18 January 2016 By Mr Prakash Chandra Behera, India.
Prevention of White Feces Syndrome, White Gut Disease and White Muscle
Disease in Shrimp
Intensive and semi -intensive aqua farming accompanies several disease problems often due to opportunistic pathogens as evident from general aquaculture. High stocking
densities, high food inputs and other organic loads stimulate the selection and proliferation of opportunistic pathogens likebacteria, virus, fungi,
Gut Track Diseases in Shrimps
Shrimp are actively “grazing” on the substrate present in the pond bottom and water column. Therefore, they highly expose to exchanges of microflora between
the environment and the digestive system. This increases the risk for the proliferation of an unfavorable gut microflora or frequent destabilization of the microflora, which can affect
the optimal functioning of the digestive system. Furthermore, the digestive system of shrimp is the main entry port for protozoan, bacterial and viral infections, which remain a major risk for the
profitability of shrimp production. Presently these are the most important Gut track diseases in shrimps:
White Feces Syndrome (WFS)
White Gut Disease (WGD)
White Muscle Disease (WMD)
White Feces Syndrome (WFS)
Accompanying acute hepatopancreatic necrosis disease (AHPND) in cultivated shrimps has been an increasing prevalence of vermiform, gregarine-like bodies
within the shrimp hepatopancreas (HP) and midgut. In high quantity of these bodies result in white fecal strings and a phenomenon called white feces syndrome (WFS).WFS appears in shrimps
from approximately 2 months of culture onwards and caused by gregarines .The vermiform bodies formations are consisting of Aggregated Transformed Microvilli (ATM).The ATM have originated
by sloughing from epithelial cells of the shrimp hepatopancreatic tubules. They accumulate at the HP-midgut junction before being discharged within feces via the midgut.
White fecal matter
When the occurrence of ATM is severe, it can lead to the formation of white fecal strings in shrimp .The high density stocked shrimp pond exhibit this
phenomenon and it lead to floating fecal strings or sometimes accumulate in floating mats (i.e., white feces syndrome or WFS). However, ATM sometimes occur together with shrimp
hepatopancreatic diseases such as the AHPND, other types of vibriosis, and parasitemia with the microsporidian Enterocytozoon hepatopenaei.
The impact of white fecal matter has been found in L. vannamei & P.monodon culture shrimps and there is no possible association with Loose shell
syndrome. The severity of the problem due to occurrence of white fecal matter has been observed to be a serious problem during the culture shrimps. Interestingly, the problem has been
observed with the L. vannamei ponds having high count of blue green algae.
Main Feature of White Gut / Feces Syndromes :
Vermiform, gregarine-like bodies within HP and midgut
Show no cellular or sub-cellular organelles
Also WFS involves other protozoan or metazoan.
Microvilli found peeled away from HP tubule cells and aggregated in HP tubule lumen
Stripped of microvilli, the originating cells undergo lysis.
Loss of microvilli and subsequent cell llysis indicate a pathological process.
May retard shrimp growth and may predispose to opportunistic pathogen
Field signs of white feces syndrome (WFS)
Gross signs of WFS in shrimp cultivation pond included white to somewhat yellow, floating fecal strings that sometimes collected in mats or could also be
found on feeding trays .The midgut junction and midgut are distended and filled with white to yellow-golden contents .When the contents of the gut or fecal strings are examined , they
consisted of masses of vermiform bodies the superficially resembled gregarines .
Severely affected ponds exhibit reduction in shrimp survival by 20–30 percent when compared to normal ponds. There is also a decreases in feed consumption,
growth rates and reduces in average daily weight gain (ADG).
(WFS in Shrimp pond)
The presence of more the number of gregarines are higher the chances of lesions and infections in cultured shrimp. The number of gregarines grows in number
and get the nourishment from the host leaving lesion for the infections to set in. The gregarines also interfere in assimilation of nutrients by the villi and resulting in the poor growth
of cultured shrimps.
Comparison of white gut and white fecal matter
The White gut and White fecal matter are the two different problems in shrimp culture ponds that can possibly lead to Loose shell syndrome. In general, the
White gut is caused by the necrosis of epithelial mucosa and resembles the haemocytic enteritis.And usually, the White fecal matter is caused because of the damage to the hepatopancreas
and sloughing of hepatocytes.The sloughed cells are released in to the gut and the gut looks white in colour. In general, the fecal matter contains undigested feed particles but in case
of white fecal matter it is from the dead hepatocytes.
White Muscle Disease
Whitish muscle disease of Penaeus vannamei in early disease occurs mostly in the shrimp's tail whitish. Also began to appear whitish from the middle of the
back and the whitish part of the loss of transparency Then this diseases forward the development of rapid spread of shrimp in serious condition muscles throughout the back White necrosis.
Began to appear the complete white muscle necrosis, the shrimp may die after 3-5 days. White muscle necrosis shows under microscopic examination such as muscle fiber disorders and stripes
clearly. Disease is difficult to see the surface of the pond shrimp, dead shrimp submerged in the underwater, early onset of normal feeding, after death, before the muscles become whitish
The WMD (White muscle disease) is observed at most of shrimp farms .The epizootic of WMD is showing mortalities ranging from 30% to 100% . The first sign
related to this disease is the poor feeding (mineral deficiency in water, poor quality feed) and lethargy of the prawns especially during the first 5 days of PL settlement resulting in
slow mortality. The signs are focal to extensive necrotic areas in tail muscle tissues, displaying a white, opaque appearance.
