Bài giảng quản lý chất lượng môi trường trong nuôi trồng thủy sản phần 2

QUẢN LÝ CHẤT LƯỢNG MÔI TRƯỜNG
TRONG NUÔI TRỒNG THỦY SẢN


Chương 3:
Khái niệm về vi sinh vật trong nguồn nước


Microbial Interactions with Macroorganisms
Aquatic environment is relatively
rich in microorganisms
Up to 105 to 106 cells / mL
Cilliates, other protists, and viruses

Macroorganisms in aquatic
environment
Constantly exposed to
microorganisms


Historical perspectives
Changes during storage
Effects on spoilage
Relationship between
environmental and fish
microflora
Basis for monitoring changes in fish
farms
Disease causing bacteria
Human
Fish & Shellfish

Increasingly, more focus on normal
microflora and their interactions
with the host organisms


Microbiology of bivalve mollusks
Microorganisms as food
Natural microflora
Filter feeders and the ecosystem

Hansen and Olafsen, 1999; Maeda, 2002


Microorganisms as food
Filter feeders
(Suspension feeders)
Feed on microorganisms that
they filter out of the
environment

Clams, oysters, barnacles,
sponge

Deposit feeders
Feed on microorganisms that
coats the surface of sediments
and soil particles

Worms, fiddler crab

Larval forms of animals may require smaller microorganisms
such as bacteria, while an adult may prefer larger
microorganisms such as flagellated protists and algae


Oyster anatomy
Labial palps

Visceral mass

Lower intestines

Draw water in over its gills
through the beating of cilia
Suspended food (plankton) and
particles are trapped in the
mucus of the gills
Sort by labial palps and transport
to the mouth, eaten, digested,
and feces expelled
Pseudofeces = particles which are
not sorted as food and are
rejected through the mouth

Affect by temperature
Rectum and anus

Greatest when water temperature
> 50°F (~10°C)

Oyster anatomy lab- />

Oyster filtering mechanism lab- />

Natural microflora of mussels and oysters
A majority of isolates are gram-negative (68%) and aerobic
(76%) bacteria
Predominant flora: Vibrio, Pseudomonas, Shewanella,
Aeromonas, Acinetobacter, and Flavobacterium
Gram-positive bacteria: Staphylococcus, Bacillus,
Streptococcus
Predominant Vibrio species includes:
V. alginolyticus, V. splendidus, and V. (Listonella) anguillarum*

Not always reflect external environment
Suggests selective process to sequester and maintain certain species

Kueh and Chan, 1985 ;Hariharan et al., 1995


Filter feeders and the ecosystems
An adult oyster can filter as much as 60 gallon per day
Oysters can filter out sediments and nutrients (nitrogen) and
deposit them on the bottom
“Top-down" grazer control on phytoplankton
Reduce turbidity, increasing the amount of light reaching the sediment
surface
Extending the depth to which ecologically important benthic plants
(seagrasses and benthic microalgae) can grow

Newell, 2004 ;Chesapeake Bay Foundation- />

Filter feeders bivalves removing inorganic and organic particles from water column and
transferring undigested particulate material to the sediment in the form of their biodeposits
Newell, 2004


Microbiology of Fish
Eggs, skin, gills microflora
Intestinal microflora


Bacteria on mucosal surface (1)
Host-parasite relationship
Host = an organism which harbors parasite (microorganisms)
Parasite = an organism that lives on or in a second organism

Surfaces such as eggs, skin, gills, and intestinal tract
Mucus layer as an adhesion site and protective layer
Indigenous vs. transient (autochthonous vs. allochthonous)
Indigenous = able to grow and multiply on the surface of the host animal
Transient = not able to grow or multiply on the surface of the host animal;
does not persist for a long period of time


Bacteria on mucosal surface (2)

Loose association

Adhesion

Invasion


Eggs microflora
Fish embryos secret inorganic and low molecular weight organic
compound, which can diffuse out through the shells
Attract bacteria utilizing these compounds and colonize egg
surface
Normal healthy eggs flora: Cytophaga, Pseudomonas
Dead eggs: fluorescent Pseudomonas
Not the cause of dead, but rather attracting to nutrient leaching

