Definition of busy. busier. ; busiest. 1a : engaged in action : occupied She's busy studying. has enough work to keep him busy for a whileb : being in use found the telephone busy. 2 : full of activity : bustling a busy seaport.
It is considered a high quality tube, and is normally constructed from SAE 1020 or 1026 steel. Note that, technically DOM refers to the process by which the tube is finished after having started as an ERW tube. Technically, DOM is not a type of steel tube, but rather a process. As so often happen though - in common use the term has become accepted to mean a specific type of tubing rather than a process.
The pneumatic duct is a tube that runs between the esophagus and the swim bladder. Goldfish may gulp and burp air to alter the pressure in the swim bladder. It is unclear to what degree they actually use burping and gulping to decrease or increase the pressure in the swim bladder.