Circulatory System in Finfish and Shellfish

system, blood is pumped by a 
heart through vessels, and 
does not normally fill body 
cavities.
The open circulatory system is 
common to 
molluscs
and 
arthropods
. 
Open circulatory systems (evolved in 
crustaceans, insects, mollusks and 
other invertebrates) heart 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. 

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Fish 
have 
a 
closed 
circulatory system with a 
heart 
that 
pumps 
blood 
around the body in a single 
loop-from the heart to the 
gills, from the gills to the 
rest of the body, and then 
back to the heart. The fishes 
heart consist of four parts: 
the sinus venosus, atrium, 
ventricle, and the bulbus 
arteriosus. 
Circulatory system 
in fish 
The circulatory system of fish is 
quite simple and consists of

Heart

Blood 

Blood Vessels 

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Heart is a simple muscular structure that is located below the 
pharynx and immediately behind the gills. It is enclosed by the 
pericardial membrane or pericardium. In most of the fishes, the 
heart consists of an atrium, a ventricle, a sac-like thin walled 
structure known as sinus venosus and a tube, known as bulbus