Mediterranean Farmed Fish Welfare. How good are we ?

Invited lecture by Dr. PANOS VARVARIGOS at the Scottish Fish Veterinary Society. Edinburgh meeting, April 2008.



Perception and expression of fish welfare

Behind welfare ethics

Current practice

Harvesting / killing

Man made diseases

Other related issues


Author: Dr. Panos Varvarigos
Freelance Veterinarian – Fish Pathologist, Athens, Greece.


Reproduction of this website (or parts of it) is illegal and strictly forbidden. No rights can be derived from this website.



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Perception and expression of fish welfare

Fish are sentient animals, capable of suffering pain, fear, frustration and even boredom. Fish feel distress by hunger, heat or cold, confinement, crowding and handling. They are also able of experiencing comfort and well-being as well as expressing preferences and learning. We do not know how fish experience the world and how they communicate, but we study how they adapt their physiology and observe their behavioural reactions. The continuous addition of new species in aquaculture furthers the knowledge gap for species specific information necessary to define and document welfare status.


The main fish species grown in the Mediterranean are:

Sea bass (Dicentrarchus labrax, family Serranidae)

Sea bream (Sparus auratus, family Sparidae).


Other farmed species comprise:

Sharp snout sea bream (Diplodus puntazzo), White bream (Diplodus sargus), Red porgy (Pagrus pagrus), Striped sea bream (Lithognathus mormyrus), Dentex (Dentex dentex), Pandora (Pagellus erythrinus), Corb or Shi drum (Umbrina Cirossa), Dover sole (Solea solea), Meagre (Argyrosomus regius).


Although physiological parameters (e.g. stress hormones) may be measured and correlated with external stimuli, thus indicating the status of wellbeing, it is the behavioural changes and the tendency to escape danger or seek comfort (fight for space, shelter and food) that actively express the will to satisfy needs. Despite not being quantifiable, it is these reactions that drive the need to secure a better living standard for the fish in culture.

Feelings and emotions (e.g. pain, fear, agony, sense of care), cannot be adequately assessed, so fish welfare is perceived as the fulfilment of biological needs for proper body functions (maintaining homeostasis) away from adverse environmental conditions and danger. Life in captivity comprises an artificial existence, to which the fish have to adapt.


In the field, we evaluate what we are able to observe, such as behavioural change, growth and health. Obscure physiological parameters, which, if measured, could have shown that homeostasis is upset, are not taken into account unless they express themselves as disease, awkward behaviour, reduced growth, inferior body condition, or bad FCR. Visible changes in colour, schooling and swimming behaviour, respiratory rate, response to feeding, presence of skin ulcers, fin erosion, haemorrhage, exophthalmia, abdominal distension, etc, are regarded as visible ill-signs associated with impaired welfare. If the faltering parameter is not rectified and welfare upgraded, disease outbreaks follow, due to compromised immune defences.


Farmed fish are forced to live in artificial confinement, far from their natural habitat.


Despite efforts to ensure adequate water quality and suitable feed it is hard to prove whether they are "happy animals".


Example: Intensive sole (Solea solea) rearing in land-based stacked tray-like basins.



Behind welfare ethics

Maintaining acceptable welfare status for the farmed fish is considered important because it safeguards fish health and efficient growth. It is seen as an insurance policy for profits. Only as such, the associated costs for upgrading technology and management may be justified.

For example, the agony of a painful death at harvest, past any moral standpoint, inflicts self-injuries and degrades the product (loss of scales, bleeding, abnormal skin colour as well as adverse muscle biochemical reactions reducing storage life). Therefore, it makes sense to try hard to minimise, or even avoid stress at harvest, by means of procedures that render fast insensitivity.

It seems that Mediterranean farmers treat their fish well because there are benefits to be gained (a 'contractarians' approach).

As regards the consumers' point of view, animal welfare has gradually become part of the total quality concept. It is not enough to produce high-quality meat unless it is documented and labelled that officially recognised welfare/ethical norms have been observed throughout production as well as harvest. This consumer driven necessity to treat fish "humanely" is strong in the Mediterranean countries where the fish are presented for sale mainly fresh, in the round and skin on. The consumer buys a whole dead animal, not just a skinless (or featherless) and/or boneless piece of its musculature.


Current practice

Question: Do Mediterranean aquaculturists practice environmentally sustainable and ethically sound fish farm management ?


Answer: Yes. Despite minor and ever diminishing exceptions, common sense management sustaining fish wellbeing, according to current knowledge is routine (expressed as good growth and health).


But more is needed:

There are gaps in the legislation and a profound lack of state interest and official controls.

There are only few, scattered and inadequate efforts in order to:

·    Establish sound, workable welfare indicators.

·    Devise a system for on-farm welfare assessment.

