An improved method of local coloring in vertical-slot fishways to enhance the fish migration effect of grass carp.

Vertical-slot fishway (VSF) has been used in many water conservancy projects to restore the river connectivity. A high-quality fishway project should facilitate fish to discovering the exit and passing through, avoiding to long stay in the fishway and delay the migration. Current research on fishway engineering has not yielded an expected passing ratio of fish migration, and it is therefore of great significance to further study the assisting effect of VSF in fish migration. To begin with, we preliminarily determined the attractive and repelling colors of grass carps based on their swimming behavior in a static water pool configured with local colors. Combined with the migration route of the grass carp in a VSF pool without local coloring, four local coloring cases were designed. Based on the camera results of the four experimental local coloring cases, a comparative analysis was conducted with the blank control group frame by frame. This was followed by the statistics of the number of successfully migrated grass carps and their total completion time. On that basis, the assisting effect of VSF in fish migration under the four cases was evaluated in terms of the reduction rate of migration route length, the reduction rate of completion time, and the improvement rate of passing ratio. The research outcomes indicated that green and blue act as attractive colors while yellow and red serve as repelling colors for grass carp. Adding colors to the training wall and dividing wall in the VSF pool, the migration route of grass carp was appropriately adjusted, alongside a shortened completion time and an improved passing ratio. Of the four local coloring cases, the recommended case showed a significant effect on migration route, with more concentrated moving trajectories and shortened route length. Typically, the migration route length decreased by 26%, and the frequency of fish long staying at the junction between the training wall and dividing wall was markedly reduced, as well as the frequency of fish swimming along the water flow from upstream to downstream. The completion time was shortened by 26%, and the passing ratio was enhanced by 44%. The approach of combining local coloring with fish behavior and fishway hydraulics in the pool surpassed the method that optimizes the fishway design only from the fishway hydraulics. The improved method greatly shortened the migration route length, reduced the completion time, and significantly improved the passing ratio of fish passage objects in the VSF. The present research mainly focuses on using model experiments to evaluate the local coloring cases. In the future studies, we will configure local colors to the sidewalls of on-site fishways using environmentally friendly paint or colored organic glass panels. With the monitoring results of the completion time and passing ratio of fish passage objects, the recommended case can be further verified and optimized, thereby providing a more reasonable and feasible local coloring case for assisting fish migration in the VSF project.

Enhancing migratory potential in fish passes: The role of pier shape in minimizing debris accumulation.

Biodiversity preservation is a primary challenge of the 21st century, focusing on restoring unobstructed river flows and mitigating the effects of barriers, supported by European biodiversity strategies up to 2030. Maintaining ecological continuity, such as unblocking fishways clogged by floating debris disrupting natural fish migration paths, remains a challenge despite conventional protective methods. This study, taking a vertical slot fish pass in Wroclaw on the Odra River as a case study and based on research on bridge piers, suggests modifying pier shapes from rectangular to rounded in order to reduce debris accumulation. Field studies, utilizing an OTT MF Pro flow meter, were conducted to validate the numerical model. The measured flow rate in the field was 3.15 [m³·s-1], while the numerical modeling yielded a flow of 3.19 [m³·s-1]. Focusing on optimizing the shape of cross-wall piers to enhance fish migration conditions, the study examined six different pier configurations, analyzing flow speed in the main slot, crucial for migration. Using 2D hydraulic modeling with Iber, it assessed the migratory potential of different pier designs by analyzing hydraulic conditions and comparing them with the swimming capabilities of fish species native to the Odra River. Results indicate that rounding the pier edges positively affects flow speeds in the main slot, enhancing fish migration possibilities, contributing to fish pass functionality improvement and supporting broader biodiversity and ecosystem health goals.

Effect of total dissolved gas supersaturation on the passage behavior of silver carp (Hypophthalmichthys molitrix) and ya-fish (Schizothorax prenanti) through an experimental vertical slot fishway.

