1. Naturally occurring pigmentation: The distribution and intensity of these pigment spots vary from fish to fish, and they are not indicative of any health issues or quality concerns. They're simply part of the fish's natural coloration.
2. Handling during processing: Sometimes, black spots can be caused by bruising of the fish during processing, transportation, or improper handling. As a result of damage to the skin, some pigment cells may leak into the flesh, leading to the formation of black spots.
3. Genetics and breeding: The occurrence of black spots in trout can also have a genetic component, meaning certain strains or breeds of trout may be more likely to exhibit these spots. Selective breeding for specific physical traits, such as improved coloration, can affect the presence and distribution of black spots in farmed rainbow trout.
It's important to note that black spots in trout fillets are harmless and do not affect the taste, texture, or safety of the fish. They are simply cosmetic and do not pose any health risks to humans when properly cooked and consumed.
If you observe black spots on rainbow trout fillets, you can rest assured that it's usually just a natural variation in the fish's pigmentation and not a sign of anything harmful.