I believe whatever the fish are eating that time of year has the greatest effect on taste, certainly how the fish dies & is kept afterwards. Immediate icing best & certainly can't hurt nor:

https://en.wikipedia.org/wiki/Ikejime

Somewhere on the Web I watched a video of a women who enjoyed raw fish. She noticed the difference in taste & texture between Ikejima & a normal slow death of a fish. It is easy to learn to do & a modern ikejima device can be found on eBay.