A mackerel is a sleek, fast-swimming ocean fish known for its striped or wavy pattern along its back. These fish travel in huge groups called schools, sometimes numbering in the thousands, moving together through the water like a silver river. Mackerel are built for speed, with streamlined bodies that help them chase smaller fish and escape from larger predators like tuna and dolphins.

People have caught and eaten mackerel for thousands of years. The fish has rich, flavorful meat that's packed with healthy oils. Fishers prize mackerel both for eating and as bait to catch bigger fish. In many coastal towns, the arrival of mackerel schools in spring means fishing season has begun.

The word also appears in the phrase mackerel sky, describing clouds that look like the rippled pattern on a mackerel's back. Sailors traditionally believed this cloud pattern meant changing weather was coming, often reciting: “Mackerel sky, mackerel sky, never long wet, never long dry.”