Diseases in fish

19.03.2012, Bergen

Hege Hellberg

Overview

Legislation

Guidelines on health and disease monitoring in

research fish

Disease detection and diagnosis

Legislation 1

Norwegian legislation is harmonised with EU

Rules and regulations on fish health and disease

monitoring mainly relate to farmed fish

Council Directive 2006/88/EC

● Prevention and control of certain diseases in

aquatic animals

Legislation 2

Omsetningsforskriften

Regulation 17.06.2008 nr. 819 implementing Council

Directive 2006/88/EC

● Prevention and control of infectious diseases in

aquatic animals – Listed diseases

List 1 Exotic to EU – stamping out

List 2 Present in EU – restrictions

List 3 National – decided by the individual member

states

Legislation 3

Akvakulturdriftsforskriften (Aquaculture Operations

Regulation)

● Minimum number of health inspections of

aquaculture facilities

● Riskbased monitoring

Suspicion of listed/notifiable disease

Increased mortality

● Authorised personnel

Veterinarians

Fish health biologists

General guidelines

General guidelines

Research facilities should have/develop SOPs for:

Quarantine

Pre-trial testing

Health monitoring

Disease prevention

Disease diagnosis and identification of pathogens

Treatment

End of trial testing

General guidelines

Different species have different diseases and

susceptibility

● Know your research species

Biology

Most common diseases

Populations may differ (wild/farmed/research bred)

● Background check

Complete history of your research individuals

Health certificates

Disease detection and diagnosis

Indications of disease

Post mortem procedure

Examples of diseases:

● Virus

● Bacteria

● Parasites

● Nutritional and

environmental

factors

Indications of disease

Mortality

Loss of growth

Clinical signs

● Behaviour

Anorexia, drop in appetite

Lethargy, low activity

Abnormal swimming pattern

● External changes and lesions

Colour

Shape

Skin lesions

CCAC 2005 – Care and use of fish..

Disease detection

Monitor fish health according to SOPs

● Observe

● Record

● Collection of moribund or freshly dead fish

● Testing

Autopsy, post mortem examination,

necropsy

Examination to identify cause of disease or death

The quality of your results is only as good as the

quality of your samples

Moribund or freshly dead fish give the best quality

samples

Live fish

Anaesthetise the fish

If you need a blood sample, take it immediately

Kill the fish

Skin scraping for microscopy

Gill biopsy for wet mount

Gill sample for histology, fix in formalin immediately

External examination

Put the fish on a stable surface

Observe and register the condition of

● the fish (thin, normal, fat, deformities)

● skin (colour, damage, ulcers)

● fins (damage)

● eyes

● examine mouth for haemorrhage and parasites

Condition of fish

Pigmentation

Foto: Renate Johansen

Skin and fins

Ulcers

Skin –fungal infection

Haemorrhage

Post mortem examination

Internal examination

Most species

● -left side up

Small fish:

● -fix with needles, left side or abdomen up

Flatfish:

● -pigmented side up

Post mortem examination

Post mortem

of small fish

Stereo

microscope

is useful

Flatfish

Post mortem examination

Cut off the operculum, exposing the gills.

Observe and register the condition of the gills

● colour

● damage

● mucus

● parasites

● Observe the gill cavity

● Examine both sides of operculum

Gills

Post mortem examination

Open the fish with a midline section

Do not to damage the intestine

Observe the abdominal cavity for ascites (fluid)

Abdominal fluid may be sampled

Abdominal cavity

Post mortem examination

Cut off the side of the fish exposing the abdominal

organs and the heart

Sampling for bacteriology/mycology

Pull the swimbladder away and expose the

kidney

● Spleen may also be sampled

Sterilize the inoculation loop in gas flame and

insert into kidney/speen

The organ must be intact before sampling to

avoid contamination with fecal bacteria

Let the inoculation loop cool off a little before

pushing it further into the kidney/spleen tissue

Remove loop, making sure that it does not

touch any organs before streaking out on agar

plate

Sampling for bacteriology/mycology

Kidney

Spleen

Post mortem examination

Observe the internal organs for abnormalities

● heart

● liver

● gall bladder

● pancreas

● digestive canal

● swimbladder

● kidney

● spleen

NB! Species differences! Know the normal anatomy and appearance of your research species.

