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FOOD SAFETY HAZARDS
IN AQUACULTURE
SEAFOOD HYGIENE
Lecture by Géza Szita
Chemical compsition of the water
Salt concentration of the sea water:
0.35 %
Chloride (Cl):
55.04 wt%
Sodium (Na):
30.61 wt%
Sulphate (SO4): 7.68 wt%
Magnesium (Mg): 3.69 wt%
Calcium (Ca):
1.16 wt.%
Potassium (K):
1.10 wt.%
Freshwater
Total water 'hardness'
(including both Ca2+ and Mg2+ ions)
Permanent hardness
is hardness (mineral content) that cannot be
removed by boiling.
CaSO4, CaCl2
MgSO4, MgCl2
Temporary hardness
is hardness that can be removed by boiling
+
Ca HCO3
▬ CaCO3 + H2O + CO2
Toxic materials in the water
Ammonia NH3
Hydroxil-amine OH- NH2
Nitrite NO2
Nitrate NO3
Hidrogene-sulphide H2S
Sulfite ions SO3
1. TERMS, PRODUCTION
~ Seafood: alI fish and shellfish (crustaceans, molluscs)
finfish: salt- and fresh-water
wild fishery I aquaculture
> 300 species
shellfish
molluscs (salt-water): mussels, snails, clams, oysters,
abalone
scallops, cuttlefish
crustaceans (salt/fresh-water): shrimp or prawns,
crayfish,lobsters, crabs etc.
Molluscs include chitons, clams, mussels, snails,
nudibranchs (sea-slugs), tusk shells, octopus and squid.
Characteristics of molluscs
Unsegmented soft body
Most have internal or external shell
Have a mantle (fold in the body wall that lines the
shell)
Muscular foot and/or tentacles
Mollusks
The mollusks or molluscs are the large and diverse phylum Mollusca, which includes a variety
of familiar creatures well-known for their decorative shells or as seafood. These range from tiny
snails and clams to the octopus and squid (which are considered the most intelligent
invertebrates). The giant squid is the largest invertebrate, and, except for their larvae and some
recently captured juveniles, has never been observed alive, although the Colossal Squid is likely
to be even larger.Mollusks are triploblastic protostomes. The principal body cavity is a bloodfilled hemocoel, with an actual coelom present but reduced to vestiges around the hearts, gonads,
and metanephridia (kidney-like organs). The body is divided into a head, often with eyes or
tentacles, a muscular foot and a visceral mass housing the organs. Covering the body is a thick
sheet called the mantle, which in most forms secretes a calcareous shell.
Mollusks have a mantle, which is a shell-like outer cover, and a muscular foot that is used for
motion. Many mollusks have their mantle produce a calcium carbonate external shell and their
gill extracts oxygen from the water and disposes waste. All species of the phylum Mollusca have
a complete digestive tract that starts from the mouth to the anus. Many have a radula, mostly
composed of chitin, in the mouth, which allows then to scrape food from the surface by sliding
back and forth. Mollusks also have a coelom, made from cell masses, where all organs are
suspended. Unlike Coelomates, mollusks lack body segmentation.
Development passes through one or two trocophore stages, one of which (the veliger) is unique
to the group. These suggest a close relationship between the mollusks and various other
protostomes, notably the Annelids.
Mollusks
Bivalves
The bivalves are the second largest class of molluscs. They differ
from snails in having two shells, usually mirror images of each other.
Some like oysters and mussels live attached to rocks and other hard
surfaces while others, like pipis, burrow in sand. Leptonoidean
bivalves (in picture) are a group which usually live commensally
with other animals. Most have a large foot and are active crawlers.
Limatula strangei. Some bivalves, such as the scallops are able to actively move when
endangered by vigorously flapping their shells and squirting out jets of water. Limatula
also moves very vigorously when disturbed. The tentacles around the mantle edge are
sticky, very mobile and parts can break off them when the animal is disturbed, leaving a
potential predator with a sticky writhing worm-like object to deal with as the Limatula
escapes (25mm).
Octopus
Hapalochlaena fasciata. There are a number of species of blue-ringed octopus in Australian waters.
They are all dangerous to handle, as the poison they use to kill their prey (crabs, snails) is highly
venomous to humans. This species is common in New South Wales. Usually a dull mottled colour, it
can become yellow with bright blue markings when disturbed.
