Use of Elevated Levels of Copper Sulfate to Eliminate...

Inside this Issue:

Use of Elevated Levels of CopperSulfate to Eliminate Snails ........................ 1

Cormorant Deterrent Systemsfor Moderate Size Farms ........................... 3

Welcome to New Personnel ...................... 3

Experimental Evaluation and EconomicAnalysis of a Fingerling-to-StockerPhase in Commercial Farming ofChannel Catfish .......................................... 4

2004 CVM Aquatic DiagnosticLaboratory Summary ................................. 6

Streptococcosis, a PreviouslyUnknown Disease of Channel CatfishBroodstock .................................................. 8

New Publications Produced by theSouthern Regional Aquaculture Center ... 9

U.S. Farm-Raised Catfish Industry:2004 Review and 2005 Outlook .................. 10

Volume 8, Number 1 April 2005

THAD COCHRAN NATIONAL WARMWATERAQUACULTURE CENTER

127 Experiment Station RoadP.O. Box 197

Stoneville, MS 38776-0197Phone: (662) 686-3242 FAX: (662) 686-3320

www.msstate.edu/dept/tcnwac

NWAC News is edited byJimmy L. Avery. Thispublication is bi-annualand is available freeupon request.

continued on page 2

Use of Elevated Levels of CopperSulfate to Eliminate Snails

David Wise, Charles Mischke, and Todd Byars

The digenetic trematodeBolbophorus sp. has beenimplicated as a cause ofmortalities and reducedproduction in farmed channelcatfish. Control of thedisease is dependent onprevention and breaking thelife cycle of the trematodeby reducing snail populationsin the pond. Current treat-ment methods rely on theapplication of hydrated limeor copper sulfate to themargins of the pond. Thesetreatments have been shownto be effective in controllingsnail populations and limitinginfection rates, provided thesnails are concentrated alongthe margins of the pond.Recent laboratory testsindicate that increasing theconcentration of coppersulfate may be effective inkilling snails dispersedthroughout the pond withoutdirectly killing catfish. Theeffects of copper sulfate onsnail mortality and on thepond environment wereevaluated in experimental andcommercial catfish ponds. Allconcentrations are reportedas ppm copper sulfatepentahydrate (CuSO4

.5H20).

The first step in establishinga treatment level was todetermine the concentrationof copper sulfate needed tokill 50% of the snails in 24hours (referred to as a24-hour LC50). Laboratory

tests showed copper sulfatecrystals had a 24-hour LC50of 2.4 ppm. There was asignificant linear relationshipbetween temperature andLC50 values for coppersulfate. As temperatureincreased from 59°F to 68°F,(15°C to 20°C) the LC50values decreased from4.4 ppm to 0.72 ppm coppersulfate, representing aseven-fold increase in toxicity.

To determine the minimumdose of copper sulfate thatwould effectively eliminatesnails without directly killingcatfish, a series of dosetitration trials were performed.The trials were conducted inplastic tanks containing 200gallons of pond water and in0.25-acre ponds. Catfish andsnails were confined (netpens) in each test unit anddosed with a range of coppersulfate solutions. Thesetitration trials indicated theminimum effective dose (snailmortality >90%) of coppersulfate ranged between2.5 and 5 ppm copper sulfate.Fish mortality was notobserved at or below 5 ppmcopper sulfate in the tank

NWAC News April 2005

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Use of Elevated Levels of CopperSulfate to Eliminate Snailscontinued from page 1

studies. However, fish mortality (2 outof 16 fish or 12.5%) was observed inone of the three net pens in the pondtreated with 5 ppm copper sulfate.

In an effort to verify the minimumeffective dose, replicate 0.25-acreand 10-acre experimental ponds weretreated with 2.5 and 5 ppm coppersulfate. All treatments were deliveredas a solution of copper sulfate granulesdissolved in pond water. Treatmentswere applied to larger ponds using achemical boat. Replicate pondtreatments verified that treatmentdoses of 2.5 and 5 ppm copper sulfatewere effective in killing snails.Average snail mortality in the0.25-acre ponds ranged between 98%and 95.5% at the low treatment doseand was 100% at the high treatmentdose. Fish mortality was observed inone of the three replicate ponds ateach treatment dose. Similar resultswith respect to snail toxicity wereobserved in the toxicity trialsconducted in 10-acre ponds. Averagesnail mortality ranged between 92%and 98% following treatment with2.5 ppm and between 98% and 100%following treatment with 5 ppm coppersulfate. In contrast to the 0.25-acrepond trials, no fish mortality or behav-ioral signs of toxicosis were observedfollowing treatment. In all pond trials,dissolved oxygen depletions were notobserved for up to 168 hours aftertreatment. Mortality in the 0.25-acreponds during both the dose titration andthe verification trials may have beencaused by exposure of confined fish tohigh concentrations of the appliedchemical before it was completelymixed with the pond water.

The treatment was then evaluated ina 13-acre commercial channel catfishproduction pond containing moderatenumbers of snails. Results of thecommercial field trial were comparableto tests conducted in the experimentalponds at 5 ppm copper sulfate.Average mortality of snails confinedin cages ranged between 95.4% and97.7%. The treatment was also showneffective against natural populationsof snails along the margins of the pond.The average number of snails per footof pond bank decreased from21.5 snails to 0.18 snails 24 hoursafter treatment, representing a 99%reduction in viable snail populationsin the habitat along the pond bank.

