The vessels through which blood returns to the heart from different parts of the body are called veins. The vascular system of roe fish can be divided into two main parts. Systemic veins and portal veins
1. Systemic veins
Systemic veins carry CO2-rich blood from different parts of the body to the ductus cuveae. Blood then enters the sinus venosus from the ductus cavae. The different types of systemic veins are as follows.
(i) Anterior cardinal vein: It brings blood from different parts of the brain via ductus cuveae.
(ii) Inferior jugular vein: It supplies blood from different parts of the brain through the ductus cuveae.
(iii) Posterior Cardinal Vein: The right and left posterior cardinal veins are joined by the anastomosis vein. It carries blood from the back of the body through the ductus cuveae.
2. Portal vein
The veins that collect blood from different parts of the body and enter another organ and re-form the capillary network are called portal veins. It consists of hepatic portal and renal portal. Portal veins are:
(i) Caudal vein: The caudal vein enters the trunk from the tail and divides into two branches to form the renal portal vein. The renal portal vein brings blood from the digestive system to the liver.
(ii) Segmental vein: It collects blood from different parts of the body.
(iii) Transverse anastomosis veins: Right and left cardinal sinuses join with some transverse veins to form transverse anastomosis veins.
(iv) Sub clavian vein: It supplies blood directly from the thoracic fins to the sinus venosus.
(v) Hepatic veins: Two hepatic veins arise from the liver and bring blood to the sinus venosus.