Coastal Shrimp Farming in Texas
 
Setsuko Izena

1. Introduction

     Sustainability is the interrelated issue of environment and human development. There are two essential contradictions between environment and human development according to ( Dovers and Handmer, 1993). The first contradiction is economic growth versus ecological limits. The second contradiction is the paradox of technology. Some think that we can have ecologically sustainable environments as well as economic growth. Others, including the World Commission on Environment and Development (WCED, 1987) consider that we should apply less environmentally damaging forms of economic growth in our future. The question is which choice is more feasible to solve problems. We face an environmental crisis destroying ozone, polluting the ocean, consuming limited resources, and endangering species. However, we can not stop developing all economic activity and productivity simply because human population has been increasing, and we have to make enough food for all people to survive on the earth, including poor developing countries. This oxymoron makes us decide which direction we are to go ahead in our future.

    Increasing productivity and sustaining resources are a paradox with human overpopulation and profligacy; all are key factors of underlying the global environmental crisis. "Humanity’s immense propensity for culture, in all its forms, and of which technology is a tangible manifestation, is the basic reason why we can impact so heavily on our environment." (Dovers and Handmer, 1993). The development and application of technology for practically all purposes have enabled, and indeed continues to encourage, an increase in our consumption of resources and production of wastes. These results of the development and application of technology threaten the Biosphere and even nature’s survival.

Texas Coastal Ecosystem

    Texas intricate coastal ecosystems are being threatened by relatively new industry on the coast, shrimp farming established in Texas in 1980. Coastal shrimp farming relies heavily on the clean water of Texas’ bays and estuaries. Coastal communities in Texas have identified environmental problems resulting from shrimp farm operations. Wild shrimp fishers are concerned about the potential for harm to native shrimp stocks from industry’s growth and some coastal communities are now hostile toward the industry.

    According to the Senate Natural Resources Interim Subcommittee’s study, aquaculture can be broadly defined as the " the business of producing and selling cultured species raised in private facilities". The facilities located within counties adjacent to the Gulf Coast are using salt or brackish water to farm shrimp. Because of their location, mariculture operations have potential impacts on bays and estuaries. This potential impact has generated a heated debate between the mariculture industry, the traditional commercial shrimp fishing industry, conservation groups, local citizens, and environmentalists.

    In Texas shrimp farms have many kinds of environmental problems, discharge waters from shrimp farms to Texas bay; harm to mangrove forests; salinization of ground water; and outbreaks of shrimp disease. I am concerned about the possibility of transmitting exotic shrimp disease to native shrimp in Texas. If scientists and researchers can prove a hypothesis that exotic shrimp disease can transmit to native shrimp, outbreaks of exotic shrimp disease will be able to wipe out native shrimp.

    There is also a possibility for other marine organisms to become extinct in future.

2. Social Aspect: Environmental an Economic Consequences.

    Shrimp farming has caused serious environmental and socioeconomic problems. Shrimp farming pollutes Texas bay discharged wastewater. It causes the destruction of coastal wetlands. Outbreak of shrimp disease from farming shrimp has harmed traditional fisheries. However, it is not easy to solve these problems by reducing shrimp farming because the result has been a social conflict; for example, many people will lose their livelihoods.

    There are two points of view. One is that economic importance is the priority. For example, Texas State government is on the shrimp farming companies side that can bring more tax to the government and make more employment. The other view is that we should be concerned for the environment of Texas first. For example, residences in Texas and environmentalists are against the development of shrimp farming.

    The Texas State government initially viewed its role not as a regulatory one but as one of promoting shrimp farming to create jobs and a more diversified economy on the Texas coast. In 1986, the Texas Department of Commerce began to actively promote shrimp farming. In 1987, the state legislature passed a law exempting shrimp farms from state water-rights permit requirements (Texas Water Code ch11.1421). In 1980, experts at Texas AM University Sea Grant program began providing support and technical assistance to shrimp farmers. The federal government has also played a significant role in promoting the U.S. shrimp farming industry in Texas. More than $20 million in federal funds over the past 10 years have gone to the U.S. Department of Agriculture(SUDA) Marine Shrimp Farming program( USMSFP, 1997). However, the government has to be responsible for the enhancement of regulatory framework to protect the environment of Texas bay for citizens.