Treatment of the commercial pondresulted in changes in fish behaviorand mortality. Within 4 hours oftreatment, an increase in the numberof moribund fish was observed.Affected fish appeared lethargic orexhibited a spiraling swimming pattern.However, it is not thought that theseobservations were solely related to thechemical treatment. Prior to treatment,mortality rates were characterized aschronic and were estimated to be150 to 200 head/day resulting in anestimated total mortality in excess of20,000 pounds. Moribund and dead fishwere diagnosed with bacterial infec-tions (Edwardseilla ictaluri andFlavobacterium columnare), parasiticinfections (Bolbophorus sp.), acutenitrite toxicosis, and clinical symptomsconsistent with visceral toxicosis ofcatfish. It was estimated thatapproximately 2,000 pounds of fishwere lost within the first 24 hoursafter treatment. Salt was added totreat nitrite toxicosis and after the first24 hours, the daily mortality ratereturned to pretreatment levels.

These trials indicate copper sulfatecan be used as an effective treatmentagainst ram’s horn snails in commercialchannel catfish production ponds.Copper sulfate treatments between2.5 and 5 ppm copper sulfate wereeffective in killing snails throughout thewater column with minimal risk to thehealth of the fish. In most trials, pondtreatments killed in excess of 95% ofthe test snails. These studies wereconducted mid October to earlyNovember when pond watertemperatures were between 68°F to75°F (20°C to 24°C), and bloomdensities were below that which istypically observed during the summermonths. Under these conditions, theconcentrations of copper used werenot shown to affect dissolved oxygenconcentrations and, under typicalproduction conditions, were not shownto affect fish behavior or mortality ofhealthy channel catfish. However, the2.5 ppm copper sulfate treatment ratewas toxic to smallmouth buffalo, andgrass carp exhibited clinical signs oftoxicosis and limited mortality at atreatment rate of 5 ppm. A coppersulfate treatment of 5 ppm was alsoshown to be toxic to fish in poorhealth; however, the viability of thesefish was highly questionable.

Considering that copper did notappear to be toxic to fish in trialsconducted in the 10-acre experimentalponds, copper treatments rangingbetween 2.5 and 5 ppm appear to besafe to channel catfish under theconditions and water qualitycharacteristics of this study. However,caution should be used when thehealth status of the fish is in question,at high pond water temperatures, orwhen bloom die-offs are likely to causeoxygen depletions.


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Cormorant Deterrent Systems for Moderate Size FarmsCharlie Hogue

A deterrent system has been devel-oped that can reduce or possiblyeliminate cormorant activity of catfishoperations. Cormorants are a signifi-cant problem to catfish farmers andtheir population levels are increasingeach year. According to a recentsurvey by the USDA National Agricul-ture Statistics Service, commercialcatfish growers in 13 states reportedthat wildlife losses (mostly frommigratory birds) accounted for$13.3 million in inventory in 2003.Farmers spent an additional$7.1 million on harassment activities tokeep cormorants off their farm. Laborcosts, wear and tear on trucks andlevees, guns, and ammunition are amajor expense every year. Somefarms report spending more money

chasing birds in the winter than spentchecking oxygen in the summer.

Moderate size farms with three or fourponds have been able to deter cormo-rants from their farm completely. Thesystem has also proven effective inprotecting individual fingerling pondson larger production facilities. Thesystem is based on the fact that, unlikeducks, cormorants land on a pond atlong angles. By using metal fenceposts, strings, and flags, a series ofobstacles is created that discouragecormorants from landing in the pond.

To construct the system, metal fenceposts are placed directly opposite eachother every 60 feet on the two longlevees of a pond. Next, a #12 untarred

string with orange flagging tied every15 feet is suspended across the pondfrom two opposite posts. The stringand flagging should be 2 to 3 feetabove the water surface. The approxi-mate cost to protect a 10-acre pond isonly $100 and only takes about a halfof a day to install. When it comes timeto harvest the pond, the posts andstrings can simply be taken down andput back up after harvest.

While this system might not be feasiblefor completely protecting largefoodfish operations, this system hasbeen used effectively on several BlackBelt farms. This method could also beused on remote ponds in the Delta thatare difficult to effectively watch forcormorant activity.

Welcome to New Personnel at NWACSarah Harris

Dr. Peter Silverstein joined theUSDA/ARS Catfish GeneticsResearch Unit (CGRU) as a ResearchVirologist/Microbiologist in June 2004.Dr. Silverstein is a native of New YorkCity. He received his undergraduateeducation at Duke University, M.A.from Lehman College of the CityUniversity of New York, and Ph.D. in1996 from the College of VeterinaryMedicine at Auburn University wherehis dissertation research focused oncharacterization of the immediate-earlygenes of channel catfish virus (CCV).Dr. Silverstein comes to us from theDepartment of PharmaceuticalChemistry at the University of Kansas(Lawrence) where he studied drugtransporters responsible for the effluxof numerous therapeutic agents,

including antivirals and antibiotics.Dr. Silverstein’s expertise in molecularvirology, combined with his broadbackground in pathogenesis of viraland bacterial diseases, will add animportant component to the work atCGRU. The focus of Dr. Silverstein’swork will be the identification of hostfactors responsible for disease resis-tance in channel catfish. Some of thisresearch will look at mechanisms ofresistance to channel catfish virus,while other projects will focus on therole of macrophages and monocytesin disease resistance. He can bereached at (662) 686-3545.

