Back when I used to work in hospitality, we'd defrost fish (both vac sealed and loose) in cold running water.
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].
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)