Squid
Tunafish
Swordfish
Swordfish
2. FOODBORNE DISEASES FROM SEAFOOD
raw shellfish or undercooked, smoked, lightly salted fishery products
shellfish: sedentary animals ~ filter their food from coastal
and estuar waters ~ often subject to pollution by sewage
effluents and rain runoff from agricultural lands
~ bacteria, chemical contaminants are concentrated in shellfish
~ quality of shellfish .~ quality of estuarine water in which they have been
harvested
. finfish: prevalance of hazards higher in coastal and inland aquaculture
post-harvest handling, processing
3. BIOLOGICAL HAZARDS
~ Parasites
large number of fish species are potential sources of important parasitic
zoonoses
consumption of raw or inadequatly cooked seefood
fish: intermediate hosts of parasites (humans. the definitive hosts)
A. Trematodiases
important diseases in various parts of the world
ingestion ofviable encysted trematode metacercariae
three important genera: Clonorchis, Opisthorchis, Paragonimus .
Chlonorchiasis
definitive hosts: humans, dogs, cats, rats
larvae ~ fresh-water snails ~ cercariae ~ metacercariae ~
fish musc1e (secondary intermediate hosts) ~ humans ~ bile duct ~
cholangitis, cholangiohepatitis
treatment: praziquantel60 mglkg orally.
Opisthorchiasis
endemic in several Asian countries
first intermediate hosts: snails
Paragonimiasis
endemic in Asia, South America, West Aftica
snails (first) ~ crustaceans (second) ~ humans, mammals parasite infects the
lungs (tuberculosis)
B. Nematodiases
intemediate hosts marine or ftesh-water fish
definitive hosts: marine mammals, birds, pigs
mode of infection: ingestion of fish infective larvae
Capillariasis
- gastroenteritis ~ may be fatal
- migratory fish-eating birds ~ natural definitive hosts ~
spread faeces contaminated with parasite eggs in freshwater fish ponds along
migratory routes
- treatment: mebendazole 400 mg/day for 20-30 days
Anisaldasis
C Cestodiases
in humans fishborne infections not common
Diphyllobothriasis
- D. latum: mainly in cold waters (Eastern Europe, USA) - humans and fisheating mammals: definitive" hosts
- fish: intennediate hosts (salmon)
- treatment: praziquantel, niclosamide
~ Bacteria
divided into two groups:
naturally present in the aquatic environment (indigenous bacteria)
present as a result of contamination with human or animai faeces
contamination during post-harvest handling and processing
Enterobacteriaceae
introduced into aquaculture ponds by animaI manure or human waste ~ significant
numbers in products from waste- fed systems
- Salmonella:
may be naturally present in some tropical aquatic environment
aquatic birds spread them
fishborne human infeétions rare
strains isolated from humans are different from those found in products from
aquaculture
- E. coli : bovine manure as pond fertilizer ~ pathogenic
strains into the pond water
0157:H7 ~ cattle ~ waterborne infection
Shigella: occasionally, very little risk
Campylobacter: little information on the occurrence in aquaculture
use of poultry manure for fertilizing ponds ~ potential risk
Vibrio spp.
