(Before answering this question, it’s worth noting that “kosher” rules — which are part of the Law of Moses — do not apply to Christians. For more on this, see the answer to ‘Is it okay for Christians to eat pork and shellfish?‘.)
The Law of Moses said:
“Of all that are in the waters you may eat these: whatever has fins and scales you may eat. And whatever does not have fins and scales you shall not eat” (Deuteronomy 14:9-10)
Puffer fish have no scales, so were not ‘kosher’ or ‘fit’ to be eaten. Instead, they have spines which become visible when the fish ‘puffs up’. Parts of the fish are edible, but other parts are lethally poisonous, causing dozens of deaths each year in countries like Japan where it is a delicacy.
Puffer fish live in warm waters, including those off the coast of Israel; but no one following the law of Moses would have died from eating it (because they would not have eaten it).
|A puffed up puffer fish shows its spines (rather than scales) in this picture from Islands in the Stream 2002, NOAA/OER.|