Morphological predictors of swimming speed performance in river and reservoir populations of Australian smelt Retropinna semoni

Resistance and propulsion trade-offs induced by different morphologies: Insights for fish conservation

Understanding the adaptive relationships between fish morphology and water flow and leveraging this knowledge to shape water flow conditions beneficial for the conservation of rare fish are critical for their protection. This study integrates a high-precision fish model with a wave equation motion framework to accurately analyze and visualize the forces acting on various parts of fish bodies during swimming. The results quantitatively reveal the trade-offs in resistance and propulsion between two fish morphologies. For Carassius auratus, a propulsive force advantage is observed within a velocity range of 0-0.6 m/s, while Schizothorax prenanti demonstrates a staged propulsive advantage as velocity increases. Specifically, S. prenanti achieves maximum propulsion more rapidly at 0.4 m/s, maintains higher propulsion values at 0.6 m/s, and demonstrates adaptability to water velocities of 1 m/s, which prove insurmountable for C. auratus. Furthermore, a detailed analysis uncovers a strong correlation between fish morphology and biomechanical performance. The long-term adaptation of S. prenanti to flowing water environments is driven by its low-resistance morphology, enabling it to dominate despite generating less propulsion than C. auratus. Conversely, C. auratus, adapted to low-flow environments, prioritizes strong propulsion at the cost of heightened resistance in high-flow conditions. This study establishes a morphology-biomechanics-flow environment framework, enabling researchers to design flow conditions that align with the mechanical advantages of target fish species. Such an approach offers a novel perspective for fish habitat management and conservation.

Revision of Schizopygopsis chengi Fang 1936 (Cypriniformes: Cyprinidae), with a description of a new subspecies

The species status of Schizopygopsis chengi, which is defined as a subspecies of Schizopygopsis malacanthus, is under debate. In the present study, comprehensive morphological and molecular analyses were performed on S. chengi, its closest relatives S. malacanthus and other Schizopygopsis fishes. The results showed that S. chengi did not form a sister lineage to S. malacanthus, with morphological differences in unbranched rays of the dorsal fin. The morphological and molecular evidence indicated that S. chengi was a valid species and was separated from S. malacanthus. By examining specimens of S. chengi from the Marke River, Keke River, Duoke River and Baoxing River, populations from the Duoke River showed morphological characteristics of mouth inferior, transverse oral fissure, relative long predorsal length than other geographic populations. The monophyly of population from Duoke River was strongly supported by mitochondrial sequence datasets. Based on morphological and molecular evidence, specimen from Duoke River is considered a newly identified subspecies and named as Schizopygopsis chengi duokeheensis.

Morphology and motor behavior of endemic fishes in the upper reaches of the Yangtze River basin

Dam construction alters the hydrodynamic conditions, consequently impacting the swimming behavior of fish. To explore the effect of flow hydrodynamics on fish swimming behavior, five endemic fish species in the upper Yangtze River basin were selected. Through high-speed video visualization and computer analysis, these species' swimming patterns under different flow velocities (0.1-1.2 m/s) were investigated. The kinematic and morphological characteristics of the fish were presented. The principal component analysis was used to analyse the main factors influencing the swimming ability of fish and to determine the correlation coefficients among fish behavior indicators. Fish exhibited three different swimming patterns under different flow velocities. Low velocity (0.1-0.3 m/s) corresponds to free motion, middle velocity (0.4-0.7 m/s) corresponds to cruising motion, and high velocity corresponds to stress motion (0.8-1.2 m/s). The fish kinematic index curves were obtained, and four of five fish species showed two extreme points, which means the optimal and adverse swimming strategies can be determined. With the increase in flow velocity, the tail-beat frequency showed an increasing trend, whereas the tail-beat angle and amplitude showed a decreasing trend. Morphological and kinematic parameters were the two main indexes that affect the swimming ability of fish, which accounts for 41.9% and 26.9%, respectively.

Testing the effects of body depth on fish maneuverability via robophysical models

Fish show a wide diversity of body shapes which affect many aspects of their biology, including swimming and feeding performance, and defense from predators. Deep laterally compressed bodies are particularly common, and have evolved multiple times in different families. Functional hypotheses that explain these trends include predator defense and increased maneuverability. While there is strong evidence that increasing body depth helps fish avoid gape-limited predators, the evidence that body shape increases a fish's maneuverability is ambiguous. We used a two-pronged approach to explore the effects of body shape on the control of maneuvers using both live fish and a robotic model that allowed us to independently vary body shape. We captured ventral video of two tetra species (Gymnocorymbus ternetziandAphyocharax anisitsi) performing a wide range of maneuvers to confirm that both species of live fish utilize fundamentally similar body deformations to execute a turn, despite their different body depths. Both species use a propagating 'pulse' of midline curvature that is qualitatively similar to prior studies and displayed similar trends in the relationships between body kinematics and performance. We then tested the robotic model's maneuverability, defined as the total heading change and maximum centripetal acceleration generated during a single pulse, at a range of different input kinematics across three body shapes. We found that deepening bodies increase the robot's ability to change direction and centripetal acceleration, though centripetal acceleration exhibits diminishing returns beyond a certain body depth. By using a robotic model, we were able to isolate the effects of body shape on maneuverability and clarify this confounded relationship. Studying the functional morphology of complex traits such as body shape and their interaction with complex behavior like maneuverability benefits from both the broad view provided by comprehensive comparative studies, and the control of variables enabled by robophysical experiments.

Conservation threats and future prospects for the freshwater fishes of Ecuador: A hotspot of Neotropical fish diversity

Freshwater fish communities in Ecuador exhibit some of the highest levels of diversity and endemism in the Neotropics. Unfortunately, aquatic ecosystems in the country are under serious threat and conditions are deteriorating. In 2018-19, the government of Ecuador sponsored a series of workshops to examine the conservation status of Ecuador's freshwater fishes. Concerns were identified for 35 species, most of which are native to the Amazon region, and overfishing of Amazonian pimelodid catfishes emerged as a major issue. However, much of the information needed to make decisions across fish groups and regions was not available, hindering the process and highlighting the need for a review of the conservation threats to Ecuador's freshwater fishes. Here, we review how the physical alteration of rivers, deforestation, wetland and floodplain degradation, agricultural and urban water pollution, mining, oil extraction, dams, overfishing, introduced species and climate change are affecting freshwater fishes in Ecuador. Although many of these factors affect fishes throughout the Neotropics, the lack of data on Ecuadorian fish communities is staggering and highlights the urgent need for more research. We also make recommendations, including the need for proper enforcement of existing environmental laws, restoration of degraded aquatic ecosystems, establishment of a national monitoring system for freshwater ecosystems, investment in research to fill gaps in knowledge, and encouragement of public engagement in citizen science and conservation efforts. Freshwater fishes are an important component of the cultural and biological legacy of the Ecuadorian people. Conserving them for future generations is critical.