Intensive Fish Production 2

Question 1

How to we do health moniotring in fish?

Answer 1

1. Observe behaviour - mov, history/records on farm
2. Examine environemnt - fish size, quality etc
3. Select your fish - avoid all dead fih autolysis rapid, avoid taking biggest, pick moribund fish and ‘normal’ ones
4. Macroscopic analysis - gills, skin , eyes etc
5. Gills, organ samples, mucus, skin scrapes

Question 2

What is the only diagnostic tool in aquaculture?

Answer 2

HISTOPATHOLOGY

Question 3

What main parasites in fish?

Answer 3

• Salmon Lice (Caligus elongatus/
  Lepeophtheirus salmonis)
• Amoebic gill disease
• Invisible dx -> Ichtyophtirius multifilis ‘white spot’

Question 4

What important fungi?

Answer 4

Saprolegnia

Question 5

Important bacteria?

Answer 5

• Aeromonas salmonicida
• Moritella viscosa

Question 6

What two types of sea lice?

Answer 6

• Caligus elongatus – affects >80 species
  of fish
• Lepeophtheirus salmonis – specific to
  salmonids, immunomodulate the host
  increasing susceptibility to secondary
  infection

Question 7

What do sea lice do?

Answer 7

feed on skin, mucus, and blood if acheivable

Question 8

What tx options for sealice?

Answer 8

Question 9

What practices to reduce exposure of salmon to lice?

Answer 9

• Single year stocking
• Site fallowing/rotation
• Improved site selection
• Genetic improvements
• Improved farm hygiene

Question 10

What other potential sea lice prevention?

Answer 10

• Some companies are keeping fish deeper, at a
  depth where sea lice are less abundant
• Some apply ‘skirts’ to the cages, which are
  permeable to water but not small copepods
• Functional feeds are being developed that reduce
  sea lice burden
• Lighting strategies
• Lasers that ID lice and strike them
• Ultrasound and vacuum in research

Question 11

What causes Amoebic Gill dx ?

Answer 11

Causal agent - Neoparamoeba peruans
* Amoeba that survives in sediment, net
pens and the water column

Question 12

What does Gill dx cause?

Answer 12

Causes, as name suggests, gill damage,
resulting in epithelial thickening, and reduced
oxygen uptake, excessive mucus production.
* This is exacerbated by higher water
temperatures – hence warming oceans is
a big problem for the salmon industry.

Question 13

Gill scoring?

Answer 13

Question 14

Histology on Gills?

Answer 14

• Top – Normal
• Bottom – extensive lamellae hyperplasia
  and mucus cell proliferation
• Arrows = Amoeba

Question 15

AGD causes …?

Answer 15

severe CV compromise,
and if environmental conditions are
unfavorable, can cause severe
mortality events >50% of stock.

Question 16

What factors/ risks of AGD?

Answer 16

• High salinity (>32ppt)
• High temperatures
• Co factors – jellyfish/algae blooms
• Biofouling of nets – reduces water
  turnover and Oxygen availability.
• Smolt quality and size

Question 17

AGD tx optionS?

Answer 17

1. Freshwater - 8% of all tx in scotland
2. Hydrogen peroxide (biggest one)
3. Emergency harvest

Question 18

describe freshwater tx?

Answer 18

• 2-3 hour baths in <3ppt salinity to lyse amoebe
• Can see morts if oxygen in pens is low
• Bath every 35-40 days until parasites are gone
• Expensive but effective. Low environmental
  impact

Question 19

Describe hydrogen peroxide tx?

Answer 19

• 18-22 mins at 1200ppm, 8-15oC
• Can see high levels of morts if disease is severe

Question 20

What is Ichthyophthirius multifilis?

Answer 20

‘WHITE SPOT’
- Enedemic to every waterr source

Question 21

Stage of parasite lifecycle of’white spot’?

Answer 21

• Parasite stage – theront. Easiest stage to
  treat
• Covered in cilia and replicates in
  epithelium
• Encysted stage – tomont. Leaves fish host,
  settles in substrate to encyst.
• Replication – cysts undergo binary fission
  to produce tomites, which then differentiate
  into theronts.

Question 22

Tx for ‘white spot’?