    There are some agencies to regulate some aspects of shrimp farming, for example, The Texas Park and Wildlife Department ( TPWD). The TPWD exercises its authority requiring exotic species permits for import, sales possession, or release of exotic shrimp, and requiring farmers to use "disease-free" exotic shrimp for culture. The Texas Natural Resources Conservation Commission.( TNREE) has the authority to require state permits for any activity producing a wastewater discharge. However, no agency is responsible for monitoring or controlling disease during production process. Although TPWD issues exotic species permits they have no authority over shrimp during production.

3. Technical Aspects: exotic shrimp diseases cause a great impact on not only farming shrimp but also native shrimp.

    Farming shrimp industries in Texas play an essential role in U. S. Aquaculture, and Texas marine shrimp culture relies on exotic shrimp.

    Shrimp have the potential to be one of the major aquaculture species produced in Texas. Nine commercial shrimp farms operate along the Texas Gulf Coast. In addition, three farms are for sale or lease, and two have been proposed, but not yet built.(Coastal Shrimp Farming in Texas, Environmental Effects of Aquaculture in the US, 1997).

    Most shrimp in aquaculture farms are exotic species, primarily the Pacific white shrimp specise. From 1975 through 1993, the number of Shellfish Culture permits in Texas varied from 4 to 32. Production by the Texas shrimp aquaculture industry continues to increase although the number of producers has declined. During 1993, more than 4 million pounds of shrimp valued at $11 million were produced by Texas shrimp farms, up 190% in weight since 1990. In 1993, five shrimp farms had 1,406 acres of pond production. (Coastal Shrimp Farming in Texas, Environmental Effects of Aquaculture in the US, 1997).

    Imports of shrimp to the United States increased 76% from 342 million pounds of in 1954 to 601 million pounds worth more than $2 billion in 1993. The development of aquaculture, especially in South America (Ecuador) and Asia (China and Thailand), has substantially increased imports of shrimp (FISHING, Texas Parks & Wildlife, 1994). These imports have an impact on prices paid to Texas shrimpers. As supply increases from imports and domestic aquaculture, market forces drive the produce of Texas wild-caught shrimp lower. Economic viability of Texas shrimpers in the future will be affected in part by the amount of total shrimp available in worldwide markets.

    Texas marine shrimp culture has traditionally relied on non native shellfish species (exotic species) because consumer demand for large species of shrimp has been increasing. Exotic shrimp grows rapidly, and their ability to survive in confined conditions is much higher than native species in an open ocean. escaped exotic shrimp species. The problems are intensifying with the shrimp farming

Exotic shrimp diseases appear in Texas

    Disease was first noted in shrimp farming research projects during the early 1970’s. With the advent of commercial shrimp mariculture facilities in the 1980’s exotic or non-native shrimp species began to appear in Texas(Texas Senate Natural Resources Interim Subcommittee Report to the 75th Legislature, Texas Aquaculture Industry, 1996).

    Disease outbreaks on US shrimp farmers-like Taura Syndrome Virus (TSV) in Texas in 1995 and 1996 and in South Carolina in 1996- has raised concerns among aquacuturists and wild harvest fishermen alike, as well as among regulators charged with overseeing these industries. Although TSV and other disease recently found in cultured shrimp pose no threat to humans, they can be devastating to the shrimp themselves and to the people whose livelihoods depend on them. The 1995 TSV outbreak in Texas resulted in the loss of more than 95% of the P. vannamei crop. Disease events in South Carolina in 1996 resulted in estimated losses of 30%~ 50% on affected farms. Although there is little evidence that it has been or ever will be a problem, especially considering the significant economic value of the industry. Currently, the US harvests approximately 200 million pounds (tails) of shrimp each year and imports another 600 million pounds (tails), collectively valued at more than $3 billion (Fish Farming News, 1998).

