSU rDNA gene of microsporidian isolates (Agmasoma sp.) from P. merquiensis and P. monodon were identical for 722 base pairs suggesting that a single parasite species infects both species of penaeid shrimp (Pasharawipas et al. 1994).

Hit by lockdown, L Vannamei broodstock now ready for sale

Rajiv Gandhi Centre for Aquaculture (RGCA), a research and development arm of the Marine Products Export Development Authority (MPEDA), has inked a Memorandum of Understanding (MoU) with the Oceanic Institute of Hawaii Pacific University, U.S.A., for supply of L. Vannamei Parent Post Larvae (PPL) to farmers in Andhra Pradesh.

After an eight-month gap caused due to the pandemic, MPEDA is supplying L.Vannamei (LV) brooders from its Broodstock Multiplication Centre (BMC) at Chepalauppada village in Bheemunipatnam mandal of Visakhapatnam district, said MPEDA Chairman K.S. Srinivas.

Order booking

He launched booking of the fresh stock of Specific Pathogen Free (SPF) L.V brooders (mother prawns) from the BMC on January 1, during his two-day tour in the State.

“Hatchery owners can confirm their bookings immediately. MPEDA is offering an early bird scheme with one-plus-one offer, for the first 10 days (for bookings made from January 1 to 10). The first batch of 25,000 SPF L.V brooders will be ready by January end,” he told The Hindu.

The RGCA will acquire Parent Post Larvae (PPL) from the Oceanic Institute of Hawaii Pacific University, which was a pioneer in producing SPF L.V. brooders.

“Brooders are raised under strict biosecurity and certified as SPF by Aquaculture Pathology Lab, University of Arizona, USA, and Central Aquaculture Pathology Lab, RGCA. The mother prawns are acclimatized to Indian weather and environmental conditions,” said RGCA Director S. Kandan.

L. Vannamei brooders supplied by RGCA will have faster growth with high survival percentage. They have passed multiple-level disease tests. The mortality of MPEDA supplied brooders during transportation will be less than 2%, said its Director M. Karthikeyan.

BMC project in charge and Assistant Project Manager (APM) D.V.S.N. Raju said that hatchery operators could book (the brooders)

