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Fresh fish – Defining What “Fresh” Means for Sushi Fish

Updated: Mar 18

Fresh Tai Red Snapper
Fresh Tai Red Snapper

What does fresh fish mean?

I often talk about the freshness of fish during the sushi class. Then, one participant asks me, “What do you mean by fresh?” I become speechless. I always thought fresh means fresh. Then, when it is time for me to explain what I mean by fresh, I find myself not being able to explain what I just said.

On the way home, I am thinking, asking myself what does it mean to be fresh? Is it about how old the fish is? Sort of. Then, if the fish is kept under the sun for two hours, it will lose it’s freshness. Fish that is gutted and gills removed will remain freshener compared to the fish whose not gutted and gills removed because bacteria and enzymes from internal organs and gills will start breaking down its flesh. How about fish that is kept in a refrigerator whose temperature is higher?

When I look at the dictionary definition, fresh means:

having its original qualities unimpaired: such as

  1. full of or renewed in vigor

  2. not stale, sour, or decayed

  3. not faded

  4. not worn or rumpled

  5. not altered by processing

  6. having the milk flow recently established

It’s time to ask Chat GPT.

I've been using Chat GPT and the GPT I created, "Everything Sushi" to help me answer some of my questions, It's been extremely useful.


The term "fresh" in the context of food, particularly seafood, has several key attributes:

Recently Harvested or Caught:

Fresh food, like seafood, is typically harvested or caught as close as possible to the time of consumption. This minimizes the time for any spoilage or degradation in quality.

Minimal Processing:

Fresh seafood usually undergoes minimal processing. It's often sold in its natural state, without being frozen, canned, or significantly altered in any way.

Appearance and Texture:

Fresh seafood should look vibrant and have a firm texture. For fish, the eyes should be clear and bulging, the skin should be shiny and moist, and the flesh should spring back when touched.


Fresh seafood should smell like the sea, not fishy or ammonia-like. A strong, unpleasant odor is a sign of spoilage.


When cooked, fresh seafood should have a clean, mild flavor characteristic of that particular species, without any off-tastes.

Storage and Handling:

Proper storage and handling are crucial for maintaining freshness. Seafood should be kept at cold temperatures, ideally on ice, and protected from cross-contamination.

In the context of sushi and sashimi, "freshness" also involves how recently the seafood was alive. In many high-end sushi restaurants, some seafood items are kept alive until they are prepared, ensuring maximum freshness. However, for some types of seafood, including certain fish and shrimp like amaebi, being "fresh" can also mean being flash-frozen soon after catch to kill parasites while preserving quality and taste.

Me: What would you call fish caught two hours ago, left under the sun, starting to spoil? Is it still considered as fresh?

Chat GPT: Fish caught two hours ago but left under the sun and starting to spoil would not be considered fresh. Despite being recently caught, the key factor here is the spoilage process that has begun due to improper handling and storage.

Freshness in seafood is not determined solely by the time elapsed since catching but also significantly by how it is stored and handled during that time. Proper storage typically involves keeping the fish at cold temperatures, ideally on ice, and protecting it from exposure to heat and sunlight, which accelerates spoilage.

In this scenario, the fish has been exposed to conditions that compromise its quality, freshness, and safety, making it unsuitable for consumption, especially in raw preparations like sushi or sashimi. Fresh fish should maintain its quality, appearance, texture, and smell, all of which are likely negatively affected in the fish left under the sun.

Me: What other conditions that would make two hour old fish not fresh?

Chat GPT: Several conditions can render a two-hour-old fish not fresh, affecting its quality and safety for consumption:

Improper Temperature Control:

If the fish is not kept at a sufficiently cold temperature (ideally on ice or in a chilled environment), it can start to spoil quickly. Fish are highly perishable and need to be kept cool to slow down bacterial growth and decomposition.

Exposure to Contaminants:

If the fish comes into contact with contaminants or unsanitary surfaces, it can become unsafe to eat. This includes exposure to chemicals, unclean water, or cross-contamination from other food sources.

Physical Damage:

If the fish is mishandled, causing bruising or tearing of the flesh, its quality can deteriorate rapidly. Physical damage can also make the fish more susceptible to bacterial invasion and spoilage.

Exposure to Sunlight or Heat:

As in your previous example, exposure to direct sunlight or high temperatures can accelerate spoilage and bacterial growth.

Lack of Aeration:

If the fish is stored in a manner that doesn't allow for adequate air circulation, it can lead to faster spoilage. Proper aeration helps in maintaining optimal conditions for preserving the fish's freshness.

Moisture and Humidity:

Excessive moisture or high humidity can promote bacterial growth and spoilage, especially in warm conditions.

Delayed Gutting or Cleaning:

Delay in gutting or cleaning the fish can also lead to a decrease in freshness. Internal organs can decompose quickly, affecting the quality of the fish.

Even if the fish is just two hours post-catch, any of these conditions can significantly compromise its freshness and suitability for consumption, particularly in raw preparations.

Me: Can you explain what fresh means for sushi fish?

Chat GPT: In the context of sushi, the term "fresh" can be somewhat misleading. While it might intuitively mean "just caught," the best sushi fish often isn't the freshest in the traditional sense. Here's a breakdown of what "fresh" really means for sushi fish:

Aging and Flavor Development:

Certain types of fish, like tuna and salmon, benefit from a controlled aging process. After being caught, these fish are often aged for a specific period to allow the flavors to develop and intensify. This process can enhance the taste and texture of the fish, making it more suitable for sushi. For example, tuna may require around five days to mature to full flavor, and salmon can also benefit from a brief aging period.

