Aquatic VPH (Foor Borne Parasites & Other Food Safety Risks)

What fish produce a majority of the food poisoning?

• Finfish - low risk

• Main risk is fro raw or lightly processed fish

• Poisoning from shellfish is more common

• No evidence of any difference between wild or farmed

Are there meat inspectors for fish?

No - EHOs inspect

What are the main causes of fish spoilage?

• Autolysis

• Enzymes in fish lissue break down muscle after death.

• Leads to softening and off-flavours.

• Bacterial Growth

• Environmental flora (Pscudomonas, Acromonas, Vibrio) multiply quickly.

• Produce slime, odours, and discoloration.

• Storage Conditions

• Warm temperatures accelerate both autolysis and bacterial growth.

• Poor handling (delayed chilling, dirty water) worsens spoilage.

• High Water Content of Fish Flesh

• Creates ideal conditions for bacterial activity.

• Rapid chilling essential to reduce spoilage

Common bacterial flora of the fish include…?

• Reflects the aquatic environment

• Common genera: Aeromonas, Flavobacterium, Pseudomonas, Vibrio, Serratia, Photobacterium, Clostridium, Bacillus

• Some act as spoilage organisms

• Others can be opportunistic human pathogens

• "Natural" contaminants (environmentalbacteria)

Clostridium, Aeromonas

• "Unnatural" contaminants (hygiene failures)

Staphylococcus aureus

E. Coli

Salmonella

Does cold-smoking, curing and other light processing eliminate bacteria?

No

What are some ways we can reduce bacterial contamination in fish?

• Pre-harvest fasting to reduce gut content

  • Temperature influences metabolism

• Hygienic slaughter & handling

• Rapid chilling using potable, chlorinated water

• HACCP: high-risk vs low-risk separation

• Removal of biofilms by effective disinfection

• Environmental & product microbiological monitoring

What are the main features of Vibrio bacteria?

What are the main features of Listeria?

What are the main features of Clostridium?

What are the main features of salmonella?

What are the main features of Anisakis simplex (Herring worm)?

• Humans are accidental host, fish are a secondary host

• Cooking, freezing and immediate gutting control

What are the main features of Diphyllobotrium latum?

Cestoda

• Cysts: white, visible on fish intestines; heavy infection → viscera may fuse. • Inactivation: killed by normal cooking & freezing; cysts disappear if fish moved to seawater.

Transmission: humans infected by eating raw/undercooked fish. Development in humans:

• Plerocercoids attach to intestine. Adults can exceed 10 m, with >3,000 proglottids.

• Each worm can release up to 1 million eggs/day. Eggs appear in faeces 5-6 weeks post-infection.

What are the main features of Fasciola hepatica and Opisthorchis?

Trematode

• One other important species is Fasciola hepatica - man may also be infected by F. hepatica through the ingestion of contaminated vegetation such as watercress.

Watercress beds and other aquatic plants that are commonly consumed raw can become contaminated with faeces containing the eggs of liver flukes.

Describe the main features of Giardia lamblia.

Describe the main features of Norovirus in shellfish.

Infection - which is why it takes a bit to develop (Inclubation)

Poisoning - immediate due to toxins

Describe the main features of Hepatitis A in shellfish.

What are the main biotoxins produced in shellfish?

Diarrhoeic food poisoning (DSP)

• Phytoplankton Dinophysis, Prorocentrum Bivalves concentrate the toxins produced by the plankton

• Range of heat-stable toxins - Okadaic acid, lactones, yessotoxins

• 1 hour after ingestion - diarrhoea, nausea, vomiting abdo pain. Recover in 3 days

Paralytic shellfish poisoning (PSP)

• Dinoflagellate Alexandrium

• Bivalves accumulate saxitoxins (many forms) - neurotoxins

• Numbness, paralysis, inco-ordination.

• Recovery within a few hours

Amnesic shellfish poisoning (ASP)

• Also known as domoic acid poisoning (amnesia not always a symptom)

• Bivalves - especially scallops

• Potent neurotoxin caused by diatom

• Pseudo-nitzschia pungens forma multiseries

• Destroys nerve cells causing cramps, disorientation, vomiting and memory loss

What are the risks of heavy metals in aquatic foods?

