RUDN University Biologist Сreates an Additive to Fish Feed to Helps Against Pathogenic bacteria

University biologist has shown that a combination of two beneficial bacteria in fish food increases their resistance to a dangerous pathogen. Such an additive will help to avoid the mass extinction of fish in fish farms. The results are published in Fish & Shellfish Immunology.

The bacterium Aeromonas hydrophila is one of the most serious enemies of the fish industry. It can cause mass death of fish of different species. To avoid this, breeders use antibiotics, often inappropriately and excessively. This harms both the fish itself and the person who eats it. A new way to fight the problem is to look for natural feed additives that allow you to fight infection. For this, for example, spirulina bacteria (Spirulina platensis ) and bacilli ( Bacillus licheniformis ) are used. A RUDN University biologist with colleagues from Iran showed that the combined effect of taking these two supplements is stronger than a single one. The combination of the two bacteria improves the health of the fish and makes them more resistant to Aeromonas hydrophila.

“The fish industry has already begun to use probiotics, algae and herbal extracts instead of antibiotics and growth and immunity stimulants. Many studies have reported the effects of spirulina and bacilli on fish growth and health separately. However, their combined effect has not yet been investigated. We compared the combined and individual effects of these additives on fish health and disease resistance,” Morteza Yousefi, Associate Professor, Department of Veterinary Medicine, RUDN University.

Biologists studied 216 fish Carassius auratus, which are called goldfish. They were divided into four groups of twelve tanks. Each group had its own diet. The control group had only regular food, no additives. The second group received Bacillus licheniformis bacteria along with the food, the third received an additive in the form of Spirulina platensis. Finally, the fish from the fourth group received both of these bacteria along with the usual food.

There was no change in growth rate in any of the four groups. But biologists RUDN found changes at the biochemical level. In fish that were fed additionally with both bacteria, the activity of the hormone ghrelin increased. It is synthesized in the gastrointestinal tract and is involved in digestion. Also increased the concentration of catalase and glutathione reductase – two important enzymes. The first decomposes hydrogen peroxide into water and oxygen, the second restores the antioxidant properties of the cell. Fish with the combined dietary supplement became more resistant to the harmful bacteria A. hydrophila – mortality from infection decreased from 65% to 50%.

“Although the addition of bacteria did not affect growth performance, it did improve immune and antioxidant responses. Moreover, their inclusion in the diet can increase the resistance of fish to A. hydrophila infection ,” Morteza Yousefi, Associate Professor at the Department of Veterinary Medicine, RUDN University.