魚介

1. Origins, structure, and basic meaning

• Structure: 魚介 (ぎょかい) is a collective noun for fish and shellfish considered together as food.
• Basic usage: 新鮮な魚介を買う makes fresh seafood the market purchase, while 魚介のうまみ specifies the source of savory flavor brought out in soup.

2. Common pitfalls and similar expressions

• Seafood ingredients and their flavor
  • 魚介 is a collective category, not one fish. 魚介のうまみ is flavor derived from those ingredients; it does not use the same noun for both the seafood and the taste.