Total dissolved gas (TDG) supersaturation caused by flood discharge water poses a threat to vital activities such as migration, foraging, and evasion in fish species upstream of the Yangtze River, which may impair the ability of fish to pass through fishways during the migration period, causing poor utilization of fishways. Previous studies have shown that TDG supersaturation reduces the critical and burst swimming abilities of fish, suggesting potential adverse effects on swimming performance. However, studies focusing on the impact of TDG on fish swimming behavior in experimental vertical-slot fishways remain scarce. Therefore, in this study, silver carp (Hypophthalmichthys molitrix) and ya-fish (Schizothorax prenanti) were used as the study species, and comparative passage experiments were carried out in an experimental vertical slot fishway to systematically analyze the effects of TDG supersaturation on their passage behavior. The passage success of the silver carp was 57%, 39%, 26%, and 27% at TDG levels of 100%, 110%, 120%, and 130%, respectively. Passage success of ya-fish was 73%, 37%, 31%, and 35% at TDG concentrations of 100%, 110%, 120%, and 130%, respectively. The passage time for both species increased significantly with increasing TDG levels. Furthermore, the passage routes of silver carp changed significantly compared to the control group, whereas the passage routes of ya-fish changed insignificantly. High levels of TDG supersaturation (≥120%) also contributed to a higher mortality rate of ya-fish passing through the vertical slot fishway. The research results provide valuable data on the influence of TDG supersaturation on fish movement behavior responses in experimental vertical slot fishways, offering a reference for the design of fishways and the formulation of reservoir operation schemes.

Vertical Slot Fishways: Incremental Knowledge to Define the Best Solution.

River artificial fragmentation is arguably the most imperilling threat for freshwater-dependent fish species. Fish need to be able to freely move along river networks as not only spawning grounds but also refuge and feeding areas may be spatially and temporally separated. This incapacity of free displacement may result in genetic depletion of some populations, density reduction and even community changes, which may in turn affect how meta-community balances are regulated, potentially resulting in functional resilience reduction and ecosystem processes' malfunction. Fishways are the most common and widely used method to improve connectivity for fish species. These structures allow fish to negotiate full barriers, thus reducing their connectivity impairment. Among all technical fishway types, vertical slot fishways (VSF) are considered to be the best solution, as they remain operational even with fluctuating water discharges and allow fish to negotiate each cross-wall at their desired depth. In the present study, we collected both published and original data on fish experiments within VSF, to address two questions, (1) What variables affect fish passage during experimental fishway studies? and (2) What is the best VSF configuration? We used Bayesian Generalized Mixed Models accounting for random effects of non-controlled factors, limiting inherent data dependencies, that may influence the model outcome. Results highlight that fish size, regardless of the species, is a good predictor of fishway negotiation success. Generally, multiple slot fishways with one orifice proved to be the best solution. Future work should be focused on small-sized fish to further improve the design of holistic fishways.

Experimental study on the passage behavior of juvenile Schizothorax prenanti by configuring local colors in the vertical slot fishways.

The vertical slot fishway is one of the most widely used fishways in the world. To solve the problems of long passage time and low passage rate of fish passing objects in the conventional vertical slot fishway, this study proposed a method of configuring local colors in the internal sidewall of the fishway pond to improve the vertical slot fishway based on the approach-avoidance effect of fishes on different colors. Taking Schizothorax prenanti as the research object, comparative fish passing experiments were carried out to analyze the effects of configuring local colors on the passage behavior. It has been found that green and yellow are the approach and repellent colors for Schizothorax prenanti, respectively. By configuring local colors of the guide wall and partition wall at the upstream and downstream of the pond, the passage track of Schizothorax prenanti was significantly changed, which in turn affected their passage time and passage rate. The configuration of local green to the guide wall and partition wall on the upstream negative side, and local yellow to the sidewall of the guide wall on the upstream negative side, the guide wall on the downstream positive side, and the partition wall on the downstream positive side can shorten the overall passage time of Schizothorax prenanti by 9 % and increase the passage rate by 23 %. Compared with the scheme that completely depends on the flow conditions to change the structure of the pond, the method of configuring local colors in the pond is an improved method combining fish ethology and hydraulics. The scheme of local color configuration significantly shortens the passage time and passage rate of fish passing objects in the vertical slot fishway, and can be applied to the fishway design and the improvement of operation effect, which has a certain practical application value.

