You do not declare what you want. There are permits you need to apply for.
Serious about needing a permit to import fresh fruit or frozen fish into Argentina?
I suggest you use a google search to see what products cannot legally be brought into the country in checked or carry on baggage.
If you do you might find this:
Prohibited: it is not permitted for any passenger to import the following as part of their accompanied baggage:
1. meat or meat products from any animal species (incl. sausages, cold cuts, ham);
2. dairy products or dairy bi-products;
3. bee products (honey, wax, etc);
4. fresh fruit and vegetables; flowers and plants with fruits, ornamental plants, trees or parts of trees, bulbs, seeds, rhizomes, buds etc;
5. insects, bacteria, fungi, viruses or any other micro-organisms for research or other uses;
6. semen, biological products used in veterinary medicine;
7. animal feed;
8. soil.
Source:
https://www.iatatravelcentre.com/AR-ARGENTINA-customs-currency-airport-tax-regulations-details.htm