A farmer’s perspective on probiotics in shrimp culture
The application and dosage of probiotics should be culture specific with more clarity and understanding provided to the farmers.
For many years, the major focus of the shrimp industry in India was on the farming of the shrimp, Penaeus monodon and vannamei. The economic benefits led to high stocking densities and use of spurious post larvae which in turn led to constant threat of diseases. Shrimp farmers began to use of antibiotics and water sanitizers routinely. This indiscriminate use of antibiotics brought negative impact on the environment and food safety as well as introduced a trade barrier for our final products in international markets.
The government reacted with strict food safety protocols in all the shrimp farming areas to disallow the use of banned chemicals. Culture techniques following Good Management Practices (GMP), Best Management Practices (BMP), organic farming, and zero water exchange systems were examined. However, probiotic claim to have a major role towards a more sustainable industry. In India, there are more than 100 companies producing probiotics targeted for the aquaculture industry. However, farmers usually do not have sufficient knowledge on microbiology and they are unsure on the benefits of probiotics.
The science behind probiotics in shrimp culture
The historic definition for probiotic as per Fuller (1989) is ‘a live microbial feed supplement which beneficially affects the host animal by improving its intestinal balance’. However, in aquaculture recently, the scientific definition of probiotic was given by Merrifield et al. (2010). According to this group, probiotics are defined as ‘microbial cells that are administrated via the diet or rearing water, with the aim of improving health and disease resistance, growth performance and feed utilization, stress response, general vigour, carcass and flesh quality and reduced malformations.
They classified probiotics into three groups: gut probiotics, water probiotics (as in bioremediation) and soil probiotics (as in detritus management system). Probiotic inoculates are either in the form of spores or as resting bodies of one or more species in a medium design to prevent germination or to re**rd growth. All these available probiotics are either in liquid or granular form coated with bacterial propagules.
Mode of action
Probiotics containing multiple strains of bacteria spores or resting bodies produce extracellular enzymes to degrade large molecules into smaller particles that can be absorbed for further degradation by enzyme-catalyzed reactions within their cells. It should be obvious that enzyme additions cannot speed up degradation of organic matter or toxic substances unless bacteria are present. Probiotics within shrimp or in their environment adhere to host surfaces and have the ability to colonize and to prevent the establishment of potentially pathogenic bacteria.
A farmer’s view:
The farmer’s understanding and definition for probiotics is simply; ‘single or multi-brand microbial products when used singly or mixed should benefit shrimp and culture ponds’. In their view, the probiotics are only of two types; feed and pond probiotics. The possible benefits of probiotics are;
- Improve health when probiotics competitively exclude the pathogenic bacteria or produce substances that inhibit the growth of the pathogenic bacteria.
- Provide essential nutrients to enhance the nutrition of the cultured shrimp.
- Improve growth and feed conversion when probiotics provide digestive enzymes to enhance the digestion of the shrimp.
- Lower environmental impact when probiotics directly uptake or decompose the organic matters or toxic materials (metabolites such as NH3, NO2, H2S, PO4, CH4, etc.) in the water, thus improving the quality of the culture water.
In addition, under investigation are other claims such as improvement of the immune response of the shrimp against pathogenic microorganisms by activating both cellular and humoral defenses (non-specific immune system) and having anti-viral effects.
However, farmers consider probiotics as miracle products, giving them quick and positive results after application. Probiotics become a curative tool rather than prophylactic. On the other hand too, farmers are often discouraged by the increased cost of operations. Probiotics are still accepted or adopted in the primary culture protocols.
Applications
This can be divided into the following phases
- Phase 1: Pre-culture application
- Phase 2: In-culture application
- Phase 3: Post-culture application
Phase 1: Pre-culture application
Pre-culture application probiotic has to be catalyzed by proper BMP protocols. This mainly involves the proper design and construction of all the culture ponds followed by proper pond preparation. The main catalytic steps to improve the probiotic effects after pre-culture application include proper drying and ploughing before starting the crop, followed by compact and levelling after ploughing. Incoming water should be well filtered and pond preparation follows the steps shown in Chart 1.
Chart 1. Steps in pond water preparation
Pond water preparation
Day 1 Fill water to 1.2 m (average depth)
Leave for 2 days to settle
Day 4 Chlorination 10pp to 40pp, bleaching powder
Dechlorination for 2 to 5 days
Dayr 9 Application of prebiotic media after fermentation
(jaggery + rice bran + yeast) – Dose 1
Leave for 1 day
Day 10 Application of probiotics for water – Dose 1
Leave for 5 days
Day 15 Application of prebiotics media after fermentation
probiotics for water (jaggery + rice bran + yeast) – Dose 2
Leave for 1 day
Day 16 Application of probiotics for water – Dose 2
Leave for 2 days, check water parameters
Day 19 Stocking of good quality tested PL 15
Note: Jaggery is a brown colored semisolid sugar
The probiotic works effectively when we apply a good prebiotic carbohydrate source. The water color after application of the prebiotic and probiotic after pond preparation before stocking of post larvae is given in Figure 1. This color shows the efficacy of probiotics with good pond preparation.
Phase 2: In-culture application
As per the guidelines from most probiotic companies, the recommended concentration of probiotics during in-culture application is given below.
Table 1. In culture application of probiotics
Water probiotics Feed probiotics
Initial start-up dose followed by weekly doses up to end of the culture recommended by company to company basis and also as per the product specification.
Dose 0.5 – 1.0 kg/ha/week (powder)
5 – 10 liters/ha/week (powder)
Administrated through feed on a daily basis from day 1 of culture till harvest. Mostly once a day (peak meal)
Dose 5 – 10 g/kg feed with a suitable binder.
The in-culture application of probiotic is mostly catalyzed by proper water quality management, optimum aeration facility, good quality and correct feeding schedule, proper check tray management and strong biosecurity. The main catalytic steps to improve the probiotic effects after in-culture application include optimum water quality parameters for better probiotic efficiency (Table 2); effective aeration for optimum in-culture probiotic effects; competent feeding program and check tray management for optimum in-culture probiotic effects.
Table 2. Optimum water quality parameters.
Dissolved oxygen > 5 ppm (morning)
pH 7.8 to 8.5
Transparency 35 – 45 cm
Alkalinity > 100 ppm bicarbonate
Salinity 12 – 25 ppt
Temperature 28 – 32 oC
Water depth Average 1.2 m
Ca : Mg ratio 1:3 especially for Litopenaeus vann
Phase 3: Post-culture application
Post culture application of probiotics in shrimp pond is one of the most important management practices, which is usually overlooked by the farmers. This practice should be done to remove excess amounts of organic load during post culture pond preparation. The post culture application of probiotics followed in our farm (MAPL) is given in Chart 2.
A healthy bottom condition is a result of the application of post culture probiotics. The stocking of good quality shrimp will also help to sustain a good pond bottom condition.
Chart 2. The post culture application of probiotics at MAPL
Flushing of pond bottom
Application of lime
Filling of water (20 – 30 cm)
Application of probiotics
Some observations and findings
The following observations and findings have been recorded during several years of culture while applying probiotics (Table 3)
Table 3. Some observations and findings with probiotic applications.
Water probiotics
Days of culture Observations Findings
01 – 50 Good initial water quality, stable bloom with good transparency. Visible and significant change in water condition.
51 – 100 Stable water color with reduced transparency. Stable water parameters, but ammonia start accumulating ( > 80 DOC)
101 – till harvest Thick bloom with abrupt color change. pH and DO diurnal fluctuation. Stressed shrimp.
Feed probiotics
Days of culture Observations Findings
01 – 50 Good initial growth with proper molting. Increased shrimp survival
> 90% of stocking
51 – 100 Good shrimp color with uniform size. Better average daily growth (ADG) with improved healthy shrimp (gut).
101 – till harvest Good growth, but < 5% shrimp with poor growth and discoloration. May be due to water quality in later stage causing stress. Improper molting.
In addition, the best water probiotic effects and performance was observed in salinity close to 20 ppt. Gut probiotic efficacy was the best at the above salinity range. The result of probiotics is purely pond specific and varies from season to season. The age of pond is also a determining factor. The cyclic nature/cropping pattern of shrimp farming also effects the permanent establishment of microbial communities. In spite of various claims, it is very difficult to eliminate blue green algae in shrimp culture ponds through water probiotics. Compared to P. monodon culture, it is easy to control water color in L. vannamei culture pond which could be due to its feeding behavior.
Main constraints of nitrifiers in ponds
Nitrifiers are fragile microorganisms, which are sensitive to acids despite the fact that they produce acid during oxidation of NH3 and NO2. Therefore, if large amounts of nitrogen are available in the water, these organisms can potentially kill themselves by metabolizing nitrogen to nitric acid unless pH is buffered. Nitrifiers are autotrophs and they need oxygen during the degradation of NH3.
The reactions of Nitrobacter spp. are inhibited by small quantities of ammonia gas, which can lead to toxic buildup of NO2, since Nitrosomonas spp. is not inhibited from NH3 to NO2 in the presence of ammonia gas. Both Nitrobacter spp. and Nitrosomonas spp. work in culture pond within pH ranges of 6.8 – 8.5 with the optimum at pH 8.2 to 8.3