Dr. Terry Greenway, a researchimmunologist, joined the research teamat NWAC in October 2004 as an

Assistant Research Professor with theMississippi Agricultural and ForestryExperiment Station. Dr. Greenway isa native of Arkansas, and received hisBS in Biology and his MS in AnimalScience-Parasitology from theUniversity of Arkansas. He recentlycompleted his doctorate in VeterinaryMedical Science-Immunology atMississippi State University Collegeof Veterinary Medicine where heinvestigated the ability of bacterialenterotoxins to act as mucosaladjuvants (substances which augmentimmune responses to vaccines) inpoultry. Dr. Greenway’s research atNWAC will revolve around vaccinedevelopment and vaccine deliverystrategies for catfish. He can becontacted at (662) 686-3583.


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Experimental Evaluation and Economic Analysis of a Fingerling-to-Stocker Phase in the Commercial Farming of Channel Catfish

Lou D’Abramo, James Steeby, and Terry Hanson

In 2004, the first controlled study ofthe fingerling-tostocker growth phaseof a three phase (fry to fingerling,fingerling to stocker, and stocker tofinal food size) modular system wascompleted. This modular system, analternative to the traditional multiple-batch farming of channel catfish,offers some distinct advantages. Themodular system addresses the need toproduce consistently larger-sized fishand improves control of inventory.Additionally, any changes in weightspecifications from processing plantscan be effectively addressed duringthe relatively short duration of the finalgrowout period through modificationof the number and size of stockersproduced in the fingerling-to-stockerphase ponds. The modular system alsooffers a decrease in the probability ofwater quality and disease problemsduring the final growout phase becausestocking density, and therefore thetotal pounds of fish in the pond, will belower. Economic loss arising from birddepredation can be minimized becausethe high density fingerling to stockerculture phase can be localized in aspecific area of the farm. The lengthof the fish harvested for stocking intophase-three ponds for the final growthphase exceeds the 4- to 8-inch rangeof lengths that has been documentedto be most susceptible to cormorantdepredation. Final growout can thenbe conducted in ponds located furtheraway from activity centers withdecreased risk of catastrophic lossesdue to bird depredation.

Pond-run fingerlings of a mean lengthof 4.33 inches were stocked intoexperimental earthen ponds at three

densities, 40,000, 50,000 and60,000/acre. There were five replicateponds for each density treatment. A36% crude protein fingerling feed wasfed to satiation once daily during a180-day growout period that extendedfrom April 30 through November 2.At all three densities, the fish fedvoraciously and growth rates weregood. Particular attention was directedto the management of dissolvedoxygen, principally achieved through afixed in-pond aerator that provided theequivalent of 4 horsepower/acre asneeded. Pond aeration was initiatedwhen levels of dissolved oxygendecreased or were anticipated todecrease to 6 ppm. If levels continuedto decrease to 3 ppm, thenpaddlewheel aeration was added. Foreach pond, the times when aeratorswere on as well as the total amount offood fed were recorded each day forthe entire period. At the end of thisgrowout phase, mean survival, totalproduction, and feed conversion ratiowere determined from the group ofponds representing each of the densitytreatments (Table 1).

The mean fish weight achieved for thisfingerling-to-stocker phase was 94%of the 250 pounds/1,000 goal that had

been set with no significant treatment-dependent differences. Although thelengths of fish harvested from each ofthe treatments were not significantlydifferent, a reduction in individualweight was obvious as densityincreased from 50,000 to 60,000/acre.Meeting the objective of a meanharvest weight of 0.25 pound appearedto be attainable because watertemperatures for the 2004 growingseason were unseasonably cool,contributing to lower food consumptionand lower growth rates. In fact, onlyonce did a daily feeding rate everexceed a level of 200 pounds/acre.Also, there were a number of dayswhen feed was not distributed to theponds due to weather conditions ordisease outbreaks in some ponds.

Economic Analysis

The economic analysis comparedengineered enterprise budgets for themultiple-batch system versus threevariations of the fingerling-to-stockerphase of the modular productionsystem. The analysis was based uponan enterprise budget developed for a

continued on next page

Table 1. Production data for different stocking density treatments. Fingerling Fish size density Survival Feed conversion at harvest Production(fish/acre) (%) ratio (lbs/1,000) (lbs/acre) 40,000 64 1.5 202 5,145 50,000 73 1.4 208 7,516 60,000 73 1.4 188 8,151


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1,100-water-acre farm becauseprevious evaluative work was donewith a producer who was using amodular system on a farm of similarsize. In the fingerling-to-stocker phaseof the enterprise budget, we used ourexperimental results to incorporatecosts for fingerlings, feed fed, andnumber of aeration hours in conjunc-tion with harvest number and weight.An additional four laborers wereincluded for the modular systembecause more harvests are requiredrelative to the multiple-batch system.

