Series4_FishDiseasePrevention

8/12/2019 Series4_FishDiseasePrevention

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o u t u i s i e s

Prevention andTreatment of Fish iseases

quaculture Fisheries DivisionAgriculture Fisherles andConservation Department


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INTRODUCTIONFish diseases e c t the survival and growth rates of fsh underculture Given that drug treatments are expensive fsh diseasesinvariably lead to lower harvest and higher cos t. Fish farmersoften suffer hefty economic losses due to fsh diseases

T alleviate such losses it is crucial to take precautions to p reve ntfsh diseases and reduce pathogen levels in water bodies . It is alsoimportant to prevent water qua lity from deteriorating and tostrengthen the natural resistance of the fsh stock

Regu lar monitor ing of fsh hea lth is an e e c t i v eway to identifyd i s e s e u s e sand appropriate treatments One major cause ofserious fsh kill is overlooking the contagiousness of fsh diseasesand thus delaying treatmen t. As such adequate care andtreatment should be given to i n f e c t e d p r o m p t l y


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Causes of fish diseasesThere are three major causes of fish diseases:

>J Presence of environmental pathogens> Low resistance of the fish stock Unsatisfactory water environment

Pathogens e.g. bacteria viruses fungi and parasitesexist in all natural water bodies yet healthy fish haveadequate resistance against them. They can also adapt to

o n a b l eenvironmental changes and in turn avoiddiseases due to pathogenic infection.

Environment Pathogens

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When the pathogen level of a water body rises sharplydue to external factors and the natural resistance of thefish stock cannot cope with the increased pathogens thefish will become vulnerable to pathogenic infection anddiseases.

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n addition external factors may also cause drastic changesin_ yater quality _ resulting i ~ poor health an _d low resista r lceof fish stock. The risks of pathogenic infection and fishdiseases or deaths are heightened.

\4 Pathogens

nvironmentdeteriorating drastically


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o prevent nd n t r o lfish diseases , we should:maintain a good culture environment nd prevent the

e t e o r t i o nof water environment ; anduse hygienic and n u t r i t i o u ss h feed to boost resistance of thefish stock nd to minimise the chance of introducing pathogensto the water body

2 1 How can we prevent the waterenvironment from deteriorating?00 not over-feed - Avoid contam ination caused by excessiveorganic matters depositing on the pond bottom/seabed.

Prompdy remove fish carcasses in fish ponds/raft netcages Avoid contamination caused by excessive organicmatters depositing on the pond bottom/seabed.

Remove fouling organisms on the raft net cages regularly, clearobstruct ions so that organic matters (an be removed from the fish u l t u zone by sea currents.

Read the Good Aquaculture Practices Series 2 EnvironmentalManagement of Mariculture and Good Aquaculture Practices Series 3Environmental Management of Pond Fish Culture booklets for goodpractices on culture environment management .

LW UH

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2 2 How to boost resistance of fish under cultureMaintain a suitable stocking density. A crowded cultureenvironment increases the risk o f disease infection and makest he fish nervous . Fish knocking against each other oftenget surface wounds and may develop diseases as aresul t.

Use a winnowing basketwithout knots to reduce the riskof nfection caused by surfacewounds .

Avoid feeding the stockwith trash fish thatcannot provide balancednutrition This type of feedlessens the natura l resistance of

and makes them more vulne rab le to pathogenic infection.

Use dry pellet feed which is hygienic , nutritious and low inbacteria . Dry pellet feed added with vitamins and minerals canfurther strengthen fish immunity Read the Good AquaculturePractices Series 1 Fish Feed Management booklet for goodpractices on fish feed managemen t

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2 3 ow to reduce p thogensin the w ter body?

Disinfect fish ponds and cu l tur e gear regu larlyRefer to the methods listed in Ta ble 1 to keepyour fish farm clean.

Store the dry pellet feed properly ,Keep pellets in a cool , dry andcovered place to preventmassive bacterial growth

Store trash fish properlyPathogens may pro liferate inimproperly preserved trash fish .Such feed may introduce largequantities o f pathogens to the waterSome pathogens can be eliminated by

deep freezing Never use trash fish that arenot clean or fresh.

