It's possible that you're thinking of:
* CO2 (Carbon Dioxide): This is commonly used in the food industry for various purposes, including:
* Packaging: To extend shelf life and prevent spoilage by creating a modified atmosphere.
* Freezing: To freeze fish quickly and evenly, preserving its quality.
* Cleaning: To remove impurities and reduce microbial contamination.
* Other Treatments: Perhaps the term "CO" is a shorthand or a misunderstanding of some other specific fish processing techniques.
To clarify what you mean, could you provide more context? For example:
* Where did you encounter this term?
* What kind of fish were you looking at?
* What was the context surrounding the term?
With more information, I can help you understand what "CO treated fish" might actually refer to.