Beginning with the weight of theharvested stocker fish from eachexperimental treatment, the stockingdensity of the growout phase was4,800/acre and a final growout weightwas assumed to be 1.7 pounds. Fixedcosts for a 1,100-acre channel catfishfarm were used for all budgets. Themodular system had 4 horsepower/acre aeration in the fingerling-to-stocker ponds and 2 horsepower/acrefor the final phase of food fishproduction, whereas all multiple-batchfood-size fish production ponds had2 horsepower/acre.

The number of stockers producedper acre was dependent upon initialstocking density. Therefore, thenumber of acres allotted to thestocker-to-food size growout phaseincreased as the initial stocking densityof the fingerling-to-stocker treatmentsincreased because fewer pond acresare needed for the fingerling-to-stockerphase at the higher initial stockingdensities of fingerlings. Thus, for a40,000/acre fingerling stocking rate,120 acres are required to produceenough stockers for the remainingacres of production of food fish.Likewise, for the 50,000 (60,000)/acrestocking density of fingerlings, 140(120) acres were required to producestockers for the remaining 960 (980)acres of ponds for production of foodfish (Table 2). The economic questionsthat were addressed in this researchare: 1) Using the same 1,100 acres ofponds, how do the net returns realizedfrom using the modular system underthe three different fingerling to stockerscenarios, and consequently with alower number of foodfish acres,compare to a multiple-batch foodfishproduction system, 2) how are net

returns affected by differentinitial stocking densities and corre-sponding final growout acreage.

Results of the economic analysis,specifically net returns per acre andcost of production estimates, for thethree scenarios of the modular systemand one multiple-batch system arepresented in Table 2. The multiple-batch and 40,000/acre modularsystems yielded similar net returns.However, the net returns for the twohigher stocking rates, 50,000 and60,000/acre, of the modular systemexceeded those of the multiple-batchsystem. Variable costs of production,or breakeven price to cover cashproduction costs, were similar for themodular system using the 40,000/acrestocking rate for the fingerling tostocker phase and the multiple-batchsystem. For the higher stocking ratesof the fingerling-to-stocker phase ofthe modular system, the per poundcash production cost was two andthree cents less, and the per pound

continued on page 12

Table 2. Comparison of acreage distribution, net returns, and cost of production for differentmodular and multiple-batch catfish production systems.

Modular system Multiple-batch fingerling stocking rate (per acre) system40,000 50,000 60,000

Area distribution, acres: Between stocker and final food fish 920 960 980 Between fingerling and stocker fish 180 140 120 Fingerling to food fish 1,100Net returns per acre, $/acre: N.r. above variable costs $ 637 $ 775 $ 841 $ 649 N.r. above variable + fixed costs $ 251 $ 389 $ 455 $ 225Costs of food fish production, $/lb: Covering variable expenses $ 0.58 $ 0.57 $ 0.56 $ 0.59 Covering variable + fixed expenses $ 0.65 $ 0.63 $ 0.62 $ 0.66


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2004 CVM Aquatic Diagnostic Laboratory SummaryAl Camus, Pat Gaunt, and Michael Mauel


Diagnostics

In 2004, the Aquatic DiagnosticLaboratory (ADL) at Stonevillereceived a total of 1,770 fish casesubmissions, 778 diagnostic and 992research. Diagnostic cases werereceived from 96 farms, or approxi-mately 25% of the Mississippi industry.In addition, 978 water quality samplesfrom 60 farms were analyzed. Com-pared to 2003, the total number of casesubmissions decreased slightly from832, while the number of water samplesincreased from 851. The ADL staffwould like to stress that we are hereto serve the industry and encourageproducers to continue to take advan-tage of this valuable free service.

As in the past, individual casesubmissions represent a compositesample of fish collected from a singlepond. The numbers reported arederived solely from submissionsprocessed by the ADL and do notnecessarily reflect actual diseaseincidence in the field. Routinediagnostic procedures includeevaluation of gill clips and skin scrapesfor parasites, external and internalinspection for signs of disease, bacte-rial and viral cultures, histopathology,and water quality evaluation. TheADL works closely with MAFES fishhealth professionals to offer treatmentrecommendations, monitor diseasetrends, provide surveillance for newand emerging diseases, provide fieldservice investigation, and maintain adatabase of epidemiologic informationon diseases of catfish. The ADLsupports the research efforts of otherNWAC units, including MAFES,MSU-Extension Service, College of

Veterinary Medicine, and USDA/ARSCatfish Genetics Research Unit.Furthermore, the laboratory providesan outlet for the dissemination ofinformation gained from researchefforts back to producers.

As in previous years, the bacterialdiseases enteric septicemia of catfish(ESC) and columnaris diseasedominated the numbers of producersubmitted cases. (The seasonalincidence of the four major diseases ispresented in Figure1.) Examined as asingle disease, ESC accounted for4.3% of cases, but in combination withother agents was diagnosed in 30.7%of cases (34.6% in 2003). While alone,columnaris accounted for 5.7% ofcases, in combination with otherpathogens, columnaris was present in40.9% of all cases (44.7% in 2003),making it the most common diseaseseen by the ADL. ESC and columnariswere diagnosed together in 6.6% ofcase submissions. These numbershave remained relatively consistentover the past 8 years, where on

average ESC was diagnosed in 36.4%and columnaris in 43.7% of all cases.Table 1 contains a summary of diseasetrends for 1997 to present.

