By: Aquaculture Magazine Editorial Team
Replacing fish meal in the feeds using various conventional and non-conventional protein sources has been the core subject of several studies. In this context, growth and digestibility trials were undertaken to evaluate a single cell protein (SCP) produced from methane-oxidizing bacteria Methylococcus capsulatus (String Bio, Bengaluru, India) as a replacement for fishmeal in the diets of Pacific white shrimp, Penaeus vannamei.
As the aquaculture sector continues to grow, there is an increasing demand for formulated feeds and protein. Feed based farmed fish and shrimp have been the largest consumers of capture fishery derived feedstuffs in the form of fishmeal (FM) and fish oil.
Although the use of fishmeal in aquatic animal feeds has many benefits, its inclusion level is reducing due to fluctuations in global availability, price instabilities, quality criteria and also in response to sustainability issues.
Replacing fish meal in the feeds using various conventional and nonconventional protein sources has been the core subject of several studies. One such alternative is the Single Cell Proteins (SCP) which belong to a broad class of constituents that includes bacterial, yeast and microalgal derivative products.
SCP has a high protein content with a very good essential amino acid (EAA) profile similar to that of fishmeal; with consistent availability and traceable production, and also holds a high sustainability index.
Pacific white shrimp is the most important farmed crustacean species in the world and its production has increased rapidly especially in India over the recent years. This has led to a consistent increase in demand for the production of shrimp feeds relying less on FM as the primary protein source using suitable and sustainable alternative protein sources.
Here are presented the results from a study designed to evaluate the SCP on growth performance and digestibility trials of Pacific white shrimp, Penaeus vannamei, using diets containing graded levels of SCP.
Materials and methods
Growth and digestibility trials were undertaken simultaneously to evaluate the single cell protein (SCP) as a replacement for fishmeal in the diets of Pacific white shrimp, P. vannamei and to determine the digestibility of the SCP.
For the growth trial, five isonitrogenous and isoenergetic diets were formulated to contain differentlevels of SCP: Control (Fishmeal, no SCP), SCP inclusion at 50 g/kg (S-5), 100 g/kg (S-10), 200 g/kg (S-20), 250 g/kg (S25). The feed formulation and their proximate composition are pre – sented in Table 1.
Results
Data on growth performances of shrimp fed the different diets over the 90 days growth trial are provided in Table 2.
The growth curves of the different groups over the trial period are presented in Figure 1. The body weight significantly (p < 0.05) in – creased in shrimp fed diet with S-10 than in the control, but there was no significant (p > 0.05) increase when compared with shrimp fed diet S-20 even though the average final body weight of S-20 was numerically higher.
There were no significant (p > 0.05) differences in the protein, lipid and ash contents among the different groups of P. vannamei. No significant (p > 0.05) differences were observed in the whole-body amino acid profiles of shrimp fed diets containing graded levels of SCP.
In terms of apparent digestibility, the SCP tested was found to be highly digestible with the digestibility coefficients of 0.91, 0.92, 0.60 and 0.70 for protein, lipid, calcium and phosphorus respectively.
The digestible protein and lipid content of SCP were calculated to be 577.7 g/kg and 57.9 g/kg respectively. The relative gene expression of lysozyme, Toll-like receptor and immune deficiency (IMD) were all significantly (p < 0.05) up-regulated in shrimp fed diet S-20 as compared to shrimp fed the control diet or other SCP diets.
Discussion
The results of the study show that it is possible to include up to 200 g/kg of SCP derived from Methylococcus capsulatus (replacing up to two thirds of fishmeal) in the diets of Pacific white shrimp still maintaining good survival, growth and feed efficiency.
In fact, at the dietary SCP inclusion level of 200 g/kg, despite lower feed intakes, the mean weight gain and feed efficiency were better compared to those of shrimp fed the control diet. It is indeed promising to see that shrimp performed well at SCP inclusion level of 200 g/kg, better than those reported by Chen et al. (2021) in Pacific white shrimp where they found that another SCP can replace 45% of dietary FM (105 g SCP/kg diet).
There was no significant difference observed in the survival of shrimp among the different treatment groups, but shrimp fed diets with 50 and 100 g/kg of SCP exhibited higher survival than the control group. Hamidoghli et al. (2019) reported an increasing trend, albeit not significant, in the survival of shrimp on the addition of a SCP obtained from a bacteria (Corynebacterium ammoniagenes), and stated that the increase might be due to the increase of non-specific immune responses by the dietary inclusion of SCP.
The increased phosphorus gain and retention in shrimp fed diets with SCP can be attributed to the higher digestibility of phosphorus in the SCP and as the phosphorus content in SCP is attributed to the levels of nucleic acids and phospholipids (Øverland et al., 2010), while phosphorus in fishmeal would be mostly in the form of a complex with calcium (calcium hydroxyapatite complex, Rajesh et al., 2022).
“Whole-body chemical composition and amino acid profile of shrimp did not vary significantly (p > 0.05) with the increasing levels of SCP.”
This is in conformity with the general observations of a relatively constant protein-bound amino acid composition of shrimp irrespective of dietary treatments (Penaflorida, 1989; Alam et al., 2002; Xie et al., 2018). The digestibility values obtained in the present study were higher than those of earlier reports with other SCPs measured in finfish (Øverland et al., 2010; Tlusty et al., 2017) and in Pacific white shrimp (Hamidoghli et al., 2019).
The cell rupture by downstream processing of the bacterial protein used here might be an important aspect to look into while increasing the digestibility of these protein sources. The plausible reason for the high digestibility in the study might be attributed to the method of the downstream process carried out in the preparation of this SCP.
Conclusion
Given the good nutrient digestibility of the SCP, good feed intake, excellent growth, feed efficiency and good survival of shrimp observed over 90 days of the study under semi-practical farming conditions clearly suggest that the single cell protein, derived from methane utilizing bacteria, holds much promise as a sustainable and reliable alternative protein source to replace a significant proportion of fishmeal in the diets of Pacific white shrimp.
The responses in terms of biomarkers of the immune system of shrimp are of great interest warranting further dedicated studies.
This is a summarized version developed by the editorial team of Aquaculture Magazine based on the review article titled “ EVALUATION OF SINGLE CELL PROTEIN ON THE GROWTH PERFORMANCE, DIGESTIBILITY AND IMMUNE GENE EXPRESSION OF PACIFIC WHITE SHRIMP, PENAEUS VANNAMEI” developed by: FELIX, N. and MANIKANDAN, K. – Directorate of Incubation and Vocational training in Aquaculture (DIVA), UMA, A. – State Referral Laboratory for Aquatic Animal Health (SRLAAH) and KAUSHIK, S. – Universidad de Las Palmas de Gran Canaria.
The original article was published, including tables and figures, on DECEMBER, 2022, through ANIMAL FEED SCIENCE AND TECHNOLOGY.
The full version can be accessed online through this link: https://doi.org/10.1016/j.anifeedsci.2022.115549.
