Salmon or trout from the wild have pink or red flesh because of their diet, which includes crustaceans or insects. However, fish raised in ponds or sea pens often have pale pink flesh due to the feeds that they take in. Thus, fish farmers add dyes derived from petroleum to the fish feed to improve the fish flesh coloration. Scientists from Royal Holloway University of London and partners developed an environment-friendly alternative to achieve the pinkish in fish flesh. Instead of making dyes from petrochemicals, they genetically engineered tomatoes to produce high levels of ketocarotenoids or high value pigments used in food and feed.

The researchers used Moneymaker tomato variety that had been genetically edited to add bacterial DNA associated with producing ketocarotenoids. Then they crossbred the modified tomatoes with another variety that expresses elevated levels of beta-carotene. This led to a new variety of tomato with high levels of ketocarotenoids. The fruits were freeze-dried and powdered then mixed into fish feed. The researchers found that the fish absorbed roughly twice as many ketocarotenoids from tomato as they did from the same amount of petrochemical-derived dye.

Read more information, read Hakai Magazine and PNAS.

Figure: Fish raised in ponds and pens are often pale or tinted gray. Farmers use dyes to give the fish a pink hue. Photo by Olena Danileiko/Alamy Stock Photo