The CTS in the tube designation means "copper tube size." This implies that the tube is sized by outside diameter and wall thickness. It follows that you might be able to use fittings from other CTS-sized tubes. Maybe a push-on "sharkbite" or similar will work. Do note that, especially with relatively soft plastic tubes, an internal stiffener may be required. This is because the pipe is retained in such fittings by forces applied from the exterior of the pipe -- but if the pipe is soft, and there's no stiffener inside the pipe to help out, then the walls of the pipe may collapse a little bit and allow the pipe to escape from the fitting.
CTS probably implies that PEX crimp bands would fit the outside of the tube. Depending on its wall thickness barbed PEX fittings may or may not fit well inside the tube..
If you do find some kind of barbed fitting that does fit inside the tube well, some kind of clamp on the exterior may be a good piece of insurance. The worm screw type hose clamp is the long-time standard, but if a copper PEX band or especially an Oetiker pinch clamp fits, they might be better choices. The Oetiker clamp is becoming more popular for PEX but it is offered in a wide range of sizes to fit other round things.
