The global expansion of aquaculture has led to increased demand on feed and feed ingredients, which are the main challenges to sustainability in aquaculture. The objective of this study is to investigate the potential of alfalfa nutrient concentrate (ANC) as an ingredient to replace fishmeal in feed for rainbow trout. The ultimate goal is to lay the groundwork for commercialization of value-added products from alfalfa in aquaculture feeds.
Five test diets were formulated (46% protein and 15% lipid) including different levels of ANC (0, 5, 10, 15, and 20%) to replace fishmeal (32% in the control diet) and were processed following a cooking extrusion protocol. Increasing levels of ANC resulted in increased pellet density and sinking pellets when the diet contained 20% ANC. However, increased water stability and durability were observed in response to the increased level of ANC inclusion. The five test diets were used to conduct two feeding trials in flow-through water systems with three replications per diet. The first trial tested feed intake and the apparent digestibility coefficient (ADC) of dietary nutrients. The results showed that ANC inclusion did not significantly impact the feed intake (P≥0.05) of rainbow trout under the experimental conditions. The ADC of dry matter and protein did not change due to fishmeal replacement, but the ADC of phosphorus was significantly (P<0.05) decreased in fish fed the 20% ANC diet. Another 9-week feeding trial was conducted to determine the effect of test diets on growth, nutrient utilization, metabolism and health of rainbow trout. Fish fed the test diets including 10% to 20% ANC had significantly lower grow rates and a higher feed conversion ratio than the fish fed the diet containing 0% or 5% ANC. Whole body composition and biochemical parameters of plasma were not different due to the different feeds except that the whole-body protein and plasma phosphorus levels decreased in the fish fed the ANC-based diets. Results based on liver metabolomic analysis showed that the 20% ANC diet significantly altered the metabolism of alanine, leucine, valine, and threonine as well as TCA cycle intermediates (succinate, malate, glycerol 3-P) and osmolytes (betaine).
The results of this study demonstrate that ANC did not influence food intake but decreased fish growth rate, which might be due to the impact of ANC on phosphorous digestibility and the alteration of nutrient metabolism under the test conditions. The potential of ANC use as an aquatic feed ingredient may be improved if the impact of phosphorous digestibility can be addressed. This is warrants for future investigation