MPEDA launches India’s first aquaframers call centre Highlights
Recently Marine Products Export Development Authority launched a multilingual call centre for Aquafarmers.

Farmers can call for guidance 24x7 on toll-free number 1800-425-4648
This is the first-of-its kind facility in the country
MPEDA chairman Srinivas says the call centre will help the aqua farmers in AP to get advice by experts regarding their concerns and to follow Best Management Practices
Call Centre
It will mainly cater to the Andhra Pradesh’s Aquafarmers. This is because, the State is one of the major fish producing state in India. Together with other states Tamil Nadu, Kerala, West Bengal and Gujarat, these state contributes more than 60 per cent of marine products of the country.
They can handle calls in English and Hindi.
Through these centres the Aquafarmers can easily seek advise from the experts regarding their concerns.
It will help the Aquafarmers follow best management practices to boost production and ensure quality of produce.
Aquafarmers can get information about the support schemes extended by Marine Products Export Development Authority

The Marine Products Export Development Authority (MPEDA), headquartered in Kochi, has launched a multilingual call centre for aquafarmers at Vijayawada in Andhra Pradesh, which will address their technical issues and impart knowledge about efficient farming methods round the clock. The call centre primarily caters to aqua farmers of Andhra Pradesh, the state that contributes more than 60 per cent of the country’s marine products export basket.
The call centre can also handle calls in English and Hindi. Launching it over video conferencing, MPEDA chairman K S Srinivas said it would help the aqua farmers in Andhra Pradesh seek advice from experts regarding their concerns. It will also help them follow the Best Management Practices (BMPs) to boost production and ensure the quality of the produce.
“I request the farmers to make use of the toll-free number 1800-425-4648 with IVRS (interactive voice response system) facility established at Vijayawada to clear their technical doubts with experts and not to fall in the trap of quacks. It will also help them seek information about the various support schemes extended by the field offices of MPEDA,” he added.“Viewed in this context, it demonstrates the enormous importance of the call centre in the state,” the MPEDA chairman noted.
Meanwhile, MPEDA director Karthikeyan said the small-scale aquaculture farmers are encountering problems while seeking authentic guidance and technical support, especially during the culture period
of farming.

