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.

Linking behavioural type with cannibalism in Eurasian perch

The propensity to kill and consume conspecifics (cannibalism) varies greatly between and within species, but the underlying mechanisms behind this variation remain poorly understood. A rich literature has documented that consistent behavioural variation is ubiquitous across the animal kingdom. Such inter-individual behavioural differences, sometimes referred to as personality traits, may have far-reaching ecological consequences. However, the link between predator personality traits and the propensity to engage in cannibalistic interactions remains understudied. Here, we first quantified personality in Eurasian perch (Perca fluviatilis), measured as activity (time spent moving) and sociability (time spent near conspecifics). We then gave perch of contrasting behavioural types the option to consume either conspecific or heterospecific (roach, Rutilus rutilus) prey. Individual perch characterized by a social-active behavioural phenotype (n = 5) selected roach before being cannibalistic, while asocial-inactive perch (n = 17) consumed conspecific and heterospecific prey evenly. Thus, asocial-inactive perch expressed significantly higher rates of cannibalism as compared to social-active individuals. Individual variation in cannibalism, linked to behavioural type, adds important mechanistic understanding to complex population and community dynamics, and also provides insight into the diversity and maintenance of animal personality.

Molecular Structure and Hybridization Patterns of Abramis brama × Rutilus rutilus Hybrids from Modrac Reservoir, Bosnia and Herzegovina

Interspecific hybridization in the Cyprinidae family has been recorded worldwide, with Abramis brama (bream) and Rutilus rutilus (roach) as one of the often-reported hybridizing pairs. The only account of such an event in Bosnia and Herzegovina has been in Modrac Reservoir. Using morphological and molecular markers, the presence of hybrids was surveyed, the hybridization direction was determined and the hybrid group structure in this ecosystem was evaluated. Our findings confirmed unhindered natural hybridization between roach and bream in Modrac Reservoir. Over 50% of the hybrid specimens were classified as F2 hybrids by the NewHybrids software, while the rest were categorized as pure parental form, making it the first such finding in Europe. The analysis of mitochondrial cytochrome b showed that 90% of hybrid individuals were of bream maternal origin. The hybrid group expressed higher mean values of observed heterozygosity and gene diversity than both parental species. Signs of introgressive hybridization between parental species were detected. The hybrid zone of Modrac Reservoir appears to follow the intermediate or “flat” hybrid model based on the balanced distribution of parental and hybrid genotypes. Further investigation is needed to elucidate the factors that enable the survival and mating success of post-F1 individuals.

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.

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.

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.