Abstract
Replacement of fishmeal in feeds is critical for sustainable aquaculture growth. However, replacement with plant protein concentrates reduces fish performance. A rainbow trout strain selected for high performance on a plant protein diet was compared to a non-selected strain to identify physiological mechanisms associated with improved performance. Nutrient digestibility in fishmeal and plant protein diets was assessed and no strain differences were found. Levels of amino acids in the hepatic portal vein and caudal vein were measured at intervals after a single force-feeding of fishmeal, four plant protein concentrates, and a mixture of the concentrates with or without supplementation of three limiting amino acids. Each ingredient affected plasma amino acid levels in a singular manner when fed individually but without predictable additive effects when fed as a mixture. Amino acid supplementation altered uptake and plasma concentrations of all the essential amino acids. The selected trout strain fed the plant protein mixture with amino acids showed a synchronous and homogenous pattern for essential amino acids over time in the hepatic portal vein in contrast to that of the non-selected strain. The results demonstrate that selection favorably altered temporal dynamics of plant protein digestion.
Highlights
Replacement of fishmeal in feeds is critical for sustainable aquaculture growth
There are several factors blamed for reduced growth of carnivorous fish fed plant protein-based diets, including reduced feed intake, antinutrients in plant products, differences in levels of biologically significant components, such as anabolic steroids or phytoestrogens in plant proteins compared to fishmeal, unidentified nutrient deficiencies and an imbalance of essential amino acids[9,10,11] In the case of the later, plant proteins generally have less lysine, methionine and threonine compared to fishmeal and are often deficient compared to dietary requirements of fish[3]
In the caudal vein (CV), plasma amino acid concentrations did not differ significantly for the two strains fed either ingredient. These results suggest that selection has altered the temporal dynamics of plant protein digestion and absorption, providing an explanation for the higher growth and protein retention observed in the selected strain fed plant protein-based diets
Summary
Replacement of fishmeal in feeds is critical for sustainable aquaculture growth. replacement with plant protein concentrates reduces fish performance. Numerous studies have shown suboptimal fish growth performance and reduced protein retention efficiency when carnivorous fish species are fed low-fishmeal, high-plant protein feeds even when all known dietary essential nutrients, including amino acids, are present above required levels[4,5,6,7,8]. Protein synthesis in cells requires that all essential amino acids are available at the moment proteins are synthesized; if one essential amino acid is not present in sufficient amounts, the remaining amino acids are alternatively metabolized for energy[3] This may result in lower protein retention efficiency and increased protein turnover, a common observation when fish are fed plant-based feeds[5,6,7,13]. The selected strain can be considered as a model to explore and identify physiological parameters associated with improved plant protein utilization in carnivorous fish
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