·    Draft and propose acceptable codes of practice.

The scarcity of funding local Institutions to carry-out species-specific research means that rules may relate to salmonid based research with inherent species-related flaws.

Fish welfare at present depends on the initiatives taken by individual companies, but there is no co-operation or consultations across companies, even among those operating sites on a single bay.


The pro-welfare actions that are in place:


Infrastructure and water (farm environment)

• Deep waters with adequate sea currents (sea).

• Modern spacious circular net cages (sea).

• Suitable borehole water, sometimes geothermal (land-based).

• Automated controls and water sanitation systems (land-based).



• Proper quality/size of dry diets for each species and age class.


Health management

• Prophylaxis (e.g. vaccination).

• Veterinary consultations (but there is scope for improvement).

• Disinfection (biosecurity) (but occasionally with outdated products).


Modern, spacious circular cages in open, deep waters.


Smaller rectangular cages are used as "helper cages" (arrows) for fish manoeuvring, partial harvest and handling (grading, treatments, etc.)


Stock management in need of more attention:


Stocking densities

The majority of the Mediterranean fish species are harvested at much smaller weights than salmon (350g to 650g), thus the number of fish per volume unit for a given biomass is much higher in comparison. While an acceptable upper limit for stocking salmon is 4 fish or 15-20 kg per m3, the respective limit for sea bream or bass is 20 fish or 7.5-10 kg per m3.

Smaller fish and fry do not utilise the space available to them but shoal and compete fiercely for food, necessitating wide dispersion of food, or multiple feeding points. Putting too many young fish in a large cage or nursery tank should be avoided. Despite a low biomass per volume ratio, crowding ensues, resulting in self injuries, fin erosion and skin lesions with opportunistic bacterial colonisation.


Handling and treatments:

·    Fry transportation (weighing, loading, transporting, delivering).

·    Grading and counting.

·    Bath treatments (crowding).

·    Vaccination.

·    Handling brood-fish.

Handling of brood-stock is performed only for brood-stock selection, because spawning is spontaneous under controlled conditions (photoperiod, water temperature) and fertilisation is natural in the brood-stock tank. There are no stripping or milking procedures for spawning and fertilisation of sea bass and sea bream.

Fish are sedated and subsequently anaesthetised for tagging, by means of microchips in the dorsal muscles, or by subcutaneous polymer colour tags. Mutilations (fin clipping) is impractical.


Examples of handling stress:

Bream and bass fry grader



Fry transport pump



Fry counter



Grading eels



Sea bass enclosed in a tarpaulin and sedated prior to complete anaesthetisation and injection vaccination



Anaesthetic overdose in the tarpaulin.


The common anaesthetic used is phenoxy-2-ethanol, which despite being safe and effective, has to be gradually added in the water, otherwise it irritates fish gills and skin hence, panic ensues among the enclosed sea bass.




Immersing sea bass in anaesthetic dilution until completely immobile (deep anaesthetisation) prior to injection vaccination.



Injection vaccination of sea bass under deep anaesthesia.





The most controversial welfare issue

Harvesting / killing


Procedures prior to killing include severe handling, such as partial netting, or swimming the fish into a smaller 'helper' cage and crowding. Such handling, no matter how gentle, invariably results in welfare degradation. If performed haphazardly, it has a negative impact on quality (abrasions, haemorrhage, muscle biochemistry leading to shorter time to rigor mortis).

During crowding panic ensues, characterised by strong escape attempts and mainly burrowing (sea bass), resulting in snout and/or eye damage. Partial cage harvest, or release of crowded fish back to their cage, after an aborted harvest attempt, should be avoided.

A three day fasting period should normally precede harvest. It may be stressful, but partly offsets the stress and hardship of harvest itself. (It also enhances product quality and prolongs storage life).

No stunning or sedation is performed prior to lifting the fish out of the water. Fish are killed by means of a cold shock, by immersing them in an ice-water slurry mixture (2:1:1 - Ice/Water/Fish) with temperature no higher than 4oC.


Killing by cold shock


On-farm experiments by the GMA (Greek Maricultures Association) have indicated that the abrupt drop in temperature by more than 16oC, shocks the fish in ~10 seconds. A state of apparent unconsciousness (complete immobility and lack of any reactions to external stimuli) is evident after 3-5 min. Sea bream is more susceptible to cold shock than sea bass of the same body weight and age and under similar field experimental conditions. Sea bream collapses completely after 3-4 min as opposed to 4-5 min for sea bass. Under no circumstances are live fish packed in ice.

Killing by cold shock precedes transport to the packing plants; where weighing, sorting and packing with ice take place. However, it does represent the initiation of the 'cold chain' for the harvested fish.