Proliferative gill disease (PGD) wasthe third most commonly diagnoseddisease, representing 10.7% of cases(10.8% in 2003). Saprolegnia, thecause of winter fungus, was presentin 3.7% of cases, down from 5.4% in2003. The number of channel catfishvirus (CCV) disease cases rose from8.9% in 2003 to 10.8% in 2004 andremained above the 8-year averageof 5.4%. The number of channelcatfish anemia (CCA) casesdecreased from 5.2% in 2003 to2.1% for 2004 and fell below the8-year average of 3.8%.Ichthyophthirius multifiliis (Ich)cases increased from 0.5% last yearto 5.0% in 2004, well above the 8-yearaverage of 1.8%. Cases of visceraltoxicosis (VTC) remained relativelyconstant at 3.2% versus 3.7% in 2003.

0102030405060708090

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Figure 1. Seasonal incidence of major catfish diseases in 2004.


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The percent of Bolbophorustrematode cases remained below thehigh of 5.6% seen in 2000, but rosefrom 1.1% in 2003. Resurgence ofthe parasite is largely attributed to theestablishment of a resident summerpopulation of white pelicans inHumphreys County. Farmers areencouraged to renew surveillanceefforts and to control ram’s horn snails(intermidiate host of the parasite),particularly if pelicans are visitingtheir ponds. Bolbophorus trematodesare capable of killing fingerlings andincreasing susceptibility to ESC, aswell as decreasing feed consumptionin larger fish.

A previously unknown streptococcalbacterial infection causing mortalities,spinal deformities, and reproductivefailure in catfish broodstock wasidentified and characterized. To date,four outbreaks have been confirmed,but at present the significance of thisemerging disease is unclear. Findingshave been submitted in the form of amanuscript to the Journal of AquaticAnimal Health. Producers notingemaciation, humped backs, andbloody sores along the jaw at thetime of broodstock selection areencouraged to contact the ADL.

Research

Research into the cause of CCA, awell-known but poorly understoodcause of mortalities, demonstrated arapid and complete resolution of thecondition in affected fish following theadministration of injectable iron in twoseparate trials. Research into potentialcauses for the development of irondeficiency anemia is ongoing.

A collaborative working group wasformed to continue research into thecause of VTC. The working group iscomposed of scientists from theADL, MAFES, USDA/ARS CatfishGenetics Research Unit, College ofVeterinary Medicine, and StateChemistry Laboratory. In laboratorytrials conducted at the ADL, thesuspected toxin was found to affecta number of fish species inexperimental challenges.

Extensive trials were conducted toevaluate the virulence of an isolate ofCCV causing unusually high mortalitieson a farm raising NWAC-103 straincatfish. Although considered prelimi-nary, results of challenge trials indicatethe field-isolate produces mortalitiesapproximately twice as high as those

caused by the original type strain ofCCV archived by the American TypeCulture Collection. The NWAC-103strain was found to be intermediate insusceptibility to the field isolate in trialsperformed cooperatively with USDAscientists.

The FDA approval process for use ofthe antibiotic florfenicol (Aquaflor®)continued to move forward. Finalapproval of the drug for use in catfishis anticipated in 2005 and will providefarmers a new tool for combatingESC. Following the success of trialsin catfish, the Schering–Ploughpharmaceutical company funded newdrug efficacy and dose titration trialsfor the use of florfenicol againstStreptococcus iniae infections intilapia. The results of these trials willbe submitted to the FDA as acomponent of the drug approvalapplication process.

A graduate student was recruited andhas begun development of a real-timePCR assay to quantify numbers ofHenneguya ictaluri spores in pondwater. When validated, the assay willbe used to predict proliferative gilldisease outbreaks and evaluate theefficacy of control measures.

Disease Average 2004 2003 2002 2001 2000 1999 1998 1997Columnaris 44.1% 40.9 44.7 44.5 37.2 42.6 45.5 44.8 49.1ESC 37.2% 30.8 34.7 39.8 36.4 33.5 41.2 41.2 33.6PGD 21.7% 10.7 10.8 16.3 20.1 29.8 30.0 16.3 28.6Saprolegnia 8.6% 3.7 5.3 10.1 10.4 10.5 8.7 8.6 6.4CCV 4.6% 10.8 8.9 5.8 7.3 2.3 1.8 3.1 3.0Anemia 4.0% 2.1 5.2 5.3 5.0 4.9 2.8 3.0 1.7Ich 1.3% 5.0 0.5 2.2 1.8 2.7 0.7 0.5 0.8Bolbophorus 2.9% 2.6 1.1 2.0 4.4 5.6 1.5 - -VTC 2.7% 3.2 3.7 2.0 2.5 - - - -No Pathogens 15.6% 20.8 18.3 16.2 19.2 15.0 15.2 11.4 13.6No. of Cases 1452 778 832 1057 1602 2189 2007 1647 831

Table 1. Trends in disease diagnosis as a percentage of diagnostic case submission over time.