Salt-tolerant organisms ~ occour naturally in marine environments in both tropical
and temperate regions
V. cholerae also occours in fresh water
frequently isolated from sediments, plankton, molluscs, finfish, crustaceans
positive correlation with admixture of contaminated human waste
12 species associated with seefood
some human pathogenic Vibrio spp. may also be fish pathogens
V. Parahaemolyticus ~ particularly associated with consumption of raw
marine crustaceans and fish
Aeromonas
part of the normal aquatic flora
A. hydrophila ~ fishbome disease'
~ risk is low
Clostridium botulinum
anaerobic, neurotoxin-producing organisms
seven types ~ type E is naturally found in aquatic ~environments ~ often
isolated from fish
prevention of toxin production
Listeria monocytogenes
frequently isolated from aquaculture products in temperate regions
risk: raw or without heat treatment
Viruses
Viruses causing disease in fish are not pathogenic to humans
transmission of enteric virus diseases through waste-water reuse
systems is far not so important as bacterial or helminthic diseases
Other biological hazards
large number of toxic compounds produced by aquatic organisms can cause human
diseases
produced by aquatic microorganisms: algae, bacteria that serve as food for the
larvae of commercially important crustaceans and finfish
possible sources of infection in farmed finfish and crustaceans:
ingestion of toxic microorganisms or toxic products in feed
marine zootoxins are among the most highly toxic substances known:
Toxin LD50 (micro g/kg) in mice
(IP)
Ciguatoxin
0.5
Saxitoxin
3.0
Tetrodotoxin
8.0
Botulinum A
0.0001
TCDD
2.0
A. Ciguatera poisoning
produced by dinoflagellate algae
small fish feed algae ~ eaten by larger predatory fish
annually 10,000-50,000 cases (USA ~ Florida, Hawaii) mostly due
to group er, red snapper, Sphyraena barracuda
ciguatoxin accumulates in the liver, intestines, reproductive organs
and muscles of the fish
Cats are particularly sensitive ~ indicator
Prevention difficult: ciguatoxin fish do not appear or taste spoiled
B. Saxitoxin poisoning (paralytic shellfish poisoning, PSP)
Saxitoxin: produced by toxic dinoflagellates ~ food base for millions of marine
organisms
toxin accumulates in the tissues of bivalve molluscs (mussels, clams, oysters,
etc.)
ingestion of a single clam, if heavily contaminated ~ can kilI a person
Prevention: coastal shellfish monitoring programs ~ prohibit harvest during
periods when toxin levels are high ("bIoom")
C Tetrodotoxin poisoning (Puffer fish poisoning)
Many species of puffer fish ~ tetrodotoxin
Major cause offatal food poisoning in Japan (fugu)
(Captain Cook nearly died of tetrodotoxin poisoning in New Caledonia in 1774)
Tetrodotoxin: potent vasopressor and neurotoxin concentrates in the liver, skin
~ flesh becomes contaminated while the fish is cleaned
Dogs, cats and birds are also susceptible
D. Histamine
Due to ingestion of spoiled fish -) mostly Scombroidae (eg, tuna, machereI)
develops post-mortem due to improper handling and inadequate refrigeration
tissues of scromboid fish contains high level of histidine -). histamine (Vibrio,
Klebsiella, etc.)
Histamine degraded orally - cadaverine and putrescine (cocontaminants) inhibit
histaminases in human intestine
Levels > 50mg histamine / 100 g of flesh ~ hazardous
4. CHEMICAL HAZARDS
Through exposure to compounds used in the aquaculture systems
or by pollution of waterways or sources of water
A. Agrochemicals
Fertilizers (urea, ammon ion, salts, trace element mixes) ~ usually no risk to food
safety when used according to good agricultural practice
Water treatment compounds (lime, oxidizing agents, flocculants)~ non-hazardous
Pesticides (algicides, herbicides) no major risk disinfectants ~ widely used ~ no risk to
consumer chemotherapeutica (antimicrobials, parasiticides)
. drugs approved
. drug residues
- Metals
(Pb, Cd, Cu, Zn, Fe )
present as a result of geochemical processes
result of pollution
pH of the water
pollutants
Mercury
Chlorinated compounds (DDT, PCBs, dioxins)
5. CONTROL OF FOODBORNE DISEASE FROM SEEFOOD
Fish
· must be washed and chilled in ice or in cold water immediatley
after catching
· all of the ship equipment use for fish chilling must be c1eaned
and disinfected after each debarkation
· fish must be eviscerated as quickly as possible
· chilling is also required during transportation to port and during
distribution for further pocessing
· thorough washing is very important ~ removes up to 95% of
putrefactive microorganisms present on the fish skin
· during transportation for long distances, the water must be aired;
optimum temperature 4-80 oC
Shellfish
environmental monitoring of water quality
US Public Health Service: shellfish growing areas are surveyed
for safety ~ only those waters not subject to sewage contamination
and havingcoliform counts <: 70 organisms/100 ml are approved
for harvesting
shellfish transferred from marginally polluted areas to
unpolluted waters and left min. 14-28 days ~ will purify
themselves (depuration)
public education about the risks associated with eating raw
shell fish
pH of fish meat = 6.8 - 7.0
H2S (lead acetate) at 50 oC
free ammonia
trimethil-amine
histamine - below 100 ppm