Fish have a closed circulatory system with a two-chambered heart. Blood moves through arteries to the gills to exchange gases and then to the body through veins. The blood contains red blood cells, white blood cells, plasma, and platelets. Red blood cells contain hemoglobin and transport oxygen, while white blood cells help fight infection. The heart pumps blood through the sinus venosus, atrium, ventricle, and bulbus arteriosus in a single circulation before returning to the heart.

1. FISH CIRCULATORY
SYSTEM
Presented By:
Uzma Nihar
Department of zoology

2. Contents:
● Circulatory System
● Fun facts about fish blood
● Fish Blood and its composition
● Formed elements of the blood
● Function of blood cells
● Fish Heart Anatomy
● Fish Circulatory System
● Dissection of Fish Protocol

3. Fun Facts
● Fish have less blood per gram of body weight than
mammals, normally between 3% and 8% of a fish’s body
weight is blood. However in the hagfish and lampreys it is
greater, for them between 8% and 20% of the animal’s
body weight.
● Fish hearts have become more efficient through the ages.
Gram for gram the heart of a modern teleost fish is 2 to 5
times more powerful than that of sharks and rays, and 10
to 25 times more powerful than the heart of a hagfish.
● The first day, after introducing the fish in the experimental
set up, the HR was during daytime 55 beats per minute
(bpm) and during night 52 bpm.

4. Fish Blood
● Similar to that of any other vertebrates.
● Consist of plasma and cellular components.
❖ Cellular Components - Red blood cells
(RBC), White blood cells (WBC) and
thrombocytes.
❖ Plasma - Liquid portion and consists of water.

5. Fish Blood Composition
● The blood of fish consists of plasma and the
various cells that move around the body in it:
erythrocytes and leukocytes.
● Plasma is basically water with a variety of ions
(Na+, Ca2+, K+) and small organic molecules
such as urea, sugars and fatty acids dissolved
in it.
● In sharks and rays, blood cells are created in
three different organs: the spleen,
the epigonal organ (which surrounds the
gonads) and the Leydig organ (which is found
in the throat near the oesophagus). However,
in teleost fish blood cells are normally only

6. ● Erythrocytes are the most common cells found
in the blood plasma and their job is to move
gases around the body. They collect oxygen at
the gills and carry it to all the cells of the
body… and from these same cells they collect
carbon dioxide which they release into the
external waters through the gills.
● The molecule that allows the erythrocytes to do
their job – and which makes them red – is
called haemoglobin or hemoglobin, and
erythrocytes are full of it..

7. ● The haemoglobin of hagfish and lampreys is
called monomeric and consists of a single large
haem-molecule with a molecular weight of
around 17,000 daltons.
● Most other fish have tetrameric haemoglobin,
which is built up from from four different protein
chains called alpha and beta chains – there are
two of each in a single haemoglobin molecule.
This type of haemoglobin is very similar to ours
and has a molecular weight of around 65,000
daltons.
● Leucocytes are a mixed collection of cells that
are united in being much less common that
erythrocytes and in not being red (because

8. What makes up fish blood?
• Red Blood Cells (Erythrocytes) – The most abundant cells
in blood; they are produced in the bone marrow and contain
a protein called hemoglobin that carries oxygen to cells.
• White Blood Cells (Leucocytes) – They are part of the
immune system and destroy infectious agents called
pathogens.
• Plasma – This is the yellowish liquid portion of blood that
contains electrolytes, nutrients and vitamins, hormones,
clotting factors, and proteins such as antibodies to fight
infection.
• Platelets (Thrombocytes) – The clotting factors that are
carried in the plasma; they clot together in a process called
coagulation to seal a wound and prevent a loss of blood.

9. Formed elements of the blood
There are three varieties of cells or corpuscles present
in blood
a) Red blood corpuscles or Erythrocytes
b) White blood corpuscles or Leucocytes
1. Agranulocytes: Have no granules in the cytoplasm;
two varieties:
i) Lymphocytesii) Monocytes
2. Granulocytes: Possess specific granules & retain
nucleus; three varieties:
i) Neutrophils ii) Eosinophils iii) Basophils
c) Platelets or Thrombocytes

10. Five Important Types of Fish Blood Cells
are:
1. Lymphocytes: are 4.5 to 12 microns in
diameter and their job is defence: in detecting
and marking foreign particles. Specifically they
mediate antibody activity. Antibodies are small
molecules that find and bind to foreign
materials so that Monocytes can find them.
1. Thrombocytes: are important in blood clotting,
thus they are important in conservation of
resources as they prevent blood loss in case of
injury.

11. 3. Monocytes: are sometimes called
Macrophages and they are important in
defence. Their role is to eat (phagocytize)
anything they come across in the blood that
might harm the fish such as bacteria, or
parasite larvae.
4. Granulocytes: are also active in defence
and they specifically attack bacteria. They also
seem to have a role in controlling stress,
however this is still being researched.
5. Non-specific Cytotoxic Cells: these are
another defence mechanism, this time against
tumors and protozoan parasites.

