Optimization of dietary manganese for rainbow trout, Oncorhynchus mykiss, fed a plant-based diet

Authors: Welker, Thomas; Barrows, Frederic; Overturf, Kenneth - Ken; GAYLORD, GIBSON - Us Fish And Wildlife Service; Abernathy, Jason

Submitted to: Journal of the World Aquaculture Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/5/2017
Publication Date: 2/2/2018
Citation: Welker, T.L., Barrows, F., Overturf, K.E., Gaylord, G., Abernathy, J.W. 2018. Optimization of dietary manganese for rainbow trout, Oncorhynchus mykiss, fed a plant-based diet. Journal of the World Aquaculture Society. 49(1):71-82. https://doi.org/10.1111/jwas.12447.
DOI: https://doi.org/10.1111/jwas.12447

Interpretive Summary: Current vitamin and mineral requirements for fish feeds were determined using either semi-purified diets or diets utilizing fishmeal as the primary protein source. As the demand for fishmeal continues to increase for use in animal feeds, availability will likely further decline and price increase. Therefore, incorporation of alternative protein sources, especially from plants, into fish feeds will increase. However, the nutrient composition and bioavailability is often different for plant protein sources compared to fishmeal, and mineral and vitamin requirements are likely different for fish, including rainbow trout, fed plant-based diets. Determination of mineral requirements for rainbow trout fed a plant-based feed is vital for optimal growth and health. We fed juvenile rainbow trout a diet formulated with plant-based protein sources. These diets were supplemented with manganese (Mn) at various concentrations for 12 weeks. We determined that 5 mg/kg diet of additional Mn is required to produce the best growth performance in rainbow trout fed a plant-based diet. Refinement of mineral requirements, such as Mn, as fish farmers move from traditional fishmeal-based feed to an all-plant diet is vital to produce the best growth and health in farmed rainbow trout.

Technical Abstract: A study was conducted to determine the optimal level of manganese (Mn) supplementation for rainbow trout fed a plant-based diet. Juvenile rainbow trout (approximately 20 g) were fed either a fishmeal control (reference only) or a plant-based diet with inorganic Mn added at 0, 0.5, 1, 2, 4, 8, 16, or 32 mg/kg diet (n=three tanks per diet; 30 fish per tank) for 12 weeks. Whole body Mn concentrations increased with increasing dietary levels. Rainbow trout fed 2, 4, or 8 mg Mn/kg diet exhibited weight gain (WG) that was significantly higher than fish fed 0, 0.5, 1, 16, and 32 mg Mn/kg diet. Feed conversion (FCR) showed a similar trend as WG. Feed conversion decreased (better feed conversion) with increasing dietary Mn until concentrations reached 8 mg/kg Mn, after which they increased. Trout fed plant-based diets supplemented with 16 or 32 mg/kg Mn showed significantly poorer FCR compared to the other experimental diets. A rational non-linear model (R2=0.84) fit to weight gain data showed that the optimal predicted supplementation level for Mn was 4.8 mg/kg. A rational model also provided the best fit for the FCR data, but the fit (R2=0.34) was poorer compared to weight gain. The optimal predicted supplementation level for Mn was similar for FCR (5 mg Mn/kg diet). This level is much lower than the NRC (2011) recommended supplementation level of 12 mg/kg diet. The recommended total dietary concentration of Mn was approximately 63 mg/kg in plant-based diets fed to rainbow trout in this study to promote optimal growth and health.