SRAC Publication No. 472

SouthernRegionalAquacultureCenter

February 1992

Submitting a Sample for Fish Kill Investigation

R.W. Rottmann, R. Francis-Floyd, P.A. Reed1, and R. Durborow2

Fish kills occur both in naturalpopulations and under aquacul-ture conditions. When fish kills ordisease outbreaks occur on a fishfarm or private pond or lake, it isusually an emergency situation.To optimize the response to a fishkill, producers should be preparedin advance.

How can I best be preparedfor a fish kill or disease prob-lem?To minimize fish losses, the fol-lowing preparations should bemade:

Have a water quality test kitand know how to use it;

Know the telephone numberand address of the fish dis-ease diagnostic laboratory inyour area;

Call the laboratory and in-quire as to how they prefersamples be shipped and whatdays and times samples canbe delivered;

Know how to collect appro-priate samples;

Have the type of container(s)needed to ship samples; and

Determine the best method oftransportation (personal de-livery, bus, air freight, over-night express) and schedulethat will ensure prompt deliv-ery.

How can I determine if I have awater quality problem?Poor water quality can cause mas-sive fish kills and is often a majorfactor contributing to fish diseaseand parasite infections. Waterquality does not remain constant.In ponds, it can change dramati-cally over a few hours. Evenwater from deep wells and springscan change over time. Commercialfish farmers should not rely on di-agnostic laboratory results to iden-tify water quality problems. It isextremely important and cost effec-tive to have a water quality testkit, know how to use it, and beable to interpret the results. Waterquality should be monitored rou-tinely to identify problems beforefish kills occur. In addition, anytime fish appear stressed or fishmortalities are observed, waterquality should be evaluated imme-diately for temperature, dissolvedoxygen, total ammonia, pH, andnitrite. Other tests may be appro-priate depending on results of theinitial screen.

How can I find the fish diseasediagnostic laboratory in myarea?Contact the fish disease specialistsin your state (listed in the Appen-dix).

What type of sample should besubmitted for evaluation?In most instances live, sick fishand a water sample are requiredto have a high probability of deter-mining the cause of a fish kill. Anexcellent sample would include

several (three to six) live fish thatexhibit obvious physical signs ofdisease such as:

■

■

■

■

open sores;

yellowish or light-colored,slightly eroded areas on thebody, fins, gills, or in the mouth;swollen, fused, or clubbed gills;oreroded or bloody fins.

An excellent sample would also in-clude fish exhibiting abnormal orunusual behavior such as lying list-lessly in shallow water or at thewater surface or swimming errati-cally or in circles. Recently deadfish that have gills, eyes, color andmucus that still appear as those oflive fish are a fair sample, if livesick fish are unavailable. Deadfish that have floated to the sur-face of a pond are useless for diag-nostic purposes. It is difficult totell if the bacteria found in thedead fish were responsible for itsdisease condition.

A water sample without fish isusually of little value in determin-ing the cause of a fish kill. Some-times, however, toxic fish wasteproducts such as ammonia and ni-trite are responsible for the deathof the fish. Toxic chemicals enter-ing ponds from outside sourcesmay be the cause of fish mortali-ties. Therefore, a water sampleshould be submitted to the diag-nostic laboratory along with thefish sample.Special sampling and handlingprocedures may need to be taken

if a toxic substance is suspected ina fish kill. In many states, veryspecific instructions must be fol-lowed if any legal action is to betaken. Request approved proce-dures from the diagnostic labora-tory in your state (listed in theAppendix) before collecting sam-ples.

What is the best method to col-lect sick fish?The best method for collecting sickfish is to walk the pond bank witha dip net or cast net and selectivelyremove fish which are at the sur-face, at the water’s edge, or other-wise appear abnormal. It maytake extra effort to find and catchsick fish in this manner, but thequality of the resulting informa-tion will be well worth it. A ran-dom sample of fish taken from aseine has a poor probability ofidentifying the cause of the fishloss, because many of the fish inthe pond may be healthy. Theworst way to collect sick fish is byhook and line. Sick fish usually donot eat; the healthiest fish in thepond will still be actively feeding.Therefore, the use of a rod and reelto collect fish will result in a sam-ple of little or no diagnostic value.