Answer 22

• Formalin – upto 170ppm for 1 hour.
• Known carcinogen – PPE!

Question 23

Saprolegnia?

Answer 23

Water mold – affects freshwater systems
* Huge problem in hatcheries
* Opportunistic and always secondary pathogen

Question 24

What does saprolegnia do?

Answer 24

Invades superficial tissue and secretes
immunomodulatory compounds
Number of spores is directly proportional to the rate
of infection.
Usually causes mortality through haemodilution

Question 25

Tx for Saprolegnia?

Answer 25

* Can prevent with malachite green, although this has been banned in food fish for years * Formalin – 37%. Although being phased out. * Hydrogen peroxide – 500-1000ppm for eggs * Saltwater treatment * Potassium permanganate * Methylene blue * Ozone – used as a disinfectant in hatcheries. Does however significantly affect hatch rate.

Question 26

What does Furunculois/ Aeromonas Salmonicida cause?

Answer 26

Causes sudden onset: * Depressed appetite * Behaviour change * Appearance change * Haemorrhage * Increased mortalities

Question 27

Dx of Furunculosis?

Answer 27

Routine bacteriology and histopathology

Question 28

Prevention of Furunculosis?

Answer 28

* Effective vaccines have reduced prevalence significantly

Question 29

Tx for furunculosis?

Answer 29

* Oxytetracycline in feed * One of only licensed antibiotics in aquaculture, alongside Florfenicol. * But wait.. * If appetite decreases when diseased, how does in feed antibiotics make sense? * Essentially, the aim is to stop the spread rather than treat those who are currently sick.

Question 30

What is Moritella viscosa/Winter ulcer dx?

Answer 30

Bacteria – M.viscosa * Gram negative rod * Favours high salinity and cold temperatures <8ᵒC

Question 31

MOA of winter ulcer dx?

Answer 31

* Virulence factors: The ability to produce proteases and other enzymes, which allow it to degrade tissues, leading to lesions and ulcers. * It is considered an opportunistic pathogen, meaning it often infects fish that are already stressed due to factors like poor water quality, overcrowding, or temperature changes.

Question 32

CLS f winter ucler dx?

Answer 32

* Winter ulcer disease manifests as open, necrotic lesions or ulcers, typically on the skin or muscle tissues, often around the head, fins, and body. These ulcers often appear as circular or irregular lesions. * Affected fish may show signs of distress such as reduced feeding, erratic swimming, and lethargy. * In severe cases, the ulcers can become infected with secondary pathogens, further complicating the disease.

Question 33

Pathophysiology?

Answer 33

commonly observed during colder months, hence the name "winter ulcer," as it tends to affect fish during the winter or early spring, when water temperatures are lower

Question 34

Risk factors?

Answer 34

* Fish that are stressed by factors such as overcrowding, poor water quality, or sudden changes in temperature are more prone to infection. * Inadequate nutrition and poor handling practices can also increase susceptibility.

Question 35

Dx & Tx?

Answer 35

* Bacteriology and PCR Treatment * Currently, there is no direct vaccine for Moritella viscosa, but managing stressors like water temperature, stocking densities, and water quality can help reduce the incidence of the disease

Question 36

Control of white ucler dx?

Answer 36

Vaccination

Question 37

What other non-infectious dx can we see in fish?

Answer 37

Question 38

What vaccination options in fish farming?

Answer 38

- Immersion - Injection - Orally (top loading feed with vaccine)

Question 39

Antibiotics licensed?

Answer 39

Only oxytetracycline and florfenicol

Question 40

2 methods for slaughter?

Answer 40

- ELectrical - Mechanical (percussive stunning) should be followed nby hbleeding out

Question 41

Process of harvest?

Answer 41

1) Fasting – reduces metabolic rate, lowers O2 demand before live transport, reduces water fouling and improves hygiene of processing 2) Crowding – allows pumping or netting out of fish to move to place of slaughter. Need to be careful of oxygen levels, and exposure to high light intensity (location dependent). RSPCA suggest fish shouldn’t be crowded for >2hr before slaughter. 3) Moving – fish either slaughtered on farm or transported to a central plant. 4) Grading – Once dead fish are graded into superior, ordinary or rebate, dependent on carcass quality (shape, size, damage etc). As any other farm animal.