Abstract
Simple SummaryFish meal (FM), as the main protein source, is used in aquafeeds due to its good nutritional profile and palatability. In recent years, because of the high cost and uncertainty in FM supply, studies have been focused to identify and evaluate alternative protein ingredients to minimize FM and reducethe cost of formulated feeds. Currently, plant protein ingredients and animal by-products are used as alternative protein sources to FM, but these components have some nutritional limitations, such as beingrich in anti-nutritional elements and deficient in certain essential amino acids. Among alternative protein sources, single-cell protein (SCP) such as bacteria, yeasts and microalgae, is considered a promising substitute for animal- or plant-derived ingredients. In this work, we aimed to evaluate the replacement of FM with a bacterial SCP, a by-product of the monosodium L-glutamic acid produced by microbial fermentation of vegetal raw materials, in diets for rainbow trout (Oncorhynchus mykiss) fry. Results indicated that the maximum replacement of FM by SCP in terms of growth and feed efficiency performance was up to 50%, while the broken-line regression analyses using DHA muscle content and weight gain showed that this value ranged between 46.9 to 52% SCP depending on the parameter considered.A 60-day trial was conducted in rainbow trout (Oncorhynchus mykiss) fry (initial weight = 2.5 ± 0.6 g) to evaluate the potential use of a bacterial single-cell protein (SCP) as an alternative protein source. Five experimental diets with different levels of fishmeal replacement (0, 25, 50, 75 and 100%) and no amino acid supplementation were tested. At the end of the trial, we found that fry fed diets, replacing 25 and 50% of fishmeal with bacterial SCP, were 9.1 and 21.8% heavier, respectively, than those fed the control diet (p < 0.05), while Feed Conversion Ratio (FCR) values were also lower in comparison to the reference group. These results were also supported by Protein Efficiency Ratio (PER) and Lipid Efficiency Ratio (LER) values that improved in fish fed diets replacing 50% fishmeal by bacterial SCP. The inclusion of SCP enhanced Feed intake (FI) (p < 0.05), although FI was reduced at higher inclusion levels (>50%), which was associated to feed palatability. High levels of bacterial SCP (>50%) affected the muscular amino acid and fatty acid profiles, imbalances that were associated to their dietary content. The broken-line regression analysis using muscle DHA content and weight gain data showed that the maximum levels of fishmeal replacement by bacterial SCP were 46.9 and 52%, respectively.
Highlights
The rainbow trout (Oncorhynchus mykiss) is the most important cold-water cultivated fish species in Iran, of which theproduction has increased from 9000 t in 2010 to 718,736 t in 2018, placing this country as the world producer leader of this salmonid species [1]
The results of the present study indicated that bacterial single cell protein (SCP) obtained as a by-product of the monosodium L-glutamic acid production can replace up to 52% of the FM in compound diets containing 46% protein for rainbow trout fry without negatively affecting their growth and feed efficiency performances
The present study indicated that bacterial SCP, obtained as a by-product of monosodium L-glutamic acid production by means of microbial fermentation of vegetal raw materials, could replace up to 52%
Summary
The rainbow trout (Oncorhynchus mykiss) is the most important cold-water cultivated fish species in Iran, of which theproduction has increased from 9000 t in 2010 to 718,736 t in 2018, placing this country as the world producer leader of this salmonid species [1]. Bacteria, yeasts and microalgae are usually displayed to have the highest potential for aquafeeds, especially bacteria and yeasts that have a relatively high protein content (50–80% and 45–55%, respectively), and an amino acid profile comparable to FM. They can potentially be used as either functional feed additives or as alternative raw materials [6]. Regardless of their contrasted nutritional value and applicability in aquafeed formulation [2,3,12,13,14,15], their use is still limited due to the high cost of production [6,16]
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