Overgrown of bacteria can hamper eggs development

Leucothrix mucor on cod eggs

Flavobacterium ovolyticus on halibut eggs
Cahill, 1990; Hansen and Olafsen, 1999


Skin Microflora
Reflect that of surrounding water
May have from 102 to 104 bacteria/ cm2
Unit of measurement per area
Surface sampled by using a sterile swab
Muscle tissue should be sterile

Gram negative: Pseudomonas, Moraxella, Vibrio, Flavobacterium,

Acinetobacter, Aeromonas
Gram positive: Micrococcus, Bacillus

Cahill, 1990


Gill Microflora
May contain 102 to 106 bacteria/ g
The number is quite low considering its high surface area and being
continual flushed by water
Extensive colonization of certain types of bacteria (Flavobacterium)

Gram negative: Pseudomonas, Flavobacterium, Vibrio,
Moraxella, Cytophaga
Gram positive: Micrococcus, Bacillus (in warmer water)

Cahill, 1990


Intestinal microflora (1)
Established at the larval stage
Developed into a persistent flora at the juvenile stage
Population of microorganisms tends to increase along the length
of the GI tract
Largest number of bacteria in the intestines (up to 108 CFU/g)
Gram negative: Pseudomonas, Vibrio, Achromobacter,
Flavobacterium, Corynebacterium, Aeromonas
Gram positive: Bacillus, Micrococcus
Influenced by stages of life, diets, feeding, water temperature,
habitat

Large number when feeding, very few when not feeding
Organic content of the environment
Vibrio dominates in seawater, Aeromonas dominates in freshwater

Cahill, 1990; Hansen and Olafsen, 1999


Intestinal microflora (2)
Microvilli of the epithelial cells of
common wolffish (A. lupus L.)

Bacteria

SEM of the enterocytes in the
midgut of Artic charr

Ringo et al., 2003


Intestinal microflora (3)
Endocytosis of bacteria in the
hindgut of spotted wolffish fry

Bacteria

TEM of Atlantic salmon gut epithelium

Ringo et al., 2003

Aquaculture of marine larval fish
Yolk-sac
First feeding
Larvae
Juvenile

More difficult to raise compared to
freshwater
Smaller egg size
Smaller size at hatching
Longer larval duration
Higher mortality rates

Mass mortality often with unknown
cause
Nutrition?
Disease?

Little is known about the role of
intestinal microorganisms

Adult

Fuiman, 2002


Fish Anatomy
Larva

Adult

Development of the intestinal
microbiology
At the time of hatching, the digestive tract of most fish species is an
undifferentiated straight tube
Prior to first feeding, microbiology reflects that of the rearing
environment
Marine larvae needs to “drink” to osmoregulate
Influence by eggs, live feed, and rearing water

Once feeding begins, microbiology is derived from live feed
ingested rather than water
As the digestive tract becomes more developed, the intestinal
microbiology becomes more stable and more complex
pH change (lower)
O2 tension (more anaerobic)
Receptors for bacteria

Ringo and Birkbeck, 1999; Birkbeck and Verner-Jeffreys, 2002


Development of the intestinal microflora
(2)
Criteria for testing whether or not microorganism is indigenous to
the intestinal tract of fish:
•
•
•
•

•

Found in healthy individuals
Colonize early stages and persist throughout life
Are found in both free-living and hatchery-cultured fish
Can grow anaerobically
Are found associated with the epithelial mucosal in the stomach, small
intestine or large intestine

Ringo and Birkbeck, 1999


Roles of intestinal microflora
Nutrition
Polyunsaturated fatty acids, amino
acids and vitamins
Extracellular enzymes: chitinase

Preventing infection from fish
pathogens
Competitive attachment
Neutralization of toxins
Bacteriocidal activity

Survival and growth
Bacterial load impact on survival &
digestive organ development
Presence of certain species influence
survival

Stimulation of the immune system
Provide antigens to trigger development
of immune responses in the gut

Pre-release China rockfish
Ringo and Birkbeck, 1999; Photo by Mark Tagal