The influence of energy nutrition on the productivity of rainbow trouts
Authors:   National University of Life and Environmental Sciences of Ukraine, Kondratiuk V. 
Published: December 2020

n the conditions of modern fish farming, the issues of product quality management, along with the achievement of high fish productivity, occupy one of the key places in scientific research. This increases the role of the system of scientific support of the technological process of production, in which the feeding of fish is important. Properly balanced feeding, with optimal growing conditions, is a key factor influencing the intensity of fish growth and economic performance of the industry. In a number of works it has been proved that by optimizing the energy supply of rainbow trout, it is possible to ensure a high level of productivity and improve the quality of their products. Thus, the study of the impact of different energy supply of rainbow trout this year in the modern industrial conditions of cold-water fish farms in Ukraine is necessary and relevant. Material and methods of research. Experimental studies on this yearling rainbow trout Oncorhynchus mykiss (Walbaum, 1792) were conducted in the farm "Shipot" Perechyn district of Zakarpattia region. The purpose of the scientific and economic experiment was to establish the influence of different levels of energy supply of this year's trout on their productivity. During the equalization period, the experimental fish consumed feed of the control group. In the main period, the level of metabolic energy in the feed of trout of the experimental groups was regulated by changing the individual components of the feed (using combined mathematical methods to optimize the calculation using the program AgroSoft WinOpti). Feeding rainbow trout this year was carried out 6 times a day, during the day at regular intervals. The required amount of feed was calculated according to the indicators of individual weight of young and the temperature of the environment at the time of feeding. The planting density of the experimental fish at the beginning of the experiment was 200 sp/m2. Growing of young was carried out in ponds with a water level of 1 m. Control catches of experimental trout were performed once every 5 days. Weighing on electronic scales was subjected to 100 individuals from each group. The research results were processed by the method of variation statistics using MS Excel and STATISTICA 7.0 software using built-in statistical functions. Research results and their discussion. It was found that at the end of the experiment (45 days) the highest mass was reached by this year of the 4 and 5 groups, which outperformed the analogues of the control group by 5.5 and 10.4%, respectively (p<0.05). At the same time, this year of the 2 and 3 experimental groups were inferior to the mentioned indicator to control peers by 1.19 and 0.52 g, respectively, or by 10.7 (p<0.05) and 4.7%. The difference between the weight of fish of the 2 and 5 groups, which consumed feed with a metabolic energy content of 15 and 19 MJ, respectively, in this period was 23.5% in favor of the latter. Data from analysis of variance show that different levels of energy nutrition of this year of trout significantly (p<0.001) affected the weight of the experimental fish. The share of influence of this factor is 79.7%, which is almost 4 times higher than the influence of other factors. Calculations of the average daily weight gain of this year's trout showed that during the growing period the nature of their changes depended on the level of metabolic energy in the feed and the corresponding dynamics of fish growth. It should be noted that in general for the main period of the experiment large average daily weight gain was characterized by this year 4- and 5 experimental groups receiving feed with metabolic energy content at the level of 18 and 19 MJ, which by this indicator exceeded the control, respectively 7.0 and 13.2%. Yearlings of trout of the 2nd and 3rd experimental groups, which consumed compound feed with a content of metabolic energy at the level of 15 and 16 MJ, in the main period of the experiment were inferior to the control indicator by 12.7 and 6.1%, respectively. The difference between peers of the 2 and 5 groups in the average daily weight gain for the main period of the experiment was 29.6%. Тhe analysis of feed costs shows that the use of compound feed with a metabolic energy content of 19 MJ (group 5) for the main period of the experiment for feeding this year trout helped to reduce their costs per unit of weight gain compared to fish that consumed feeds with lower energy levels. Thus, the cost of feed per 1 kg of weight gain in this year of the 5 group was 0.794 kg, which is 0.31; 0.86; 0.57 and 0.19 kg less than in the 1, 2, 3 and 4 groups, respectively. It should be noted that the safety of the experimental fish throughout the experiment was quite high and ranged from 74.3 to 76.7%. It can be stated that the increase in nutrient content of feed from 15 (2 group) to 19 MJ (5 group) leads to an increase in ichthyomas during the main period of the experiment by 6.9-37.5%. As a result of different feed costs per unit weight gain of fish, this indicator and its cost per total increase in ichthyomas differed markedly by experimental groups. All this, in the end, affected the unit cost of growth of ichthyomas of this year's trout, was the lowest in fish that consumed food with a nutritional value of 17 MJ (1 group). In particular, according to the mentioned indicator, they outperformed analogues of all other groups, respectively (according to the scheme of the experiment) by 17.0; 19.4; 2.9 and 2.1%. Thus, from an economic point of view, when growing trout this year, they should be fed compound feeds with a metabolic energy level of 17 MJ.