Thanks Peter you got exactly my question right. I guess cod roe is more a Northern European thing and is not well know in the US - it is indeed something completely different from caviar.
As I have in the past cooked whole fish with roe and liked it, I started my experiments with cooking at the same temperature I generally cook cod, ie 55C. 20 minutes were enough for small ones but 40min were needed for bigger ones (400g). The result was very different from the traditional (in the UK) boiled roe: the colour had changed and the inside was very soft and moist, meaning that the slices needed handling with care (and keeping the rind), but they were to my liking, after a quick searing in the pan (heavier searing for those liking a firmer texture). I have to try your 80C version, I understand that higher temperatures will also need longer times but I am a bit surprised by the 1h45, it sounds to me long even for 400g. But I’ll try it.’