VPP 322: Aquatic Animal Diseases, Health Care and Management (1+1)

COLLECTION OF BLOOD

• The regular monitoring of fish blood is a very useful diagnostic tool in establishing the health status of fish farm stocks. Different techniques which can be used to collect blood samples from fish are
  • Severing the caudal peduncle
  • Puncturing the caudal vessel
  • A cardiac puncture
  • A dorsal aorta puncture
• However more advanced techniques include puncturing the common cardinal vein (duct of Cuvier) and cannulisation, which allows repeated extraction of blood from a single fish through a cannula which is surgically inserted, usually through the gills of the fish. In general, whenever blood samples are taken, the tubes and syringes to be used should be treated with an anticoagulant (HT 2 Blood 1.1) such as heparin to prevent clotting. However, when serum is required this is not necessary as the blood is first allowed to clot (i.e. fibrinogen is converted to insoluble fibrin) in tubes and is then centrifuged to remove blood cells and fibrin. Coagulation is the process of changing into a clot, by which an organic liquid solidifies, eg. the clotting of blood.

Severing the caudal peduncle

• This sampling technique is suitable for smaller fish (eg. less than 10 cm). It should be noted that it is sometimes quite difficult to collect blood efficiently using this method. As coagulation tends to occur rapidly, the blood sample must be collected immediately after the tail is severed.In this procedure the fish is killed (sacrificed) to obtain blood by administering an overdose of anaesthetic solution.
• Anaesthetics are chemicals used to relax and facilitate handling, surgery and spawning procedures. Commonly used agents include tricane methane sulfonate (MS-222), benzocaine and quinaldine which are widely used in handling freshwater fish. Ethyleneglycol-monophenylether is an anaesthetic agent more suitable for marine fish species. It is usually administered by immersing fish in a bath solution.

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Puncturing the caudal peduncle

• This is a method which can be used to repeatedly to take blood samples from larger fish (generally more than 10 cm long). From 0.5 to 1 ml of blood can be drawn from fish of 200 g every week without causing high mortalities or serious debilitation.  

A cardiac puncture

• This is a method which can be used to repeatedly to take blood samples from larger fish (generally more than 10 cm long).

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Puncturing the dorsal aorta

• This is a method which can be used to take blood samples repeatedly  from larger fish (generally more than 10 cm long).Render the fish unconscious in an anaesthetic solution before collecting blood.