Dear Don - two versions of this haven't been posted yet - - so one more time:

Dear Dr Stadlen,

Perhaps to lay your mind at rest - -

The woman buys fish when it is already dark,whereas a traditional Jewish woman would have prepared the Sabbath meal long before dusk.

Actually - - she doesn't buy the fish, does she? She remembers something and changes her mind, arriving home just ten minutes after her husband. I thought she remembered that he didn't have the key, but perhaps she remembered the Sabbath too.

Thanks to Jansy I can provide the relevant part of the text:

When they emerged from the thunder and foul air of the subway, the last dregs of the day were mixed with the street lights. She wanted to buy some fish for supper, so she handed him the basket of jelly jars, telling him to go home. He walked up to the third landing and then remembered he had given her his keys earlier in the day.  

In silence he sat down on the steps and in silence rose when some ten minutes later she came, heavily trudging upstairs, wanly smiling, shaking her head in deprecation of her silliness. They entered their two-room flat and he at once went to the mirror. Straining the corners of his mouth apart by means of his thumbs, with a horrible masklike grimace, he removed his new hopelessly uncomfortable dental plate and severed the long tusks of saliva connecting him to it. He read his Russian-language newspaper while she laid the table. Still reading, he ate the pale victuals that needed no teeth.

My italics, of course, suggest that they did not eat fish - - though fish is pale, I should think it difficult to eat fish without one;s teeth.