Quality of Protein Isolates and Hydrolysates from Baltic Herring (Clupea harengus membras) and Roach (Rutilus rutilus) Produced by pH-Shift Processes and Enzymatic Hydrolysis

Fractionation is a potential way to valorize under-utilized fishes, but the quality of the resulting fractions is crucial in terms of their applicability. The aim of this work was to study the quality of protein isolates and hydrolysates extracted from roach (Rutilus rutilus) and Baltic herring (Clupea harengus membras) using either pH shift or enzymatic hydrolysis. The amino acid composition of protein isolates and hydrolysates mostly complied with the nutritional requirements for adults, but protein isolates produced using pH shift showed higher essential to non-essential amino acid ratios compared with enzymatically produced hydrolysates, 0.84–0.85 vs. 0.65–0.70, respectively. Enzymatically produced protein hydrolysates had a lower total lipid content, lower proportion of phospholipids, and exhibited lower degrees of protein and lipid oxidation compared with pH-shift-produced isolates. These findings suggest enzymatic hydrolysis to be more promising from a lipid oxidation perspective while the pH-shift method ranked higher from a nutrient perspective. However, due to the different applications of protein isolates and hydrolysates produced using pH shift or enzymatic hydrolysis, respectively, the further optimization of both studied methods is recommended.

Fish helminths in reservoirs of the Zarafshan river

The results of the study of the helminth fauna of 8 species fish of the lower reaches reservoirs of the Zarafshan River are presented - carp (Cyprinus carpio), crucian carp (Carassius auratus gibelio), roach (Rutilus rutilus), oriental bream (Abramis brama), pike perch (Stizostedion lucioperca), silver carp (Hypophthalmichthys molitrix), pike (Esox lucius), Turkestan barbel (Barbus capito conocephalus). 27 species of helminths were identified, including 12 species of cestodes (Caryophyllaeus laticeps Pallas, 1781; Caryophyllaeus fimbriceps Annenkova - Chlopina, 1919; Biacetabulum appendiculatum Szidat, 1937; Khawia sinensis Hsu, 1935; Bathybothrium rectangulum Bloch, 1782; Bothriocephalus opsariichthydis Yamaguti, 1934; Ligula intestinalis Linnaeus, 1758 larvae; Digramma interupta Rudolphi, 1810 larvae; Proteocephalus torulosus Batsch, 1786; Neogryporhynchus cheilanoristrotus Wedl, 1855 larvae; Gryporhynchus pusillus von Nordman, 1832 larvae; Valipora campylancristrota Rudolphi, 1819 larvae), 5 species of trematodes (Sanguinicola inermis Plehn, 1905; Orientocreadium siluri Bychowsky et Dubinina, 1954; Allocreadium isoporum Looss, 1894; Diplostomum spathaceum Rudolvae, 1832 lare; (Dioctophyme renale Goeze, 1782 larvae; Rhabdochona denudata Dujardin, 1845; Desmidocercella numidica Seurat, 1920 larvae; Camallanus truncatus Rudolphi, 1814; Camallanus lacustris Zoega, 1776; Philometra ovatachenko Zeder, 1803; 1779 larvae) and 2 species of acanthocephalus (Pomphorhynchus laevis Muller, 1776; Acantocephalus lucii Muller, 1776). This work includes the results of the research of the helminthes of the fish of waterbodies in the lowers of the Zarafshan River. As a result, the infection of fish with 27 species of helminthes, belonging to cestodes (12), trematodes (5), nematodes (8), and acanthocephalans (2) was established.

