Here is the truth: that line is not a vein at all. It is the shrimp’s digestive tract — essentially its intestine. Depending on what the shrimp ate before it was caught, the tract can look dark brown, black, or even slightly greenish. It is harmless, but it does raise fair questions about taste and appearance.
And it is safe. As long as the shrimp is fresh and cooked properly, leaving the tract in poses no health risk, because heat kills any bacteria. The decision to remove it comes down to flavor, texture, and presentation rather than food safety
