Ikijimi method of killing fish
Once you have caught your fish it is most important that you handle and care for it correctly to ensure that it does not deteriorate to the point it is wasted. Deterioration occurs both through chemical and bacterial processes. Depending on the time taken and subsequent treatment of catch this will affect the taste and texture of meat.
All wanted fish should be killed humanely and quickly. The best method is known as "ikijimi" - spiking the fish in the brain with a sharp instrument just behind the eye. You will know that you have found the correct area as the fish will convulse, flare its mouth and fins then relax, with no further movement.
Poor handling can allow enzymes to leach out of the muscles and gut which will eventually attack the surrounding flesh.
Bacterial contamination of fish may take some time to develop. However it is prudent to concentrate on cleaning the main areas of a fish that contain bacteria. These are the skin, gills and gut.
Storing fish even for a short period in dark plastic bags on a hot day will allow bacteria to grow at an advanced rate as well as partially cook the flesh. Keeping your catch cool is the best way of ensuring freshness. Ice or cold water is ideal for daily catch storage.
When freezing, make any packaging holding the fish as airtight as possible to reduce the rate at which freezer burning occurs. There will be some deterioration in the fish during and following freezing due to enzyme reactions and moisture loss on thawing. As a rule fatty fish can be kept at -18'C for at least 2-3 months whilst white lean fish may be kept for 3 - 5 months without a large discernible loss in taste.
Beneficial nutrients may be lost from fish flesh if it is not prepared properly. Protein, vitamins and moisture are all lost during any thawing process. Certain nutritional oils are also lost during the cooking process and overcooking tends to dry out the flesh and make it coarse and bland.
People can assess the quality of the fish by smell, sight, touch, and in the case of sashimi, taste.
Whole fish should have bright red gills and shiny skin. Eyes should be clear and not sunken.
Fillets should be firm and the flesh should be consistent in texture.