Reference for Chullin 149:21

בעי רב חסדא

only in the case of animals whose vital force is considerable but not in the case of fishes whose vital force is slender.<span class="x" onmousemove="('comment',' It might therefore be said that a fish, considering its low state of vitality the moment it sustains a physical injury is regarded as dead and is susceptible to contract uncleanness.');">¹²</span>

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