I have, in 40+ years of eating whitebait, never heard of anyone poaching them. To my knowledge, they should be lightly coated in seasoned flour, and then fried in very hot oil until golden in colour and crisp in texture. Poaching them would make them soft at best, and disintegrate at worst. They should be crisp enough to eat with the fingers if need be.
I'd strongly advice against that. A cure only works as long as the salt and sugar concentrations are high enough. And although Gravlax does a decent job of infusing the salmon with both the content in the salmon itself is not nearly high enough to keep it preserved, it is the crust on the fish itself that keeps it ok to eat.
It is not a problem to keep your ...
The "24 hours" time is irrelevant.
The only issue is the temperature of the meat at the time you rescued it.
If the bags are still frozen, it should be okay.
If not, but the meat still feels very cold, it's probably okay.
But if the meat is warmer (over 4°C), you have no idea how long it has been warm enough for bacteria to grow, so don't take a chance.
In The Art of Fermentation, Sandor Katz notes that he has fermented shiitake and some other mushrooms, but does not specify fresh or dried.
Christopher and Kristen Shockey, authors, owners of Mellonia Farm and the website Ferment Works, include a recipe for Pickled Shiitake in their book Fermented Vegetables that calls for dried shiitake. In the recipe ...
Fish is tricky because the smell does not come from bacteria but from degrading enzymes. Cod tends to smell fairly early while being perfectly good to eat.
More generally for food to spoil you need water, warmth, a nutrient and oxygen (in most situations),so in the case of your fish it is likely to be good to eat, being vacuum packed and chilled.
The water ...
I guess it's impossible to say yes or no as to whether it is safe.
However, I did manage to conclude it was not safe. Whilst waiting for responses, I left the fish out (out of the packet, towel dried and resting on the side in a cool room).
After those 30 minutes, the fish stunk! I don't know why it didn't smell straight away! I know when I open duck out ...
There are many recipes on the internet for lacto-fermented products. There are saurkrauts fermented with caraway and kim-chi and countless others.
I would avoid the oil containing products as I have never seen that in a recipe and think it would form a layer that cuts off exchange of gas, producing a potentially anaerobic environment.