Why are fished brain spiked as soon as they are caught?

Commonly called Ikejime, when fish struggle after capture they produce large amounts of lactic acid and stress hormones. Brain spiking kills them instantly (and humanely) and stops nervous system activity, thus limiting the release of lactic acid and stress hormones.

Brain spiking affects taste in several ways:

Cleaner taste
Better bleeding removes blood from the flesh which can create strong “fishy” flavours.

Sweeter meat
Lower stress means less lactic acid build up.

Better shelf life
The meat breaks down more slowly.

Better cooking quality
Firm flesh holds together during cooking.

So there you have it!