Seafood, including fish and shellfish, is highly perishable because of its biological composition and the conditions in which it is harvested. Here’s why it spoils so quickly:
1. High Moisture Content
Fish and shellfish contain a lot of water, which creates an ideal environment for bacterial growth and enzymatic activity that lead to spoilage.
2. Unsaturated Fats
Unlike land animals, fish have a high concentration of unsaturated fats, particularly omega-3 fatty acids. These fats oxidize quickly when exposed to air, leading to rancidity and a "fishy" smell.
3. High Enzyme Activity
Fish and shellfish have active enzymes that break down muscle tissue rapidly after death. This process softens the flesh and contributes to spoilage.
4. Bacterial Load
Seafood naturally carries bacteria adapted to cold water conditions. When the fish is stored at warmer temperatures, these bacteria multiply rapidly, accelerating spoilage.
5. Weak Connective Tissue
Fish muscle structure is different from land animals—it has weaker connective tissue, which means the flesh breaks down much faster.
6. Ammonia and Trimethylamine (TMA) Production
As fish decomposes, it releases ammonia and TMA, compounds responsible for the strong, unpleasant smell of spoiled seafood.
How Long Does Fresh Seafood Last?
The shelf life of fresh seafood depends on storage temperature and type:
Type of Seafood | Refrigerated (0-4°C / 32-40°F) | Frozen (-18°C / 0°F or lower) |
---|---|---|
Fresh Fish (whole) | 2-3 days | 3-6 months |
Fresh Fish (fillets) | 1-2 days | 3-6 months |
Shellfish (shrimp, crab, lobster) | 1-2 days | 6-12 months |
Oysters, Mussels, Clams (live) | 1-2 days | Not recommended (except shucked) |
Scallops | 1-2 days | 3-6 months |
Cooked Seafood | 3-4 days | 2-3 months |
Best Practices for Extending Freshness
- Keep seafood cold: Store it on ice or in the coldest part of the fridge.
- Dry storage for shellfish: Keep live shellfish in a breathable container with a damp cloth (not in airtight plastic).
- Freeze properly: Use airtight packaging to prevent freezer burn.
- Use quickly: The fresher the seafood, the better the taste and safety.
How to Tell If Seafood Has Gone Bad
Since seafood is highly perishable, knowing the signs of spoilage can help you avoid food poisoning and unpleasant meals. Here’s what to look for:
1. Appearance
Fish (Whole & Fillets)
- Fresh fish should have clear, bright eyes (for whole fish) and shiny, moist skin.
- If the flesh looks dull, discoloured, or dry, it’s starting to spoil.
- Brown or yellowish patches (oxidation) are a sign of age.
Shellfish (Shrimp, Scallops, Lobster, Crab, etc.)
- Should be firm and translucent.
- If they appear milky, slimy, or greyish, they are likely bad.
Oysters, Clams, and Mussels (Live)
- Shells should be tightly closed or close when tapped.
- If they remain open, they are dead and unsafe to eat.
2. Smell
- Fresh seafood has a mild, ocean-like smell (like saltwater or seaweed).
- If it smells strongly “fishy,” sour, or like ammonia, it is spoiled.
3. Texture
- Fresh fish and shellfish should feel firm and springy when touched.
- If the flesh is mushy, sticky, or slimy, it has started to break down.
4. Expiration Date & Storage Time
- If the seafood is past its sell-by or use-by date, it’s safer to discard it.
- Even before the expiry date, always check for smell, texture, and colour changes.
5. Cooking Reaction
- If seafood smells overly strong while cooking, it may have gone bad.
- Shellfish (like shrimp and scallops) that fail to firm up or release excess liquid when cooked may be past their prime.
Safe Consumption Tips
- When in doubt, throw it out. Spoiled seafood can cause serious food poisoning.
- Cook seafood properly (internal temp of 63°C / 145°F for fish, 74°C / 165°F for shellfish).
- Don’t refreeze thawed seafood unless it was thawed in the fridge.
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