Geoff Thomas: Icy slurry key to freshness

These gurnard and snapper will be in top condition when kept in a slurry.

How things change. It was only a generation ago that the only bait you could buy was frozen fillets of trevally which came in a blue and white cardboard box.

Today, we have a choice of fresh squid or mullet and a host of frozen options such as mackerel, pilchards from Chile or South Africa, bonito, and even baby salmon. Bait is a $30 million business every year.

And fish that we used to spurn as good only for bait are now delicacies. Trevally makes the finest sashimi, and we even eat pilchards which are presented as sardines in some of the top restaurants. Tuna came only in cans until somebody showed us how to dip tiny slivers in soy and wasabi or marinate steaks for the barbie.

The speedsters of the ocean need oxygen-rich blood delivered to their muscles to fuel the energy needed to catch their prey. Fish such as trevally, kahawai and kingfish come into this category, but tuna is at the apex.

They are like machines which never stop swimming and never stop eating, and their high rate of metabolism converts food to energy very efficiently. Just compare the size of a tuna's stomach in relation to its body with slow leviathans such as hapuku. Tuna are so well designed that their fins fit snugly into slots for the utmost hydrodynamic efficiency.

So when we decide to keep a tuna or a kahawai for dinner, the way we handle our catch has a bearing on how it finishes up on the plate.

We need to do three things: kill the fish, get rid of the blood and drop the body temperature quickly. Fish can be dispatched by a rap over the head with a stout stick, or by inserting a knife or sharp point into the brain.

Tuna are easily bled by inserting a knife on the lateral line two fingers' width behind the pectoral fin, cutting through to the backbone.

This severs a main artery and if done on both sides the fish will bleed out quickly.

It can be held over the side with a rope through the gills to keep the blood outside the boat.

Large fish such as kingfish can be handled in the same manner, but the cut is made by running a knife behind the gills, severing the membrane around the gill arch. Cutting through the throat will achieve the same result but it is tougher.

Smaller fish such as snapper, kahawai and trevally can be sliced through the throat.

White-fleshed fish which have been bled make superior table fillets and the flesh will be opalescent in colour. Those which have not been bled will have grey-tinged flesh with a stronger fishy taste.

It is said that every hour in direct sun reduces the fridge life of a fish by one day, which is

a powerful lesson. The old days of putting the catch into a wet sack on the bottom of the boat are long gone.

There is a good reason why commercial fishermen keep their catch in a slurry of salt ice and water, sometimes for five or six days before the fish go to market. Salt ice is the greatest step forward when it comes to looking after fish. It is actually made from fresh water mixed with salt, not frozen sea water and has a higher salt content than seawater. As a result it freezes at a much lower temperature than fresh water, and also keeps much longer. Flake salt ice packed into a large chillybin will last for several days.

If on a long range trip, the fish can be put straight on to the flake ice; but if it is a day trip, the key is to tip a bucket of sea water into your bin to make a slurry. The correct ratio is one part water and three parts salt ice.

Freshly caught fish dropped into this slurry will chill instantly, lowering the core temperature to zero degrees, setting the flesh, and keeping them in top condition.

The adage of "straight out of the sea and into the frying pan" is not as accurate as you might think. Like a hogget or beast that is hung in a chiller for several days before processing, fish benefits from time for the flesh to set.

A day in a slurry will achieve this, but so will a night in the fridge. If kept on ice, a fish does not have to be gutted or filleted when you get home.

It will be even better if wrapped in newspaper to avoid dripping juices, and filleted the next day. It is easier to slice the fillets off as the flesh has firmed up and the flavour is also better.