    However, exposing native shrimp populations to these diseases could decimate current populations and set off a chain reaction throughout the coastal ecosystem. Although the brood stock was grown from seed and was certified by the U. S. Marine Shrimp Farming Program as healthy, 1995’s crop was afflicted with the Taura Syndrome virus. In cooperation with the Texas Parks and Wildlife Department, shrimp farms agreed to halt discharges from their facilities until the virus’s effect on native populations could be determined. Shrimp farmers estimate that the virus resulted in economic losses approaching $40 million(Texas Senate Natural Resources Interim Subcommittee Report to the 75th Legislature, Texas Aquaculture Industry, 1996). Although stopping the discharge of water from shrimp farming industries helped to contain the spread of Taura Syndrome virus, shrimp producers believed the virus was being spread outside their facilities by the hundreds of sea gulls feeding on the small and dying shrimp within their ponds. After feeding, these gulls returned to nearby island and bays, and spread the virus to whatever came into contact with their feces.

    According to a researcher Robert W. Mcfadrlane( personal communication) in Texas, pathogens have been released to the local environments with the discharged exchange water or pond drainage water but scientists and researchers do not know what impact, if any, has resulted. "Part of the problem is detecting a disease in a wild population. The three native commercial shrimp species are eaten by just about everything in the bays. So if a shrimp becomes ill and lethargic, it may be a little slower to detect or be eaten by a predator, and it is gone. If a shrimp were to die, it would be immediately scavenged by crabs, catfishes, and also disappear. So the only way to detect the presence of a disease in the wild shrimp is to capture them and deliberately test and search for the disease organisms. Testing by the Texas Parks and Wildlife Department (TPWD) started doing that in October 1997; thus far they have found nothing unusual. This past summer some disease shrimp started turning up in Galveston Bay. Some were preserved in a proper fixative and sent to the Gulf Coast Research Laboratory (GCRL) in Mississippi. The GCRL is a member of the U. S. Marine Shrimp Farming Consortium. They got very interested in the diseased shrimp, asked for more samples, even sent a technician here to collect more shrimp. They have refused to tell anyone what they found that is of such great interest. Some sort of political interests, or self preservation, have caused the researchers to stop talking about the issue."

    There have been outbreaks of the Taura Syndrome Virus(TSV) in Texas even though all of the shrimp nauplii and post-larvae imported were certified to be "disease free". Although the shrimp farms are required, by their import permit, to report disease outbreaks to the Texas Parks and Wildlife Department, TPWD has been unwilling to share that information with members of the public. "I know that white spot virus and yellow head virus have also appeared in Texas but mostly in experimental operations at university facilities. Also NHP(Necrotizing Hepatopancreatitus), a bacterial disease, is present. The percentage of farms or ponds infected, are unknown. The farmers do not report that data to any compiler that I have been able to locate." In addition, the exotic shrimps have escaped from the farms, and been caught in shrimpers' nets at least twice. The exotic virus, TSV, has shown up on multiple farms three years in a row. The farmers blame the Oceanic Institute, which provided the specific-pathogen- free shrimp; and OI blames the farmers for breaches in "biosecurity," that is, letting their "undiseased" shrimp get sick. Finally he concluded that aquatic organisms are swimming in their environment and the potentials for disease transmission are far greater although respiratory pathogens which influence to terrestrial animals, like chickens and hogs are suspended in air, and move some distance. Pathogens in water can be suspended for much longer periods since there are gravity rules in the air and pathogens in air descend to the ground.

Taura Syndrome Virus

    In 1994 the cause for Taura Syndrome was uncertain in Hawaii. Work conducted in Hawaii and Arizona led to the discovery of a previously unknown virus now called the Taura Syndrome Virus. Subsequent to the discovery of TSV, researchers at the University of Arizona have shown TSV as the direct cause of Taura Syndrome. While Taura Syndrome Virus can infect both Penaeus vannamei and P stylirostris, the expression of the disease and the severity of its symptoms differ in each animal. In general, P. stylirostris is much more resistant to TSV than P. vannamei, and P. stylirostris stocks afflicted with TSV may cause mortality rates as high as 75-80% in P vannamei, significantly impacting the crop’s economic viability.( Shrimp Disease, CTSA Publication No. 121, 1996)

    Host: Panaeus vannamei and causes less severe disease in Penaeus stylirostris

    Range: worldwide distribution

Features: Tentatively classified as either a picornavirus or a nodavirus, TSV is believed to be the cause of Taura syndrome (TS). TS occurs in peracute and recovery phases. The peracute phase is the most common manifestation in juvenile shrimp, and they usually die during molting (some ponds have reported outbreaks with mortality rates of over 95%). Those animals which survive molting either recover or are chronically affected; the chronically affected have scattered black- spot lesions along their outer skin or shell. Gross signs include the appearance of a distinct blue or red hue on the shell and tail( this is the result of chromatophore expansion and the color depends on the dominant chromatophore for the specific animal). Infected shrimp usually have empty digestive tracts. Distinctive histopathology in the peracute phase consists of multifocal areas of necrosis of the cuticular epithelium and subcutis, with pathognomonic variably sized eosinophilic to basophilic cytoplasmic inclusion bodies.