Tab le 1: Disinfect ion of fish farms and cul ture gear

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Fish pondbottom

Culture gear ,tanksand

pipes

D r a i nand sun d h e pond for 3 monthsor sho rten the t.ime by us ing a ste rilising agent)

After drain ing an ,d sun dry ng the pond for 3 weeks ,

2 sprinkle with q_uick l m ~(calciu Tl oxide ), ,(5.00 .9 for e y r ysqua re metre). un dry for another week befre fill ingwith water.

s i r c t with electric steam gun for about 5 m inutes.

Immerse in 1 4 ,000 formaldehyde (i.e. 100 ml of2 ?r ma l ~ e h y d e ~ l u t io 1for ~ v e r y O .~ t o n ~ w t e ~) for

about 1 hour , then rinse thoroughly with water.

Immerse in 1 2,000 domestic bleach i.e. 500 mlof b leach for3 1 o n of w a r about 3 hours , hen neutralise with i u mbicarbonate soda) and rinse thoroughly with water.


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reatment

Disinfect fertilised eggs and fry properly -Fe rt ilised eggs and fry may be infectedby pathogens that are present intheir parents. Treat fertilised eggswith a sterilising agent and treatnew fry with freshwa ter (form arine fish) or potassiumpermanganate prior tostocking.

Purchase quality fry . Fishfarmers should purchasehealthy fry with healthcertificates from reputablesupplie rs.

. ... ....,1Join the fry health inspection

Fish farmers canfry samples to the

ulture , Fisheries andDepartment

AFCD) for fr tests onpathogens and harmfulsubs tances before placing

purchase orders.Read the Good Aquaculture

Practices Series 5 Fry Hea lthManagemen t booklet for

good practices on managingthe health of fry.


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While p r u t o n sshould be taken to prevent diseases closemonitoring of disease is equally important It is an effectiveway to detect sick fish and identify the cause of disease at anearly stage so that appropriate treatment can be given andtransmittable fish disease can be controlled For this reason the AFCD e n c o u r g e s f r m e r sto join the Fish HealthInspection Programme and conduct a simple health check ontheir fish stocks every day

3 1 AFCD s Fish Health Inspection rogrammeAFCD staff v isit marine fish culture zones and fish ponds regularly toprovide free fish health inspections and to introduce fish diseaseprevention practices Serv ices o this programme include:

Full physical examination

Tests for bacteria parasites andvlruses

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On-site demonstration of water qual ty

test and i sh disease prevention measures

t n troduction of simplefish health inspectionroutine

t dvice on good fish farmmanage ment

J : \ .Fish farmers are welcome to call the FCD s quacultureM m g e m e n t s e c t i 8 9 to make e n

bookings or obtain programme details.

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3 2 How to inspect the he lth of your

fish stockFish farmers should carry out a simple hea lth inspectionroutine every day. To begin with , observe fish behaviourstage one). See i f the fish are reduci n g feed intake or

showing abnormal swimming patterns. If you arecertain th t the abnormal behaviour is notconnected with environmental facto rs, carry out adetailed health inspection stage two). Forexample , check the body surface , fins andgills, and see if there are any surfaceparasites. If disease symptoms aredetected , seek assistancefrom the AFCD. Our staff willvisit your farm to follow up thefish disease and recommendappropriate treatmen t.

Stage One : Observe fish beh viour Table 2)

Feed intake Reduced feed intake is the first s ign of many fish diseases.Fish farmers should therefore keep daily feeding records toensure they have sufficient information to compare generalintake trends.

Abnormal Examples are fish Iying flat , rubbing against the bottom orswmmng net cage edges , jumpi ng out of the water , circling in water

p or losing buoyancylbalance. AIIthese may be signs of disease.

Table 2: Differentiatingbetween sick and hea lthy fisht t 3 Uh i r : f l l m l i l Activity wimming slowly;sluggish response Swimming actively;sha rp and respons ive

BodyColour Dull, darkor discoloured Brightand glossy

Body Surface Wh ite layered patche s Intact

BodyShape Thin Normal s ze

Feed Intake Poorappe tite Good appetite

Organs Dfferent fish diseases cause Internal organs are healthy and normaldamage to different organs

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Loss o f sca les

t Check the g ills - f the gills are whitened or show ulcers or with deep redspots. or there are gill flukes. excessve mucus or obstructve substances the fish may be nfected and gill functons may be mpared.


