Traditional sources of protein in aquaculture feeds are fishmeal and soy, but availability of these components is becoming limited due to the gradual depletion of the World's oceans. From this point of view, insects can be a valuable source of protein as an alternative protein for aquaculture. In Russia, larvae of the tropical fly Hermetia illucens L. are more often used to obtain vermicompost after food waste conversion, however recently the cultivation of larvae for the production of fish feed has become more popular. Therefore, the investigation aimed to evaluate the replacement of fishmeal with the larvae in the diet of yearling rainbow trout (Oncorhynchus mykiss). Based on the results of a study investigating the growth efficiency of rainbow trout raised on a commercial feed supplemented with black soldier fly larvae, it was observed that an experimental diet containing frozen insects and wheat gluten processed using an extruder had a positive impact on fish farming and biological effects. Especially for the experiment, two feed recipes have been developed (for the experimental and control groups), in one of which the fish meal has been replaced with H. illucens larvae. The experiment was conducted on genetically homogeneous groups of fish that were kept in a closed water supply system for 77 days. For individual control of biometric and morphological parameters, a microchip was placed into each fish in the dorsal fin area. The relative increase in fish weight in the experimental group was 13 % higher than in the control group. The differences between the arithmetic means become obvious on the 50^th day from the beginning of the experiment and reach a maximum towards its end.

   The formation of water quality in the reservoir and watercourses of the Verkhniy pond basin is caused by complex processes and is influenced by numerous natural and anthropogenic factors. The speed of metabolism and the short time of generation of microorganisms allow them to react to changing environmental conditions much faster than other components of biota. As a result of the analysis of the structure of the microbial community of the Verkhniy pond, heterogeneity of microbial populations has been revealed. Gram-negative bacteria of the families Enterobacteriaceae, Pseudomonadaceae, Vibrionaceae have been found in the composition of the bacterioflora of water. Gram-positive microflora included microorganisms of the genera Bacillus, Micrococcus, Staphylococcus. Gram-negative rod-like bacteria of the genus Pseudomonas, belonging to group 4 «Gram-negative, aerobic/micro-aerophilic rods and coccus», subgroup 4A, were widely distributed in microbial populations. Significant changes in microorganism communities (increase in the proportion of gram-negative bacteria) have been noted. The number of rod-like bacteria of the genus Aeromonas peaked in May 2023 (74.94 % of all isolated bacterial strains). The change in the structure of microbial communities towards an increase in the proportion of gram-negative bacteria indicates a pronounced anthropogenic pressure. The numbers of heterotrophic bacteria utilizing readily available organic matter in water ranged from 1,2х10³ to 4,2х10⁴ CFU/ml. The highest levels have been observed near the estuary of the Botanical Stream, indicating a high content of organic matter in the water. An increase in the number of heterotrophic bacterioplankton may be an indirect indicator of incomplete destruction, incomplete transformation of organic matter entering the watercourse, including anthropogenic origin. In the microflora of the water of the Verkhniy pond, the presence of sanitary-significant bacteria of the fecal group, which belong to the indicators of sanitary malaise of the aquatic environment has been detected.

   Changes in nonspecific immune resistance of 25 persones before and after exposure on their blood in vitro by low-concentration priming solutions (LPS) obtained from aqueous extracts of Kamchatka’s laminariacean algae Arthrothamnus bifidus and Laminaria repens are discussed. Their blood samples have been activated by HPR twice: at the beginning of the experiment and after thirty days of daily oral using of algalgel obtained from Hedophyllum bongardianum. The immunomodulatory effect was assessed by the phagocytic activity of neutrophils, phagocytic number, absolute phagocytic index and the amount of phagocytosis. It has been shown that the substances contained in algalgel in an accessible form are able to soak from the gastrointestinal tract into the bloodstream and have a normalizing effect on the leukocyte profile of the blood. The LPS concentration of 0.25 % was ineffective; at the concentration of 5 % and higher, suppression of phagocytosis was observed. LPS 0.5, 1 and 2 %, especially from two-year-old samples of A. bifidus and L. repens, had the greatest priming effect on neutrophils and was complemented by inactivation of bacteria in the extracellular environment. LPS from L. repens induced extracellular degranulation processes, and those from A. bifidus led to the formation of neutrophil extracellular traps. The results of our study showed that the investigated species can be raw materials for the production of dietary supplements with an immunomodulating effect.

   The purpose of this study was to assess the ecological state of a floated quarry based on the results of integrated observations during a period of increased recreational load. In 2019, during field trips, 33 water samples were taken at three shore stations of the Schoenflies pond.

