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

What makes up fish blood?

• Red Blood Cells (Erythrocytes) – The most abundant cells inblood; they are produced in the bone marrow and contain aprotein called hemoglobin that carries oxygen to cells.

• White Blood Cells (Leucocytes) – They are part of theimmune system and destroy infectious agents calledpathogens.

• Plasma – This is the yellowish liquid portion of blood thatcontains electrolytes, nutrients and vitamins, hormones,clotting factors, and proteins such as antibodies to fightinfection.

• Platelets (Thrombocytes) – The clotting factors that arecarried in the plasma; they clot together in a process calledcoagulation to seal a wound and prevent a loss of blood.

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) Lymphocytes ii) Monocytes

2. Granulocytes: Possess specific granules & retain nucleus; three

varieties:

i) Neutrophils ii) Eosinophils iii) Basophils

c) Platelets or Thrombocytes

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

Blood Circulatory System

Circulatory Systems: system of organs and tissues, including the heart, blood,blood vessels, lymph, lymphatic vessels and glands, involved in circulating bloodand lymph through the body

The two types of animal circulation systems are:

1. Open Circulatory Systems: pump blood into a hemocoel with the blooddiffusing back to the circulatory system between cells. Blood is pumped by a heartinto the body cavities, where tissues are surrounded by the blood.(Circulatory fluid: hemolymph, also called haemolymph found in molluscs andarthropods.

2. Closed Circulatory Systems: blood flows through closed vessels of differentsize and wall thickness; blood is pumped by a heart through vessels, and does notnormally fill body cavities

(Circulatory fluid: blood. Blood is constrained within the heart and blood vessels)

Two types of closed circulation systems are:

1. Single Circulatory Systems: blood passes through the heartonly once on each circuit around the whole of the bloodcirculation system of the animale.g. in fish

2. Double Circulatory Systems: blood passes through theheart twice during one complete circuit around the blood

system through the body of the animal e.g. in mammals

The circulatory system of fish:

The circulatory system of fish of fish is quite simple. It consists of a heart,

blood, and blood vessels. The heart of a fish is a simple muscular structure that

is located behind (and below) the gills. It is enclosed by the pericardial

membrane or pericardium.

The heart consists of an atrium, a ventricle, a thin-walled structure known as

sinus venosus, and a tube called bulbus arteriosus. Though it has four parts, the

heart of a fish is considered two-chambered. Unlike humans, the four parts of a

fish heart do not form a single organ. Usually, they are found one behind

another.

Blood and Blood Vessels:

The blood contains plasma (the fluid portion) and blood cells. The red

blood cells or the erythrocytes contain hemoglobin, a protein that carries

oxygen throughout the body. The white blood cells comprise an

indispensable part of the immune system. The thrombocytes perform

functions that are equivalent to the role of platelets in the human body,

i.e. they help in blood clotting.

Fish Circulatory System – Parts:

Bulbus arteriosus: pear shaped chamber that functions as a capacitor,maintaining continuous blood flow into the gill arches.

Atrium: each of the two upper cavities of the heart from which blood ispassed to the ventricles (each of the two main chambers of the heart, leftand right)

Blood Circulation:

Blood vessels carry the blood throughout the body. While arteries carry

oxygenated blood from the gills to the rest of the body, veins return

deoxygenated blood from different parts of the body to the heart.

Arterioles are small, thin-walled arteries that end in capillaries, while

venules are tiny veins that are continuous with capillaries. Capillaries are

minute blood vessels located within body tissues, and they form the link

between arteries and veins.

The cardiovascular system of fish:

The cardiovascular system of a fish comprise a heart, veins, arteries, blood, andfine capillaries. The capillaries are microscopic vessels that form a networkcalled a capillary bed, where the arterial and venous blood get linked. Capillarieshave thin walls that facilitate diffusion, a process through which oxygen andother nutrients from the arterial blood are transferred into the cells. At the sametime, carbon dioxide and waste materials are moved into the capillaries.

Capillaries with deoxygenated blood (contains carbon dioxide) drain into smallveins called venules, which in turn drain into larger veins. The veins carry thedeoxygenated blood into the sinus venosus, which is like a small collectionchamber. The sinus venosus has pacemaker cells that are responsible forinitiating contractions, so that the blood is moved into the thin-walled atrium,which has very few muscles.

The atrium generates weak contractions so as to push blood into the ventricle. The

ventricle is a thick-walled structure with lots of cardiac muscles. It generates enough

pressure to pump the blood throughout the body. The ventricle pumps blood inside it

into bulbus arteriosus, a small chamber with elastic components.

While bulbus arteriosus is the name of the chamber in teleosts (rayfinned, bony fish),

the structure is known as conus arteriosus in elasmobranchs (fish with cartilaginous

skeleton and placoid scales). Conus arteriosus has many valves and muscles, whereas

bulbus arteriosus has no valves. The main function of this structure is to reduce the

pulse pressure generated by the ventricle, in order to avoid damage to the thin-walled

gills.

Gills are the primary respiratory organs of fish. They facilitate exchange of gases,

i.e. absorption of oxygen from water and elimination of carbon dioxide. Arteries

carry the oxygenated blood (from the gills) throughout the body.

Arteries branch into arterioles, which drain into capillaries, where the arterial blood

becomes venous blood, as it supplies oxygen and other nutrients to the cells and

absorbs carbon dioxide and waste materials. The venous blood is carried to the heart,

which pumps it to the gills, where the carbon dioxide gets replaced with oxygen.

The oxygenated blood is supplied to the cells in the body, and the cycle continues.