Truth about Nitrite Control
Plankton crashes, feed consumption drop & over feeding and organic material accumulates on pond bottoms.
This factors causing increase the ammonia and nitrite levels in the pond. Sea salt chloride only used for to decrease the toxicity level in the animal side(nitrite toxin inhibitor purposes).
It's not working for waste degradation and nitrite to nitrate convert function( nitrogen cycle biological process).
Adding a concentrate of Ammonia Oxidizing Bacteria (AOB) Nitrosomonas/ Nitrite Oxidizing Bacteria (NOB) Nitrobacter may cure the problem quickly, but the population of AOB/NOB will rapidly drop to natural background levels.
An addiitional problem with AOB/NOB concentrates is their need to be refrigerated and their short shelf-life (3 - 6 months maximum). Without refrigeration, the AOB/NOB concentrate drops in activity to what you see in natural waters.
Nitrifiers are inhibited by many common compounds.High organic loadings lower D.O. which results in inhibition.
Like a narrow range of environments for growth
Growth is best in pH between 7.5 - 8.2. Temperatures 20 - 38 Deg C. Outside this range, growth rates decrease to critical levels.
Given all the challenges for maintaining ammonia and nitrite oxidation, how can you make sure that the nitrifiers are well cultivated?
Nitrifiers are slow growers
Compared to most wastewater heterotrophs, nitrifiers are slow growers. Even in the best conditions, AOB take up to 12 hours for cell division. Remember that many common heterotrophs can divide every 30 - 60 minutes
Farmers must be understood this matter.
So what can be done to prevent ammonia and nitrite from impacting the fish or shrimp?
Good permanent solutions;
a) Probiotics application
(waste biodegradation by Heterotrophic bacillus probiotics & molasses or jaggery application).
b) Photosynthetic bacteria (PSB) probiotics application.
c) Avoid over feeding.
d) Water parameters maintain.
e) Increase the sufficient aeration.
f) Proper Water Exchange (for poor quality water).
Heterotrophic bacteria additions help balance the pond - they degrade sludge/wastes on the pond bottom, remove nitrite/nitrate under anoxic conditions, and uptake nitrogen to build new cells.
Add alkalinity if necessary - we want stable pH for animals, bacteria, and beneficial algae.
Key answer is that microbial additives in aquaculture need to be started before problems arise. Using waste degrading microbes early will help with pollution related stress, disease, and keep the desired ecological blance between animal stock, waste degrading microbes and algae.

EHP infection
EHP infection in shrimp can not be detected by visual inspection and there are no specifically distinctive gross signs except that it is suspected to be associated with growth re**rdation. EHP can be confirmed by molecular tests such as polymerase chain reaction (PCR),
The target organ for EHP is shrimp hepatopancreas (HP). HP being power house of the animal, infection in the digestive organ may cause impairment of metabolism, ultimately resulting in stunted growth and size variation.
What is EHP?
EHP is an abbreviation for Enterocytozoon hepatopenaei, a microsporidean which is a spore forming parasite. It is a type of fungal infection. According to experts, there are more than a million species, many of which are hosted by insects. Many are parasitic on crustaceans and fish and generally require a secondary host. Previously the most well known microsporidean in shrimp was Thelohania, which causes the condition called cotton shrimp. This microsporidean has an intermediary host of a carnivorous fish such as snook, and causes the cottony looking tail in shrimp occasionally. EHP does not infect mussel tissue, but infects the hypatopancreatic tissue, the same organ that the toxin in EMS targeted. EHP also requires a intermediate host for infection.
The severity of EHP impact is directly related to the number of spores in the hepatopancreas of the shrimp. The higher the number of spores, the greater impact in stunted growth. The spore count generally increases with the time the shrimp are in the ponds, so that after 40 days there is a higher parasite load than initially.
There is no specific treatment available for the control of EHP infection.
Best management practices (BMPs) are the only way to prevent EHP.
In hatcheries, EHP can be prevented by using EHP free live feeds and carrying out complete disinfection of hatchery facility with 2.5 % sodium hydroxide solution and by a week-long drying, followed by rinsing with acidified chlorine (200 ppm).
In grow out system, EHP can be prevented by application 6 tons of lime (CaO) per hectare, followed by thorough ploughing and sun drying of pond soil.
Stocking EHP free seed tested by PCR.