(White muscle disease in bigger size L. vannamei)
Gross signs of the disease are similar to the WGD. It is likely that the involvement of the
Gram-positive cocci, Lactococcus garvieae in WMD could possibly have been a secondary infection. The disease progressively destroyed the abdominal
muscular organization of the prawns especially the striated muscles finally leading to mortality.
White Gut Disease (WGD)
White Gut Disease (WGD) By Vibrio
The occurrence of five types of diseases: tail necrosis, shell disease, red disease, loose shell syndrome (LSS) and white gut disease
(WGD) is by Vibrio spp. in shrimpfrom culture ponds
Among these, LSS, WGD, and red disease caused mass mortalities in shrimp culture ponds. Six species of Vibrio—V.
harveyi, V. parahaemolyticus, V. alginolyticus, V. anguillarum, V. vulnificus and V. splendidus—are associated with the diseased
shrimp. Mortalities due to vibriosis occur when shrimps are stressed by factors such as: poor water quality, crowding, high water temperature, low DO and low water exchange.
The white gut disease (WGD) observed in shrimp farms and Vibriosis is one of the major disease problems agent in aquaculture. Vibriosis is a bacterial
disease responsible for mortality of cultured shrimp worldwide. Vibriosis is caused by gram-negative bacteria in the family Vibrionaceae. Outbreaks may occur when environmental factors
trigger the rapid multiplication of bacteria already tolerated at low levels within shrimp blood or by bacterial penetration of host barriers. The exoskeleton provides an effective
physical barrier to pathogens trying to penetrate the external surface of crustaceans, as well as the foregut and hindgut.
(White Gut Diseaseby vibrio in L. vannamei)
The occurrence of five types of diseases: tail necrosis, shell disease, red disease, loose shell syndrome (LSS) and white gut disease (WGD) is
by Vibrio spp. in shrimps. Among these, LSS, WGD, and red disease caused mass mortalities in shrimp culture ponds. The diseased shrimp showed symptoms of stunted growth
and opaque white gut visible through the transparent cuticle as a white streak. The shrimp consumed feed in large quantities and released fecal matter in the form of a white fluid
material. Mortality rate in affected ponds leads in high.
White Gut Disease (WGD) By Micro parasite
(Microsporidian infection of the abdominal muscles of Shrimps)
Shrimps have purplish-mauve coloration on the cuticle and to have large white tumors or cysts in the muscle. Shrimps have a disease known as cotton or milk
shrimp caused by a parasite infection of primarily the abdominal muscle. The muscle has a cottony appearance, which is externally visible as white opaque patchy areas under the carapace.
The disease is caused by a severe infection of parasitic microsporidia. The white mass is not a cancerous tumor or cyst but is caused by hundreds of microscopic parasites. The presence of
the parasite can elicit a host response by the shrimp that leads to a buildup of blue-black pigmentation in the cuticle.
(White Gut Disease (WGD) By Microparasite)
Prevention & Control Measures
Effective management of the health of shrimp requires consideration of delicate balance between the host, pathogen and environment. Disease and production
problem are vary during the different phase of shrimp culture. Production shortages resulting from shrimp mortality, slow growth and high FCR occur and affect the economics of shrimp
Most often pathogens are present in association with the environment and shrimp are apparently healthy and show normal growth. Often conditions such as high
stocking density, poor water quality, and sudden changes in environmental factors precipitate diseases in shrimps. Some of the important strategies for gut health management have been
Sustainable approaches to modulate the gut microflora in farmed shrimps for preventing gut diseases.
The use of selected bacteria to inoculate the gut (probiotics)
Specific nutrients promoting the development of selected bacterial strains (prebiotics) in gut.
Specific natural compounds (mostly derived from yeast and herbal extracts, so called “phytobiotics”) capable of modulating the microflora towards a
Favoring the development of beneficial bacteria and inhibiting potentially pathogenic micro-organisms in gut.
A synergistic blend of herbal extracts has the bacteriostatic and bactericidal properties against pathogenic and potentially pathogenic bacteria.
Furthermore, this synergistic blend has proven to be a powerful interrupter of bacterial and effectively modulate for the gut flora.
The presence of a synergistic blend of phytobiotics provides an array of antimicrobial activities in the shrimp’s digestive system. This offered additional
protection against co-infections with opportunistic bacteria such as vibriosis.
Management of Diseases Controls
PCR screening of brood stock before spawning and PCR screening of larvae (PL) before stocking can help to avoid the entry of pathogens into aquaculture
Mortalities are precipitated by sudden stress from the changes of wide fluctuation of climatic condition.
Total disinfection and sanitization to the whole culture system have a chance to eradicate the pathogens and other diseases.
Feeding of shrimps with immunostimulants has been shown to help overcome diseases / infection
Application and mode of probiotic culture system will reduces the chances of diseases.
Bacterial and other diseases can be treated and hold under control with application of various chemicals and other biological products.
Avoidance of pathogens: This can be done through selection of specific pathogen free broodstock, exclusion of carrier animals in
culture systems, screening of healthy and disease free shrimp brooders ,nauplii and larvae through quarantine systems ,stocking of SPF /SPR seeds ,filtration and sanitization of water
Improving host conditions through good nutrition and immunostimulation: A number of microbial molecules such as feed additive
probiotic, b 1,3 glucans, peptidoglycans, polysaccharides have been shown to stimulate the non-specific immune mechanisms in shrimp
Improving environmental conditions: The environment has a greater role and significant impact on shrimp health, growth and production
.Most disease problems are triggered by deterioration of water and soil quality. Application of probiotic can capable of oxidizing toxic wastes and be useful in improving soil & water
quality in shrimp culture ponds.