Texture and Firmness:

Freshly caught fish can sometimes be too tough or lack flavor. Aging allows the flesh to tenderize and develop a more desirable texture for sushi. This is particularly true for certain types of white fish like halibut.

Freezing for Safety:

Contrary to what might be expected, "fresh" sushi fish is often frozen. Freezing is a critical safety measure to kill parasites. The U.S. Food and Drug Administration (FDA) recommends freezing at specific temperatures for a certain duration to ensure that any parasites are destroyed. This is especially important for fish like salmon, which is known to carry parasites.

Handling and Processing: Freshness also refers to the way the fish has been handled and processed after being caught. Proper handling minimizes the growth of bacteria and maintains the quality of the fish. This includes maintaining the cold chain from the moment the fish is caught until it is prepared as sushi.

Appearance and Quality Indicators:

Fresh sushi fish should have a vibrant color (deep red for tuna, bright and clear for white fish), clear and bright eyes, bright red gills, firm flesh, and a shiny appearance. These characteristics indicate that the fish is of high quality and has been properly handled.

In summary, "fresh" for sushi fish is a combination of proper aging, safe freezing practices, meticulous handling, and overall quality preservation, rather than just being recently caught.

Me: How do you define the word fresh?

GPT: The word "fresh" generally refers to something that is newly made, obtained, or experienced. In different contexts, its definition can vary slightly:

Food and Produce:

In the context of food, particularly perishable items like fruits, vegetables, fish, and meat, "fresh" often indicates that the item is recently harvested, caught, or prepared. It suggests that the food is in its natural state, not preserved or frozen, and is still in its peak condition in terms of flavor, texture, and nutritional value. For example, fresh fish typically means it hasn't been frozen or treated and is relatively recently caught.

General Usage:

More broadly, "fresh" can describe something that is new or different in a refreshing way. It can refer to ideas, perspectives, or experiences that are novel or revitalizing.

Appearance and Sensation: It can also describe the appearance or sensation of being clean, invigorating, or crisp. For instance, fresh air is clean and possibly cool, suggesting a rejuvenating quality.

Unspoiled or Untainted:

"Fresh" is sometimes used to indicate that something is not spoiled, stale, or degraded. For example, fresh water typically means it's clean and safe for drinking, as opposed to stagnant or contaminated water.

In essence, "fresh" conveys a sense of newness, cleanliness, and purity, whether it's used in reference to food, experiences, or objects.

Me: What would you call fish caught two hours ago, left under the sun, starting to spoil? Is it still considered as fresh?

GPT: Fish caught just two hours ago would initially be considered very fresh in terms of time since catch. However, if it has been left under the sun and is starting to spoil, it would no longer be regarded as fresh. The quality of fish deteriorates rapidly, especially under improper storage conditions like exposure to direct sunlight and warm temperatures. Such conditions accelerate bacterial growth and spoilage, making the fish unsafe for consumption, particularly in raw preparations like sushi.

In this case, despite being recently caught, the fish would be classified as spoiled or degraded due to the improper handling and storage. Freshness in seafood is not only a matter of how recently it was caught but also how well it has been preserved from the time of catch to the point of consumption. Proper handling, including keeping the fish at a cool temperature and protecting it from environmental factors, is crucial to maintain its freshness.

Me: Given this, would you define "Fresh" as: Combination of time, and how the fish is stored.

What do you think about this definition?

GPT: Your definition of "fresh" as a combination of time and how the fish is stored is quite accurate and well-suited, especially in the context of seafood. This definition comprehensively captures the two critical aspects that determine the freshness of fish:

Time Since Catch: This aspect acknowledges that the closer the time of consumption is to the time of catch, the more likely the fish is to retain its original quality, flavor, and nutritional value, assuming it has been properly handled.

Storage Conditions:

This is equally important because even recently caught fish can rapidly deteriorate if not stored correctly. Proper storage usually involves keeping the fish at a consistently cool temperature, often on ice, and protecting it from environmental factors like sunlight, oxygen, and contaminants that can accelerate spoilage.

By incorporating both these elements, your definition effectively addresses that freshness is not just about the time elapsed since the fish was caught but also critically depends on the care taken during its handling and storage. This is particularly important for fish intended for raw consumption, such as in sushi, where the freshness directly impacts both the taste and safety of the dish.

Me: Anything you would add to the above definition?

GPT: The definition you've provided for "fresh" in the context of fish — focusing on a combination of time since catch and storage conditions — is quite comprehensive. However, a few additional nuances could further refine this definition:

Quality at Time of Catch:

The condition of the fish at the time of catch also plays a role. Fish that is healthy and in good condition when caught will likely remain fresher for a longer period post-catch compared to fish that was stressed or in poor health.

Method of Catch and Handling:

How the fish is caught and handled immediately after catch can affect its freshness. For example, fish that is caught and immediately bled, gutted, and iced will retain its freshness longer than fish that is not processed quickly.

Sensory Characteristics:

Freshness can also be defined by sensory characteristics such as appearance (bright, clear eyes and shiny skin), smell (should not be overly fishy or ammonia-like), and texture (firm flesh that springs back when touched).

Safety for Consumption:

Especially relevant for fish intended for raw consumption, the definition of freshness should implicitly include its safety for eating. This includes considerations for parasites and microbial spoilage.

Adding these aspects provides a more holistic understanding of what constitutes "freshness" in seafood, emphasizing that it's a multifaceted concept influenced by various factors from the point of catch to the point of consumption.

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