How many fish and how muchwater should be included in thesample?Ideally, a minimum of three to sixsick fish should be submitted forexamination. If only one fish issubmitted it is possible that an in-accurate or incomplete diagnosiswill result; one fish is usually notcompletely representative of apopulation. Most fish disease out-breaks involve more than oneproblem, Therefore, a repre-sentative sample is essential forgood management decisions.In ponds larger than one surfaceacre, a minimum of two one-pintwater samples should be collectedfrom opposite ends of the pond foranalysis. Dissolved oxygen shouldbe checked by the producer at thepond bank; this parameter cannotbe accurately measured at the labo-ratory. Do not combine fish andwater in the same container.

What containers are best forshipping samples to a diagnos-tic laboratory?Ideally, sick fish should be trans-ported live. If the diagnostic lab iswithin an hour’s drive, sick fishcan be transported in a containerof water. Sick fish can also beshipped live in a plastic bag withwater and oxygen for severalhours. The bag is sealed and isplaced in an insulated shippingith ice to keep water tem-perature cool. For longer shippingtimes, sick fish or fish that havejust died should be wrapped in amoist paper towel, placed in a plas-tic bag (without water), and trans-ported on crushed ice in a cooleror styrofoam lined shipping box.A sample handled in this mannershould be of diagnostic value forup to 48 hours. Sick or recentlydead fish can be frozen and usedfor bacterial cultures but are of lit-tle value for parasites identifica-tion on skin, fins, and gills.Water samples can be collected inany clean glass or plastic jugs orjars. The water sample, of at leasta pint in volume, should be trans-ported on ice with the fish sample.As previously mentioned, specialinstructions must be followed incases where a toxic substance maybe involved.

What information should beprovided with the samples?The following information shouldbe included with each sample sub-mitted to a fish disease laboratory.

1.

2.

3.

4.

Name, address, and phonenumber of the owner of thefish.

Name or designation of pondor tank from which fish wereremoved. (Note: Fish collectedfrom different ponds or tanksshould be labeled and shippedin separate containers and ac-companied by a water samplefrom each unit.)

Dimensions of pond or tank, in-cluding depth.

Species, number, and averagesize of fish stocked.

5. Date when fish were laststocked (include number, spe-cies, and size stocked).

6. Amount fed per day. (Are fishstill eating? If not, when didthey stop eating?)

7. Date when mortalities werefirst noticed.

8. Number of fish that have diedper day since mortalities werefirst noticed.

9. The most recent treatmentused, including treatment dateand amount of chemical used.

10. Condition of the planktonbloom, determined by themaximum depth that a pieplate attached to a yardstickcan be seen.

11. Any water quality data col-lected by the owner.

What steps can be taken tocontrol losses while awaitingresults?Individual laboratories vary in thetime period required to processthe sample and communicate the results to the producers. In mostcases, water quality data and re-sults of the necropsy and parasitol-ogy examination should beavailable within 24 hours of re-ceipt of the fish. Depending on cir-cumstances and the degree of fishloss, a preliminary assessmentmay be made at that time.

Microbiology (bacterial isolationand sensitivity), virology (identifi-cation of virus), and histopathol-ogy (microscopic examination ofspecially prepared tissues) takemore time. Bacterial isolation andsensitivity are usually completewithin 48 to 96 hours, but virologyand histopathology may take oneto two weeks for completion.

The best approach is to improvewater quality while waiting for di-agnostic results. Increased aera-tion and a fresh water flush canhelp alleviate many problems.

ConclusionsFish kills occur both in naturalpopulations and under aquacul-ture conditions. In aquaculture fa-cilities, good management and

nutrition practices, however, canhelp prevent fish kills. When fishkills do occur on a fish farm or pri-vate pond or lake, it is usually anemergency situation. To optimizethe response to a fish kill, produc-ers must be prepared to checkwater quality parameters, obtain aproper fish and water sample, andtransport it as quickly as possibleto a diagnostic laboratory. Whilewaiting for diagnostic results, thebest approach is to improve waterquality.

AppendixAlabamaFish Health LaboratorySwingle HallAuburn University, AL 36849-5419(205) 844-9220

Alabama Fish Farming CenterP.O. Box 487Greensboro, AL 36744(800) 423-5496 / (205) 624-4016

ArkansasFish Disease LaboratoryArkansas Cooperative Extension

ServiceChichot County Extension OfficeHighway 85 and 62Lake Village, AR 71653(501) 265-5883

Fish Disease LaboratoryArkansas Cooperative Extension

ServiceLonoke Agricultural CenterP.O. Drawer DLonoke, AR 72086(501) 676-3124

Fish Farming Experimental LaboratoryU.S. Fish and Wildlife ServiceP.O. Box 860Stuttgart, AR 72160-0860(501) 673-4483