Biosecurity: The biosecurity systems have used in aquaculture as well as for regulations and policies to prevent and control the
spread of diseases. The key elements of biosecurity are a reliable source of stocks, adequate detection and diagnostic methods for excludable diseases, disinfection and pathogen
eradication methods, best management practices, and practical & acceptable legislation. Hence, the strict principles and guide lines of biosecurity to be adapted in individual farms
and cluster wise in farming areas.
The Best Management Practice (BMP), quarantine system and good feed management practice are to be followed entire culture period to overcome the disease
problems in shrimp culture.
Controlling total ammonia-nitrogen (TAN) concentration is imperative
Trickling filters are simple and robust biological filters that provide nitrification, degassing of carbon dioxide and oxygenation in one component. However, due to the low specific
surface area of the media, they are generally larger than most modern filters.
The production of aquatic products in land-based systems using tanks and recirculating aquaculture system (RAS) technology continues to expand worldwide. This trend is driven by the need for
intensified production practices that utilize and discharge less water.
A description of these technologies can be found in our previous columns in the Global Aquaculture
Advocate. While the installment in the July/August 2015 issue described how to determine the recirculated flow required to the biofilter in an RAS, this article focuses on how to
estimate the size of biofilter required for a specific application.
Sufficient capacity, feed rates
To size a biofilter for use in an RAS, the primary concern for the designer is to provide enough biofilter capacity to control the total ammonia-nitrogen (TAN) concentration in the culture
tanks to a preset upper limit. Knowing this concentration is very important, as the removal rate of a biofilter is related to the concentration of ammonia-nitrogen available to the bacteria
in the filter.
The lower the limit of the TAN concentration selected by the designer, the lower the removal rate will be for a biofilter. The result will be the requirement of a large biofilter for a given
Also critical to the process of sizing a biofilter is specifying the maximum feed rate for the system. The ammonia-nitrogen production rate can be estimated based on the rate of feed addition
and the protein content of the feed used within the system.
The biofilter media of this moving-bed reactor initially looks white and floats readily.
The May/June 2015 column noted that the best way to size the nitrification capacity of a biofilter was by determining the volumetric TAN conversion rate (VTR) of the biofilter media in units
of g TAN/m3/day. It is critical that the designer under.stand the conditions under which this VTR is determined and compare them to those found within the RAS in question under peak loading
Remember, the lower the TAN concentration going into a biofilter, the lower the VTR for that filter will be. This is the most difficult part of sizing a biofilter for a particular use and, in
most cases, is based on previous experience with a given biofilter media in a specific biofilter configuration.
Thus there are four steps in sizing a biofilter for a particular use in recirculating aquaculture production systems:
Identify the maximum allowable TAN concentration within the culture tank.
Estimate the maximum feed rate for the system and calculate the maximum
rate of total ammonia-nitrogen generation.
Determine from previous experience or manufacturers’ specifications the
VTR for the biofilter media being used.
Calculate the estimated biofilter media volume requirement.
Biofilter sizing example
After four months, the “seasoned” media looks brownish and has less buoyancy.
In an example, consider a freshwater RAS operating at a water temperature of 25° C, and assume there is no oxygen limitation, as the dissolved-oxygen concentration of the water is above 4
mg/L to the biofilter. Further assume that the pH and alkalinity of the system are 7.2 and 100 mg/L, respectively, and the maximum desired TAN concentration is 2 mg/L. Additionally, assume
the maximum feed rate for the entire system on this biofilter will be at its highest at 60 kg/day of 40%-protein feed.
We now need to estimate the rate of TAN generation cre.ated daily by this feed rate. See equation 1 below (from the July/August 2015 Advocate).
TAN produced (kg/day) = 60 kg Feed/day x 40% Protein x
50% Nitrogen wasted x 0.16 g Nitrogen/g Protein x
1.2 g TAN/g Nitrogen
TAN produced = 2.3 kg TAN/day
Note that the percentage of protein and nitrogen wasted in the equation above should be entered as decimal fractions — 0.4 and 0.5, respectively.
Perhaps the most difficult task in this exercise is the third — determining the VTR that will be used. As noted before, this rate is a function of the type of biofilter media selected and the
conditions within the system.
The authors’ experience and published research results indicate the VTR for trickling biological filter media with a specific surface area of 200 m2 under the water quality conditions cited above is
approximately 90 g TAN/m3/day. Likewise, a conservative estimate of the VTR for media in
a moving-bed reactor under similar conditions is 350 g TAN/m3/day. Equation 2 below can be used to estimate
the volume of biofilter media needed to convert the TAN produced to relatively harmless nitrate-nitrogen.
Biofilter media volume (m3) = TAN production (g TAN/day) ÷
VTR (g TAN/m3/day)
We can use this equation to calculate the volume of media a trickling filter would need as:
2,300 g TAN/day ÷ 90 g TAN removed/m3/day = 25 m3
If this trickling filter were sized at 2.5 m square, the media height would be 4.0 m. In trickling filter design, there is space both above and below the biofilter media. In all, this
trickling filter might be 5.3 m high with 0.3 m available for water distribution above the media and 1 m below the media to collect and direct the water back to the production system.
