Malic acid improves the health of fish

University biologist with colleagues from Iran and Turkey found that malic acid can enhance the immunity of fish and strengthen their antioxidant status. The results are published in Aquaculture.

Fish farmers are keen to speed up the growth of the fish and often use antibiotics. This harms the health of fish, leads to antibiotic resistance in bacteria, pollutes the water and ultimately poses a threat to humans. Therefore, it is necessary to look for natural feed additives that could improve the health of fish and at the same time not harm either the animals themselves, or the environment, or humans. RUDN University biologist with colleagues from Iran and Turkey found that malic acid can help with this.

“Feed additives are one of the best and most practical ways to promote fish growth and health. In this regard, malic acid has been studied the least of all organic acids. Meanwhile, it affects the growth of fish and the health of their intestines. Our goal was to evaluate how the addition of malic acid to feed affects growth rates, antioxidant and immunological parameters in rainbow trout,” said Morteza Yousefi, Associate Professor of the Department of Veterinary Medicine, RUDN University.

In an experiment, biologists studied 180 rainbow trout (Oncorhynchus mykiss) fry weighing about 25 grams. The fish were randomly divided into 4 groups. Three groups received different amounts of malic acid in addition to the main diet, and the fourth was used as a control.

After 8 weeks, biologists RUDN University compared physiological parameters in fish from different groups. It turned out that malic acid had practically no effect on growth, weight gain and survival. However, the changes were noticeable at the molecular level. In fish that received malic acid, the activity of several enzymes increased: alanine aminotransferase, lysozyme, catalase, superoxide dismutase, glutathione peroxidase. The first two are involved in metabolism and protection against bacteria, the rest affect the antioxidant mechanisms of the body. In addition, fish that received 0.5% malic acid supplementation had an increase in total immunoglobulin levels. In terms of the sum of improvements, the most effective was the 0.25% addition of malic acid to the feed.

“The addition of malic acid to the diet of rainbow trout in the amount of 0.25% improved the antioxidant status and immune responses of fish without any negative impact on growth rates,” said Morteza Yousefi, Associate Professor of the Department of Veterinary Medicine of RUDN University.