Flavour enhancement of freshwater farmed barramundi (Lates calcarifer), through dietary enrichment with cultivated sea lettuce, Ulva ohnoi

• A functional feed that alters the flavour of farmed freshwater fish is described.
• Diets containing 20–30% Ulva ohnoi increased marine-type flavours in farmed freshwater fish.
• Changes to flavour were achieved within 7 days and increased in intensity up to 21 days.
• An 8 fold increase in dimethylsulfide was observed in fish fed Ulva ohnoi diets.

Nutrition plays an important role in shaping the organoleptic properties of fish as key flavour compounds are principally sequestered from the diet. Conventional aquaculture feeds are primarily formulated to maximise somatic growth with little consideration given to the effect on organoleptic attributes such as flavour, taste and aroma. We assessed the efficacy of the marine macroalgae Ulva ohnoi to alter the organoleptic properties of cultured freshwater barramundi (Lates calcarifer) by feeding a short term finishing diet. Barramundi were finished on diets containing 0%, 10%, 20% and 30% of dried U. ohnoi for 7, 14 and 21 days. Following harvest the organoleptic properties of fish were subjected to human sensory assessment. The flavour of barramundi finished on diets containing ≥ 20% inclusion level of U. ohnoi was described as being more ‘desirable’, ‘sweeter’, and ‘rich and complex’ when compared to fish finished on a standard commercial rearing diet. Fish finished with U. ohnoi also developed a crab-like/seafood flavour and a cooked crab aroma, resulting in significant increases in these organoleptic attributes.Fillets were subsequently analysed for bromophenol compounds and dimethylsulfide. Bromophenols were not detected at any time in fillets of barramundi that were finished on either U. ohnoi or a standard commercial diet. However, dimethylsulfide was found to be more elevated (~ 8 fold) in fish fed U. ohnoi.Feeding cultured freshwater fish a diet containing the marine algae U. ohnoi was effective in altering the organoleptic profile of fillets, imparting a rich and complex seafood-like flavour. The potent flavour compound dimethylsulfide was associated with this change and appears to be a key flavour compound in this instance. The application of a finishing diet that enhances flavour and aroma properties pre-harvest would enable aquaculture growers to exert direct control over these properties. This is especially important for freshwater finfish species as growers could conceivably produce fish that have organoleptic similarity with wild caught marine species.Statement of relevanceA functional feed providing a mechanism to produce low cost freshwater fish with flavours that are more characteristic of wild caught marine species is presented. This diet caused farmed freshwater fish to develop marine aromas and flavours and increased sweetness and flavour complexity during 21 days of feeding.