Likewise, we can calculate the volume of moving-bed media required for the system in this example. That volume is estimated using equation 2 as:
2,300 g TAN/day ÷ 350 g TAN removed/m3/day = 6.57 m3
To allow the media to have room to be mixed with aeration in moving-bed reactor designs, the reactor is designed so the media takes up no more than 70 percent of the reactor volume. Hence,
the volume of a reactor with 6.6 m3 of media would be 9.4 m3. If this reactor were 2.5 m in diameter, the volume needed by
the media and water would require the height to be 1.9 m. Adding 0.3 m to the reactor for “freeboard” above the water and media, the overall reactor height would be 2.2 m.
From these estimates of biofilter sizing, readers can easily understand why moving-bed reactors have come to dominate the industry. Similar estimates can be made for other biofilter media.
However, the designer must have a good idea of the VTR capacity of a specific media under the specific conditions that will be encountered in the commercial production of the aquatic crop
planned for the system.
Editor’s Note: This article was based in part on research conducted by the author at North Carolina State
University and published in the Volume 23, 2000 Journal ofAquacultural Engineering. The spreadsheet in that publication presents all of what is described here.
Kentucky State University researchers
explore production, marketing
The tank at KSU raised shrimp to over 24 grams in 98 days.
Indoor shrimp production is growing in popularity in some parts of the world, including the United States. By growing shrimp in a closed building, producers can dramatically increase
biosecurity, produce shrimp more consistently, grow shrimp year-round and locate production centers near markets.
Biosecurity is enhanced through restricted access and controlled inputs. Indoor systems experience minimal water quality variations in temperature, dissolved-oxygen or pH levels. Furthermore,
if a consistently productive system can be developed, it may be sited nearly anywhere and sized for the markets it supplies. This may fit well with local foods movements, allow live animal
distribution and reduce transportation costs, allowing farmers to receive substantial prices for their products.
In an effort to support industry involvement in this growing field, researchers at Kentucky State University (KSU) are exploring production and marketing aspects of indoor shrimp production.
This work was conducted inside the newly equipped Aquaculture Production Technologies Laboratory at KSU. The 1,300-m2 lab building houses a variety of recirculating
aquaculture systems. The air temperature of the building is maintained at approximately 23° C year-round using electric boilers.
A 3.1-m3 rectangular raceway was used as a
nursery and outfitted with an external 190-L settling chamber and a 190-L biological filter filled with plastic biomedia. Ten-day-old postlarvae of Pacific white shrimp (Litopenaeus vannamei) were obtained from a hatchery in Florida, USA, and stocked into the nursery at a density of 2,500/cubic meter.
After the nursery phase, 5,250 shrimp weighing an average of 0.55 g each were stocked in a 20-cubic meter fiberglass growout raceway with water containing artificial sea salt at a salinity of
The raceway was equipped with a 1-hp pump, which delivered water to three aeration nozzles distributed around the raceway and one nozzle that fed a foam fractionator.
The nozzles inside the raceway drew air in through snorkels extending above the water surface and directed water around a central wall. The fractionator nozzle delivered finely aerated water
into the foam fractionator, which was used as needed to maintain turbidity at approximately 40 nephelometric turbidity units.
Two 3,000-watt submersible heaters in the growout raceway maintained a water temperature of approximately 28.5° C. A dry shrimp probiotic was initially added to the water over a two-week
period, and 3 L of biomedia from the nursery was placed in a mesh bag and submerged in the water to help establish a bacterial community.
The growout tank was managed as a biofloc system, with the only external filtration being the foam fractionator to remove dissolved and suspended solids. There was a 1.3 mg/L spike of total
ammonia nitrogen one week after stocking shrimp, and a 3.5 mg/L spike in nitrite-nitrogen concentration one month later. Neither spike resulted in noticeable mortality. Sodium bicarbonate was
used to maintain pH, which got as low as 7.0. The aeration system was effective at maintaining dissolved-oxygen levels above 6.5 mg/L.
Ray, Table 1
Final weight (g)
Growth rate (g/week)
Feed conversion ratio
Showing 1 to 5 of 5 entries
Shrimp performance during the first production
There was 15 cm of tank freeboard above the water surface and 46 cm of vertical netting surrounding the tank. Regardless, 457 shrimp jumped out of the growout tank during this project, mostly
on two occasions. Netting was then placed tightly over the top of the tank, which prevented shrimp from escaping. Lights turned on and off in the building may have startled the shrimp,
resulting in much of the jumping.
Shrimp were grown in the growout tank for 98 days. Shrimp weighed 24.3 g at harvest and there were 91.8 kg harvested. Survival was 69.1 percent, although adding the shrimp that jumped out of
the tank would have made the survival 80 percent. The feed-conversion rate was 1.3:1, and the growth rate was 1.7 g/week. The shrimp performance is summarized in Table 1.
Harvested shrimp were sold at a farmers market in Frankfort, Kentucky, USA, where farmers are able to sell a variety of products directly to consumers. Frankfort has a population of
approximately 27,500 residents, who had a mean annual per-capita income in 2013 of $24,100. The shrimp were sold fresh on ice at $26.40/kg. A total of 37.2 kg were sold at this market in only
an hour and a half. Also, samples of shrimp were cooked and offered to patrons at the market.