Sea bass caught from their cage with a purse net and off-loaded in ice slurry causing cold shock and expected insensitivity within 10 sec.


The "cold chain" of the products to the market starts here.


Stunning/killing alternatives

·    Narcosis with CO2 causes alteration of gill coloration (brown instead of bright red), which is unacceptable by the Mediterranean consumer. (The fish are not bled and the bright red colour of the gills is a fundamental characteristic of freshness.)

·    Electrocution requires a vast amount of energy due to the high conductivity of sea-water (salinity at 38-40ppt) and electric power is not available in all cage sites (an underwater cable would be necessary).


Man made diseases

There is direct relation of husbandry with fish welfare. Frequent repercussions of mismanagement or occasional negligence comprise:

·    Suffocation during transport (water quality degradation).

·    Skin injuries and fin erosion during transport (excessive biomass density per m3).

·    Handling trauma (careless net manoeuvres, grading, etc.).

·    Over-feeding and lipoid liver degeneration (feeding ad libidum with energy rich diets all year round).

·    Sea bream winter syndrome (feeding fatty diets during the cold season).

·    Chronic copper poisoning (careless use of copper-based antifouling agents to impregnate the pen nets).

·    Excessive antagonism for food leading to behavioural hierarchies and marginalization of the less active fish in the cage (improper stocking).

·    Gas supper-saturation (inadequate degassing of pumped borehole water).

·    Nefrocalcinosis (high biomass density with simultaneous supply of liquid oxygen to sustain it).


Examples of man-made problems:

Copper and copper compounds leach in the water from copper oxide based antifoulants which are used to impregnate nets.

These products contain 18-20% copper oxides.


Chronic copper toxicity is frequently diagnosed by staining blood smears. Intoxicated erythrocytes are bent or spindle shaped.





Gas supersaturated water on land based installations can cause gas bubble disease, whereby bubbles are formed and trapped within soft tissues. When gills are affected by gas bubble embolism the condition is fatal.



Nefrocalcinosis is induced in nursery units when fry are overcrowded while liquid oxygen is injected in their water to sustain respiration and metabolism.

However, excessive amounts of carbon dioxide are also produced, the water pH drops, fish blood acidifies and renal calculi (often CaCO3) are formed. These may be diagnosed by X-ray mammogrammes.


When the kidney osmoregulatory function is impaired, skin ulceration is provoked.



Overfeeding sea bass with energy rich diets results in excessive visceral fat deposits and fatty degeneration of the liver.

Such fish are prone to infectious diseases, such as vibriosis.





Sea bass fingerling with inflamed and ulcerated skin due to deteriorated water quality during prolonged transportation.



Skin wounds and fin erosion due to hardship during partial harvesting of net pens (some fish get trapped in the nets, or panic and collide with one another and onto the netting.

(Above: meagre, below: sea bream.)






Other issues related to welfare

·    Genetically engineered fish (transgenics).

o  Questioning whether genetic manipulation is compatible with welfare ethics.

o  Concerns as regards escapes of transgenic fish into the wild.

·    Intensive phenotype-based breeding.

o  Concern when traits of highly productive fish escape.

·    Organics

o  Welfare incompatibilities concerning disease treatments.

·    Environmental impact of fish farms.

o  Farms should not foul their own existence (e.g. antifouling paints polluting sea and sediment with copper).

·    Predator control.

o  Intrusion prevention, but with no harm to predators (sea birds, seals, dolphins).


Concluding remarks

Fish health is the central key component of any welfare regulations, guidelines or farming codes of practice. The EU recommendations describe common sense tactics to ensure healthy fish and unhindered growth, considering these to be the most prominent welfare indicators.

These recommendations do not add much to current practice, nor to the improvements that are being put in place for farming to remain viable/profitable.

In the lack of solid species-specific biological evidence, perceptions of fish welfare vary among countries, cultures and individual people.

Views are shaped by the apparent intensity of fish reaction and sustained harm when exposed to evidently adverse conditions.

Mediterranean aquaculture would welcome and has the capacity to adapt to an 'International Code of Practice for Ethical Aquaculture', but with species-related provisions.

Projects, like the EU funded 'Benefish' are expected to provide proof that such a move is not only theoretically desirable, but profitable and sustainable, consistent with modern science.


Author: Dr. Panos Varvarigos
Freelance Veterinarian – Fish Pathologist, Athens, Greece.


Reproduction of this website (or parts of it) is illegal and strictly forbidden.
No rights can be derived from this website.


Every effort has been made to ensure that the information is accurate until the date of last editing. It is based upon the accumulated personal experience of applied veterinary work. The author cannot take responsibility for incorrect interpretation or any resulting consequences. The contents may be used as an educational guide and are definitely not meant to become a stand-alone diagnostic tool or operations manual.


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