Industrial discharge, mining, agricultural runoff, natural sediments

• Key metals of concern

• Mercury (Hg) - bioaccumulates in predatory fish (e.g. tuna, swordfish)

• Cadmium (Cd), Lead (Pb), Arsenic (As) → can contaminate shellfish and benthic feeders

Health risks

• Mercury → neurotoxicity, risk to foetal development

• Cadmium/Lead → kidney damage, bone toxicity

• Arsenic (inorganic forms) → carcinogenic potential

Trends

• Farmed fish generally have lower levels due to controlled diets and shorter grow-out periods

• Wild, long-lived predators have highest concentrationsControlsMaximum residue limits (MRLs) set by legislationMonitoring of seafood supply chains

Dolphins - big concern is heavy metal, specifically methylmercury, high levels recorded

What are important considerations for drug resides in aquaculture?

• Risks

• Allergic reactions in sensitive consumers

• Contribution to antimicrobial resistance (AMR)

• Controls

• Maximum Residue Limits (MRLs) set by legislation (EU, FDA, etc.)

• Withdrawal periods ensure fish are free of residues before harvest

• Routine monitoring of aquaculture products

• Trends

• Residues are rare in regulated aquaculture if guidelines are followed

• Greater risk in regions with less strict regulation or oversight

What is taint in fish?

Unwanted flavour or odour in fish flesh.

Unnatural causes

• Chemical pollutants (e.g. petroleum from oil spills)

• Agricultural or industrial contaminants

Natural causes

• Bacterial or algal metabolites

• "Earthy" flavours in trout & catfish from cyanobacteria and phytoplankton (e.g. geosmin, MIB)

• Some produced by bacteria

Why do farmed fish have lower parasite burdens and contaminant levels?

Low Parasite Burdens

Controlled environment

• biosecurity, water treatment, and feed management reduce exposure.

No access to intermediate hosts (e.g. copepods, snails) that are common in natural food webs.

• Commercial feed (pellets) replaces raw prey items, breaking parasite life cycles.

• Regular health monitoring and veterinary oversight detect issues early.

• Stocking density may increase bacterial disease risk, but generally lowers exposure toparasites compared to wild fish.

• Geographical control

• Farms are located away from high parasite transmission zones when possible.

Low Contamination Levels

Controlled feed → formulated diets are screened for contaminants (e.g. mercury, PCBs, dioxins).

• Shorter food chains - farmed fish do not accumulate toxins via predation like wild carnivorous fish.

Faster growth & younger harvest age → less time to bioaccumulate pollutants.

Monitored environments → water quality and contaminant levels are checked regularly.

Regulawal persise forced in aquaculue remits (MRLs) and

Wild fish may bioaccumulate heavy metals & persistent organic pollutants from polluted ecosystems.

How does the parasite burden and contamination levels change across production systems?

Parasite Burden

• Cage culture (open water)

High exposure to wild hosts: risk of sea lice, trematodes, Anisakis (marine fish).

• Pond systems

• Risk of digenean trematodes if snails present.

• Higher burden in regions using sewage fertilisation.

Recirculating Aquaculture Systems (RAS)

• Minimal parasite exposure (closed loop, filtered water).

• Risk if biosecurity fails, but easier to eradicate.

Shellfish farming

• Filter-feeding: high risk of protozoan parasites (Giardia, Cryptosporidium) if effluent contamination.

Contamination levels

Cage culture

• Similar contaminant exposure to wild fish.

• Accumulate pollutants present in local environment.

• Pond culture

• Possible agricultural runoff (pesticides, fertilisers, heavy metals).

• RAS

• Lowest contaminant risk (water treated, feeds controlled).

• Monitoring of inputs is essential.

• Shellfish farming

• Accumulate heavy metals, toxins, and human pathogens from polluted water.

• Contaminant levels highly dependent on site location.

What are the general trends of farmed vs. wild caught fish?