Scientists of Siberian Federal University, together with colleagues from the Yenisey branch of Glavrybvod Federal State Budgetary Institution, have studied the composition and content of omega-3 and omega-6 fatty acids in juvenile Siberian sturgeon grown in aquaculture. The young of fish is commonly fish from the larval stage to the beginning of puberty. Having found out how different diets affect the content of valuable acids in the muscle tissue of this group of fish, the scientists came closer to developing a balanced diet that will help Siberian sturgeon fry to better adapt when moving from aquaculture to natural conditions.
Sturgeons, in particular the Siberian sturgeon (Acipenser baerii), which lives in the Yenisey, are considered one of the most valuable fish species. Today, the number of sturgeon in Russian rivers is recovering after a significant decline over the past 50 years. Sturgeons were on the verge of complete extinction due to overfishing, poaching, pollution and changes in the level regime of the rivers. Unfortunately, the restoration of the Siberian sturgeon is currently difficult due to the ongoing poaching and specific features of the fish. It takes a long time for the Siberian sturgeon to reach puberty. What is more, the time gap between spawns is considerable, and not as many juveniles survive in the natural environment as we would like.
One of the main ways to restore the population of the Yenisey sturgeon is to grow sturgeon juveniles in aquaculture and then return them to a natural habitat. Aquaculture rearing of baby sturgeons implies a comfortable temperature and salinity of the water, an optimal concentration of oxygen, as well as a certain amount and quality of fodder. Another necessary condition for the successful maturation of fish larvae is the optimal composition of fatty acids (FA) in the food. First of all, these are polyunsaturated fatty acids (PUFAs): omega-6 arachidonic acid, as well as eicosapentaenoic (EPA) and, in particular, docosahexaenoic (DHA) acids of the omega-3 family.
“We have found out the composition and content of valuable omega-3 and omega-6 fatty acids in the biomass of Siberian sturgeon juveniles grown at the Beloyarsk fish hatchery (Republic of Khakassia, the settlement of Izykh Kopi). This fish farm annually releases more than 2 million sturgeon juveniles into a river. Fish-breeding caviar was obtained from wild spawners caught in the natural habitat and delivered to the Beloyarsk fish hatchery for further incubation and rearing of sturgeon fry. The sturgeon larvae and juveniles grown from the caviar were fed with commercial fodder produced in the Netherlands. To conduct the study, we were provided with samples of these fry at different stages of postembryonic development, as well as the food that the fish ate during adulthood,” said Anastasia Rudchenko, associate professor of the School of Fundamental Biology and Biotechnology, SibFU.
By studying endogenous (at the stage of development of the embryo in the egg) and exogenous (as the hatched larvae mature) nutrition, scientists came to the conclusion that the composition of fatty acids in the biomass of juveniles is greatly influenced by a food source. Saturated and monounsaturated fatty acids are used by Siberian sturgeon juveniles as energy sources for growth and development. At the same time, polyunsaturated fatty acids and docosahexaenoic acid (DHA) accumulate in the biomass of sturgeon from the pre-larval stage to the juvenile stage (up to one year). The content of eicosapentaenoic acid (EPA) and omega-3 DHA significantly decrease when sturgeons reach the age of underyearlings. This is probably due to a decrease in the total fatty acid content in the biomass of juvenile sturgeon. Nevertheless, the levels of valuable fatty acids in the biomass of Siberian sturgeon underyearlings were at a relatively high level before release into the natural habitat. According to the scientists, this means that when the “teenagers” of the Siberian sturgeon are released into natural conditions, they will be able to adapt, and the chances of survival will be quite high.
“Fatty acids take part in stress reactions of the body in young fish. They are part of the membrane of nerve cells and take an active part in the formation of nerve tissues. The deficiency of these acids in larvae and juveniles leads to a disruption of the brain development, the reaction to stress worsens, immunity decreases, and developmental anomalies appear. The lack of omega-3 and omega-6 acids in the feed of sturgeon growing in aquaculture can provoke increased mortality of juvenile fish when it is released into its natural habitat,” continued Ms. Rudchenko.
The scientists found that the high content of certain fatty acids in sturgeon prelarvae and larvae is affected by the nutrition of their mother eating benthic organisms, special algae and microorganisms. At the stage of organ formation in the prelarva, some acids are consumed and others are selectively accumulated. Growing up, sturgeon fry lose a large amount of useful acids, getting energy from them for active growth.
The fodder studied by the experts could also have been a reason for the low content of omega-3 and omega-6 in the biomass of juvenile sturgeon due to its high fat content. The composition of the fodder from the Netherlands, studied by the scientists, can cause an increase in the size of the liver and its obesity, which will negatively affect the survival of young fish. It is necessary to develop domestic fodders with a balanced composition of fatty acids, aimed not at growing commodity fish with a large weight, but at growing healthy young sturgeons. Despite this, in the biomass of the Siberian sturgeon underyearlings grown on artificial feed, the level of these acids is still sufficient to maintain a normal level of vital activity of young Siberian sturgeons and can provide a high level of their survival.
“At this stage of the work, we cannot fully assess whether the level of fatty acids obtained from the feed is sufficient for the full formation of the nervous system, the development of motor reactions, the normal functioning of the visual and auditory systems in sturgeons grown under artificial conditions in a fish hatchery. We will continue the study to get more accurate estimates of the survival of Siberian sturgeon juveniles in the Yenisey River,” concluded the scientists.
