Gill Health in Finfish Aquaculture

Dr. Hamish Rodger

Gill Health in Finfish Aquaculture

Outline

Gill disease background

Aetiologies of gill disease

Pathologies

Control & treatments

• Gas exchange (O2, CO2)

• Acid – base balance

• Osmoregulation

• Excretion of nitrogenous waste products (mainly NH3)

• O2, CO2 sensors (neurons)

© H. Rodger

Gill Health in Finfish Aquaculture

Main gill functions

• UK – amoebic gill disease (AGD), proliferative/hyperplastic gill disease, algae, jellyfish

• Norway – proliferative gill inflammation (PGI), AGD, pox virus

• Australia & Japan – AGD, plus…

• Chile & USA – AGD, harmful algae, others?

• Canada – harmful algae, Loma sp., PGD-type?

Gill Health in Finfish Aquaculture

Gill disorders – finfish farms

Causes of gill disorders

Gill Health in Finfish Aquaculture

• Harmful algal blooms (physical, toxins or deoxygenation)

• Harmful zooplankton swarms (nematocysts)

• Amoebic gill disease & other parasites

• Bacterial gill disease

(Tenacibaculum sp., others)

• Viruses

• Fungi

• Chemical (hydrogen sulphide,

• hydrogen peroxide)

• Multiple and/or sequential

Gill Health in Finfish AquacultureCauses of gill disease

© H. Rodger

Primary insult to gills

(phytoplankton,

zooplankton, others)

Change in environmental

conditions

Infestation or infectionColonisation of gills by

harmful bacteria

Infestation by protozoans

(costia, trichodina)

Proliferation of

parasites, other

bacteria

Direct pathology &

impact

Bacterial gill

disease/epitheliocystis/P

GI or D?

Gill disease (AGD, pox

virus, etc.)

Exposure to pathogens

0.0

5.0

10.0

15.0

20.0

25.0

30.0

% W

eekly

Mo

rtali

tySite A 08GS1 Weekly Mortality Per Pen

C1

C2

C3

C4Tenacibaculum sp. bacteria

Trichodina, marine costia, amoeba

Hyperplasia, fusion, necrosis & epitheliocystis

Gill Health in Finfish Aquaculture

Harmful algae

Gill Health in Finfish Aquaculture

Harmful algae blooms (marine)

• > 200 harmful species

• Karenia mikimoti (dinoflagellate)

• Noctiluca scintillans (dinoflagellate)

• Pseudo-nitzschia sp.

• Chaetoceros sp. (diatom)

Gill Health in Finfish Aquaculture

Harmful algae blooms (HAB); clinical signs

Photo by A. MacAteer

Fragile, bleeding gills,

inappetance, behaviour

change, visibility

Gill Health in Finfish Aquaculture

Harmful algae blooms (HAB); gross pathology

Increased mucusDiffuse necrosis,

haemorrhages

© H. Rodger © H. Rodger

Gill Health in Finfish Aquaculture

Harmful algae blooms (HAB); histopathology

© H. Rodger

Diffuse epithelial

apposition,

sloughing &

necrosis (Karenia

mikimotoi)

© H. Rodger

Gill Health in Finfish Aquaculture

Harmful jellyfish or zooplankton pathology

Gill Health in Finfish Aquaculture

What are Jellyfish?

jellyfish Little jellyfish Siphonophores Comb jellies

(Scyphomedusae) (Hydromedusae) (Siphonophores) (Ctenophores)

Gill Health in Finfish Aquaculture

Harmful jellyfish or zooplankton pathology

Stinging cells (nematocysts)

- Mechanical damage

- Toxic Damage

Gill Health in Finfish Aquaculture

Hydroids (Ectopleura larynx) & biofouling organisms

Gill Health in Finfish Aquaculture

Jellyfish pathology

Muggiaea atlantica & Phialella sp. Aurelia aurita

Gill Health in Finfish Aquaculture

Harmful zooplankton gill histopathology

Focal epithelial necrosis, sloughing and

haemorrhage/thrombosis or haemolysis

(Aurelia aurita)

Concurrent or secondary bacterial

infections

Progression or healing?

© H. Rodger

Gill Health in Finfish

AquaculturePotential vectors for pathogens?Phialella quadrata and Pelagia noctiluca: implicated as vectors of the

bacterial disease Tenacibaculum maritimum

Delannoy et al. 2011

Muggiaea atlantica© H. Rodger

© H. RODGER

Gill parasites

Gill Health in Finfish

Aquaculture

Gill Health in Finfish

AquacultureAmoebic gill disease

© H. Rodger

Neoparamoeba perurans

© H. Rodger

Gills affected with Ichthyobodo sp. & fungi (Saprolegnia sp.)

• Tenacibaculum sp. • T. maritimumBacteria

Epitheliocystis in Seriola sp.

Importance of diagnosis

Increasingly complex

Many infectious agents ubiquitous

Cause-and-effect relationship not defined for all

Predisposing factors of greater significance?

Differential diagnosis

Clinical history & signs

Water quality, plankton sampling

& observations

Fresh gill smears (on site microscopy)

Histopathology

PCR, bacteriology

Treatment & control

• HAB & zooplankton: stop feeding,

aerate/oxygenate?, move pens?,

enclose pens ? but early warning

required.

• Biofouling?

• AGD: freshwater baths,

hydrogen peroxide,

improve environment

• Bacterial gill disease: improve environment, antibiotic?

Monitoring• Daily secchi disc (and phytoplankton)

• Zooplankton

• Gross gill scores • Histopathology

• Gross gill scores

• Fresh gill smears

• Gill amoebae • Microsporidians

Surveillance via RT-PCR

• Gill disease highly significant health challenge

• May be uni- or multifactorial

• Accurate, early diagnosis crucial

• Monitoring, gill disease can be progressive

• Treatments available for some conditions

• Improve rearing conditions

• Much research required

Summary

asia.fishvetgroup.com