Aquatic Animal Production

Question 1

What two factors does mussel growth rely on?

Answer 1

• The presence of natural plankton

- A stable natural habitat

Question 2

Describe the process of wild harvest mussels

Answer 2

Mussels grow naturally in large beds either subtidally or between the tides. Wild harvest of mussels occurs in many areas by towed dredge or hand-raking at low tide.

Question 3

Describe the process of mussel farming

Answer 3

Mussel farming can be carried out by cultivation on the seabed or using suspended culture. This involves locating and fishing seed mussel of around 10mm shell length from offshore beds and then relaying in a more productive and protected location, termed a ‘lay’, set aside for this purpose.

Question 4

Describe a Lay

Answer 4

A more productive and protected location for mussel farming, termed a ‘lay’, set aside for this purpose.

Question 5

Describe suspended culture mussel farming

Answer 5

In suspended culture, the mussels are cultivated on a system of ropes and floats where they grow until harvest 18-24 months later.

Question 6

Give the 5 EU End Product Standards for mussels

Answer 6

This states that mussels should be:

Alive;
Fresh and in good condition;
Contain inter-valvular fluid;
Respond to a sharp tap;
Meet specified bacterial and toxin standards

Question 7

Describe the activities of the Scottish Shellfish Marketing Group

Answer 7

Co-operation of shellfish farmers who co-ordinate the marketing and sales of their shellfish to the customer.

Question 8

Give the three institutions involved in licencing of scottish fish farms

Answer 8

Planning Permission from local regional Council

Marine Licence from Marine Scotland Discharge license from Scottish Environment Protection Agency (SEPA).

Question 9

What determines MAB?

Answer 9

Maximum Allowed Biomass (MAB) for individual sites is determined based on the environmental concerns, namely the capacity of the local marine environment to accommodate the fish farm.

Question 10

What organisation determines production limits for fish farms?

Answer 10

Competition Commission Authorities

Question 11

Describe the salmon farming process

Answer 11

In salmon production system, juveniles (smolts) are produced at specialised freshwater hatcheries. Once they reach six months of age they are introduced to seawater cages. Finally, they are harvested at 2+ years of age (weighing 2-3 kg).

Question 12

What is the name for a juvenile salmon?

Answer 12

Smolt

Question 13

At what age and weight are salmon harvested?

Answer 13

2+ years

2-3 kg

Question 14

What is the most commonly farmed trout in the uk?

Answer 14

Rainbow trout - harvested at 300-400g

Question 15

What is the term for a juvenile trout?

Answer 15

Fingerling

Question 16

Describe the trout farming system

Answer 16

Hatcheries: they are specialised in producing juveniles (fingerlings) to be sold to ongrowing farms. Their number is reduced.
Onwrowing farms: They produce the final product. There are more than 300 trout farming sites in UK. All very variable in size and practices

Question 17

Why is all of the UK rainbow trout stock female?

Answer 17

5.4. Rainbow trout broodstock
All rainbow trout stock in the UK is female. This is because they can growth to the desired weight (300-400g) without reaching sexual maturity. When reaching sexual maturity, the growth rate of trout will slow down and also there will be condition loss at spawning time.
Males reach sexual maturity below the 300g and then stop growing and loss condition. Hence it is preferred not to use them.

Question 18

How are trout reproduced for farming

Answer 18

Males kept as brood stock are killed and then stripped of milt. Females are stripped of eggs while they are alive. Eggs are then fertilised.

Question 19

Describe the production of triploid trout

Answer 19

Triploids: Eggs can be subjected to temperature or pressure shock in order to induce triploidy (sterile/no sexual maturity). That’s normally done when larger/heavier trout are required (beyond 400g).

Question 20

Give the 6 keky stressors in aquaculture environment

Answer 20

Water ­quality: contaminated water can make it hard to breathe.
Crowding: intense crowding can result in cannibalism.
Handling: invasive handling results in stress in poor health.
Disturbance: farm workers and wild animals.
Nutrition: nutritional deficiencies can weaken the immune system and affect development (e.g. spinal deformities).
Hierarchy: inability to form a stable social hierarchy, resulting in cannibalism.

Question 21

How are many diseases prevented in fish farms?

Answer 21

Prevention of many diseases is achieved through vaccination at an early stage and during freshwater. Vaccines are widely used commercially to reduce the risk of health challenges.

Question 22

Describe the pathology of sea lice and their management in fish farms

Answer 22

They can infect the salmon skin and if not controlled they can cause lesions and secondary infection. Sea lice are controlled through good husbandry and management practices, cleaner fish (different wrasse species and lump suckers, which eat the lice off the salmon) and when necessary licensed medicines.

Question 23

Describe pancreas disease in fish(include cause, symptoms and treatment)

Answer 23

PD is caused by the Salmonid Alphavirus and is present in Europe. It is a contagious virus that can cause reduced appetite, muscle and pancreas lesions, lethargy, and if not appropriately managed, elevated mortality. PD affects Atlantic salmon and Rainbow trout in seawater and control is achieved mainly by management and mitigation practices. Vaccination also available.

Question 24

Describe Salmonoid riskettsial septicaemia in fish(include cause, symptoms and treatment)

Answer 24

SRS is caused by an intracellular bacteria. It occurs mainly in Chile but has also been observed, but to a much lesser extent, in Norway, Ireland and the UK. It causes lethargy, appetite loss and can result in elevated mortality. SRS is to some extent controlled by vaccination, but medicinal intervention (licensed antibiotics) may also be required.

