Intensive Fish Production 2 Flashcards
How to we do health moniotring in fish?
- Observe behaviour - mov, history/records on farm
- Examine environemnt - fish size, quality etc
- Select your fish - avoid all dead fih autolysis rapid, avoid taking biggest, pick moribund fish and ‘normal’ ones
- Macroscopic analysis - gills, skin , eyes etc
- Gills, organ samples, mucus, skin scrapes
What is the only diagnostic tool in aquaculture?
HISTOPATHOLOGY
What main parasites in fish?
- Salmon Lice (Caligus elongatus/
Lepeophtheirus salmonis) - Amoebic gill disease
- Invisible dx -> Ichtyophtirius multifilis ‘white spot’
What important fungi?
Saprolegnia
Important bacteria?
- Aeromonas salmonicida
- Moritella viscosa
What two types of sea lice?
- Caligus elongatus – affects >80 species
of fish - Lepeophtheirus salmonis – specific to
salmonids, immunomodulate the host
increasing susceptibility to secondary
infection
What do sea lice do?
feed on skin, mucus, and blood if acheivable
What tx options for sealice?
What practices to reduce exposure of salmon to lice?
- Single year stocking
- Site fallowing/rotation
- Improved site selection
- Genetic improvements
- Improved farm hygiene
What other potential sea lice prevention?
- 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
What causes Amoebic Gill dx ?
Causal agent - Neoparamoeba peruans
* Amoeba that survives in sediment, net
pens and the water column
What does Gill dx cause?
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.
Gill scoring?
Histology on Gills?
- Top – Normal
- Bottom – extensive lamellae hyperplasia
and mucus cell proliferation - Arrows = Amoeba
AGD causes …?
severe CV compromise,
and if environmental conditions are
unfavorable, can cause severe
mortality events >50% of stock.
What factors/ risks of AGD?
- High salinity (>32ppt)
- High temperatures
- Co factors – jellyfish/algae blooms
- Biofouling of nets – reduces water
turnover and Oxygen availability. - Smolt quality and size
AGD tx optionS?
- Freshwater - 8% of all tx in scotland
- Hydrogen peroxide (biggest one)
- Emergency harvest
describe freshwater tx?
- 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
Describe hydrogen peroxide tx?
- 18-22 mins at 1200ppm, 8-15oC
- Can see high levels of morts if disease is severe
What is Ichthyophthirius multifilis?
‘WHITE SPOT’
- Enedemic to every waterr source
Stage of parasite lifecycle of’white spot’?
- 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.
Tx for ‘white spot’?
- Formalin – upto 170ppm for 1 hour.
- Known carcinogen – PPE!
Saprolegnia?
Water mold – affects freshwater systems
* Huge problem in hatcheries
* Opportunistic and always secondary pathogen
What does saprolegnia do?
Invades superficial tissue and secretes
immunomodulatory compounds
Number of spores is directly proportional to the rate
of infection.
Usually causes mortality through haemodilution
Tx for Saprolegnia?
- 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.
What does Furunculois/ Aeromonas Salmonicida cause?
Causes sudden onset:
* Depressed appetite
* Behaviour change
* Appearance change
* Haemorrhage
* Increased mortalities
Dx of Furunculosis?
Routine bacteriology and histopathology
Prevention of Furunculosis?
- Effective vaccines have reduced prevalence
significantly
Tx for furunculosis?
- 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.
What is Moritella viscosa/Winter ulcer dx?
Bacteria – M.viscosa
* Gram negative rod
* Favours high salinity and cold temperatures <8ᵒC
MOA of winter ulcer dx?
- 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.
CLS f winter ucler dx?
- 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.
Pathophysiology?
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
Risk factors?
- 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.
Dx & Tx?
- 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
Control of white ucler dx?
Vaccination
What other non-infectious dx can we see in fish?
What vaccination options in fish farming?
- Immersion
- Injection
- Orally (top loading feed with vaccine)
Antibiotics licensed?
Only oxytetracycline and florfenicol
2 methods for slaughter?
- ELectrical
- Mechanical (percussive stunning)
should be followed nby hbleeding out
Process of harvest?
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.