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Diagram 1 : Fish disease monitoring w chart

fif( MttI Is feed intake reduci ng?

re fish exhibiting abnormalsw imming patt e rns

YES( rubbing aga inst theb o t t o ~or net cage edges umping

u tof the water. circling hwater orlosin9 buoyancylbalanc. l

s h e h e a y . Continue t a y r e g u hea lth inspectiona n m o n i t o rs h hea lth

NO YES

Is it related to environmentalfactors . 9. s asonal c han9.s inwater temperature oilcontamintion or red tide ?

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The eggs or spores of most pathogens infect new hosts and transmitfish diseases through the medium of water or by direct contac t.When there are environmental abnorma lities water qualitydeterioration unbalanced nutrition bodily injuries or parasiticgrowth which weaken natural r e s i s t n e b e c o m evulnerab le topathogenic infection and diseases The following are common fishdiseases in Hong Kong and their symptoms and treatments

4 1 Ectoparasitisme n e d e n i a s i s

8enedenia white and transparent S 6mm long and 3 4mmwide.

8enedenia lay masses of e9gs After hatching the larvae can

survive in seawater for about a day to seek new hostsThese parasites live in the mouth eyes skin and fins of fish andcause bodily wounds and excessive surface mucus The sick fish getvery restless and circle continuously or rub against net surface resulting in loss of scales a nd hence infection. The fish gradually loseappetite and eventually die of weakness and exhaustion

Put the sick fish in freshwater and the parasitic 8enedenia

will comei n

1 to 2 minutes Immerse in freshwater for 10 minutesthree times every 1 2 weeks and appl y strong aeration

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Cryptocaryoniasis Seawater) / Ichthyophthiriasis Freshwater)

rypfocaryon rrfans / Ichfhyophfhrus mulff l s . wh ite , ovate or

spherical and ciliated , ranging from 40 to 400 microns in length.

Juveniles can survive for more than 15 days in water after leaving afish to seek new hosts. When they find a new host they will burrowinto the fish skin and sett le there.

White spots will appear on th caudal and pectoral fins and graduallyextend to the body surface and gil ls Eventually the growing whitespots will form a film . The sick f ish get irritable and restless. Theycircle continuously or rub aga inst net surface which results in loss ofscales , muscular inflammation and ro t . The eyes become white andturbid and th fish gradually lose appetite , get thin and appearsluggish. Eventual ly g ill tissues are badly damaged and th fish willdie of suffocation.

Immerse in freshwater for 5-15 minutes , or immerse in solution of1 4,000 o r m h y o r 1 250 ,000 potassium permanganate for onehour. Apply strong aeration .For correct app licat ion o f fish drugs , see Ta ble 4


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richodiniasis

Tr;chod;na about 100 m icrons in length with peripheral cilia.

Tr;chod;na lay hundreds or even thousands of spores whichcan survive in the sedimen t of fish ponds to wait for suitableenvironment for hatching . The larvae can survive for 1 to 2 days inthe water to seek new hOSlS

Symptoms are similar to tho se of Cryptocaryoniasis. The i nfectedfish show white spOlS on the body and gills.

Similar to th t for y l o c r y o n;lan5


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hilodonellasis

hllodonell about 40 mcrons long and 30 mcrons wide

h l d o n e l l acarry out asexual reproduction by cell divisioninside fish bodies After leaving a fish they can survive for 2 to 24hours to seek new hosts

Symptoms are similar to those of ichthyophthiriasis The

infected fish have patho logical changes in the body and gills

Similar to th t for ichthyophthiriasis


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Dactylogyrosis

a c l y l l y r u s g e n e r a l l y0.5 mm long with 4 anterior dorsal eye spots

aclylogyrus have full reproduction capacity t birth. They transmitfish disease by direct contac t

a c l y l y r u scause extensive wounds on the fish body surface andincrease the chance of fu n gal and bacterial infection. The sick fishget irritable and restless . They swim frantically to the surface orswim sideways rapidly near the bottom. Body colour darkens andmovement becomes sluggish. The fish would eat less , becomeweak and have difficulty in breathing. Death will eventually c c u rwhen the gills and body ro t.