Shrimp were dispersed to chefs in Louisville, Kentucky, through two distribution centers. Shrimp were also given to two chef/restaurant owners and a grocery store in Lexington, Ky.
Consumers and chefs who tried the shrimp were given a questionnaire. In total, five chefs and 27 consumers completed questionnaires. Their responses are outlined in Table 2.
The questions asked participants their opinions of the Kentucky-grown shrimp regarding taste, texture, freshness, size, overall and appearance. For each topic, the respondents could select: 1
= loved it, 2 = liked it, 3 = it’s OK, 4 = disliked it or 5 = hated it.
Respondents were also asked what price they would expect to pay for the fresh whole shrimp, as well as the most they would pay for them. Their options were “will not buy,” $17.60/kg or less,
$19.80/kg, $22.00/kg, $24.20/kg, $26.40/kg, $28.60/kg, $30.80/kg, $33.00/kg, $35.20/kg, $37.40/kg, $39.60/kg, $41.80/kg and $44.00/kg or more.
Ray, Table 2
What is your opinion of the shrimp for:
2.0 +/- 0
1.3 +/- 0.1
2.2 +/- 0.5
1.3 +/- 0.1
1.0 +/- 0.5
1.0 +/- 0
2.2 +/- 0.2
1.3 +/- 0.1
2.2 +/- 0.2
1.1 +/- 0.1
1.8 +/- 0.2
1.1 +/- 0.1
What price would you expect to pay ($/kg)?
21.6 +/- 2.4
25.9 +/- 2.3
What is the maximum you would pay ($/kg)?
26.0 +/- 2.5
28.6 +/- 1.5
Showing 1 to 9 of 9 entries
Mean responses from chefs and consumers who tasted the
Responses were rated 1 to 5, with 1 the best rating
The recurring costs of nursery and growout production for this project were approximately $12.10/kg. Calculated at $0.04/kWh, electricity fees accounted for 25 percent of production costs.
Labor at $10/hour accounted for 28 percent, while feed reflected 29 percent of the total costs. Postlarvae at 16 percent and other consumables at 2 percent made up the
remainder of the total.
If 14 growout tanks were used, one tank could be harvested weekly all year. If more tanks were used, an economy of scale effect should be realized, bringing down costs. Other cost
considerations include heating the air, infrastructure, taxes and distribution. These should be considered carefully and vary depending on a farmer’s circumstances.
Shrimp grew very well during this project. They had an efficient feed conversion, and a substantial amount of the mortality that occurred could easily be prevented. Survey respondents were
very accepting of the product and scored it highly. Consumers appeared willing to pay more than chefs, possibly because chefs are motivated more by the profitability of their restaurants.
The highest-scoring attribute was freshness of the product, a quality that cannot easily be achieved without year-round, indoor, local shrimp production. A direct-to-consumer approach for
shrimp sales could prove to be profitable. At a sale price of $26.40/kg, there appears to be room for profit, and according to survey responses, a higher price may be acceptable to consumers.
Future efforts at KSU will focus on increasing shrimp stocking density and survival to enhance production output and augment the potential profitability of this approach. The sale of live
shrimp will also be explored.
Hatcheries, farms should monitor levels of essential nutrients
Aquatic animals can get the essential nutrients calcium and magnesium from both culture water and their food.
Concentrations of calcium and magnesium are seldom measured in waters for aquaculture, but total hardness is determined rather often. Hardness is the concentration of divalent cations —
mostly calcium and magnesium — in water expressed in milligrams per liter (parts per million) of equivalent calcium carbonate.
Hardness sometimes is expressed in different forms: total hardness and calcium hardness with the difference being magnesium hardness. Calcium hardness plus magnesium hardness, of course, is
total hardness. The factors for converting between hardness cations and hardness are as follows: calcium x 2.5 = calcium hardness, and magnesium x 4.12 = magnesium hardness.
The major sources of hardness in freshwater are dissolution of limestone, calcium silicate and certain feldspars. In arid regions, the dissolution of calcium and magnesium sulfates and
certain other minerals is a source of calcium and magnesium. Most liming materials used in aquaculture are made from limestone, which imparts hardness to water.
In most freshwater, hardness and alkalinity are of similar concentration and range from less than 5 mg to over 150 mg/L. In arid regions, hardness usually exceeds 100 mg/L and often is
greater. Hardness frequently exceeds alkalinity in arid regions.
Seawater has an average of 400 mg/L calcium and 1,350 mg/L magnesium, resulting in a hardness of over 6,000 mg/L — much more than its average alkalinity of about 140 mg/L. Estuaries
usually have a lower hardness than seawater, but much greater than freshwater. Hardness concentrations vary greatly from place to place and over time in estuaries because of the mixing of
seawater and freshwater in these systems.
Calcium and magnesium are essential nutrients for aquatic plants and animals. For example, fish need calcium for bone development, because bone consists largely of calcium phosphate. However,
the concentrations required for phytoplankton — the most abundant plants in aquaculture ponds — are only about 2 mg/L for calcium and even less for magnesium.
Calcium is important in fish hatchery water supplies. High levels of alkalinity and hardness can lead to precipitation of calcium carbonate from the water.
