Farmed and wild-caught fish are killed using many methods, some of which cause prolonged suffering. Research into humane fish slaughter has identified effective stunning methods that are not yet universally used.
The welfare of farmed fish at slaughter is one of the most tractable welfare improvements available in aquaculture. Replacing live chilling and CO2 immersion with effective electrical or percussive stunning can dramatically reduce suffering at death for billions of fish annually. Technology exists; what is lacking is regulatory mandate and widespread industry adoption. Consumer pressure and welfare certification can accelerate adoption.