Evaluation of swimming performance for fish passage of longnose dace Rhinichthys cataractae using an experimental flume

Design and initial evaluation of a novel tubular fishway for the rubber dam on the Huangbai River, a tributary of the Gezhouba Reservoir

Tens of thousands of low-head dams (LD) built in southwest China's river systems have disrupted fish migration pathways, posing a critical challenge for balancing hydropower development with ecological sustainability. An increased number of LD in small mountain river systems in southwest China is suitable for constructing low-cost fish passage facilities under minimal costs, presenting new demands for such dam development in the area. The primary objective of this study was to assess the effectiveness of an innovative low-cost PVC-made tubular fishway based on the hydraulic siphon principle to facilitate the fish passage over dams. The study was conducted at the Huangbai River dam within the Gezhouba Reservoir. Using the radio frequency identification (RFID) technology, we monitored the fish passage performance of the upstream migration of grass carp (Ctenopharyngodon idella) from the dam and quantified key evaluation metrics including attempt rate, passage rate, return rate, and return frequency. Cox proportional hazards regression method was used for modelling fishway attempt rates and passage rates and to identifying key factors affecting the effectiveness of the tubular fishway. Results showed that: (1) the tubular fishway effectively facilitated fish migration through the LD, with an attempt rate of 45.1 % and a passage rate of 56.8 % respectively. (2) The attempt rate was significantly influenced by water temperature, water transparency, and dam spillover conditions (P < 0.05). The attempt rate was low during spillover than non-spillover conditions and increases with rising water temperature but decreased with increasing transparency. (3) Passage rate was primarily affected by water temperature and the attempt number (P < 0.05). Passage rate increased with higher water temperatures along with increased attempts by the target fish. These findings highlight the potential of the tubular fishway as a cost-effective and environmentally sustainable solution for a fish passage in LD. As a first of this kind to develop and test this prototype in southwest China' river systems, our research provides a foundation for future optimization and broader implementation of the tubular fishways in the region.

Evaluation of Volitional Swimming Behavior of Schizothorax prenanti Using an Open-Channel Flume with Spatially Heterogeneous Turbulent Flow

Effective fishway design requires knowledge of fish swimming behavior in streams and channels. Appropriate tests with near-natural flow conditions are required to assess the interaction between fish behavior and turbulent flows. In this study, the volitional swimming behavior of S. prenanti was tested and quantified in an open-channel flume with three (low, moderate, and high) flow regimes. The results showed that, when confronted with alternative flow regimes, S. prenanti preferred to select regions with low flow velocities (0.25−0.50 m/s) and turbulent kinetic energy (<0.05 m2/s2) for swimming, while avoiding high-turbulence areas. Moreover, S. prenanti primarily employed steady swimming behavior to search for flow velocities lower than the average current to conserve energy in low- and moderate-flow regimes. It is hypothesized that in regions with higher flow velocities, fish may change their swimming strategy from energy conservation to time conservation. Additionally, the average and maximum burst speeds of S. prenanti were 2.63 ± 0.37 and 3.49 m/s, respectively, which were 2.21- and 2.28-fold higher than the average (1.19 m/s) and maximum (1.53 m/s) burst speeds estimated from the enclosed swim chamber for fish of similar length. This study contributes a novel research approach that provides more reliable information about fish volitional swimming behavior in natural habitats, as well as recommendations for hydraulic criteria for fishways and the identification of barriers to fish migrations.

Development of behavioral rules for upstream orientation of fish in confined space

Improving the effectiveness of fishways requires a better understanding of fish behavior near hydraulic structures, especially of upstream orientation. One of the most promising approaches to this problem is the use of model behavioral rules. We developed a three-dimensional individual-based model based on observed brown trout (Salmo trutta fario) movement in a laboratory flume and tested it against two hydraulically different flume setups. We used the model to examine which of five behavioral rule versions would best explain upstream trout orientation. The versions differed in the stimulus for swim angle selection. The baseline stimulus was positive rheotaxis with a random component. It was supplemented by attraction towards either lower velocity magnitude, constant turbulence kinetic energy, increased flow acceleration, or shorter wall distance. We found that the baseline stimulus version already explained large parts of the observed behavior. Mixed results for velocity magnitude, turbulence kinetic energy, and flow acceleration indicated that the brown trout did not orient primarily by means of these flow features. The wall distance version produced significantly improved results, suggesting that wall distance was the dominant orientation stimulus for brown trout in our hydraulic conditions. The absolute root mean square error (RMSE) was small for the best parameter set (RMSE = 9 for setup 1, RMSE = 6 for setup 2). Our best explanation for these results is dominance of the visual sense favored by absence of challenging hydraulic stimuli. We conclude that under similar conditions (moderate flow and visible walls), wall distance could be a relevant stimulus in confined space, particularly for fishway studies and design in IBMs, laboratory, and the field.

Wild longnose dace downstream of wastewater treatment plants display an obese phenotype

Wild fish living downstream of wastewater treatment plants (WWTPs) often have increased body condition factors or body mass indices compared to upstream fish. This observation has been largely attributed to increased nutrient loading and food availability around wastewater effluent outflows. While a higher condition factor in fish is generally considered a predictor of healthy ecosystems, the metabolic status and capacity of the animals downstream of WWTPs may be a better predictor of fitness and potential population level effects. To address this, we sampled wild longnose dace (Rhinichthys cataractae), a native species in North American waterways, from sites upstream and downstream of WWTPs. Downstream fish had higher body mass indices, which corresponded with higher nutrient (lipid, protein, and glycogen) storage in somatic tissues compared to upstream fish. Liver transcriptome analysis revealed metabolic reprogramming favoring lipid synthesis, including higher hepatic triglyceride levels and transcript abundance of targeted lipogenic genes. This suggests that effluent exposure-mediated obesity in dace is a result of changes at the transcriptional level. To determine potential ecological consequences, we subjected these fish to an acute stressor in situ to determine their stress performance. Downstream fish failed to mobilize metabolites post-stress, and showed a reduction in liver aerobic and anaerobic metabolic capacity. Taken together, fish living downstream of WWTPs exhibit a greater lipid accumulation that results in metabolic disruption and may compromise the ability of these fish to cope with subsequent environmental and/or anthropogenic stressors.

Swimming performance of 12 Schizothoracinae species from five rivers

A series of stepped velocity tests were carried out in a Brett-type swimming respirometer and the overall range in swimming performance for 12 Schizothoracinae species was measured. The relative critical swimming speed U_crit and burst speed U_burst decreased with body length, while absolute U_crit and U_burst increased with body length. U_crit increased with temperature up to approximately 15^° C and then decreased. Species with a high U_crit also displayed a higher U_burst .