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Streptococcosis, a Previously Unknown Disease ofChannel Catfish Broodstock

Al Camus and David Wise

A previously unknown bacterialdisease has been identified in channelcatfish broodstock on four commercialoperations in Mississippi. The caseswere submitted to the Aquatic Diag-nostic Laboratory at the NWAC duringFebruary 2002, September 2003,February 2004, and July 2004.Producers reported chronic low-levelmortalities, poor reproductive success,and the presence of small skin sores,muscle wasting, and arched backsnoted at the time of broodstockselection.

The diseased fish were in poor physi-cal condition and had a variety ofvisible signs indicative of the disease.The most consistent finding was thepresence of small (less than 1/4 inch)bloody sores located along the bottomof the lower jaw. Similar sores wereoften located at fin bases. Examinationrevealed the sores penetrated intounderlying muscle and entered joints atthe angle of the jaw and bases of fins.Tracts leading from the skin surface tothe affected joints contained reddish-brown fluid.

The arching of the back (Figure 1)was due to spread of the infection tothe backbone, resulting in the destruc-tion and collapse of individual verte-brae. Collapsed vertebrae were oftendisplaced to the point of crushing thespinal cord. Thick, reddish-brownfluid was also associated with sites ofspinal damage and extended from thevertebrae into the adjacent musclesof the fillet.

Microscopically, tissue damage waslimited primarily to bone, surroundingmuscle, and the spinal cord. In areasof vertebral damage, inflammatory

cells surrounded the spinal cord, achange known as meningitis.Examination also confirmed compres-sion of the spinal cord. Inspection ofthe major internal organs revealed nosignificant changes in any fish.

Culture of affected tissue sites resultedin the isolation of a bacterium identifiedas a Streptococcus species, however,complete characterization of theorganism is ongoing at this time. Thebacterium was subsequently injectedinto laboratory-reared catfish, whichdeveloped sores and joint changesidentical to those seen in the fieldcases. The poor condition, damage tojoints, and involvement of the back-bone suggest a slowly progressivecourse in which mobility and feedingactivity is progressively impaired. It islikely that fish with damage to thespinal cord may be paralyzed in thelower body and tail, interfering withtheir ability to feed and spawn.

Several different species of relatedStreptococcus bacteria are known tocause disease in a variety of culturedfish in both fresh and saltwater. This

group of diseases, collectively referredto as streptococcosis, causes majorlosses annually in certain fish speciesand appears to be increasing in inci-dence worldwide. Despite this, similarinfections have not been recognizedas a disease of channel catfish.

At present, the importance of thisemerging disease and its distributionon commercial channel catfishaquaculture operations is unknown, butis the subject of ongoing investigation.It seems probable that suppression ofthe fish’s immune system, possiblyrelated to low winter temperatures,or stress related to spawning activity,may be required for the disease tomanifest itself. Based on limitedinformation provided by producers,it is evident that the problem may goundetected for long periods of time,as broodstock typically are observedclosely only once annually. Producersare encouraged to examine fish forsigns similar to those described aboveat the time of broodstock selection andreport their observations or submit fishto the ADL at (662) 686-3305.

Figure 1. Broodfish with Streptococcus infection.


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New Publications Produced by theSouthern Regional Aquaculture Center

Craig Tucker and Sarah HarrisSouthern Regional Aquaculture Center

For information on all SRACprojects, visit our website at:

http://www.msstate.edu/dept/srac

In addition to the wide variety ofinformation offered, you can printcopies of all SRAC publications,obtain the address of your stateAquaculture Extension Specialist,and link to many other useful sites.

In its 17 years of existence, theSouthern Regional Aquaculture Center(SRAC) has distributed almost$10 million in funds to supportaquaculture research and extension.Research conducted with these fundshas lead to many innovations andimprovements in aquaculture, butSRAC may be best known for theabundant literature produced throughthe “Publications, Videos, andComputer Software” project.

The SRAC “Publications” project isin its tenth year of funding and isunder the editorial direction ofDr. Michael Masser and staff atTexas A&M University. To date, the“Publications” project has generatedmore than 170 fact sheets withcontributions from 123 authors fromthroughout the southern region.

The efficiency and effectiveness ofthe SRAC “Publications” project isrooted in the benefits of using aregion-wide pool of experts to developeducational materials and thenallowing SRAC to cover the costs ofwriting, editing, and initial publication.This process assures that eachpublication is written by the mostknowledgeable person in the regionand it prevents duplication of effortamong states.

During the past two years, researchand extension scientists from thefollowing institutions and agencies

have contributed to SRACpublications: Auburn University,Clemson University, Harry K. DupreeStuttgart National AquacultureResearch Center, Kentucky StateUniversity, Louisiana State University,Mississippi State University,Mississippi-Alabama Sea GrantConsortium, Purdue University, TexasA&M University, University of

Arkansas at Pine Bluff, University ofFlorida, and University of Georgia.You will find information on just aboutany topic you can imagine from the listof 170 titles available from SRAC. Togive you some idea of the variety ofmaterial available, here are somerecent titles:• Aquatic Weed Management:

Herbicide Technology andApplication Techniques

• Cost Economics of Small-ScaleCatfish Production

• Pond Mixing• Aquaculture Food Safety

• Trematode Infestations in Catfish• Channel Catfish Virus Disease• Partitioned Aquaculture Systems• Growing Bull Minnows for Bait• Hybrid Striped Bass Fingerling

