Fish Flashcards
Comparison to terrestrial farming
- In some systems FCR ratio can be < 1.0, gaining kilo of meat for less than kilo of food; FCR 1.3 in Atlantic salmon in Scotland, lower carbon footprint
- Most resource-efficient animal protein
- Selective breeding only occurred for 14 generations
Species of farmed fish
(In order of most popular, > 600 species)
- Carp
- Tilapia
- Catfishes
- Marine shrimps
- Salmons
- Marine fishes
- Freshwater crustaceans
- Trouts
- Milkfish
- Eels
Production of fish
- Majority of world’s fish are extensively in Africa + Asia in freshwater ponds
- Transition from extensive to intensive -> inc stocking density, natural productivity dec (algae, phytoplankton) , exogenous feeding inc
- European intensive aquacultures - predominance for cage aquaculture + inc in recirculating aquaculture system (RAS)
- Norway, Chile, Scotland = world leaders in industry
Extensive fish farming
- Natural food only - relying what is in the pond, algae, plankton
- African + Asian farming
- Possibly w/ fertilisation
- Low stocking density
Semi intensive fish farming
- Natural food w/ fertilisation
- Possibly w/ supplementary feeding
Intensive fish farming
- Usually dependent on complete artificial feeds
- High stocking density
Intensive production considerations
- Complete diet - meets all nutritional requirements
- Additional supply of oxygen - inc water flow, inc aeration + oxygenation (most effective at high stocking densities) (mechanical failure can cause big problems)
- Removal of metabolic waste + uneaten feed
- Pathogen control
- Behaviour + welfare considerations
Concept of ‘Degree days’
- Fish = poikilothermic (cold-blooded) - rate of metabolism depends on temp of environment
- Higher the temp, higher metabolism
- Used for estimating breakdown of drugs + fish developmental stages
- E.g. Statutory minimum withdrawal of AB = 500°D
- E.g. 2 Atlantic Salmon eggs take 250°D to reach ‘eyed’ stage (neural chord visible)
- 25 d at 10°C = 250°D / 50 d at 5°C = 250°D
Salmon lifecycle
Egg -> Alevin -> Fry -> Parr -> Smolt -> Adult
- 1). Adult broodstock carefully selected
- 2). Females stripped of eggs, males stripped of milt (sperm-containing fluid). Usually based on strict genetics to maintain healthy stocks
- 3). Fertilisation
- 4). 250ºD to eyed eggs = neural chord visible
- 5). 250ºD to hatching
- 6). 300ºD to first feed (yolk sac runs out and alevins become fry)
- 7). Fry become parr at roughly 5 - 10cm long
- 8). Smoltification occurs (adapt from freshwater to seawater), depending on system. Can be achieved in 6 - 9 months by altering light and photoperiod. These stages are commonly in RAS facilities
- 9). Once fish are smolts, they need to be transferred to seawater. It is common at this stage to move fish from RAS facilities to sea or loch sites
- 10). By 2 years old salmon should be around 5 - 5.5kg and ready for harvest, or selection as brood stock.
- 11). If selected as broodstock, a series of genetic tests will happen, and only the best will be retained. Can reach as big as 15 kg by stripping
- 12). Whole cycle of egg to egg currently takes 3 - 4 years
Hatcheries - key aspects + factors
- Year round production is key to profitable production
- Most systems need 2 - 3 egg inputs per year
- Varies hugely dependent on system type
- High quality genetics
- Exceptional biosecurity (Fungus is a huge issue)
- High quality brood stock
- High quality environment
- High quality management + husbandry
Hatcheries
- Once selected, a 10 kg female can produce upwards of 20,000 eggs
- E.g. Hatchery in Iceland has the capacity to hold up to 400 million eggs at one time
- Eggs are disinfected in an iodine solution (0.01%) for 10 mins prior to being ‘laid down’ at 3 - 5 ºC
- Dead eggs should be removed to avoid fungus proliferation
- Hatch time varies hugely between species Eggs hatch around 500ºD later
Where is the lifestyle of salmon manipulated?
- 1). Early sexual maturation of salmon
- 2). Smoltification
Early sexual manipulation of salmon
- Once fish matures, energy is directed toward gondadogenesis (egg/sperm development), rather than growth, and the quality of the carcass drops dramatically
- To allow fish to continue growth to harvest weight, maturation must be delayed - by production of sterile fish, or monosex cultures
- Problem in aquaculture industry - quality of carcase drops as going to be smaller
Smoltification
- Smolt = stage where anatomical changes occur to adapt to living in saltwater; metamorphosis in response to inc daylight following the winter (spring time)
Changes seen in smoltification
- Chloride cell proliferation - actively transport Na+, Cl- + K+ out of the tissue - plasma chloride levels
- Na+-K+- ATPase pump reversed
- Endocrine changes
- Molecular isoform changes alpha to beta
Testing if smolts are ready for sea
- Measure gill Na-K-ATPase activity via enzyme assay
- Measure plasma chloride levels via blood sample
- Test if live in saltwater
- Advanced testing - molecular testing, gene testing, ratio calculations
Smoltification manipulation of salmon
- Conversion of Parr to Smolt occurs with some anatomical changes
- Smoltification is initiated by a decreasing day length (Autumn/Winter)
- Then completed on an increasing day length (Spring/Summer)
- Most systems (RAS facilities) alter daylight and temperature provided to the tanks, and give an artificially short winter of 6 - 8 weeks
- This can result in smolts being ready for sea transfer in 6 - 9 months, an advance of 3 - 6 months
Why are only females selected?