Schizothorax prenanti swimming behavior in response to different flow patterns in vertical slot fishways with different slot positions.

Fish swimming behavior is a critical parameter for the design of vertical slot fishways. Although Schizothorax prenanti is a significant reproductive potamodromous migratory fish species in the upper reaches of the rivers in Southwest China, its swimming behavior has not been extensively researched. Therefore, in this study, a comparative experiment was conducted in vertical slot fishways to analyze the behavior of Schizothorax prenanti in response to different flow patterns, with respect to different slot positions. The experimental model was designed with a length scale of 1:4, and a method for selecting the appropriate fish size in the scaled physical model was proposed. Based on these experiments, it was found that the typical upstream trajectories of Schizothorax prenanti are traceable to the sidewall of the pool, which are characterized by low velocity and turbulent kinetic energy (TKE). The hydraulic variables exhibited an asymmetric distribution within the vertical slot, and the fish were found to pass through the area with the lowest velocity and TKE. A flow pattern with a guide wall length-to-pool width ratio of P/B = 0.25, in which Schizothorax prenanti can immediately find the sidewall, is suitable for fish migration. Therefore, this is the recommended value for the construction of effective vertical-slot fishway structures.

Fish passage post-construction issues: analysis of distribution, attraction and passage efficiency metrics at the Baguari Dam fish ladder to approach the problem

Fish passages are considered the oldest management tool used to minimize the impact of blocking fish migratory routes by hydroelectric power plants. However, fish passages are being installed without specific criteria in Brazil, with severe consequences to the conservation of the local fish fauna. Therefore, basic data gathered for fish passages already constructed could contribute to define operational rules, in addition to offer subsidies to decision-making and design of future facilities. Thus, the fish ladder of Baguari Dam was evaluated regarding temporal distribution, attraction, and ascension of the local fish fauna. A total of 20 fish samples were conducted immediately downstream of the dam and inside the fish ladder, from January 2010 to June 2011. Seasonal variation in fish abundance and richness was registered below the dam and inside the passage, with higher number of migratory fish in the reproductive season (Kruskall-Wallis, p = 0.04 and p = 0.05). Furthermore, higher concentration of migratory allochthonous and non-migratory species was registered for the spill bay (Wilcoxon, p = 0.009 and p = 0.006) compared to the tailrace, where the fish ladder entrance is located. This result suggests low efficiency of the attraction system of the mechanism during the reproductive period. Once entering the fish ladder, migratory species apparently ascend the facility due to the similar distribution throughout different stretches. Generally, the results showed that an operational rule for the Baguari Dam fish ladder should consider running the facility only during the reproductive period, unless the objectives of the passage are well defined. The attraction system must be more precisely evaluated, using technologies such as radiotelemetry. Similarly, fish ascension also should be better analyzed to evaluate the time spent to ascend and its influence in the reproductive biology of the species using the ladder. Pit-tag system could be used to approach this analysis. It is expected that the discussion of these results would be useful for companies of the energy sector and for environmental agencies in Brazil, subsidizing decisions related to the management of fish passages already installed and to the construction of new facilities in the country.

