Fish health Flashcards
(35 cards)
Why do farmed fish get sick
Increased stocking densities (lower profit margins) Infected carriers (Largely brood stock) Infected facilities Poor nutrition (we are way behind) Substandard water quality
Biggest problem: Greater susceptibility via weakening of resistance under intensive culture conditions
Fish innate immunity - 2 lines of defence
First line of defence is external:
- Skin, scales and mucous membranes which produce secretions
Second line of defence is internal:
- Triggered by chemical signals, employs antimicrobial proteins and phagocytic cells and the inflammatory response
Fish immunity - Mucous
Skin, gills and gut are covered in mucous
Continual trapping of micro-organisms and sloughing. Inhibits colonisation of opportunistic pathogens
Mucous is a glycoprotein layer containing:
- Immunoglobulins: antibodies
- Lysozyme: can kill bacteria
- Complement: mediates inflammatory response
Major player in non-specific defence system
Fish immunity - Skin
A protective barrier Covered in mucus Specific immunoglobulins: - Lysozyme - Rapid healing
Fish skin is relatively simple in structure
Epidermis is relatively thin
Unicellular mucous glands are abundant in the epidermis
Dermis is composed of dense fibrous connective tissue
Attached to the underlying muscles by a layer of loose connective tissue
Scales of fish are located within the dermis
Fish Immunity - Gills
Covered in mucous - rapid repair
Fish immunity - Lymph
4 times the volume of blood
Important for the movement of the immune cells, chemicals and enzymes around the body
No secondary lymph nodes in fish
Fish immunity - Kidney
Major Lymphoid tissue
Most important for immunity and haematopoiesis
Early immune response handled by entire kidney
Head kidney (anterior) is important for making white and red blood cells
Head kidney also serves as a secondary lymphoid organ
Blood flows through the kidney and antigens are trapped or exposed to macrophages and endothelial cells and can capture ~70% of blood borne bacteria
Head kidney is a major producer of antibody (memory)
Fish immunity - Spleen
One of the major lymphoid tissues - secondary to kidney
Made of red and white pulp
Red pulp contains macrophages and lymphocytes
White pulp is important in plasma filtration and capturing blood borne substances
Fish Immunity - Liver
Involved in production of complement cascade - not very clear
Fish Immunity - Thymus
Production of T lymphocytes
Not always seen across different fish species
Fish - Non specific humoral factors
Soluble substances secreted in mucous, lymph and blood
Protective function by inhibiting growth of microorganisms
Fish immunity - Complement
o A lytic compound
A cascade of >20 serum proteins and glycoproteins that act as enzymes
Activated by antibodies or bacterial antigens - Lysis of pathogen cell walls
Can work at low temperatures 0-4 degrees Celsius in fish
Leads to direct killing or opsonisation and phagocytosis
Works on Gram negative bacteria
Key participant in the inflammatory process
Fish Immunity - Lysozymes
More active in fish than other higher vertebrates
Targets bacterial cell wall peptidoglycans resulting in lysis
Works best against Gram +ve bacteria (peptidoglycan is more accessible to enzyme)
Also works against Gram -ve bacteria in fish (Gram negative bacteria have a lipopolysaccharide and protein layer that surrounds the peptidoglygan layer of the cell wall)
- When the outer cell wall of Gram-negative bacteria is disrupted due to the action of complement and other enzymes expos-ing the inner peptidoglycan layer of bacteria, then lysozyme becomes effective
Can activate the complement pathway and phagocytosis
Fish Immunity - Cytokines
Cytokines are intracellular signalling molecules released from leucocytes to coordinate immune response
Interferon: Antimicrobial protein in serum - anti-viral activity, inhibits viral replication and is not virus specific
Tumour necrosis factor: Stimulated by bacterial lipopolysaccharide, results in an increase of phagocytosis, antimicrobial
Interleukins: Activate other cytokines leading to inflammation; IL-6 is also antibacterial
Fish Immunity - Transferrin
Growth inhibitor
Binds iron
Iron is essential for bacterial survival
Pathogenic bacteria may produce chelating agents to overcome this defence
Fish Immunity - Lectins
Proteins able to bind certain sugars
Activates the lectin pathway of complement
Increased opsonisation and phagocytosis
Fish Immunity - C-reactive proteins
Pattern recognition proteins that are important components of the acute phase of infection/injury
Higher levels in fish
Binds to phosphoryl choline on the surface of the bacterial cell walls
Activates the complement pathway
Fish Immunity - Natural Antibodies
Produced with out any apparent specific antigen stimulation
High production in fish
Low specificity-binds to bacterial, parasitic and viral proteins
Low affinity but high avidity
Activates phagocytosis and the complement pathway
Present in the: mucus, lymphoid tissue, plasma and other body fluids
Fish Immunity - Non-specific immune cells:
Monocytes and tissue macrophages:
- Most important cells in immune response
- Produce cytokines
- Primary cells involved in phagocytosis and first killing of pathogens
Neutrophils:
- Primary cells in early stages of inflammation
- Produce cytokines to recruit immune cells to damaged or infected area
- Phagocytic
Natural killer cells:
- Use receptor binding to target cells and lyse
- Important in parasitic and viral immunity
Fish Immunity - Inflammation
Basic protective response to tissue damage regardless of cause
Key feature is vasodilation and influx of leucocytes from blood to the site of inflammation
Arrival of the neutrophils and macrophage cells is the start of inflammation of infected tissue
The cells are attracted to the infection site by tissue damage and chemokines
Fish Immunity - Specific Immune Response
Humoral immunity:
- Production of soluble antibody (immunoglobulin)
Cell-mediated immunity:
- Mediated by several cell types including lymphocytes and macrophages
Immunological memory:
- Adaptive change in the lymphoid cell populations
- Mounts secondary responses if challenged again with same pathogen
Fish Immunity - T cells
o Cell mediated immune response
It is known that there are T cells
- Helper T cells?
- Cytotoxic T cells?
Unlike humans most of the phenotypes and how the T cells interact have not been extensively elucidated
What are the main types of antibody produced by humans?
IgM, IgG, IgE, IgA & IgD
What are the main types of antibody produced by fish?
IgM, IgT & IgD
