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This study is the first reference regarding the length-weight relationships of freshwater fishes inhabiting one of the most important spawning waters of the endemic endangered Danube salmon (Hucho hucho). Fulton condition factor (K) was calculated for 1366 individuals belonging to 16 species from Ruscova River, north of Romania. Length-weight relationships were determined for 1362 specimens from 14 species. The smallest slope value (b) was determined for Romanogobio uranoscopus (b=2.2437) and the highest value for Telestes souffia (b=3.6058). The Danube salmon (Hucho hucho) showed positive allometric growth, having the calculated value of the slope of 3.3879. The mean values of Fulton condition factor (K) for the captured specimens were: Cottus gobio (1.161), Alburnus alburnus (0.3726), Alburnoides bipunctatus (0.8142), Barbus barbus (0.9434), Barbus carpathicus (0.9202), Chondrostoma nasus (0.8867), Romanogobio uranoscopus (0.8196), Phoxinus phoxinus (0.9888), Squalius cephalus (1.137), Telestes souffia (0.898), Barbatula barbatula (0.6693), Eudontomyzon danfordi (0.1293), Hucho hucho (0.8454) and Thymallus thymallus (0.9522). [ABSTRACT FROM AUTHOR]

Simple Summary: Rainbow trout is one of the main freshwater fish species farmed in Romania, in a temperate continental climate. Blood biochemistry parameter values are well known for humans and other higher vertebrates, including some species of fish, and are fundamental for the assessment of physiological status. In this study, we examined the physicochemical parameters of water quality and the blood profile (hematological and hormonal profiles, antioxidant enzyme activities) of rainbow trout females reared in three farms, during the summer season, to monitor stress. These findings permit the progress of knowledge of blood parameters in fish and will encourage efforts to expand hematological and biochemical studies to assess the health of salmonids, which is essential for the sustainable development of aquaculture. Blood biochemistry parameters are valuable tools for monitoring fish health. Their baseline values are still undefined for a multitude of farmed fish species. In this study, changes in the blood profile of rainbow trout females (Oncorhynchus mykiss) from three farms were investigated using different biomarkers during the summer season. In the given context, the main water physicochemical parameters were investigated and twelve biochemical parameters were measured from blood samples of rainbow trout reared in the Fiad, Șoimul de Jos, and Strâmba farms. We selected these farms because the genetic background of the rainbow trout is the same, with all studied specimens coming from the Fiad farm, which has an incubation station. Forty-five samples were collected monthly (May to August) throughout summer to observe the changes in the blood profile of rainbow trout. Principal component analysis showed a clear separation both among the studied farms and months. Furthermore, significant correlations (p < 0.05) between the majority of the biochemical parameters were found, indicating that the environmental parameters can influence several blood parameters at the same time. The present study provides several useful norms for assessing the welfare of rainbow trout, indicating that the relationships among different parameters are important factors in interpreting the blood biochemical profiles. [ABSTRACT FROM AUTHOR]