Comparative characterization of the roach Rutilus rutilus heckelii (Nordmann, 1840) sampled in different areas of the Sea of Azov during its spawning season in 2021, based on its physiological and biochemical parameters

Four samples of Rutilus rutilus collected in various water bodies of the Azov Sea Basin have been investigated. Individuals were examined during their spawning migration in the spring season of 2021. The differences in some physiological and biochemical parameters between the studied samples were considered. It has been found that the content of lipids in the sexual products of males was higher than in the gonads of females, and the protein was lower. Biochemical analysis of fish blood serum showed differences in the level of albumin between females and males and in the amount of triglycerides in the individuals from different fishing sites. In the liver of the fish from the Vostochno-Akhtarskoe (East Akhtarsk) Hatchery, a low activity of all investigated enzymes of the antioxidant system has been recorded.

Biochemical and hematological parameters of the roach Rutilus rutilus heckelii (Nordmann, 1840) from the Sea of Azov stock in the spring season of 2020–2021

This work presents the results of the investigation of the physiological state of the roach Rutilus rutilus heckelii breeders from the Sea of Azov stock during the spawning period. It has been established that, in the spring season of 2020 and 2021, the content of proteins and lipids in fish tissues, as well as hematological parameters in all investigated roach specimens from different water bodies were consistent with the average long-term values. The content of proteins in the muscles and liver of roach does not differ by sex. A higher protein content in the gonads of females is characteristic of the pre-spawning period due to the process of gonad maturation. The high content of lipids in the gonads of males apparently results from the lower energy consumption for maturation of the gonads and spawning. The average concentration of sodium and potassium ions decreased in comparison with the values obtained in 2020, while the concentration of chloride anions increased. It has been concluded that the physiological state of all investigated roach specimens was normal.

Openness of Fish Habitat Matters: Lake Pelagic Fish Community Starts Very Close to the Shore

Fish communities differ significantly between the littoral and the pelagic habitats. This paper attempts to define the shift in communities between the two habitats based on the European standard gillnet catch. We sampled the benthic and pelagic habitats from shore to shore in Lake Most and Římov Reservoir (Czech Republic). The 3 m deep pelagic nets were spanned across the water body at equal distances from two boundary points, where the depth was 3.5 m. The benthic community contained more fish, more species, and smaller individuals. The mild sloped littoral with a soft bottom attracted more fish than the sloping bank with a hard bottom and less benthos and large Daphnia. The catch of the pelagic nets was dominated by eurytopic fish—rudd (Scardinius erythrophthalmus) and roach (Rutilus rutilus) in Most and bleak (Alburnus alburnus) in Římov. With the exception of one case where overgrown macrophytes extended the structured habitat, the largest shift from the benthic to the pelagic community was observed only in the first pelagic gillnet above the bottom depth of 3.5 m. Open water catches were relatively constant with small signs of decline towards the middle of the lake. The results indicate that the benthic gillnet catch is representative of a very limited area and volume, while most of the volume is dominated by the pelagic community. This has important consequences for the assessment of the community parameters of the whole lake following the European standards for gillnet sampling design.

THE STUDY OF THE BIOLOGY OF THE ROACH RUTILUS RUTILUS CASPICUS (JAKOWLEV, 1870) IN THE KRAYNOVSKY COAST OF THE CASPIAN SEA

The offshore zone of the western coast of the Caspian Sea is one of the most highly productive. Of the 63 species of fish that live in the Caspian Sea, 34 species are found on the Krainovsky coast, 42 % of which are carp. The most numerous is the roach Rutilus rutilus caspicus (Jakowlev, 1870), which makes up 50–86 % of the number of semi-passerine and river fish. The article presents the results of studies of the peculiarities of the biology of the roach Rutilus rutilus caspicus of the Krainovsky coast of the Caspian Sea. The roach is noted in the catches constantly. Her age in the networks ranges from 2 to 10 years. The share of 3-5-year-olds accounts for 81 %. Females in catches make up 66 %, males - 34 %. The parameters of the Bertalanfi equation are characterized by the following values: L =38.8 cm, K = 0.12, t° = -2.67. The fecundity of the roach on average is 30.2 thousand eggs and tends to increase with increasing length and weight of the fish. As the roach grows, the composition of its food changes significantly. The maximum fed roach length from 10 to 20 cm.