Using dietary additives to improve palatability of diets containing single-cell protein from methanotrophic bacteria in yellowtail kingfish (Seriola lalandi) diets

Single-cell protein (SCP) derived from methanotrophic bacteria has significant potential as a fishmeal alternative in aquafeeds. However, SCP has known palatability issues, to overcome these issues tuna hydrolysate and garlic powder were tested as palatability enhancers against basal diets without these additives. This study tested the inclusion of SCP at four dietary levels of 0%, 10%, 20% and 30%, representing 0%, 25%, 50% and 75% fishmeal replacement in juvenile yellowtail kingfish (Seriola lalandi) (YTK) diets. YTK were fed these diets in triplicate over 35 days. Compared with the control diet, fish fed the SCP10% diet ate less feed, but had equal growth and subsequently an improved FCR. Feed intake decreased with increasing SCP inclusion, and the palatability enhancers were ineffective at improving intake. Despite the significant reduction in feed intake, FCR was equal across all SCP inclusion levels, demonstrating that the reduced growth performance at these higher inclusion levels was a function of only the reduced intake. Data showing equal protein retention efficiency and apparent digestibility coefficients across diets support this finding. This study showed that SCP derived from methanotrophic bacteria can replace 25% of fishmeal in a 400 g/kg FM diet and suggests if palatability issues can be overcome then higher inclusion of SCP could be achieved in YTK diets.