Preferisco il pesce fresco a quello surgelato.

In Italian, it is very common to use the definite article when talking about food or a category in general. So il pesce fresco can mean fresh fish as a general thing, not necessarily one specific fish.

English often drops the article in this kind of sentence, but Italian usually keeps it:

• I prefer fresh fish
• Preferisco il pesce fresco

Because in Italian, adjectives often come after the noun. The normal, neutral order is:

• pesce fresco
• carne fresca
• pane caldo

Putting the adjective after the noun is especially common when you are simply describing something. So pesce fresco is the most natural order here.

Because preferire is an -ire verb that takes -isc- in some present-tense forms.

Its present tense is:

• io preferisco
• tu preferisci
• lui/lei preferisce
• noi preferiamo
• voi preferite
• loro preferiscono

So preferisco is the correct form for I prefer.

After preferire, Italian normally uses a to mean to in the sense of comparison:

• preferire X a Y = to prefer X to Y

So:

• Preferisco il pesce fresco a quello surgelato

This does not mean movement toward something. It is just the preposition required after preferire when comparing two things.

Quello stands in for il pesce, so Italian does not have to repeat the noun.

So:

• quello surgelato = the frozen one

In natural English, you would usually say frozen fish, but Italian often uses quello/quella/quelli/quelle to avoid repetition.

The full repeated version would be:

• Preferisco il pesce fresco al pesce surgelato

Yes, absolutely. That sentence is correct too.

The only difference is that it repeats pesce, while quello avoids repetition and sounds smoother.

Also note the contraction:

• a + il = al

So:

• a il pesce surgelato → al pesce surgelato

Both words are related to freezing, but they are not exactly identical in feel.

• surgelato is very common for commercially frozen food
• congelato is more general and simply means frozen

In a sentence about food sold as fresh vs frozen, surgelato is especially natural.

Because they refer back to pesce, and pesce is grammatically masculine singular.

So the forms must agree:

• il pesce fresco
• quello surgelato

If the noun changed, the forms would change too:

• la carne fresca ... quella surgelata
• i gamberi freschi ... quelli surgelati
• le verdure fresche ... quelle surgelate

Here it means fish in general as food.

Italian often uses a singular noun with the definite article to talk about something as a general category:

• Mi piace la pasta
• Preferisco il pesce fresco
• Non mangio il burro

So il pesce fresco here is not necessarily one individual fish. It means fresh fish in a general sense.

You can, and you may hear:

• Preferisco il pesce fresco piuttosto che quello surgelato

But for learners, preferire X a Y is the clearest and most standard pattern.

So this is the best model to remember:

• Preferisco il pesce fresco a quello surgelato