A protein -dense bacterial single-cell protein [SCP:76-87% crude protein (CP) on dry matter (DM) basis] , produced from an environmentally friendly fermentation process , using a non- GMO Methylovorus menthalis , was examined as an alternative protein source in salmon feeds over a series of four in vivo studies . In a freshwater digestibility trial , triplicate groups of juvenile Atlantic salmon ( average weight: 23.7 ± 1.0 g), reared at a water temperature of 14 ± 0.2 °C, were fed two digestibility diets: one with a 100:00 blend (reference) and another with an 80:20 blend of reference to the test ingredient ( i.e., SCP). The study lasted 25 days, and fecal material was collected using the passive settling column method. Results demonstrated that nutrients in SCP were highly digestible, with apparent digestibility coefficients of DM , CP , energy, and essential amino acids of 85.3%. 92.4%, 87.9% and 85.5-100.0%, respectively.
In a freshwater growth study , SCP was tested i n four diets with graded inclusion levels of SCP (0: control , 10, 20 and 30%) by replacing a mixture of commonly used animal and plant protein ingredients . Each diet was fed to triplicate groups of 35 juvenile fish (27.5 ± 0.7 g) for 84 days at a water temperature of 14.2 ± 0.3 °C . Fish fed diets with up to 20% SCP showed feed intake and weight gain comparable to the control group. At the 30% inclusion level of SCP, FI and WG significantly decreased compared to the control, but FCR remained consistent across all treatments, ranging from 0.9 to 1.0.
In a 132-day saltwater growth study , post-smolt fish (423.7 ± 3.8 g), reared at a water temperature of 13.8 ± 0.4 °C, were fed one of four experimental diets containing 0, 10 , 20 and 30 % inclusion levels of SCP. The feed formulation aimed to primarily replace soy protein concentrate (soy PC) from 24-0% . The findings revealed no significant differences in FI and WG among fish fed 0-20% SCP. The 30% SCP-fed group exhibited inferior feed consumption and growth performance compared to the other groups , but all groups achieved FCR values of 0.9-1.0 .
In a 168-day saltwater growth study, four experimental diets with 0, 8, 16 and 24% inclusion levels of SCP, replacing soy PC, were fed to triplicate groups of post-smolt fish weighing 1005.9 ± 22.7 g. Fish were reared at a water temperature of 13.7 ± 0.5 °C . Findings showed no significant difference in FI, WG and FCR between treatments , whereas fish fed SCP from 8-24% had notably higher fillet redness than fish fed the control.
In saltwater trials, whole-body proximate, amino acid, and fillet fatty acid profiles were similar across all dietary treatments. Blood biochemistry and gut histopathology showed no abnormal health signs or enteritis symptoms. The studies concluded that SCP is highly digestible for Atlantic salmon and can be safely included in their diets up to at least 20%.