White spot syndrome baculovirus (WSBV) (Cryptocaryon irritans)
 
    White spot syndrome associated baculovirus (WSBV) is the causative agent of a disease that has recently caused high shrimp mortalities and severe damage to shrimp cultures. In this study, a strain of WSBV from black tiger shrimp Penaeus monodon was used to develop a diagnostic tool for the detection of WSBV and related agent infections in shrimp. The virions were purified from p. monodon infected with WSBV. Viral genomic DNA was extracted from purified virions by treating the virions with proteinase K and cetyltrimethylammonium bromide (CTAB) followed by phenol- chloroform extraction and ethanol percipitaiton. A qualitative assessment was performed using polymerase chain reaction (PCR) analysis on the viral DNA and primers specific to shrimp genomic DNA in order to monitor shrimp DNA contamination in the viral DNA preparation. By using PCR with this primer set, it was demonstrated that the causative agents of white spot syndrome in different shrimp species are closely related. An effective diagnostic tool is thus provided for screening shrimp for WSBV infections, and may be important in preventing the further spread of this disease (Diseases of Aquatic Organisms, DAO Volume 27, 1996).

TS and Penaeus vannamei

    Taura Syndrome generally attacks juvenile P. vannamei (0.1 to 5.0g) within two to four weeks after stocking in growout ponds or tanks. TSV is primarily an illness of the cuticle epidermis (outer exoskeleton) in shrimp. Shrimp in the chronic phase of TSV have scattered, black-spot lesions along their outer skin or shell. During TSV outbreaks, dead and dying shrimp will often be seen in seines or cast nets used for routine population sampling or found lying along the bottom of the grow-out tanks or raceways. Shrimp afflicted with the acute phase of TSV appear weak and disoriented have soft-shells, and have expanded chromataphores (pigment spots) that may alter their color slightly. Infected shrimp also have empty digestive tracts ( Shrimp Disease, CTSA Publication No. 121, 1996).

Yellow head baculo-like virus (YBV)

    Host: Penaeus monodon

    Range: Thailand

    Features: Reported to cause yellow-head disease in cultured black tiger shrimp in Thailand. An acute and lethal condition usually resulting in cumulative mortality of 100 % in 3 days, thus making it probably the most acute and lethal disease currently affecting cultured penaeids. Early signs of disease include lack of appetite and lethargy; appear weak several hours before death ( sink to the bottom). In tiger shrimp, typical signs of yellow-head disease include characteristic yellowing of the hepatopancreas and gill. The virus can be transmitted to Penaeus stylirostris and Penaeus vannamei, and is thus a potential problem in farmed populations in the Western hemisphere (Shrimp Disease, CTSA Publication No. 121, 1996).

New research

    Researchers at Texas A & M University (TAMU) have recently been awarded a grant by the Texas Higher Education Coordination Board to develop methods to control a major class of shrimp viruses called baculoviruses. The research is led by Linda Guarino and Donald Jarvis of the TAMU Entomology Department. The project will focus on isolating and characterizing genes that have been shown to be important for the replication and infectivity of insect baculoviruses, which could lead to ways to combat shrimp baculoviruses. In the study, the researchers will determine if viral-encoded RNA polymerase (an enzyme that is essential for viruses to develop) can be inhibited in shrimp. They hope to develop antibodies that could work against the membrane protein of baculovirus particles and slow the spread of virus infection. Eventually, the researchers hope that these methods will be widely used in commercial shrimp aquaculture operations in Texas and elsewhere (Treating Shrimp Viruses is Goal of TAMU Study).

