## Common ground
All options describe sauces made from crustaceans, molluscs, and other aquatic invertebrates like shrimp, crab, and oyster.
## Options at a glance
**1605 – High-invertebrate sauce**
- **Defining trait:** Contains more than 20% by weight of crustaceans, molluscs, or other aquatic invertebrates.
- **Typical examples:** Rich seafood pastes, concentrated crab sauces, oyster-based gravies.
- **Best fit when:** The sauce is primarily made from seafood with a high proportion of whole or ground shellfish.
**2103.90 – Low-invertebrate sauce**
- **Defining trait:** Contains not more than 20% by weight of crustaceans, molluscs, or other aquatic invertebrates.
- **Typical examples:** Flavor enhancers, blended sauces with small seafood bits, umami-rich condiments.
- **Best fit when:** The sauce uses seafood mainly for flavor, not as the primary ingredient.
## Key differences
| Feature | 1605 | 2103.90 |
|--------|------|--------|
| Seafood content | >20% by weight | ≤20% by weight |
| Primary ingredient | Seafood (crustaceans/molluscs) | Non-seafood base with seafood flavoring |
| Use case | Main ingredient in dishes | Flavor booster or condiment |
## How to choose
- Does the sauce contain more than 20% crustaceans, molluscs, or aquatic invertebrates by weight? → 1605
- Is seafood used mainly for flavor, not bulk? → 2103.90
## Overlaps & pitfalls
A sauce with exactly 20% seafood falls under 2103.90 (not more than 20%). The distinction hinges on weight percentage, not taste or appearance. If the product’s main purpose is to deliver seafood as a core ingredient, use 1605; if it's a flavoring agent, use 2103.90. No option is vague—both are clearly defined by weight threshold