Aquatic animals can get calcium and magnesium both from the water and their food. Hardness usually is great enough to supply enough calcium and magnesium for aquatic animals in fertilized
ponds, and in ponds with feeding, calcium and magnesium are obtained from the feed when the hardness is low. Ponds with low-alkalinity water usually have low calcium and magnesium
concentrations, and when liming materials are applied to remedy this problem, hardness also increases.
Freshwater ponds in arid regions and ponds filled with estuarine water or seawater usually have plenty of hardness for aquaculture. When such ponds are limed, the benefit that may accrue is
from increasing alkalinity rather than hardness. From a productivity standpoint, alkalinity is a more important variable than hardness.
In fertilized ponds, the amount of phosphate fertilizer necessary to maintain an adequate phytoplankton bloom can be greater in water of high calcium concentration — especially if pH is
elevated. For example, about three times as much phosphate fertilization was required in ponds in Israel where hardness was over 300 mg/L to give the same amount of tilapia production as
achieved in ponds in Alabama, USA, with a hardness of about 45 mg/L.
Other important effects
Several other effects of calcium and magnesium deserve mention. In ponds, calcium functions to minimize the rise in pH that can occur when photosynthesis rates are high. After plants deplete
the water of free carbon dioxide, they can use bicarbonate as a carbon source. But when using bicarbonate, plants release carbonate that hydrolyses and causes pH to increase. Calcium ions
react at elevated pH to precipitate carbonate ions as calcium carbonate, and this reaction minimizes the amount of carbonate in the water to hydrolyze and increase pH.
There are some pond waters in which the alkalinity is high and calcium concentration is low. This combination can lead to dangerously high afternoon pH when photosynthesis is proceeding
rapidly. Calcium sulfate can be applied to increase the concentration of calcium ion. As a general rule, it is desirable to have a hardness similar to or greater than the alkalinity
— roughly 2 mg/L of calcium sulfate are required to provide 1 mg/L of hardness.
Hardness in water also facilitates flocculation and precipitation of suspended clay particles to lessen turbidity. An abundance of calcium and magnesium ions tends to neutralize the negative
charges on suspended clay particles, allowing them to floc together and create a mass great enough to precipitate. Calcium sulfate often is applied to ponds to clear turbidity from the water.
The recommended treatment rate usually is 1,000-2,000 kg/ha.
Calcium ions affect the toxicity of trace metals to fish and other aquaculture species. The presence of calcium blocks the uptake of metal ions across the gills, thereby increasing the
dissolved concentration of metals required to cause a toxic effect.
The lethal concentrations of metal ions such as copper, zinc, lead, cadmium and chromium usually are considerably greater in harder water than in softer water. To illustrate, the 96-hour
lethal concentration 50 (L.C.50) of copper to channel catfish was reported by Drs. David Straus and Craig Tucker to be 0.051-0.065 mg/L in water with a hardness of 16 mg/L, but 1.040-1.880
mg/L in water with a hardness of 287 mg/L. L.C. 50 is a standard measure of the toxicity of a medium that will kill half of the sample species population in a specific period of exposure.
Calcium also is important in fish hatchery water supplies. Eggs tend to hydrate at low calcium concentrations and do not develop and hatch normally. The minimum concentrations of calcium ions
for good development and hatchability have been reported as 10 mg/L for eggs of brown trout and 4 mg/L for those of channel catfish. A recent study suggested the minimum calcium concentration
for channel catfish hatcheries should be 10 mg/L, and best hatchability and fry survival were achieved at around 30 mg/L.
High concentrations of alkalinity and hardness can lead to precipitation of calcium carbonate from the water. This is especially common when groundwater that has high alkalinity and hardness,
as well as elevated carbon dioxide concentration, is brought into contact with the atmosphere. For example, the alkalinity and hardness in well water used to supply ponds at an inland shrimp
farm in Alabama, USA, were 275 and 325 mg/L, respectively. Once put into ponds, the water equilibrated with atmospheric carbon dioxide, and alkalinity and hardness dropped to 120 and 168
mg/L, respectively, as a result of calcium carbonate precipitation.
Although calcium carbonate precipitation is not usually of great concern in ponds, it can be troublesome in hatcheries. The author has observed that at a shrimp hatchery supplied with saline
groundwater with initially high concentrations of carbon dioxide, alkalinity and hardness, calcium carbonate precipitated onto the larvae and resulted in high mortality. The same phenomenon
probably can occur with eggs in a fish hatchery.
The ideal situation in freshwater aquaculture is to have hardness and alkalinity concentrations of at least 60 mg/L. There apparently is little problem with high hardness concentrations
— even when they greatly exceed alkalinity concentrations — provided the total dissolved solids concentration is not excessive for the cultured species. Total hardness concentration
does not appear to be a negative factor in ponds filled with estuarine or seawater.
In some inland, low-salinity waters, low magnesium concentrations have been reported to lessen the survival and growth of shrimp. Magnesium concentrations in such waters can be increased by
the application of potassium magnesium sulfate. Magnesium sulfate (Epsom salt) also is a soluble source of magnesium.
There is no definitive recommendation on the ideal concentration of magnesium in low-salinity water for shrimp culture, but the ratio of magnesium in milligrams per liter to salinity in parts
per thousand in seawater is about 40:1. Thus, one approach to estimating a suitable magnesium concentration in low-salinity, inland aquaculture is to multiply salinity in ppt by 40 to
determine the suitable concentration of magnesium. At 2.5 ppt salinity, the suitable magnesium concentration is 100 mg/L.