Innovative way to inhibitors of the pathogen Enterocytozoon hepatopenaei(EHP)

Please note:
The tests have been done with purified spores
under laboratory conditions and the contact of spores with the chemicals or physical factors were direct.
The active EHP spores were exposed to different temperature (−20 °C, 4 °C and 33 °C) and chemical treatments including calcium hypochlorite, formalin, potassium permanganate (KMnO4) and ethanol to identify the conditions that can be used to inhibit the extrusion of the polar tube. Complete inhibition of activity was demonstrated either by freezing the spores at −20 °C for at least 2 h or by treating them with chemicals. The chemicals that yielded 100% inhibition were 15 ppm KMnO4 for 15 min, 40 ppm of 65% active chlorine for 15 min or 10 ppm of 65% active chlorine for 24 h and 20% ethanol for 15 min. However 200 ppm formalin resulted in a maximum reduction of 95.33%. Taken together, our protocol demonstrates for the first time that living EHP spores can be isolated and purified, providing a potential platform for future testing and development of EHP's control strategies.
In order to apply this information to use under farming conditions, the environmental effect has to be taken into consideration.The general knowledge about this species will help
with in the implementation of biosecurity strategies in the industry and in the academic area, a better understanding of host-parasite interactions.
Article (PDF Available) in Aquaculture 490 · February 2018
DOI: 10.1016/j.aquaculture.2018.02.039.

Mycotoxins : The silent threat in shrimp farming

In aquaculture production, mycotoxins can cause serious negative effects on fish and shrimps.

Most of the problems currently confronting the shrimp farming industry are related to the widespread occurrence of disease, e.g. parasitic infestation, or bacterial and viral infections. These disease problems can lead to heavy losses to the industry and as such, the industry has focused much of its attention to deal with such threats. However, there are other potential threats like additional diseases caused by other factors, such as culture environments and feed that also can greatly influence the success of shrimp culture. Nonetheless, these factors have been somehow disregarded by the industry.

One such factor is the presence of mycotoxins in shrimp feed. Contamination of feed for aquatic species is common in humid tropical regions, such as all South East Asia. The problem can be caused by many factors, such as low quality of feed ingredients and inappropriate methods of feed storage.

To ensure a continuous growth of aquaculture output and to increase its sustainability, there is an increasing trend to use plant-based ingredients as partial or complete replacement of fishmeal and fish oil in aquafeed formulations. Consequently, the mycotoxin risk in aquaculture production is increasing.

The aquafeed industry is now using many cereal products such as soybean meal, corn or wheat gluten meal and rice bran. Considering their current inclusion rates in aquafeeds, these ingredients should be handled carefully because they are known to contain a risk of mycotoxin contamination. Taking soybean meal as an example, Olmix Myco’Screen Overview showed that 96% of the analyzed samples were contaminated with one or several mycotoxins. Additionally, 72% of the samples analyzed showed polycontamination for several mycotoxins, of which FUM (60% > LOQ) and DON (35% > LOQ) were most prevalent.

Five most common Mycotoxins found worldwide in aquafeed and raw material used for feed formulation:
Aflatoxins (Afla),
Zearalenone (ZEN),
Trichotecenes (T-2 & HT-2),
Fumonisins (FUM),
Ochratoxin A (OTA).

Shrimp & Fish species are more affected
Aflatoxin
According to this, the target organ for Aflatoxin is liver, causing liver necrosis and liver carcinom.

Beside, Aflatoxin can produce different damages and pathological manifestations such as:
Small cell carcinoma
P***e gills
Abnormalities in shrimp hepatopancreas.

Ochratoxin A:

Induce mutagenic and toxic effects
Degeneration of kidneys and liver
Provoque poor performances.

Zearalenone
Zearalenone is a mycotoxin which dominantly affects:

Reproductive parameters in different aquatic species
Causing change of relative fecundicity,
Acceleration of sexual maturation
Reducing of spawning frequency

Fumonisins
FUM has been generally associated with:

Reduced growth rate
Lower feed consumption
Poorfeed efficiency ratio
impaired sphingolipid metabolism
Cause lesions in exocrine and endocrine pancreas as well in inter-renal tissue

Trichothecenes
Trichotethenes presence is related to decreased production of bacterial cell wall breaking enzymes and decreased resistance to oxidative damage.
In shrimp T-2 and HT-2 leads to in homogenous growth and physiological disorders.