Baculovirus penaei (BP)

    Host: Penaeus duorarum juveniles and adults, Penaeus aztecus larvae and adults, penaeus setiferus larvae, Penaeus vannamei larvae and post larval stages, Penaeus stylirostris larvae and post larval stages, Penaeus marginatus juveniles.

    Range: Restricted to the USA and the Pacific Coast side of Central and South America

    Features: High morbidity as a hatchery epizootic disease with high mortality in larval and post larval stages. Unspecific signs such as poor growth rates, anorexia and lethargy as well as epicommensal fouling due to reduce grooming activity. The virus mainly attacks cells of the hepatopancreatic epithelium but it can infect mid-gut epithelium. Diagnosed by characteristic multiple polyhedral intrauclear occlusion bodies in the hepatopancreas and mid-gut. Transmission is orally, with mature virions being released into the lumen of the midgut and getting excreted into the environment via feces where they are consumed by other shrimp (Shrimp Disease, CTSA Publication No. 121, 1996).

Monodon baculovirus( MBV)

    Host: Larval, post larval juvenile and adult Penaeus monodon, Penaeus kerathrus, Penaeus merguiensis, Penaeus semisulcatus

    Range: Asia, as well as areas of the Indopacific, Mediterranean, Phillippines, Taiwan, Malaysia, Hawaii, Tahiti, Singapore Kuwait, Kenya, Israel, Italy

    Features: Often with severe mortality with the most serious losses in the late post larval and juvenile stages. Apparent horizontal transmission by oral exposure to contaminated tissues or fomites. Clinical signs include lethargy anorexia, suppressed preening activity, retarded growth, grey-blue to blueish-black coloration, shell disease and microbial epibiotic fouling. Diagnosis based on histopathological exam of wet mounts of the hepatopancreas and mid-gut epithelium, and the presence of characteristic eosinophilic intranuclear inclusions (Shrimp Disease, CTSA Publication No. 121, 1996).

Problems: Concerns about transmissible disease from exotic shrimp to native shrimp is an important issue in sustainable Texas ocean.

    There is an environmental issue that exotic shrimp escape into natural ecosystem, and they might influence exotic shrimp disease to native shrimp. Its impact will be enormous not only on native shrimp but also on the coastal ecosystem. Residences and environmentalists are concerned about the environmental damage of Texas bay. The unique nature of Texas’ bays and estuaries makes it easier to introduce foreign bacterial and viral strains into these bays and estuaries because most of these bodies of water are shallow and are characterized by little tidal movement. These characteristics constrain such processes as circulation, diffusion, and transport. These characteristics of Texas bays could pose a substantial threat to native species.

    The shrimp diseases such as Taura Syndrome Virus and others viruses such as white spot virus and yellow head virus have broken out in Texas shrimp farming as shown in official reports. Texas farmed shrimp have been infected with TVS due to imported exotic shrimp, although these exotic shrimp were certified to be disease free by Oceanic Institute. The major problem is lack of confirmation of permit from Oceanic Institute. According to Robert W. Mcfadrlane (personal communication), OI does not clarify what kinds of tests OI uses to certify disease free shrimp to the American public. Therefore, nobody can tell if OI uses correct tests for detecting exotic shrimp disease, and if it is accurate or not. The second problem is if exotic shrimp disease can transmit to native shrimp, and outbreak of the disease starts among native shrimp, there is no medication to cure.

Problem 1: Unknown of the process how exotic shrimp diseases enter into Texas farmed shrimp and lack of confirmation of permit from Oceanic Institute in Texas.

    Reports show that shrimp still had TSV in 1995 and 1996 even though they were inspected by OI before being imported. There is a couple of hypothesis for this problem.
 

None of these possibilities have been proven by official reports because of the difficulty of detecting a disease in a wild population. However, we still can say that OI ‘s permit for free disease shrimp has a lock of confirmation unless OI proves that their test for detection of disease is reliable.

Problem 2: Outbreak among native shrimp due to exotic shrimp’s infections

    Second problem is that environmentalists and scientists are concerned about infection of diseases from exotic shrimp to native shrimp in Texas. There have been no official reports that an epidemic disease outbreak among native shrimp was due to exotic shrimp’s infections. However, there is evidence that native shrimp could get TVS, yellow head virus and white spot virus, as well as other shrimp diseases since pathogens have been released to the local environments with the discharged exchange water or pond. Last summer in 1997, some diseased shrimp started turning up in Galveston Bay but the result is unknown so far (personal communication, Robert W. McFarlane).