Question 25

Describe Heart and Skeletal Muscle Inflammation in fish(include cause, symptoms and treatment)

Answer 25

HSMI is currently reported in Norway and Scotland. Symptoms of HSMI are reduced appetite, abnormal behaviour and in most cases low mortality. HSMI generally affects fish the first year in seawater and control is achieved mainly by good husbandry and management practice

Question 26

Describe Infectious Salmon Anaemia in fish(include cause, symptoms and treatment)

Answer 26

ISA is caused by the ISA virus and is widely reported. It is a contagious disease that causes lethargy, anaemia and may lead to significant mortality in seawater if not appropriately managed. Control of an ISA outbreak is achieved through culling or harvesting of affected fish in addition to other biosecurity and mitigation measures. Vaccines are available and in use where ISA is regarded to represent a risk.

Question 27

Describe Infectious Gill disease in fish(include cause, symptoms and treatment)

Answer 27

GD is a general term used to describe gill conditions occurring in seawater. The changes may be caused by different infectious agents; amoeba, virus or bacteria, as well as environmental factors including algae or jelly-fish blooms. Little is known about the cause of many of the gill conditions and to what extent infectious or environmental factors are primary or secondary causes of disease.

Question 28

Describe three effects of fish farming on local aquatic environments

Answer 28

Reduced O2: Water returning to the system will have a lower concentration of oxygen.
Nitrogenous waste products: The presence of large populations of fish can result in a higher levels of nitrogen in water and eutrophication.
Chemical/drugs: Residues of drugs/chemicals used in fish farming could be present in water and contaminate the environment.

Question 29

Describe the fish processing line

Answer 29

Gutting & deheading: Removal of viscera and head.
Desliming: Removal of fish slime in order to improve presentation of the product. Some equipment in highly mechanised plants use high water pressure, to wash and rinse the product. Removal of slime also reduce the bacterial.
Weighing
Filleting: Cutting the fish in filets. It can be done manually or mechanically. Efficiency of the process is essential in order not to affect the yield.
Trimming: Trimming methods vary from one factory to another, depending on factors such as throughput, labour costs, and traceability requirements. Systems range from highly advanced automatic systems to basic manual trimming. Most manual lines are designed as active lines, whereby trimming is conducted on the conveyor belt while it is running, with throughput depending on fish size and trim level.
Pinbone removal.
Skinning.
Fillet washing: Prior to packing, freezing, or further handling, a washing unit could be used to rinse off any slime, blood, and any remains from the filleting, trimming, and pinboning processes. This process can also reduce the total count of bacteria.
Grading

Question 30

Describe D.latum (where its found, zoonotic risk, type of pathogen)

Answer 30

Its plerocercoid is found in musculature and viscera of a variety of fish species (marine and freshwater). Other animal species, such as birds, bears, seals, walruses and dogs can be part of the cycle. Humans are not the end host.
The parasite can be found in the mucosa of ileum and jejunum of infected humans. The infection is usually asymptomatic. However, it could cause malabsorption, anaemia and weight loss.
As this is a cestode, praziquantel is the election treatment in infected humans.

Question 31

Describe Anisakis (where its found, zoonotic risk, type of pathogen)

Answer 31

Anisakis spp.has a complex lifecycle involving marine crustaceans, fish, squid and mammals. Larvae can be found in viscera and muscle of many fish species. The definitive hosts are marine mammals.
The adult nematode can be found in the intestine of infected humans.

There is a non-invasive and an invasive form.

Non-invasive form: asymptomatic.
Invasive form: severe reaction, including bloody stools, nausea, ulcers.

Question 32

Give the name of the pathogen that causes the condition Aquarists finger and describe the symptoms

Answer 32

Mycobacterium marinum is a ubiquitous resistant bacteria which causes disease in ornamental fish. It is commonly known as aquarist’s finger.

In humans can cause a cutaneous nodular lesions in humans, which is normally wound associated. Antibiotic treatment has a slow response.

Question 33

Describe algal toxins (where its found, zoonotic risk, type of pathogen)

Answer 33

Filter feeding shellfish accumulate these toxins within their flesh, posing a risk to human health if they are consumed

Diarrhetic shellfish poisoning (DSP): Persistent problems in some UK coastal areas.

Question 34

Give 4 methods used to control zoonotic infections from aquatic species to humans

Answer 34

Freezing, cooking, water depuration as well as cleaning and disinfection of the equipment in food processing plants can have a positive effect on food safety.

Question 35

What organisation monitors biological and viral contamination of bivalve molluscs?

Answer 35

Centre for Environment, Fisheries and Aquaculture Science (Cefas)

Question 36

Describe the effect of freezing on fishery products

Answer 36

Certain fishery products destined to be eaten raw in dishes (such as sushi or cold smoked) need to be frozen before use. This is to protect consumers against parasites, unless certain risk-based freezing exemptions can be applied.

Question 37

Describe the process of freezing treatment

Answer 37

• 20°C for not less than 24 hours

- 35°C for not less than 15 hours

Question 38

Describe the process of water depuration and what it works well against

Answer 38

In good farming systems, shellfish are held in tanks of seawater that is continuously pumped through an ultraviolet chamber.
Depuration works well for bacteria. Bacteria of concern are normally faecal contaminants, hence they are excreted and present in the water and they can be exposed directly to the UV light and killed.