Analysis of retinol, 3-hydroxyretinol and 3,4-didehydroretinol in North American farm-raised freshwater fish liver, muscle and feed

Vitamin A (VA) is an essential micronutrient in fish, vital for reproduction, vision and immunity. Freshwater fish species store and use VA in the form of retinol (ROL), as well as uncommon forms such as 3,4-didehydroretinol (DROL) and 3-hydroxyretinol (3ROL). We developed and validated an HPLC method capable of measuring ROL, DROL and 3ROL in the feed and tissues of North American freshwater fish, for which little information on retinoid concentrations is available. DROL and ROL were higher than expected in both fish feed and fish liver (at 9.5-29.6 mg kg^-1 DROL and 26.9-79.2 mg kg^-1 ROL for feed; and 19.8-548.8 μg g^-1 DROL and 10.4-128.8 μg g^-1 ROL for liver). Interestingly, DROL concentrations were lower than ROL in fish feed, but often substantially higher in fish liver. Concentrations of ROL and DROL were similar to each other in muscle. 3ROL was detected in fish liver only. To our knowledge, this is the first publication to measure DROL concentrations in North American farm-raised fish and commercial fish feed. Monitoring of not only ROL, but DROL and 3ROL as well, may be advisable to better assess the VA content of fish feed and tissue.