Sinus venosus catheterization for repeated vascular access in the hybrid striped bass

Placement of vascular cannulae for repeat ed venous blood sampling has prov en to be a useful technique in many fish species. The anatomy and size of t he hybrid striped bass (striped bass Morone saxatilis female x M. chrysops male) makes this procedure challenging in this species. The sinus venosus w as determined to be the best site for catheter placement based on size, acc essibility, and ability to stabilize the catheter within it. Catheterizatio n of the sinus venosus with a 20-gauge x 3.8-cm flexible Teflon catheter wa s unsuccessful because the catheter folded on itself, occluding the lumen. Catheterization with an 18-gauge x 3.8-cm hypodermic needle was also unsucc essful because the sinus wall occluded the needle lumen when negative press ure was applied. However, 18-gauge x 3.8-cm intravascular needles remained patent in free-swimming fish for 2 weeks without major complications. An ex ternal fixation device to prevent migration of the catheter out of the sinu s venosus and laceration of the sinus wall during normal swimming movements improved the technique.