Normal liver in salmon and cod

Post mortem examination

Remove the digestive canal and open it

Observe and register contents of stomach and

intestine

Post mortem examination

Make several deep cuts in the muscle to check for

muscle lesions (discolouration, bleeding, cysts,

boils)

Sampling for histology

Cut thin pieces of internal organs

(2-5 mm) and fix in neutral

buffered formalin

Use one container for each

individual fish and label it

Sample a full set of organs from

several fish

● You can decide later if you

want to examine all

Post mortem examination

Sampling for histology

Larvae may be fixed whole

Juveniles may be opened in the abdomen and fixed

whole or cut in 3:

● head

● abdominal organs

● tail

Post mortem examination

The following organs may be sampled for histology:

Gill

Heart

Liver

Pancreas

Intestine

Kidney

Spleen

Skin and muscle

Brain

Eye

Post mortem examination

Sampling for virology

Kidney, heart and brain may be sampled and frozen

on -20ºC or -80ºC or put in transport medium

Tissue on RNA-later for conservation for PCR

Examples of disease in fish

Diseases caused by:

● Virus

● Bacteria

● Parasites

● Nutritional factors

● Environmental factors

Systemic and local

Systemic disease involves the entire organism

Local disease is limited and usually less serious

Viral infections

Local viral infections

Skin

Gills

Often associated with

immunosuppression/decreased disease

resistance caused by e.g. pollution

Lymphocystis, Platichthys flesus

Papillomatosis, salmon fingerling

Systemic viral infections

Usually serious and mortality rates can be very high.

External signs

Haemorrhages (bleeding)

● Skin + base of fins

● Vent

● Mouth

● Eyes

Exopthalmia (”pop eye”)

Swollen abdomen (caused by ascites)

Scale pocket oedema

Poor growth

Infectious salmon anaemia (ISA) in salmon

fingerling

Infectious pancreatic necrosis (IPN) in

juvenile halibut

Systemic viral infections

Internal signs

Acute changes (take short time to develop)

Haemorrhages in internal organs

● Liver

● Intestinal wall

● Swimbladder

● Heart

● Perivisceral fat

Haemorrhages in muscle

Anaemia (loss of blood)

Anaemia – pale gills

Haemorrhage in peritoneum

Bleke gjeller

Haemorrhage in muscle of rainbow trout

Bacterial infections

Local bacterial infections are usually caused by

opportunistic pathogens that gain access after damage to

the skin, eyes or gills

The bacteria that become established are often part of

the in-house bacterial flora (e.g. Pseudomonas spp.,

motile Aeromonas spp., Vibrio spp.)

Local infections can become systemic if:

● The colonizing bacteria are very aggressive

● The fish are immunosuppressed

Immunosuppression

Stress lowers disease resistance, making the individual

more vulnerable to infections

Physiology

● Metamorphosis

● Sexual maturation

Nutrition

Environment

● Water temperature

● Water quality

● Pollution

Systemic bacterial infection in fish

Systemic bacterial infections are serious and mortality

rates can be very high

Bacteria travel to all organs via the blood

● Kidney and spleen are immunologically active

organs and bacteria are often ”trapped” here

● Kidney and spleen are used for inoculation on

culture media for bacterial examination

External signs of systemic bacterial

infection in fish

Haemorrhage

● Skin

● Base of fins

● Anal orifice

● Mouth

● Eyes

Ulcers

Exopthalmia (”pop eye”)

Ulcers in rainbow trout, caused by

Flavobacterium psychrophilum

Ulcers in Atlantic salmon, associated with

Moritella viscosa

Skin haemorrhage in flounder, caused by

vibriosis (Vibrio anguillarum)

