The use of dietary supplements has become a popular solution among aquaculturists to reduce rearing costs and enhance feed efficiency as the industry continues to grow. Sodium propionate is one such dietary supplement with significant potential.
Rainbow trout, a crucial aquaculture species, has shown favorable responses to dietary supplementation with sodium propionate. However, optimizing the dosage is crucial to maximize benefits and avoid adverse effects.
In this regard, scientists from RUDN University and the Inland Waters Aquatics Resources Research Center published a study delving into the effects of sodium propionate in the diet of rainbow trout (Oncorhynchus mykiss), exploring its influence on growth performance, hepatic lipid deposition, intestinal enzyme activity, inflammation, bacterial populations, and antioxidant capacity.
Propionic Acid Salts
Sodium propionate, a short-chain fatty acid (SCFA), has emerged as a promising food additive to improve growth performance, hepatic lipid deposition, and intestinal activity in various fish species of interest to the aquaculture industry.
Propionic acid salts (propionates) are used as food additives for humans and animals. For instance, propionate enhances fish growth. The dosage varies for each type of fish and is selected experimentally. The optimal dose of propionate for rainbow trout was not previously known.
The Experimental Journey
For 70 days, rainbow trout were subjected to diets supplemented with varying levels of sodium propionate: 0 g/kg (CTL), 1 g/kg (P1), 2.5 g/kg (P2.5), or 5 g/kg (P5). The research aimed to unravel the intricate relationships between sodium propionate levels and a spectrum of parameters crucial for fish well-being.
Upon the experiment’s completion, scientists evaluated fish growth rate, liver lipid deposits, digestive enzyme activity in the intestine, microflora, and the fish’s antioxidant activity.
Growth Performance and Feed Efficiency
Results indicated a significant dose-dependent relationship between sodium propionate levels and growth performance parameters.
Growth performance and feed efficiency significantly improved in the P1 and P2.5 treatments compared to the control group. This enhanced growth is attributed to sodium propionate’s ability to modulate nutrient absorption and energy metabolism in fish. However, excessive levels of sodium propionate (P5) led to growth retardation, emphasizing the importance of optimizing the dosage.
Intestinal Enzymes and Antioxidant Capacity
The P1 and P2.5 treatments showed lower viscerosomatic indices and exhibited elevated levels of intestinal amylase, lipase, trypsin, chymotrypsin, superoxide dismutase (SOD), and catalase (CAT). At the same time, they demonstrated reduced levels of intestinal malondialdehyde (MDA), plasma glucose, and triglycerides compared to the CTL treatment. Conversely, the P5 treatment showed contrasting trends, highlighting the delicate balance in sodium propionate supplementation.
Hepatic Lipid Deposition
Sodium propionate supplementation had a significant impact on hepatic lipid deposition in rainbow trout. The hepatosomatic index, an indicator of liver size relative to body weight, significantly decreased in the P1 and P2.5 treatments compared to the control group. This reduction in liver size suggests a favorable effect of sodium propionate on regulating liver fat content.
Interestingly, the P5 treatment resulted in an elevated hepatosomatic index, indicating increased hepatic lipid accumulation. This observation underscores the importance of maintaining appropriate levels of sodium propionate to prevent adverse effects on liver health.
Intestinal Health
Intestinal health is crucial for nutrient absorption and the overall well-being of fish. Sodium propionate supplementation demonstrated notable effects on various aspects of intestinal health in rainbow trout.
Firstly, sodium propionate positively influenced the activity of intestinal digestive enzymes. Intestinal amylase, lipase, trypsin, and chymotrypsin activities were significantly higher in the P1 and/or P2.5 treatments compared to the control group. These enzymes play crucial roles in the digestion of carbohydrates, fats, and proteins, promoting efficient nutrient utilization.
Secondly, sodium propionate modulated antioxidant capacity and markers of oxidative stress in the intestine. Intestinal superoxide dismutase (SOD) and catalase (CAT) activities, indicators of antioxidant defense, significantly increased in the P1 and P2.5 treatments, while malondialdehyde (MDA), a marker of oxidative stress, decreased significantly. These findings suggest that sodium propionate enhances intestinal antioxidant capacity, protecting against cell damage caused by reactive oxygen species.
Intestinal Microbial Community
The intestinal microbiome plays a fundamental role in maintaining intestinal health and fish physiology. Sodium propionate supplementation has been shown to modulate the intestinal microbiome of rainbow trout.
In this study, the total count of viable bacteria in the intestine significantly decreased in the sodium propionate-supplemented groups, with the lowest levels observed in the P2.5 treatment. This reduction in total bacteria can be attributed to the selective effects of sodium propionate on specific bacterial groups.
In particular, sodium propionate supplementation significantly increased the abundance of beneficial Lactobacillus sp. while reducing the presence of pathogenic bacteria such as Aeromonas hydrophila, Yersinia ruckeri, and Streptococcus iniae. This shift towards a more beneficial microbiome likely contributes to the observed improvements in intestinal health.
Stress Response and Inflammatory Markers
Stress can negatively impact fish growth and intestinal health. Sodium propionate supplementation has been shown to modulate stress response and inflammatory markers in rainbow trout.
In this study, the intestinal expression of heat shock protein 70 (HSP70), a stress response protein, was significantly regulated in sodium propionate-treated groups, indicating an enhanced ability to cope with stress.
Inflammatory markers such as tumor necrosis factor-alpha (TNF-α) and interleukin-1β (IL-1β) significantly decreased in the P1 and P2.5 treatments compared to the control group. This reduction in inflammatory markers suggests that sodium propionate may mitigate intestinal inflammation.
Conclusion
In essence, sodium propionate in the diet emerges as a potential boon to improve both the growth and intestinal health of rainbow trout. The study advocates for a balanced approach, pinpointing 2.5 g/kg as the optimal supplementation level.
Higher concentrations, while potentially beneficial in some aspects, pose risks of growth retardation, hepatic lipid accumulation, and induction of intestinal oxidative stress, inflammation, and dysbiosis.
“Dietary supplements with propionate improve growth indicators, immunological parameters, antioxidant activity, and the work of fish digestive enzymes. However, an excessive amount of propionate harms their health. Rainbow trout is one of the most important types of aquaculture. This fish is loved worldwide,” concluded Morteza Yousefi, Associate Professor in the Department of Veterinary Medicine at RUDN.
The study was funded by the RUDN University Scientific Projects Grant System.
Contacts
Morteza Yousefi
Department of Veterinary Medicine
RUDN University
6 Miklukho-Maklaya St, Moscow 117198, Russian Federation
Email: myousefi81@gmail.com
Seyyed Morteza Hoseini
Inland Waters Aquatics Resources Research Center
Iranian Fisheries Sciences Research Institute, Agricultural Research, Education and Extension Organization
Gorgan, Iran
Email: seyyedmorteza.hoseini@gmail.com
Reference
Morteza Yousefi, Seyyed Morteza Hoseini, Evgeny Vladimirovich Kulikov, Elena Valentinovna Kharlitskaya, Nikolay Vladimirovich Petukhov, Nikolay Gennadievich Khomenets. 2024. Dietary propionate administration improves growth performance, hepatic lipid deposition, and intestinal activity of digestive enzymes, inflammation, bacterial population, and antioxidant capacity in rainbow trout, Oncorhynchus mykiss, Aquaculture, Volume 578, 2024, 740099, ISSN 0044-8486,
https://doi.org/10.1016/j.aquaculture.2023.740099.
