Oily fish is defined as fish with a proportion of fat higher than 5-6% of their muscle mass: sardines, longfin tuna, mackerel and horse mackerel are some the most well known examples.

When it comes to value for money and nutritional density, it’s hard to go past tinned fish. While tuna is the most common ... a single serve of mackerel offers more than three times the daily ...

Mackerel is under immense pressure from overfishing, conservationists warned, as they lowered its rating in the latest sustainable fish guide ... and farmed bluefin tuna remaining red rated ...