Use a 1:400 ,000 potassium permanganate solution for extendedimmersion or immerse in solution of 1 4 ,000 formaldehyde for onehour and pply strong aeration. When considering to useTrichlorofon for immers ion , consult veterinarian advice beforetreatmen t.

o rcorrect appl icat ion of fish drugs see Table 4

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Gyroda ctylosis

Gyrodactylu similar to Daclylogyrus in appearance butwithout ey spots

ame as that of dactylogyrosis

ame as those of dactylogyrosis bu t not always caus ingextensive wounds

Same as that for dactylogyrosis


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Copepods commonly known s fish lice)

There are many species of fish lice. They range from several millimetres

to several centimetres n length.Same as th t of anchor worms.

ish lice are parasites found on fish body surface. The sick fish willshow decelerated growth due to anorexia and develop surfacewounds as they rub their bodies against objects. This increases thechance of getting other infections. Most lice would not causeserious harm to fish but a few species s e e t etoxins that makeinternal organs ro t.

Same as th t for lernaeosis.


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4.2 ndoparasitism

Glugea disease

lugea - spores are black granular and 5-10 cm long.

lugea spores reproduce in m sses inside the fish. They are thendischarged out of the o d y with urine and faeces or th roug h thebody surface to look for new hosts. Dead fish with glugea diseasealso release large quantities of lugea spores when they ro t.

Parasitic lugea in the large intestinal wall mucosa causein ammation . The sick fish will lose appetite and gradually wasteaway .

None .

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e

anguin icolosis

anguinicola spp 10-20 microns long.

anguinicolafind their w y to the water through fish gills and look forsnails as intermediate hosts where they reproduce in masses Whenthe opportunity arises they invade fish and cause damage totheir circulatory system.

Parasitic anguinicola in the fish circulatory system will causeanaemia. They will also cause damage to gills and kidneys. There areno distinctive initial symptoms but as the disease develops , gills willshow dark spots , or there may be anaemic symptoms such as bloatedbelly and s in amed anus , upright fins and protruding eyes

Give Praziquantel by oral administration or injection veterinarianprescription only).


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4 3 Fungal infectionSaprolegniasis

Saprolegnia

Saprolegnia grow in trash fish fish feed culture gear and benthicorganic matters. Masses of free spores are released from the bodysurface faeces and rotten carcass of infected fish to look for new hostsin the water. Some Sa prolegnia can survive forseveral years in benthicsediments in the water. As a result fish may get infected continuously.

aprolegnia can burrow into the fish body from surfacewounds. They can also invade the digestive tract when fish eat foodcontaining them. They bore holes in the intestinal wall and reachinternal organs through the circulatory system reproducing andspreading across the body. Affected fish have greyish white woollyfungi on the body surface Some aprolegnia can causegranu loma -like lesion in in t ernal organs.

None. When saprolegnias i s is diagnosed all infected f ish must bedestroyed and no new fish are to be purchased or introduced untilthe fish farm is deared and thoroughly disinfected.

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4 4 8acterial infectionVibriosis

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v1btio are pre sent in water. When immunity of fish is poor or there isany surface wound infection may occur. Fish can also get vibriosisbyea ting trash fish with v i

Different species of V ib r a t t a c kdifferent parts o the fish.Some make the body s u r f a gillsand fins rot or make the body mblack. O th e a t t a c kintemal organs like the hea rt liver spleen andintestines.

Immerse in antibiotics or use them as oral drugs. 8ther way i t must ep r e s c r i d by a veterina rian. Please note that s o m e : l r i ohave

V e P e ddrug resistance to common antibiotics.


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4.5 Viral infection

Viral infe tion

l M W

l r i o t S

Lymphocystis disease virusNOd MrUSSpring viraemia virus

Vruses are transmitted from trash fish, b toodstock or infected fish toother fsh. Transmission is very rapid and all the fsh in a fsh farmcan be infected within 12-24 hours. The death rate can be 100 . Fryunder one year old are particularlyvulnerable. Weather or water qualitychanges can also lead to il1lfection.

Infection symptoms vary across i r n tviruses. The sick fsh mayswim abnormally (e.g. cirding) or show poor appetite , body woundsor darkened body colour.

None. Neither antibiotics nor other fsh drugs have any treatmente e c t However, s a preventive measure , vitamin can be added inthe feed to boost resistance.