At a typical inland shrimp farm in Alabama, USA, pond water has about 2.5 ppt salinity, but the magnesium concentration is only around 5 mg/L in the water supply. It would be extremely
expensive to raise the magnesium concentration to 100 mg/L. But good shrimp survival and production have been achieved when magnesium concentrations were maintained between 10 and 30 mg/L.
Black tiger trials with fewer daily feedings show improved conversion results
In lined, aerated ponds, Penaeus monodon fed four times daily had lower FCRs after one month of
a culture cycle.
In recent years, shrimp aquaculture costs have increased in every sector. Farmers need to find ways to reduce costs to maintain the profitability of the industry. Currently, one possibility
for cost reduction is to manage feed consumption without affecting shrimp growth and total harvest.
Growout production costs for raising black tiger shrimp (Penaeus monodon) in Australia are relatively
high compared to those in other countries. Feed, labor, maintenance and power costs all contribute to the situation. Feeding management that lowers feed-conversion ratios can have a direct
impact on reducing the costs of production in growout ponds.
The feed-conversion ratio (FCR) is a measure of shrimp’s efficiency in converting feed mass into increased body mass. FCR is defined as the mass of the food eaten divided by the body mass
gain, all over a specified period. For P. monodon, the typical feed-conversion ratio is 1.8.
FCRs are important because higher FCR values indicate uneaten feed that can leach out nutrients in ponds. Leached nutrients impact water quality in growout ponds and potentially increase the
nutrient load in the farm effluent. In general, a high FCR means more feed waste and costs, which leads to lower profitability for the farm.
Alternative feed management
In Penaeus monodon growout ponds in Australia, shrimp are usually fed five times daily after they
have been in the pond for one month. Shrimp farmers believe that feeding smaller amounts regularly is an effective strategy in maximizing FCR over the entire crop.
An alternative feeding frequency was introduced in the last seven years for Gold Coast Marine Aquaculture’s grow-out ponds. This method involved feeding the shrimp only four times daily. As a
result, consistently lower FCRs have been achieved (Table 1).
Shrimp performance achieved with fewer daily feedings.
Four feeds per day, at 5 a.m., 11 a.m., 5 p.m. and 11 p.m. Feeding is
applied using a vehicle with a feed blower, which spreads feed evenly across ponds.
The three feeding trays used in every pond are employed at the same time
the feeding vehicle spreads feed and checked after about three hours. The amount of feed placed on every tray is 0.5 percent of the total individual feeding.
If no feed is left in the trays, a 3 kg increase in feed volume is made
during the next feeding for an average shrimp body weight up to 10 g. An increase of 5 kg is made for shrimp with average body weight greater than 10 g.
If feed is left on the trays, a 20 to 80 percent decrease is
made in the next feeding. Previously, Gold Coast Marine Aquaculture only decreased feeding by 10 to 30 percent when feed was left on the trays. This was due to the belief that a
large decrease in feed would lead to a higher rate of cannibalism in P. monodon stocked at
Shrimp do require regular feeding due to their small stomachs and rapid digestion. However, from previous observation, shrimp generally feed and rest periodically before returning to the
water column in search of more food.
Since the time gap between feedings is a constant six hours, this provides enough time for shrimp to rest before resuming their eating cycle. This allows the shrimp to properly digest their
source of nutrients. This simple act can help maximize molt cycle and growth performance.
There is also enough time for pond staff to complete their feeding rounds without needing to rush. This reduces human error when setting and checking feed trays. Monitoring of feed
consumption becomes more effective.
Although monitoring of shrimp feed consumption with feed trays has become very important in controlling FCR in intensive operations, this method requires special human attention and an
increase in workload for farm staff during production periods, so the trays may sometimes be sidelined or even neglected. Gold Coast Marine Aquaculture reduces this possibility for error by
maximizing the time gaps between feeding times.
Shrimp farmers always hesitate to decrease feed volume during shrimp cultivation due to their belief that P. monodon are highly cannibalistic. If the amount of feed is decreased, especially during molting periods, they think, this will cause a decrease in
biomass due to cannibalism. Observations made by Gold Coast Marine Aquaculture show the opposite.
As aquaculture intensifies, so will the prevalence and severity of parasite infections
Commonly encountered parasites of aquatic animals include (from left) Caligus elongatus, the monogenean Gyrodactylus salaris, the ciliate protozoan Trichodina and Anisakis nematodes. On
the second row, right, the eggs of the turbellarian Bdelloura candida are shown on the gills of a horseshoe crab. The image on the third row shows Gyrodactylus salaris on the fin of an
Atlantic salmon, followed by the sessile peritrich Apiosoma on the skin of a freshwater fish and the monogenean Dictyocotyle coeliaca from the body cavity of a ray.
Obligate and opportunistic parasites play a critical role in determining the productivity, sustainability and economic viability of global finfish aquaculture enterprises. Without stringent
and appropriate control measures, the impacts of these pathogens can often be significant.
Estimating the true impacts of each parasite event, however, is complicated, as costs can be affected by a diverse assortment of environmental and management factors. The factors can range
from direct losses in production to the more indirect costs of longer-term control and management of infections and the wider, downstream socioeconomic impacts on livelihoods and satellite
industries associated with the primary producer.
Certain parasite infections may be predictable, as they occur regularly, while others are unpredictable because they arise sporadically. In each case, there can be costs for treating and
managing infections once they are established, but for predictable infections, there also are costs associated with prophylactic treatment and management.
