Don't buy products that exploit the oceans, such as coral calcium, shark cartilage supplements, and coral jewelry, and if you take fish oil, you can substitute equally healthy flaxseed oil.

Like their close relatives the sharks, the 200-odd species of stingrays are boneless fish that boast skeletons made of tough tissue called cartilage.

Sharks have a different structure to most fish: instead of a skeleton made of bone, I hey have a tough elastic skeleton of cartilage.