    Recently, a local processing plant contacted TPWD with a report of strange looking shrimp. Department biologists and obtained samples from the processor and from local shrimp trawlers and sent them to the Perry R. Bass Marine Fisheries Research Station in Palacios, Texas for testing. The shrimp were later positively identified as Pacific white shrimp. This month the department launched a coastwide monitoring effort to determine the presence or absence of viral disease in shrimp population native to Texas waters, including Taura virus, White Spot Syndrome Virus (WSSV), and Yellow Head Virus Syndrome (YHV). The three exotic shrimp viruses which have been identified from Texas shrimp farms could potentially affect the health of wild shrimp populations if they were to spread beyond aquaculture operations. (NEWSSTAND, Texas Parks & wildlife, October 13,1997). These articles are evidences of that exotic shrimp disease can transmit to native shrimp.

    Exotic shrimp have escaped from the farms and been caught in shrimpers nets at least twice (personal communication, Robert W.McFarlane). Far fewer shrimp are believed to have escaped last week than during the last significant incident in fall 1991, when hundreds of pounds of exotic shrimp were accidentally released from Hung Shrimp Farm into the Arroyo Colorado in South Texas. The farm eventually paid TPWD about $ 63,000 in fines. Exotic shrimp can leave the shrimp farms and enter public water through wastewater discharge canals that empty into Texas bays or rivers. (NEWSSTAND, Texas Parks & wildlife, 1997). These are evidences that show how native shrimp could get TVS from exotic shrimp.

    One of the most important experimental reports by Robin M. Overs is that he demonstrated the possibilities of death of Penaeus setiferus by infection of TVS. To determine whether such shrimp species can be infected or can maintain an infection was the purpose of this study. He consequently found out that all three of those penaeids; Penaeus setiferus, Penaeus aztecus and Penaeus duorarum , native to the southeast United States can serve as carriers or reservoir hosts of TSV without necessarily exhibiting disease.

    However, shrimp diseases pose a serious threat to commercial quaculture operations. Currently, there are no treatments available to cure viral infections of shrimp, and if viral outbreaks occur, there will be the only way to prevent the virus from spreading by destroying the whole crop. The reason why people can not prevent the virus from spreading among farmed shrimp is because it has been difficult to identify and produce medications that can kill the viruses without harming the shrimp.

5. OPPORTUNITIES: Enforcing OI regulatory system for disease free, discharge water; and finding new antibiotic for shrimp disease.

    Although we do not know an exact result of this disaster, an epidemic disease could start in native shrimp due to transmission of exotic shrimp disease. We have to figure out how we protect native shrimp and avoid environmental destruction.

    There are two kinds approaches to solve this problem. One is that we make OI’s regulatory system enforced. For instance, studying how TSV starts infecting shrimp in ponds with disease certified exotic shrimp is essential because it is the cause we have to prevent. In addition, OI ‘s tests for being disease free should be reconsidered if they are appropriate tests. We have to regulate the discharge water from shrimp farm and to prevent exotic shrimp from escaping.

    The second approach is that we expect scientists and researchers to find out new antibiotic for shrimp diseases. There are some new research reports I have cited, that researchers at Texas A & M University have developed methods to control a major class of shrimp virus called baculaviruses. It will be the beginning of developing an antibiotic for shrimp disease.

Conclusion

    Texas shrimp farming is an essential industry for both U.S and the Texas state government. The consume demand of shrimp is increasing U.S. as well as other countries in Asia. However, there is a serious problem. Taura Syndrome Virus, Yellow head virus and white spot virus can transmit to native shrimp, and it can cause outbreaks among native shrimp. If it happened to the coastal ecosystem, the coastal ecosystem in Texas bay could be affected tremendously. There is a regulatory system to prevent farmed shrimp and native shrimp from exotic shrimp disease, such as Oceanic Institute; however, there is evidence that exotic shrimp disease are found in native shrimp. If shrimp which OI permitted to be disease free were certainly disease free, outbreaks did not occur in Texas shrimp farming.