Table 1 provides some estimates of economic loss associated with notable protistan and metazoan parasite events in some of the world’s leading finfish production industries. The figures
provided in Table 1 were extracted from a larger study by the authors in which the potential economic costs related to 498 specific events attributable to a range of key parasite pathogens
Acceptance of losses
A significant proportion of stock losses occur within the hatchery/nursery phases of production. In many industries, these are factored into and accepted as part of normal operational
Such fatalistic acceptance means losses are frequently underreported, hiding the severity and impacts of parasites such as omycete species belonging to the genera Aphanomyces and Saprolegnia; the dinoflagellates Amyloodinium
ocellatum and Piscinoodinium pillulare; ciliate protozoans such as Trichodina species, Ichthyophthirius multifiliis and Cryptocaryon irritans; and species
belonging to the monogenean genera Gyrodactylus and Dactylogyrus.
Estimating global costs
The authors recently began to estimate the global costs of parasitism by following production at four commercial Nile tilapia, Oreochromis niloticus, farms in Thailand over the course of 12 months to determine average mortality rates in the earlier stages of production. The data are
presented in Figure 1. From these values, the following survival rates can be determined: egg production (77.5 percent hatch rate), swim-up fry (77.8 percent survival from hatched eggs, 60.8
percent survival of starting egg number), 21-day post-monosex fry (78.9 percent survival from swim-up fry, 48 percent survival of starting egg number) and in 2.5-cm nursery-size fish
(83.3 percent survival from 21-day monosex stage, 40 percent survival of starting egg number).
Hatchery-based losses were then calculated using local production costs — 0.1 Thai baht (U.S. $0.0028) for each egg to swim-up stage, 0.2 baht ($0.0057) for each swim-up to monosex fry
and 0.3 baht ($0.0085) for each monosex to nursery-size fish — and by assuming that 20 percent of the mortalities can be directly attributed to parasitic infection.
Given the broad diversity of aquaculture, the 267 food finfish species and categories listed by the Food and Agriculture Organization (FAO) of the United Nations and the vast spectrum of
parasites that can impact their production, it is almost impossible to ascribe a single value that captures all the losses induced by parasite activity in each industry. Likewise, despite
continuous health monitoring by on-site diagnosticians, it is technically impossible to determine the cause of mortality of every fish on site.
From the figures provided above and in Figure 1, for example, about 1.2 million 21-day post-monosex fry are lost each month (about 40,000/day). From a parallel study conducted by some of the
current authors, it would appear that parasites account for an annual loss of $62 million to $175 million, representing 5.8 to 16.5 percent of the value of aquaculture production in the
United Kingdom across all species reared in freshwater, brackish and marine systems.
To begin moving toward an estimate of loss attributable to parasitism, the figure of 20 percent is applied here to estimate stage-specific losses due to parasites within the hatchery phase of
production. This is based on this latter study on aquaculture activities in the U.K. It is important to stress, however, that this is not 20 percent of global harvest production.
In 2013, the last year for which complete figures are available from FAO, the global production of finfish through aquaculture was 47.07 million metric tons (MT). If we assume an average sale
weight of harvest-sized fish of 0.4 to 0.5 kg, the total number of harvest fish sold annually can be estimated at 94.14 billion to 117.68 billion.
If this figure is adjusted by assuming a 10 percent loss of fish between nursery and harvest, the annual number of post-nursery fish can be estimated as 103.55 billion to 129.44 billion.
If the same percentages of parasite-induced loss are applied for each stage of finfish hatchery production, and assuming that $1.00 = 32.16 Thai baht, the annual global loss of juvenile fish
can be estimated at between $107.31 million and $134.14 million.
Using the annual production of all farmed tilapia species for 2013, for example, which was 4.82 million MT, we can estimate there were 9.7 billion to 13.4 billion post-nursery fish produced
and that the economic losses of juvenile tilapia to parasitic infection were $4.84 million to $6.66 million at the nursery stage, $5.84 million to $8.02 million at the monosex stage and $5.13
million to $7.05 million at the swim-up stage.
However, these estimates are for the direct losses due to parasitic infections and do not account for the role that parasites can play in facilitating secondary infections and the resultant
Considering post-nursery losses, the total production in 2013 was 40.50 million MT of freshwater fish valued at $1,641/MT, and 6.57 million MT of brackish and marine fish valued at
$4,203/MT. If we assume parasites are responsible for the loss of 1 to 10 percent of harvest-size fish, then the value of these fish can be estimated at $945.00 million for 1.0 percent loss,
$2.36 billion at 2.5 percent loss, $4.72 billion for 5 percent and $9.45 billion at 10 percent loss. If the hatchery and growout figures are combined, the annual global
cost of parasites in finfish aquaculture can be very loosely and tentatively estimated at $1.05 billion to $9.58 billion.
Moving toward an accurate estimation of the global cost of parasite-associated impacts is dependent on detailed, high-quality data and the resources necessary to undertake such studies.
However, as global aquaculture continues to grow and intensify, the prevalence and severity of parasite infections will similarly rise, as will the attendant economic costs of parasitism.
In addition, the increased trade in finfish and their products may facilitate the spread of parasites into new environments. Changing climatic conditions will also place increased pressure on
aquaculture systems, current production practices and the interactions among wild and farmed aquatic stocks, parasite life cycles and transmission pathways.