Oil-rich fish (or oily fish) are those that have oil distributed through their body, as opposed to white fish, whose main concentration of oils is located in the liver. Although oily fish contain higher levels of oil, they are an essential part of a healthy diet due to the presence of the fatty acid, long-chain omega-3. Oil-rich species include the mackerel and tuna group, herring and anchovy group, as well as salmon and trout. The most sustainable varieties of oily fish are mackerel, pilchards, sardines, herring and skipjack tuna (usually sold canned).
In most cases, fresh is best when it comes to choosing oil-rich fish species because the natural fats occurring in these fish deteriorate and they lose their quality quickly. Oily fish tend to be landed and sold ungutted to maintain their quality. They’re generally also good value for money. Look for fish that are still stiff and rigid and in ‘rigor mortis’ – this will indicate that the fish has been out of the water for no more than a day or so. At this stage the fish will have bright, clear eyes, the gills will be a vibrant, red colour and it will hardly have any smell at all. As the fish loses condition it will become softer and its smell will become stronger.
Oily fish must be stored in as cool a place as possible and eaten quickly, ideally on the day of purchase. Arrange it in a single layer on a tray and keep cool by covering the fish with ice. Oil-rich species freeze well for a short period of time: gut or fillet them, pack into freezer bags as whole fish (or two portions at a time), extract the air and secure the bag. Defrost the fish for a few hours in the fridge before use.
Oily fish are versatile. They suit grilling, barbecuing, roasting and baking and, in some cases, pan-frying. The natural oils give these fish an intense flavour that pairs well with other strong flavours.