Defrosting vac sealed fish in cold water over 20 minutes and immediately cooking it carries roughly zero risk of botulism, for 2 reasons:
1. The optimal growth temperature for C. botulinum is between 20-45 C [1], exponentially dropping off outside that range. That's why improperly canned food is risky, as it's usually stored in that range for weeks or months.
2. The bacteria is slow growing and doesn't cause illness itself, it also can't grow in the acidic conditions of the adult human gut. Rather, it's the excreted toxin that's dangerous, which takes several days to form [2].
[1] https://www.publish.csiro.au/bi/pdf/bi9530178 (p.p. 182)
[2] https://journals.asm.org/doi/pdf/10.1128/aem.62.8.3069-3072.... (p.p. 3071)
The what now? My fridge at home is uniformly at 4C, surely that can't be dangerous.
What high-speed defrosting methods are there to replace this? is it okay to just open the fish for 30 minutes, re-seal it and then put it in the recirculator?
Really I'm just concerned about a reliable method of defrosting which doesn't take a week. Putting food from the freezer into the fridge has been a hit-and-miss endeavour sometimes taking up to a week.