- Male aggression
- Male anatomy changes + can cause more damage to self + others, e.g. hooked jaw
- Males must be harvested before maturation
Production of sterile fish - ‘neo-males’
- Eggs hatch from XY x XX -> swim up frey fed 17a methyltestosterone for 75 d until 2 g
- Now all fish phenotypically male, converted males retrieved - have deformed gonads + hand-stripped of milt
- Converted male bred (XX) w/ normal female (XX) -> all offspring have XX -> heat/pressure shock => only produce females
Production of sterile fish - triploidy
- = 3 full sets of chromosomes = entirely sterile
- Achieved by heat/pressure shocking eggs that have been fertilised as normal
Adv - Higher growth rates, no energy channelled into maturation, although males can develop 2y sexual characteristics + larger gonadal growth
- Salmon farms - if fish escape, no genetic introgression to wild salmon stocks
Disadv - More susceptible to disease
- Poorer welfare
Grow out
- Freshwater RAS systems transferred to seawater systems at smoltification
- At any given site, there can be upwards of 30 - 50,000 fish per pen, and as many pens as 20 per site. (Sometimes upwards of 1 million fish per site!)
- Stocking densities typically < 15 kg/m^3, resulting in a 98.5 : 1.5 ratio
- A variety of cage/pen types, metal squares are typically used in sheltered sites, and polar circles are used in exposed sites
- Huge technological and engineering inputs – work boats, well boats, treatment boats, lighting, automated feeders, cameras, feed barges etc.
- Feeding can be either at the surface or at depth
- Fish are cropped, harvest of the largest fish, allowing smaller fish to grow quicker
- General harvest weight will be 5 - 5.5 kg
Sea lice
- Most economically sig to affect Atlantic salmon > £700 million globally per year
- Caligus elongatus - affects > 90 species of fish, less host-specific
- Lepeophtheirus salmonis - specific to salmonids, (salmon + trout) immunomodulate the host, inc susceptibility to 2y infection
- Feed on skin, mucus + blood if achievable
Sea lice - Tx + management
- 1). Vet med - Emamectin Benzoate in feed, organophosphates - v effective historically , act immediately but v expensive, poor environmental impact, widespread resistance, withdrawal periods, poor public image
- 2). Biological, cleaner fish - ballan wrasse + lumpfish, ratio 25 : 1, salmon to cleaner fish ratio, effective - predate on lice + remove from salmon
- 3). Mechanical, car wash - fish passed through system of water jets to remove lice, small mortalities seen if high burden
- 4). Thermal, thermolicer - fish moved through warm water where lice drop off + die
- 5). Chemical, hydrogen peroxide - tarpaulin Tx method, dilutes water + O2 so minimal environmental impacts
Amoebic gill disease
- 2nd biggest issue
- Causal agent = Neoparamoeba peruans, amoeba that survives in sediment, net pens and the water column - hard to get rid of
- Causes gill damage - > epithelial thickening, reduced oxygen uptake, excessive mucus production. (Exacerbated by higher water
temperatures – hence warming oceans is a big problem for the salmon industry) - Devastating disease, causing huge losses in Scottish industry
- In 2011 an outbreak caused loss of 13,600 tonnes of salmon, a loss of approximately £54 mil
Amoebic gill disease score monitoring
Gill scores recorded weekly
- 0 = No sign of infection, healthy colour
- 1 = white spot, light scarring or necrotic streaking, few white discolourations
- 2 = 2 - 3 spots, small mucus patch
- 3 = Established thickened mucus patch/spot groupings up to 20% of gull surface area, think of emergency harvest - cull stock + harvest what you can - will have compromised CVS if make it through lice Tx
- 4 = Established lesions covering up to 50% of gill SA
- 5 = Extensive lesions covering most of gill SA
Amoebic gill disease - histopathology
- Only true Dx
Ichthyophthirius multifilis - ‘ white spot’
- ‘Ich’ - endemic to almost every single water source, both fresh and sea
- Parasite stage - theront = Easiest stage to treat, covered in cilia + replicates in epithelium
- Encysted stage – tomont - leaves fish host, settles in substrate to encyst, hard to get rid of, in all water sources
- Replication – cysts undergo binary fission to produce tomites, which then differentiate into theronts
- Treatment = Formalin – up to 170 ppm for 1 hour, known carcinogen – PPE!, contradictory Tx
Saprolegnia
- Water mold – affects freshwater systems
- Huge problem in hatcheries
- Opportunistic + generally secondary pathogen
- Invades superficial tissue + secretes immunomodulatory compounds
- Number of spores directly proportional to the rate of infection
- Usually causes mortality through haemodilution
Aeromonas Salmonicida - Furunculosis
- Ulcerative bacterial disease
- Causes sudden onset: depressed appetite, behaviour change, appearance change, H+, inc mortalities
- Dx - routine bacteriology + histopath
Aeromonas Salmonicida - Furunculosis
- Prevention - effective vacc, reduced pravalence
- Oxytetracycline in feed (only licensed AB in aquaculture, alongside Florenicol)
- Prevents spread rather than Tx those affected, reduce spread in stock
Non-infectious disease - genetic
- Not common in wild - don’t survive
- Common in farmed
Aquatic public health - zoonoses
- Main zoonotic disease of concern is Fish TB
- Caused by Mycobacterium spp.
- People infected though open wounds if working w/ infected fish or water
- Treatment can be problematic - may need protracted chemotherapy
- Control in stocks based on exclusion and destruction of infected stocks
- Drugs not used - costly and resistance is high
Anisakis - worms usually killed by freezing or cooking. Mainly reported in Japan, where raw fish is consumed frequently