As passagens ou sistemas de transposição de peixes são uma das ferramentas de manejo mais antigas utilizadas para minimizar o impacto do bloqueio de rota migratória de peixes pela implantação de barragens. Todavia, sua implantação tem sido realizada sem muito critério no Brasil, trazendo consequências muitas vezes graves à conservação da ictiofauna local. Por essa razão, dados básicos obtidos para as passagens de peixes em funcionamento podem contribuir para definição de sua regra operativa, além de subsidiar tomada de decisões e o design de futuros sistemas. Assim, a escada de peixes da UHE Baguari foi avaliada quanto à distribuição temporal, atração e subida da ictiofauna local. Foram realizadas 20 amostragens a jusante da barragem e no interior da escada de peixes entre janeiro de 2010 a junho de 2011. Observou-se variação sazonal na distribuição e riqueza de espécies de peixes a jusante da barragem e dentro da escada, sendo que as espécies migradoras foram registradas em maior abundância durante o período reprodutivo (Kruskall-Wallis, p = 0,04 e p = 0,05). Além disso, nesse mesmo período, maior concentração das espécies migradoras alóctones e não migradoras foi registrada para a bacia de dissipação da barragem (Wilcoxon, p = 0,009 e p = 0,006) quando comparado ao canal de fuga, local onde se encontra a entrada da escada. Isso sugere que a eficiência do sistema de atração do mecanismo não seja a esperada nesse período. Uma vez dentro da escada, aparentemente as espécies migradoras percorrem todo o mecanismo, distribuindo-se de forma similar ao longo de sua extensão. Em geral, os resultados obtidos demonstram que, aparentemente, a regra operativa da escada deva indicar seu funcionamento apenas no período reprodutivo, ao menos até que os objetivos da transposição de peixes na UHE Baguari sejam de fato definidos. Já o sistema de atração da escada deverá ser avaliado de forma mais precisa, utilizando-se tecnologias como radiotelemetria. Da mesma forma, a subida dos peixes pela escada deve ser melhor analisada para se avaliar o tempo gasto e a influência desse período sobre a biologia reprodutiva dos peixes. O sistema de Pit-tag pode ser utilizado para realizar essa análise. Espera-se que a discussão das informações obtidas no presente trabalho possa ser utilizada pelas empresas do setor elétrico e órgãos ambientais para subsidiar decisões relacionadas ao manejo de sistemas de transposição de peixes já em funcionamento e à construção de novos empreendimentos.

Reynolds shear-stress and velocity: positive biological response of neotropical fishes to hydraulic parameters in a vertical slot fishway

The barriers created by dams can cause negative impacts to aquatic communities, and migratory fish species are directly affected. Fishways have been developed to allow the upstream passage of fishes through dams. In Brazil, after the implementation of environmental laws, these structures have been built based on European and American fishway designs. Studies have shown selectivity for different neotropical fishes in some Brazilian fishways, and the main challenge has been to promote upstream passage of a large number of diverse fish species. The patterns of flow circulation within the fish ladder may explain fish selectivity although few studies detail the fish response to hydraulic characteristics of fish ladder flow. This paper presents a laboratory study, where a vertical slot fishway was built in a hydraulic flume and the behavior of two neotropical fish species (Leporinus reinhardti and Pimelodus maculatus) were analyzed. The structure of flow was expressed in terms of mean velocity, Reynolds shear-stress and velocity fluctuation fields. The individuals of Leporinus reinhardti had higher passage success than Pimelodus maculatus in the laboratory flume. Both species preferred areas of low to zero Reynolds shear-stress values. In addition, different preferences were observed for these species concerning the horizontal components of velocity fluctuation.

Interrupções em rios, como as causadas por barragens, provocam impactos negativos sobre as comunidades aquáticas e as espécies migratórias de peixes são diretamente afetadas. A fim de permitir a passagem de peixes, mecanismos de transposição são construídos junto a barramentos. No Brasil, após a implantação de leis ambientais, estas estruturas passaram a ser amplamente construídas e foram baseadas em projetos desenvolvidos na Europa e na América do Norte. Análises de mecanismos já construídos têm mostrado grande seletividade para espécies neotropicais e as demandas da diversa fauna de peixes neotropical são apresentadas como principal desafio ao projeto de passagens para peixes. Os padrões de escoamento dentro de escadas para peixes podem explicar a seletividade destes mecanismos, mas poucos estudos detalham a resposta dos peixes às características hidráulicas encontradas dentro das escadas. Este estudo apresenta uma análise realizada em um laboratório onde foi construída uma escada do tipo ranhura vertical e analisados os comportamentos de duas espécies neotropicais (Leporinus reinhardti e Pimelodus maculatus). O escoamento foi estudado considerando os campos de velocidade média, tensão cisalhante de Reynolds e flutuações de velocidades. Os indivíduos da espécie Leporinus reinhardti apresentaram maior sucesso de passagem do que os da espécie Pimelodus maculatus. Ambas as espécies preferiram áreas de tensão de Reynolds igual a zero. Além disso, diferentes preferências foram observadas para cada espécie em relação às componentes horizontais da flutuação da velocidade.