   Based on the results of the hydrochemical, microbiological and algological analyzes, conclusions were drawn about the ecological state of the studied reservoir. According to hydrochemical indicators, a discrepancy between the oxygen content and standard values with a pronounced difference between stations was found. Nutrients dissolved in water is within MPC. According to sanitary and microbiological analyzes, contamination of water was low. Composition of the aquatic microflora of the Schoenflies pond throughout the entire observation period was formed by aerobic and facultative anaerobic rod-shaped (62 %) and coccal bacteria (38 %). The largest number of bacterial species was observed in summer and autumn. The basis of the algoflora complex of the pond was formed by 75 species and taxa up to the genus of departments. The average number of phytoplankton during the observation period varied within 0.3–3.7 million cells/l, biomass – 0.5–4 mg/l. The peak of algae development was observed in September. According to the results of comprehensive research, water of the Schoenflies pond belongs to the category of pure water. The results of the hydrochemical monitoring for most parameters comply with the established ranges for mesotrophic water bodies (according to the saprobity class, oligosaprobic waters). The results obtained suggest that the recreational load, even in the absence of flow, is not a determining factor in changing the ecological state of the pond in summer.

   Fish processing wastes are rich in a connective tissue protein collagen, which has a high potential in foods when extracted as a hydrolyzate. One of the possible directions of its application is replacement of animal fat and partial meat raw materials. The article deals with the problem of the extraction and further usage of this protein to obtain heat stable food filler with solid structure. Collagen hydrolyzate, liquid at 20 °C, has been obtained from the common carp heads. With adding a multifunctional mixture to it, samples of a protein filler with a gel-like structure have been developed. The heat stability, organoleptic and strength characteristics of the samples have been determined depending on the content of the mixture. The filler's heat stable when brought to culinary readiness (72 ± 2 °C) in samples containing 4 or more percent of multifunctional mixture is accepted. It is shown that the strength value is higher if mixture is added into the liquid structure hydrolyzate (17 ± 2 °C) than into a cooled (liquid jelly structure at 4 ± 2 °C). It has been recorded that storage of the hydrolyzate in frozen form (minus 18 °C) for 30 days, followed by defrosting, reduces the strength of the filler by 13.5%. The impact of the addition of milk powder and food coloring to protein filler on its color characteristics was studied. It is shown that the introduction of milk powder makes the structure more uniform and lighter. The use of food coloring in the composition of PF is proposed to obtain a component of the food industry that imitates the meat part of the product. Thus, according to the results of the work, the technological parameters for obtaining protein filler from carp processing wastes have been substantiated.

   Peptides are among the important biologically active substances. In recent decades, great efforts have been made by scientists to develop and produce short (low molecular weight) peptides that exhibit higher pharmacological properties than their prototypes. The source of natural peptides with high biological activity can serve as secondary fish raw materials – waste obtained during fish cutting. A large amount of fish collagen-containing waste accumulates at the fish processing enterprises of the Kaliningrad region. The article describes the possibility of obtaining low-molecular-weight peptides from secondary collagen-containing fish raw materials by combined hydrolysis methods combining both enzymatic and thermal treatment. Secondary fish raw materials have been studied and used- sardine scales, walleye heads, river perch ridges and salmon skin. The processes of protein splitting of raw materials under the action of three types of hydrolysis in an aqueous medium – enzymatic-thermal, thermal-enzymatic and thermal-enzymatic-thermal have been studied. In the experiments, the enzyme preparation of microbiological synthesis Alcalase® 2,4 L from Novozymes, Denmark, and an experimental enzyme preparation from the digestive organs of bream, manufactured on the basis of Biotech LLC, have been used. It has been revealed that the combined two- and three-stage hydrolysis methods provide the maximum yield of protein hydrolysates with low molecular weight peptides. The molecular weights of peptides, amino acid composition have been studied and a high biological value of the obtained protein hydrolysates with low molecular weight peptides has been established. The presence of all essential amino acids in hydrolysates has been determined, as well as an increased content of proline, glycine, alanine, glutamic and aspartic acids, which are necessary to increase immunity, ergodynamics of the body and the work of the human musculoskeletal system.

   The paper shows that the use of energy-saving frequency-controlled asynchronous electric drives in ship power plants instead of traditional ones (contactor-induction motor) makes it possible to reduce electricity consumption in fractional modes several times and significantly expand the functionality of the equipment. Ho-wever, during the operation of a frequency-controlled electric drive, higher current harmonics are emitted into the supply network, and voltage harmonics are supplied to the asynchronous electric motor along with the main harmonic. Current harmonics, propagating through the power supply system, lead to a decrease in the efficiency of the elements of ship power plants in which they are part of. It has been found that in all modes of operation of the electric drive, there are large values of the consumed reactive power. With a large number of frequency-controlled asynchronous electric drives on a ship, diesel generators will not be able to fully load them in terms of active power. During the operation of a frequency-controlled electric drive, current harmonics that are multiples of three are emitted into the supply network. These harmonics are zero sequence currents. Since the ship's network does not have a neutral wire, the third harmonic current from one phase is closed through the wires of the other two phases. This current creates a zero-sequence field in electrical machines with the ensuing consequences. Of greatest interest are the results of experimental studies of the vibration spectrum at 10 % load on the shaft of an asynchronous motor: at a frequency close to 20 Hz, which may indicate asymmetry of the poles of the asynchronous motor under study, at a frequency of 300 Hz from the interaction of moments of the fifth (reverse sequence) and seventh (positive sequence) harmonics, at a frequency of 50 Hz, due to the influence of the main harmonic.

