Much of the fish-handling techniques now applied by the commercial sector and by canny anglers came from the Japanese. They are the masters at handling fish, because they value it so highly.
It is easy to check the condition of "fresh fish" displayed for sale, often in melted ice, which is a breeding ground for bacteria. Eyes should be bright and clear, not clouded and grey; gills should be bright red, not pale pink and slimy; the flesh should spring back into shape when a finger is pressed into the flank, not remain depressed; and there should be no strong, fishy odour.
When you catch a fish, a spike into the brain is the humane way to dispatch it instantly. This prevents the fish flapping, which bruises the flesh. In Japan, this is called iki jime (live killing).
For round-bodied fish such as gurnard, kahawai and tuna, the spike should penetrate between the eyes at an angle of 45 degrees facing backwards.
Flat-bodied fish such as trevally and snapper are spiked from the side behind and above the eye. A thin spike works fine but hitting the "sweet spot" can be a little hit and miss, and the reaction will indicate success: the fish arches its body then relaxes. A sharpened Philips screwdriver is a handy iki spike and, with large fish like tuna, the handle is helpful when extra grunt is needed.
With snapper, our weapon of choice is a short-bladed bait knife. These have wide blades that, when driven home and twisted, destroy the whole area including the brain.
Fast-swimming fish such as kingfish, tuna and kahawai benefit from bleeding for they have a web of vessels that deliver oxygen-rich blood to the muscles.
The flesh will be far superior if the blood is emptied. This is done by slicing the membrane which curves around the inside of the gill arches, cutting the throat or, in the case of tuna, inserting a knife point on the lateral line two fingers' width behind the pectoral fin on one side. This severs a major artery and the thick blood will flow.
Commercial fishers then put the catch into a slurry of three parts flake salt ice and one part seawater - never fresh water. This lowers the body temperature quickly to zero degrees, and such fish may be kept for four or five days before reaching the factory and then on to the fish shop.
Flake ice is readily available at bait shops and ice factories, and lasts far longer than conventional ice.
A makeshift alternative is to freeze milk bottles filled with water and use them to cool seawater in a chilly bin.
If ice is limited another alternative is to gut fresh-caught fish and pack the cavity with ice, which brings down the core temperature.
Fish treated this way are much easier to fillet than fresh-caught fish. The flesh will be nice and firm, delivering superior fillets.