12. Functions of blood cells:
● Respiration- Transport of Oxygen
● Nutritive- Carries nutrient material
(glucose, amino acid & fatty acids,
vitamin)
● Excretory- Carries waste materials (urea,
uric acid, creatine etc.)
● Exchange of electrolyte and other
molecules
● Contains regulatory agent such as
hormones

13. Fish Heart Anatomy
● At the centre of the static (comparatively) parts
of the fish circulatory system is the fish’s heart,
which is normally situated below the pharynx
and immediately behind the gills.
● A fish’s heart has four chambers. But unlike us,
the chambers of their heart are not all muscular
and are not so built into a single organ. Rather
they are located one behind the other. This is
particularly evident in the sharks and rays.

15. Sinus venosus. The first chamber is called the
sinus venosus. It is the preliminary collecting
chamber. In teleosts, it is filled from two major
veins called the hepatic veins and the left and
right branches of the Curvierian ducts – which in
turn collect blood from the paired (left and right)
lateral veins, the inferior jugulars, the anterior
cardinals and the posterior cardinals. However in
the elasmobranchs only one hepatic vein leads
into it.
Atrium. From the sinus venosus the blood flows
into the atrium. The atrium is the largest of the
chambers in the fish heart and only weakly
muscular. It pushes the blood, with weak
contractions in the ventricle.

16. Ventricle. The ventricle is the only well muscled
chamber, nearly as large as the atrium. Its
contractions drive the blood around the body.
Bulbus arteriosus. The last chamber of the fish
heart is called the bulbus arteriosus in the
teleosts, but cornus arteriosus in the
elasmobranchs. The difference between these
chambers is that the cornus arteriosus of sharks
and rays contains many valves, while the bulbus
arteriosus of bony fish contains none.

17. BLOOD CIRCULATORY SYSTEM
Circulatory Systems: system of organs and tissues, including the
heart, blood, blood vessels, lymph, lymphatic vessels and glands,
involved in circulating blood and lymph through the body
The two types of animal circulation systems are:
1.Open Circulatory Systems: pump blood into a hemocoel with
the blood diffusing back to the circulatory system between cells.
Blood is pumped by a heart into the body cavities, where tissues
are surrounded by the blood. (Circulatory fluid: hemolymph, also
called haemolymph found in molluscs and arthropods.
2.Closed Circulatory Systems: blood flows through closed
vessels of different size and wall thickness; blood is pumped by a
heart through vessels, and does not normally fill body cavities
(Circulatory fluid: blood. Blood is constrained within the heart
and blood vessels)

18. Two types of closed circulation systems are:
1. Single Circulatory Systems: blood passes through
the heart only once on each circuit around the whole
of the blood circulation system of the animal
e.g. in fish.
2. Double Circulatory Systems: blood passes through
the heart twice during one complete circuit around the
blood system through the body of the animal e.g. in
mammals.

20. Mechanism of Blood Circulation in Fishes
● When ventricle contracts the blood is being
pumped out of the heart. And when the
ventricle relaxes it is filled with blood again.
There is a one-way valve at the exit of the
ventricle which prevents the blood that was just
pumped out flowing back into the ventricle.
● Scientists call the emptying of the heart
the systole part of the pulse and the filling of
the heart the diastole part of the pulse. Systole
= beat and diastole = space, together they
make one pulse.

21. ● From the arteriosus, the blood enters the ventral artery
which takes it to the gills, where it loses CO2 and gains
O2 before heading out to the body through the dorsal
artery.
● Various branch arteries supply the muscles and different
organs of the body through a network of ever finer
capillaries. Further capillaries take the blood, now low in
O2 and higher in CO2, into a series of veins that ultimately
join up with the major veins mentioned above: the hepatic
veins, lateral veins, inferior jugulars, anterior cardinals and
posterior cardinals.
● Not all the plasma of fish blood returns through the
capillaries. Some of it mixes in with the fluid that surrounds
the cells of every tissue and is eventually drained away
into the lymphatic vessels.

22. ● This secondary circulation of lymph vessels
eventually empties into the main blood veins.
However because it left the main circulatory
system, it is unaffected by the beating of the
heart and its flow is slow.
● In some fish it is helped along by small lymph
hearts, muscular valved tubes which help
express the fish’s blood into the veins.
Lymphatic hearts can be found in various
places, in those species that have them. The
Eel (Anguila anguila) has one lymphatic heart
situated in its tail.

24. Fish Dissection

25. Step 1

26. Step 2

27. Step 3

28. Step 4

29. Step 5

30. Step 6

31. Step 7

32. Step 8

33. Step 9

34. Step 10