However, what is the most important is that ALL MYCOTOXINS are immunosuppresive, ALL MYCOTOXINS are increasing mortality and cause poor productive performances. (growth, FCR, daily intake)

Effect of Mycotoxins on the immune system

Evidence suggests that consumption of diets contaminated with mycotoxins suppresses the immune system and decreases disease resistance. This can occur even when animals are consuming low or moderate contaminated products, as such its effects pass unnoticed and the economical losses are normally just associated with the disease outbreak causing the damage.

Mycotoxins that impair the immune system include AFB1, T-2 toxin, OTA, DON and fumonisin. The effects of mycotoxins on immunological responses of terrestrial animals have been examined extensively. Most of this toxins cause impairment of the immune system by inhibiting the synthesis of key proteins associated with the immune function. Haemocytes, in conjunction with fixed phagocytes form the immunocompetent components of the shrimp immune system, and as such a reduction on their numbers can result in a decreased disease resistance, making the shrimp more susceptible to infections.

Consumption of trichotecene mycotoxins causes suppression of immune response by reducing both phagocytic activity and chemotaxis by macrophages (Maning, 2001).

Total hemocyte, granulocyte and phenoloxidase activity were reduced in shrimp fed with T-2 toxin and zearalenone (Supamattaya et al., 2006). Conversely, no difference in numbers of haemocytes in blood circulation was observed between shrimp fed various concentrations of OTA and DON (0 – 2000 ppb) after 8 weeks period (Supamattaya et al., 2005). The results of phenoloxidase (PO) activity however, showed that feeding with high level of OTA (1000 ppb) caused significant decreasing of PO activity (Supamattaya et al., 2005).

The effect of aflatoxins on the immune system is to reduce the production of certain cell components such as C4 complement and lymphokines e.g interleukins, and T lymphocytes (Maning, 2001). Aflatoxin, suppresses phagocytosis by macrophages, which alters subsequent processing and presentation of antigen to B lymphocytes with consequential reductions in disease resistance (Maning, 2001).

A negative correlation between the number of haemocytes and dietary concentration of AFB1 was reported by Boonyaratpalin et al. (2001) when feeding shrimp diets ranging from 0-2500 ppb AFB1 during a 8 week period. A biochemical change of the haemolymph by AFB1 was also reported by Bintvihok et al. (2003). A decline in the activity of such immuno-competent cells causes a decline in shrimp’s immune response (Boonyaratpalin et al., 2001).

Combating mycotoxins

The contamination of feeds and raw materials by mycotoxins is a reality and its increasing on a global basis making it increasingly likely that any given feedstuff could contain one or, more likely, several mycotoxins. They are invisible, odorless and tasteless toxins with a major impact on animal health.

Although the presence of mycotoxins in feed represents an increase threat to aquaculture operations there are a number of options available to feed manufacturers and farmers to prevent or reduce the risk of mycotoxicosis associated with mycotoxin contamination. These range from careful selection of raw materials, maintaining good storage conditions for feeds and raw materials, and using an effective mycotoxin deactivator product to combat the widest possible range of different mycotoxins that may be present.

Binders or adsorbents have been used to neutralize the effects of mycotoxins by preventing their absorption from the animal’s digestive tract. Unfortunately, different mycotoxin groups are different in their chemical structure and therefore it is impossible to equally deactivate all mycotoxins using only one single strategy. Adsorption works perfectly for aflatoxin but less, or non-absorbable mycotoxins (like ochratoxins,
zearalenone and the whole group of trichothecenes) have to be deactivated by using a different approach.

Biotransformation is defined as detoxification of mycotoxins using microorganisms or enzymes which specifically degrade the toxic structures to non-toxic metabolites.

Which raw materials and other vectors are the main causes?
With fishmeal and oil becoming very expensive, the inclusion of terrestrial plant-based proteins in commercial aquaculture feeds has gained widespread acceptance.
The most common plant feedstuffs used in aquafeeds are:
Corn
Soybean meal
DDGS
Canola
Cottonseed
Peas/lupins
Rice bran
Cassava
Wheat

Conclusion

Mycotoxins are found worldwide and their economic impact is likely underestimated throughout the entire food chain. The literature is not yet abundant for fish and shrimp, but already it corroborates the harmful impacts observed on farms in the presence of mycotoxins. The increasing trend of using plant-based raw materials for the production of more sustainable aquafeeds (in particular cereal co-products that are a higher risk than cereals, such as gluten meal, bran, etc.), suggests that mycotoxin risk management will be of similar importance in aquafeed as it now does in other animal feeds. The use of wide spectrum toxin binders should be part of this mycotoxin risk management.