Physiology of Finfish and Shellfish (2+1)

2.2.28. Circulatory physiology

The heart of a 450g lobster beats at a rate of 50-136 beats per minute and has an estimated hemolymph volume turnover time of 3-8 minutes. Blood pressure in the heart ranges from 9 to 22mm Hg at systoll and 0-5mm Hg at diastole blood flow has been described as intermittent in the ventral thoracic sinus moving at a rate of 0.3-0.5 cm/sec and increasing to 5cm/sec with abdominal flexion.

The flow to the major arteries could be regulated by opening or closing valves in the heart. These are sensitive to octopomine, proctolin but not to serotonin.

Hemolymph

Hemolymph is one of the fluid containing throughout the body has a pH of 7.6. It transports gases, nutrients, cellular waste, hormones and molecules associated with internal denfence. The volume of hemolymph in the lobster varies with the molt cycle. During molt stage, hemolymph volume is apporoximately 30% of the animal’s wet weight. It rises to 55% after moulting.

Hemolymph contains lot of protein in their structure. These are three types of proteins. They are

• Hemocyanin
• Coagulogen
• Defensive proteins

In these three types of proteins hemocyanin is one of the most important protein in circulatory system. In the blood hemocyanin present in the form of “Hemocytes”.

Hemocytes

The two major categories of blood cells of crustaceans are

• Hyaline hemocytes
• Granulocytes

Hyaline hemocytes

It is in ovoid shape size range from 8 to 16 mm in the longest dimension. It compose approximately 22% of the total in intermolt lobsters.

Granulocytes

These are larger than hyaline hemocytes. It contains most cytoplasmic granules. This shape is varying from cuiptical to teardrop shaped.

The functions of hemolymph

In circulatory systems, hemolymph takes an important role in the circulation of blood to the heart and all over the body. The main functions are

• Clotting
• Exoskeleton hardening
• Clearence of foreign material etc.

These are all the main functions of hemolymph.