Production• Crawfish Aquaculture: Harvesting• Management of Ammonia in Fish

Ponds• Protozoan Parasites• Saprolegniasis (Winter Fungus) and

Branchiomyosis of Channel Catfish• Crawfish in Earthen Ponds without

Planted Forage• Liming Ponds for Aquaculture• Koi and Goldfish• The HACCP Seafood Program and

Aquaculture• Aquaculture Research Verification

Programs• Catfish Broodfish Management• Catfish Hatchery Management

All SRAC Fact Sheets, as well as avariety of other printed materials, arereadily available. If you have Internetaccess, the easiest way to obtainSRAC publications is to visit theSRAC website (see the box above)and browse the list of publications.When you find the publication ofinterest, simply click on the title andprint. If you do not have access to theInternet, copies of SRAC publicationscan be obtained from Dr. JimmyAvery, Aquaculture Extension Special-ist at the NWAC in Stoneville or yourlocal Aquaculture Extension Specialist.


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U.S. Farm-Raised Catfish Industry: 2004 Review and 2005 OutlookTerry Hanson

2004 Review

The U.S. catfish industry generated$438.5 million in farm sales in 2004.The growth of the catfish industry hasbeen rapid with less than 6 millionpounds being processed in 1970 to662 million pounds in 2003. In 2004,production decreased by 4.7% to630 million pounds with the top fourcatfish producing states, Mississippi,Alabama, Arkansas, and Louisiana,producing 95% of all catfish grownin the U.S.

During the first half of 2004, catfishproducers faced rising feed costswhile fish prices started to rise. Asfish prices stabilized higher during thesecond half of 2004, catfish feedprices decreased due to record cornand soybean crops. Thus, 2004 couldbe described as a transition year forthe U.S. farm-raised catfish industry,transitioning out of three prior yearsof low producer fish prices and into aperiod of higher fish prices. However,producers will need a string of goodyears to make up for three years oflow revenues, lost equity, and cashflow problems.

Live Fish Prices. The average catfishpond bank price in 2004 was$0.696/pound, up $0.115/pound from2003’s average price of $0.581/pound(Figure 1). The 5- and 10-year monthlyaverage prices follow a seasonalpattern of price increases fromJanuary through May and then declinethroughout the rest of the calendaryear. Producer catfish prices generallyfollowed the seasonal pattern exhibitedin the 5- and 10-year average priceranges in 2004, but went above the

10-year average price in the last threemonths of 2004 (Figure 1).

Producer Inventories. Catfish invento-ries of small-, medium- and large-sizedfood fish have continued to decreasesince July 2001. For the top fourproducing states, July 2004 food sizefish inventories were down 40 millionfish or 9% from July 2003 levels.While large and small stocker fishwere down by 4% and 3%, respec-tively, fingerlings and fry were down13% from 2003 levels. Thus,indications are that catfish supply tothe processors and to the producerswill be lower in 2005 than in 2004.This should provide some stability tothe current higher pond bank prices,keeping them within the 5- to 10-yearaverage monthly price ranges.

Variable Costs. Catfish feed pricesrose sharply in the first five months of2004. May 2004 prices for 28% and32% protein feeds had increased by$77 and $80/ton over May 2003 pricelevels, to $298 and $310/ton, respec-tively. Feed costs for an average

250-acre catfish farm producing foodsize fish experienced a 20% increasein overall cash feed costs sinceOctober 2003 (Table 1). However,since the end of May 2004 catfishfeed prices have fallen to the $230range. The 2004 corn and soybeancrops have been the major cause ofthe drop in catfish feed prices andmay bring catfish feed prices downto comparable 2001 and 2002 levelswhen catfish feed sold in the $200to $210/ton range.

Another production price increaseoccurred with petroleum products(i.e., gas and diesel) in 2004. InOctober 2003 gasoline prices wereapproximately $1.50/gallon foron-road gas and $1.05 for off-roaddiesel. In June 2004 gas pricesincreased to $1.74/gallon and dieselprices rose to $1.19/gallon, 16% and13% percent increases respectively(Table 1). Combined with feed costincreases, these input costs haveincreased catfish cash production costsby nearly 20% since October 2003.


0.510.530.550.570.590.610.630.650.670.690.710.730.75

Jan Feb M ar Apr May Jun Jul Aug Sep Oct Nov Dec

$/lb

10-yr avg.

5-yr avg.

2004

2003

Figure 1. Average monthly catfish price received by producers.


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Fillet Prices. The frozen fillet is thebellwether product form of the U.S.catfish processing industry, and as thedirection of frozen fillet prices go forthe processor, so goes the direction ofpond bank prices for the producer.The price received by processors forfrozen fillets began decreasing in April2000 from a high of $2.88/pound to alow of $2.41/pound in December 2001,a drop of $0.47/pound or 16% over20 months. From the January 2002 toDecember 2003 period, frozen filletprices remained in the $2.36 to $2.46price range. Only in 2004 did the filletprice rebound to $2.70/pound beforedeclining to $2.60/pound in November.Though the 2004 price range increaseddramatically, they are still below the2000 price range of $2.70 to$2.88/pound; thus the industry hasstill not fully recovered from the2001 to 2003 slump.