FloridaIFAS Extension Veterinarian for

AquacultureAquaculture Animal Medical Lab7922 NW 71st StreetGainesville, FL 32606-0300(904) 392-9617

Aquaculture Extension SpecialistHillsborough County Extension Office5339 State Road 579Seffner, FL 33584(813) 621-5605

Northwest Florida Aquaculture FarmP.O. Box 434Blountstown, FL 32424(904) 674-8353

GeorgiaAthens Diagnostic LaboratoryCollege of Veterinary MedicineThe University of GeorgiaAthens, GA 30602(404) 542-5568

Animal Science DepartmentCoastal Plain Experiment StationThe University of GeorgiaP.O. Box 748Tifton, GA 31793-0748(912) 386-3364

Extension Aquaculture and FisheriesDepartment

The University of GeorgiaAthens, GA 30602(404) 542-1924

Warm Springs Fish Health CenterU.S. Department of InteriorFish and Wildlife ServiceRoute 1, Box 105 AWarm Springs, GA 31830(404) 655-3620

KentuckyState Specialist for AquacultureCooperative Extension ProgramKentucky State UniversityFrankfort, KY 40601(502) 227-6581

LouisianaLouisiana Wildlife & Fisheries

CommissionDistrict 11P.O. Box 4004Monroe, LA 71203(318) 343-4044

Aquatic Animal Diagnostic LaboratorySchool of Veterinary MedicineLouisiana State UniversityBaton Rouge, LA 70803(504) 346-3312

MississippiDelta Research and Extension CenterFish Disease Diagnostic LaboratoryBox 197Stoneville, MS 38776(601) 686-9311

Mississippi Cooperative ExtensionService

Fish Disease Diagnostic LaboratoryBox 631Belzoni, MS 39038(601) 247-2917

Fish Diagnostic LaboratoryCollege of Veterinary MedicineDrawer VMississippi State, MS 39762(601) 325-3432

North CarolinaNorth Carolina Cooperative Extension

ServiceNorth Carolina State UniversityDepartment of CASSCVM-NCSU4700 Hillsborough StreetRaleigh, NC 27606(919) 829-4200

North Carolina Cooperative ExtensionService

North Carolina State UniversityDepartment of ZoologyMHCREC-NCSU2016 Fanning Bridge RoadFletcher, NC 28732(704) 684-3562

Rollins Animal Disease DiagnosticLaboratory

P.O. Box 12223Blue Ridge at Reedy Creek Rd.Raleigh, NC 27605(919) 733-3986

Animal Disease Diagnostic LaboratoryP.O. Box 38, Paradise RoadEdenton, NC 27932(919) 482-3146

Rose Hill Animal Disease DiagnosticLaboratory

P.O. Box 37Rendering Plant RoadRose Hill, NC 28458(919) 289-2635

Northwestern Animal DiseaseDiagnostic Laboratory

P.O. Box 70Eldin, NC 28621(919) 526-2499

Western Animal Disease DiagnosticLaboratory

Airport RoadArden, NC 28704(704) 684-8188

OklahomaSoutheast District Fish Disease

Diagnostic LaboratoriesOklahoma Cooperative Extension

ServiceP.O. Box 1378Ada, OK 74820(405) 332-4100

Fish Culture ProjectLangston UniversityP.O. Box 730Langston, OK 73050(405) 466-3836

Puerto RicoDepartment of Marine SciencesUniversity of Puerto RicoP.O. Box 5000Mayaguez, Puerto Rico 00709-5000(809) 899-2048

South CarolinaCooperative Extension ServicesDepartment of Aquaculture, Fisheries

& WildlifeG 08 Lehotsky HallClemson UniversityClemson, SC 29634-0362(803) 656-2810

TennesseeDepartment of BiologyUniversity of TennesseeMartin, TN 38238(901) 587-7170

TexasFish Disease LaboratoryWildlife and Fisheries Sciences

DepartmentTexas A&M UniversityCollege Station, TX 77843-2258(409) 845-7473

VirginiaAquatic Animal Medicine LaboratoryVirginia-Maryland Regional College of

Veterinary MedicineVirginia TechBlacksburg, VA 24061(703) 231-5131

Extension Aquaculture SpecialistVirginia State UniversityP.O. Box 540Petersburg, VA 23803(804) 524-5903

The work reported in this publication was supported in part by the Southern Regional Aquaculture Center through Grant No. 89-38500-4516 from the United StatesDepartment of Agriculture.