Variation in fish body morphology represents an important aspect of phenotypic diversity and plays a fundamental role in understanding fish evolution and ecology. The complex oceanographic conditions of the Northwest Pacific Ocean create diverse selective pressures, making it an ideal system for studying how environmental variability shapes fish body morphology. While previous macroecological studies have linked fish morphology to environmental factors, the driving factors of regional morphological differences were seldom explored. In this study, morphological variations among different body regions (entire body, head, torso and tail) of 22 fish species from the Northwest Pacific Ocean were analysed to explore the phylogenetic and ecological drivers of these variations with geometric morphometrics (GMs) in a phylogenetic framework. The results showed significant morphological differences among orders and species. Entire body, head, torso and tail exhibited low to moderate phylogenetic signals. Ecological factors, including latitudinal range, temperature preference, fecundity and trophic level, significantly shaped morphological variations, thus emphasizing the complex interplay between ecological and evolutionary pressures. We confirmed that different body regions are subject to distinct selective pressures, reflecting the combined influence of genetic and environmental factors. Overall, this study highlights the combined influence of phylogenetic history and ecological pressures in shaping fish morphology. These findings improve understanding of fish evolutionary biology and provide a foundation for conservation and species management in the Northwest Pacific.
Acrossocheilus fasciatus is an economically important freshwater fish species in China. In recent years, Citrobacter freundii infection has caused significant harm to the aquaculture industry. In this study, we performed histological observation and RNA-seq analysis of the intestines and spleens of control (CK) and C. freundii infected A. fasciatus (EG). The results showed that infected fish exhibited abdominal haemorrhage, intestinal villous shedding, hydropic degeneration of hepatocytes and splenic sinus dilation with congestion. RNA-seq analysis identified 3054 DEGs in the intestine and 7706 DEGs in the spleen, with 1247 overlapping DEGs identified by combined analysis. A substantial portion of these genes clustered within biological activities linked to immunity and metabolic regulation, particularly engaging immune-related routes such as endoplasmic reticulum-based protein maturation, alongside the complement system and coagulation signalling cascades. This study systematically reveals the synergy and division of labor between the intestine and spleen during C. freundii infection, providing fundamental data for understanding the immune response mechanisms of A. fasciatus and a theoretical basis for optimising disease prevention and control strategies.
The Cape galaxias, formerly treated as the single African representative of the family Galaxiidae under the name Galaxias zebratus (Castelnau, 1861), has long masked substantial hidden diversity. We consolidated all available molecular data and generated additional sequences to fill sampling gaps, providing the most comprehensive assessment of historically isolated lineages within this complex to date. Analysis of mitochondrial cyt b and COI sequences identified 15 genetically distinct lineages, most with restricted geographic ranges. Previous phylogenetic studies demonstrated that the African galaxiids are not closely related to Galaxias truttaceus Valenciennes, 1846, the type species of Galaxias, suggesting they may be misclassified. Detailed morphological and osteological examinations identified consistent diagnostic characters separating the Cape galaxiids from Galaxias and other galaxiid genera. Molecular and morphological evidence supports reinstatement of the genus Agalaxis Scott, 1936, for the African galaxiids. We further revalidate Agalaxis punctifer (Castelnau, 1861) and A. dubius (Gilchrist & Thompson, 1917), describe A. peninsulae sp. nov. and designate a neotype for and redescribe A. zebratus s.s. By resolving the application of available names, we establish a taxonomic framework for resolving the remaining undescribed diversity and recognise the Cape galaxiids as a diverse endemic radiation within the Cape Fold Ecoregion.
Abstract Co‐ordinated circular swimming by tiger sharks ( Galeocerdo cuvier ) was documented by divers in the Fernando de Noronha Archipelago, Brazil, on 1 October 2023 under non‐provisioned conditions. At least six individuals maintained circular movement over 20 min. A second observation in October 2024 documented at least three sharks, although co‐ordinated swimming could not be confirmed. Passive acoustic telemetry from 12 tagged tiger sharks revealed simultaneous detections of up to three individuals, indicating temporal co‐occurrence near the site. These observations document an uncommon behavioral pattern and highlight the need for long‐term studies.
Abstract The interaction between flow and riverbed structures creates spatially heterogeneous turbulent microhabitats that influence fish station‐holding strategies and energy allocation. This study investigated the hovering behaviour of Schizothorax grahami in complex turbulent microhabitats formed by rock arrays of different scales using flume experiments. Video analysis and data storage tag (DST) tilt sensors were combined to quantify five multidimensional kinematic indicators: ground swimming speed (), angular velocity of swimming direction (), tail‐beat angular velocity (), pitch angular velocity () and roll angular velocity (). As rock‐element size increased, fish hovering positions shifted from dispersed distributions to regions with local velocity gradients around rock elements, with clear positional overlap observed under some large‐rock‐array conditions. Increasing discharge generally increased the mean values and standardized within‐condition variances of most kinematic indicators. Trial‐level Spearman correlation analysis showed that had the strongest positive correlation with . Generalized linear mixed models further revealed functional differentiation among kinematic responses: and were mainly driven by flow velocity () and turbulent kinetic energy, whereas , and showed weaker hydrodynamic responses. These findings suggest that fish hovering is an active multidimensional regulation process in which position maintenance, directional correction, propulsion and postural stabilization show partially differentiated response patterns. These findings provide new insights into the locomotor and postural strategies that enable benthic fish to maintain stability in heterogeneous turbulent environments and improve our understanding of fish behavioural adaptation to complex flows.