   Due to the growing trend of aging of the ferry fleet, there is a great need to design new vessels of this type or modernize existing projects. Thus, according to an analysis of the Register Book of the Federal Autonomous Institution “Russian Classification Society”, over the past 10 years, only 3 ferries were launched for 115 ferry crossings on the Inland Waterways of the Russian Federation (here in after referred to as the IW of RF). In this connection, the article is devoted to the rationale for the modernization of a medium-haul car-passenger ferry for the Russian Federation, as well as
its impact on seaworthiness. The modernization under consideration is carried out on the basis of the newest medium-haul automobile-passenger ferry, which is being built on the territory of the Russian Federation, for the needs of the Baltiysk-Baltiyskaya Kosa ferry crossing. The selected prototype has contours characteristic of this type of vessel, sufficient cargo capacity and other features. At the same time, this project also has a number of negative factors affecting seaworthiness. Based on the described negative qualities of the prototype vessel, a theoretical drawing of the modernized vessel has
been designed. The effect of modernizing the theoretical drawing on seaworthiness was determined by testing physical models of the prototype vessel and the modernized vessel in the test pool of the Shipbuilding Research Center. The studies have been carried out in calm water, at speeds equivalent to the operational speeds of a full-scale vessel. At the same time, during the model tests, races have been carried out in regular oncoming waves, with wave characteristics determined by the Russian Classification Society. Based on the results of the described races, a number of advantages of the modernized vessel have been determined in comparison with its prototype.

   During exploitation of marine engine oil, its aging occurs, the main factors of which are oxidative high-temperature degradation and contamination with soot, wear metals, fuel, water and coolant. In this work, a number of used marine oils have been studied by relaxation dielectric spectroscopy to determine their characteristics associated with lubricant degradation and engine wear. For marine oils Total DISOLA M4015, Shell Rimula, Mobil 5W40, Mobil 10W40, Navigo TPEO 12/40, the dependences of the relative permittivity and the tangent of the loss angle on frequency have been experimentally obtained. The dielectric constant of marine motor oils ranges from 2.1 to 2.4 and depends on the viscosity, density of the oil, the content of paraffin, naphthenic and aromatic compounds in it and the additive package. An increase in the additive content increases the dielectric constant of the oil. The authors investigated the relationship of the dipole relaxation times of fresh and used oils with kinematic viscosity, with the content of additives and wear products. The desired array of relaxation time distributions has been calculated by regularization and the least squares method using the CONTIN algorithm. The calculations have been carried out in the RILT program running in the MatLab environment. It has been shown that polarization and subsequent dipole relaxation are caused by additive molecules that are triggered during engine operation. Differences in relaxation times can also be caused by the formation of associations involving dipole molecules. The data obtained in the work can be used in the future to build an expert engine diagnostics system and to determine the parameters of unknown oils.

   The Vistula Lagoon is the second largest shallow lagoon-type basin of the Baltic Sea, located in its southeastern part. This is a transboundary water body with a total area of 838 km², the northeastern part of which (510 km²) is under the jurisdiction of Russia and is called the Kaliningrad Bay, and the southwestern part (328 km²) is under the jurisdiction of Poland. It is separated from the sea by a stable sand barrier, and water exchange with the sea is carried out through the navigable Baltic Strait. The Kaliningrad Bay is an object of plural economic use and is experiencing a large anthropogenic load. The article compares the results of grain size parameters of bottom sediments sampled in the Kaliningrad Bay from the surface layer (0–7 cm) at the same points with an interval of 29 years. Studies have shown that the bottom sediments of the bay in 1993 year were represented by sands, silty sands, sandy silts, silts and clayey silts. To date, there have been changes in the composition of the fractions, but the types of precipitation at the control points have not changed. In 1993 year the proportion of sand particles in sand deposits averaged 72 % and in 2021 year – 78 %. In the silts the sand content increased from 17 to 23 %, and in clayey silts from 3 to 7 %. As for silt particles their share in the sandy fraction over 28 years decreased by an average of 6 %, in silts by 2 %, and in clayey silts by 4 %. The value of the changes that occurred in the composition of sediments over the specified period is not the same and depends on the types of sediments. A feature of modern sedimentation in the bay is regular resuspension of the upper layer of bottom sediments, accompanied by redeposition of sedimentary components and partial transportation of fine particles in suspension to the sea.