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4.6on

pathogen related diseasesUnbalanced nutrition

F a y l i v e r

Fish f r u l a r f yon high fat f d with no essential fatty acids (suchas trash fish i l l e rfrom t o x i c U S I y peroxidationo unsaturated fa t. Appetite is poor and growth is s l o w . m y l s o

lead to bone defect or anaemia .

Improve fee q u a l s r efish f d properlyand use suitable additves.For details, read the Good Aquaculture Practices Series 1 Fish FeedManagement booklet.


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one rnajor a e o f f i s hkill s O V I k i n gthe contagiousnesso f s h diseases and thus delaying treatment To maximise thechance o f successful treatment , n f e c t e ds h must be isolated fortreatment immediately I f a n y s h is found infected , isolate timmediately and give appropriate treatment or destroy it

5 1 Rules for using fish rugsThe Harmful Substances In Foo d Regulations ( ap 132AF provi de s tatueagainst any food conta ining proh ibifed subs tances (e.g. ch loramphenico l;see Sche dule 2 to Cap 132AF) or con taining cer tain su bstances inexcessive concentrat ion (e.g. Mal ach ite green, Furazo lidone andTetracycline; see Sche dule 1 to Cap 132AF).

Fish farmers must no t use any fish d rugs no t p rescr ibed by the A F D or areg istere d veterinarian, or any fish drugs w ith unknown ingredients. Whengiving drugs , stick to the p r e s c r b d o s a g eand observe the withdrawa l per iodafterwards . In case of doubt, seek ass is tance from the F D

The following fish drug s are not p rohib ited but fish fa rmers must adhereto the following ru les :

Hydrogenperoxide

Formaldehyde

Potassiumpermanganate

|lIr 'mImmerse fish in a solution of 1 2,000 30% hydrogenperoxide (i.e. 500 ml of hydrogen pe roxide for 1 ton ofwater)for 1 hour.

Immerse fish in a : 1 0 f o r m a l d e h y d es o l u t i o n 1 0 0mlof frmaldehyde for 1 ton ofwater) for 1 hour. If necessary ,i n c r s l eC I l Ce n t r a t iO i lto 1 4 0 l of o,malde.hydef o r O .4 nof water . Do not use any formaldehyde solutionwith white sediments.

Immerse fish in 1 250,000 potassium permanganatesolution i e f potass ium permanganate for 1 ton ofwater for 1-3 hours. For extended immersion, use a 1 4 0 0 opotassium permanganate solution i.e. 2.5 9 potassiumpermanganate for 1 on ofwater) for 24 hours.


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[ 1

5 2 Correct use of fish rugsDrug bath is a o r o ur s e o treatment for fsh diseasesThe o r r e c tway o preparing a drug bath is as follows :

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Prepare r r e c tdose of fishdrug , aerat ing equipment and awater bag sene or large tank

Apply drug and ?ti well Put asmall nurber of fish into thedrug bath frst and observe theirrea Ction to the drug Introducethe major_ t o c ~only when_ h ~reactio of the first batch of fishis norma l

s r vhow the fish react n u l r l yand pump air continuously If

thensh behave strangely, stop

immersion immediately andconsider other treatments


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5 3 Safety rules for using fish drugsWhen app lying fish drugs, avoid contact wth y o uskin or clothing or inhalation into lungs.

Wear persona l protect ion gear, such as safe ty g o g g gloves , protect ive dothing and mask.

Some fish drugs are highly volatile. Maintan go

ventilation at all times. Containers should be correctly labelled a ,d cove.red

Empty containers may have residues of hazardousdrugs.

Stay well ~ e a rof gn it ion s o u r ~ e sa ~ dd a n g ~ ~ o ~ schem icals likeoxides, strong acids and strong alkaliswhen us ing fish drugs

>t ~ h o u l danypart of your. b dy co , ,:, e into conta c twi hfish drugs, rinse well with plenty of water immediately.

In case of contact with y rinse wellwith p lentyof water immediatelyand liftthe uppe r and lowereye lids to rinse slowly for more than S minutes.See k medical attention right w

Store fish drugs in a cool, dry and well ventilatedplace and away from direct sunlight.


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echnicalupportFish farmers are welcome to te lephone the AFCD for free inform tion

and technical advice:

General Aquaculture Information: 247 1 9142 p o / 2150 7083 ma rine fish Fish Health and Disease : 2471 9 1 4 2 2 1 5 R d e and Water Quality : 2150 7124


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