Imports. The primary competitiveimport is basa or tra (formerly called“catfish”) frozen fillet productsmarketed to the food service industry.In 2003 the International TradeCommission and Department ofCommerce ruled that unfair tradingpractices had been used, and imposedtariffs on Vietnam basa and traexporters ranging from 37% to 64%.

Imports of channel catfish were60% below 2003, though it is difficultto track these fish as U.S. Customsput these fish into an “other” fishcategory where they could not bedistinguished from other imported fish.However, in August 2004 Pangasiusand Siluriformes “catfish” categorieswere added to the Ictalurus categoryin the International Trade Commission’simport reporting. This accounted forthe large reported “increase” inimports in August through December2004. Imports of Ictalurus remained inline with its trend for the last year.Concern is now focused on possibleChinese production and export ofIctalurus punctatus to the U.S.

2005 Outlook

The growth in the U.S. farm-raisedcatfish industry is expected to continuebut not at the rapid pace seen in the1980’s and 1990’s. This reduced paceof expansion will be influenced by anumber of factors, primarily the healthof the U.S. economy and consumerconsumption of fish products.

Because of the relatively low pondinventories of food size fish and importtariffs restricting some substitute fishproducts, U.S. farm-raised catfish will

be in short supply in 2005. This short-age will keep pond bank prices stable,higher than in the past three years,and within the 5- to 10-year averagemonthly price ranges. Producer pricesare likely to remain in the $0.65 to$0.75/pound range throughout 2005.Higher catfish producer prices andlower feed prices should bring positivenet returns back to U.S. farm-raisedcatfish enterprises. On the demandside, an improving economy willincrease the rate at which new jobsare created and should increaserestaurant visits, adding to catfishsales and stimulate increasedcatfish production.

Interestingly, as the National Agricul-ture Statistics Service pricing seriesgrows, a trend may be emergingregarding catfish pricing cycles. Thecatfish industry may be in a 10-yearprice cycle. Nominal catfish priceshave gone below $0.60/pound threetimes, in 1982 ($0.55/pound), 1992($0.60/pound) and 2002 ($0.57/pound),i.e., at 10-year intervals, and after thelow-price mark, prices have reboundedfor two to three years. If this is areliable cycle, it would appear thatpond bank catfish prices may beheaded upward for the next one tothree years (2005 to 2007).

Table 1. Effect of feed and fuel price increases on a 250-acre catfish farm’s variable costs.

Fuel Feed & FuelOct-03 Feed Gas Diesel Cash Cost Price $ 250/ton $ 1.50/gal $ 1.05/gal Farm Cost $ 474,650 $ 15,800 $ 23,175 $ 513,625

Jun-04 Price $ 300/ton $ 1.74/gal $ 1.19/gal

Farm Cost $ 569,580 $ 18,331 $ 26,125 $ 614,036

Change in $ $ 94,930 $ 2,531 $ 2,950 $ 100,411Change in % 20.00% 16.02% 12.73% 19.55%


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Mention of a trademark or commercial product does not constitute nor imply endorsement of the product by theThad Cochran National Warmwater Aquaculture Center or approval over other products that also may be suitable.

Mississippi State University and U.S. Department of Agriculture Cooperating

Mississippi State University does not discriminate on the basis of race, color, religion, national origin, sex, age, disability, or veteran status.

Experimental Evaluation andEconomic Analysis of a Fingerling-to-Stocker Phase in the CommercialFarming of Channel Catfishcontinued from page 5

total cost of production was three andfour cents less than correspondingcosts for the multiple-batch productionsystem (Table 2). Thus, combinedwith the previously stated non-cashbenefits of the modular productionsystem, the economic analysisadditionally supports the modularproduction system as an alternativestrategy to produce larger fish at alower cost to producers -- a truenecessity to successfully compete inthe global market for fish products.

Both the 50,000 and 60,000/acredensity for the fingerling-to-stockerphase of the modular system appear to

offer promise, given the higher netreturn and a lower cost of production,even with the smaller stocker sizeproduced at the highest stockingdensity. At 60,000/acre, the goal of amean weight of 0.25 pounds for thestocker may be achieved with aslightly warmer growing season.Critical to the success of the fingerling-to-stocker system is sufficient fixedaeration to manage high levels ofoxygen consumption caused by thehigh total weight of fish in the pondand the corresponding high feedingrates. Without sufficient aeration, fishgrowth will likely decrease due to lessthan optimal levels of dissolved oxygenand chronic disease (ESC) may leadto substantial mortality. The fingerlingto stocker phase seems most suitablefor larger farms where large numbersof stockers could be effectivelytransported short distances within a

farm without incurring mortality. Safetransport of stockers to other farmslocated elsewhere may prove to becost prohibitive because multipleshipments of a reduced number offish (lower density) would be requiredto stock growout ponds.

During 2005, further research devotedto the fingerling to stocker phase of themodular production system will focuson the assessment of production usingslightly larger fingerlings (5 inches totallength) and a less expensive (32%crude protein) feed. Both approachesare designed to increase efficiency andreduce production costs. Continuedverification discussions with producerswho have already incorporated thisphase into their production strategythrough different approaches willcontinue to complement our small-scale research.

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