Fin haemorrhage and swelling in cod,

caused by vibriosis (Vibrio anguillarum)

Exophthalmia ”pop eye” in salmon,

caused by bacterial kidney disease

(Renibacterium salmoninarum)

Ulcers in cod, caused by francisellosis

(Francisella noatunensis)

Ulcers in cod, caused by francisellosis

(Francisella noatunensis)

Internal signs of systemic bacterial

infection in fish

Acute changes (take short time to develop)

Haemorrhages in internal organs

● Liver

● Intestinal wall

● Swimbladder

● Heart

● Perivisceral fat

Haemorrhages in muscle

Furuncles (boils) in muscle

Liver haemorrhages in salmon, caused by

cold water vibriosis (Vibrio salmonicida)

Muscle haemorrhage in salmon, caused by

yersiniosis (Yersinia ruckeri)

Internal signs of systemic bacterial

infection in fish

Chronic changes (take long time to develop)

White spots (necrosis or granulomas) in internal organs

● Liver

● Spleen

● Heart

● Kidney

Liver necrosis in salmon, caused by

piscirickettsiosis (Piscirickettsia salmonis)

Kidney granulomas in salmon, caused by

bacterial kidney disease (Renibacterium

salmoninarum)

Spleen granulomas in cod, caused by

francisellosis (Francisella noatunensis)

Parasitic fish diseases

Four categories:

Ectoparasites

● Macroscopic

● Microscopic

Endoparasites

● Macroscopic

● Microscopic

The procedure for post mortem examination includes a basic examination for parasites

Ectoparasites are very quickly lost from dead fish!

Ectoparasites, macroscopic

Ectoparasites, microscopic

A microscope is necessary for the diagnosis of

microscopic ectoparasites

Gill biopsy

Skin scraping

Ichthyobodo sp. in gills

Endoparasites, macroscopic

Anisakis infection Cestoda – tape worm

Endoparasites, microscopic

Diagnosis of microscopic endoparasites requires the

use of a microscope

● Blood samples for diagnosis of blood parasites

● Histology for diagnosis of parasites in tissues

● Wet mounts and direct microsopy of:

Cysts

Intestinal contents

Gall

Urine

Squash preparations of organs

Larvae

Endoparasites, microscopic

Myxobolus cerebralis- whirling disease

Nutritional and Environmental Fish

Diseases

To diagnose a disease problem caused by or

associated with environment or nutrition, you

usually need to rule out infectious diseases

Nutritional disease

Feed requirements will vary due to

● Species

● Age

● Physiological stage

Start feeding/Weaning

Smoltification

Metamorphosis

Sexual maturation

Nutritional disease

Feed related factors

● Type of feed (certain problems are associated

with certain types of feed)

Live feed

Formulated feed

Raw fish

● Feed quality

Production

Storage

● Recent change of feed?

Nutritional disease

Deficiency of essential nutrients

Lipids

● FFA

● PUFA

Amino acids

Minerals

Vitamins

Cataract associated with zinc deficiency

Poor nutrition of larvae and juveniles

In general:

● Lower rate of survival

● Lower disease resistance

Abnormal pigmentation in halibut Deformities in cod larvae

Environmental Diseases

Water quality

● Organic particles

● pH and water chemistry

● Pollutants

● Temperature

Technical equipment

● Oxygenation/aeration

● Feeding systems

Abnormal Normal

Poor water quality can cause gill irritation and

branchitis

Environmental disease

Environmental Disease

Water temperature

● Deformities in salmon in hatcheries caused by

high temperature during incubation

Environmental Disease

Technical failure

● Acute high mortality caused by hypoxia

Technical failure

● Supersaturation of water can cause gas bubble

disease

Environmental disease

In conclusion

There are many infectious and non-infectious diseases

in fish

● Observe

● Sample

● Analyse

Thank you for your attention!

Veterinary Institute home page: www.vetinst.no