Journal of fish biology最新文献

The genus Sinocyclocheilus represents the world's most diverse cavefish radiation, typically exhibiting troglomorphic traits such as scale regression and eye degeneration. Notably, Sinocyclocheilus macrolepis from a tributary of the Long-Jiang of the Pearl River retains fully developed scales despite inhabiting epigean streams, a rare trait among its cave-adapted congeners. The Sinocyclocheilus specimens collected from a tributary of the Hongshui-He of the Pearl River in South Guizhou exhibit overall similarities to S. macrolepis with fully developed scales and normal eyes. Phylogenetic analyses using mitochondrial Cyt b and ND4 genes reveal that these specimens represent a novel species, sister to S. macrolepis but with significant genetic divergence, and closely related to Sinocyclocheilus ronganensis. This new species was designated as Sinocyclocheilus pingchowensis in this study. Morphologically, S. pingchowensis differs from S. macrolepis in lateral-line scale counts, head width, gill-opening position and pelvic-fin ray counts. S. pingchowensis along with S. macrolepis and S. ronganensis are herein defined as the S. macrolepis group based on the shared synapomorphies and phylogenetic affinities. The phylogenetic tree suggests that the retention of scales in the species pair of S. pingchowensis and S. macrolepis represents a rare case of evolutionary reversal from cave-adapted degeneration. This phenotypic re-emergence correlates with their re-colonization of surface water, likely reflecting a synergistic adaptation to both photic exposure and occupation of the niche of mid-upper water strata, coinciding with relaxed selection on cave-associated trade-offs. The divergence of S. pingchowensis from its sister species was likely triggered by the river capture event between the two rivers.

The vertical slot fishway (VSF) has been widely installed to help fish pass hydropower dams, mitigating migration barriers from dam construction. Current research on VSF construction has not fully incorporated the fundamental principles of fish swimming kinematics and the quantification of trajectory characteristics, which is of great significance for optimizing existing VSFs and guiding future development. This study investigated the swimming behaviours, kinematics and trajectory characteristics of Procypris rabaudi (P.R.), Onychostoma sima (O.S.) and Squalidus argentatus (S.A.) in a VSF. Kinematics metrics included tail-beat frequency, angle, amplitude, midline kinematics and wavelength. The results demonstrated that the passage rate for the three fish species (8-10 cm body length) decreased as the outlet velocity increased. Analysis of trajectory hydraulic complexity revealed that swimming along side walls and baffles provided greater energy benefits. Furthermore, fish exhibited the lowest tail-beat frequency in recirculation zones, whereas the midline oscillation amplitude and wavelength progressively decreased from recirculation zones to the mainstream and slots. Long-term retention behaviours were also observed to adversely affect passage efficiency. This study thereby enhances understanding of fish swimming strategies and trajectory characteristics in VSFs.

Dynamic changes in colour and pattern facilitate key behavioural functions in animals, particularly camouflage for predator avoidance. However, the benefits of colour change depend on the environmental and behavioural contexts. We tested how colour change interacts with movement behaviour in a freshwater fish by filming individuals in an open-field test following a stressful stimulus. Fish with lighter patterns, brighter colour and/or those that changed to lighter colours were more likely to move. Our results highlight the interconnected roles of behaviour, colour change and environmental context in effective camouflage.

Dasyatis hypostigma is a species of ray found primarily in coastal and estuarine waters of the Atlantic Ocean. It plays an important role in marine ecosystems by regulating populations of small fish and invertebrates. The aim of this study was to evaluate the influence of different anticoagulants and processing times on the haematological parameters of D. hypostigma, as well as to describe the morphology of its blood cells. Blood samples from 11 D. hypostigma individuals housed at the Marine Aquarium of Rio de Janeiro were collected following tonic immobilization techniques and distributed into tubes containing different anticoagulants (K₂ EDTA, sodium citrate, lithium heparin and sodium heparin). The samples were analysed immediately after collection and again 6 h later. The results showed significant effects of the anticoagulants on haematological parameters such as packed cell volume, mean corpuscular haemoglobin concentration and mean corpuscular volume. Time also influenced some parameters, particularly in samples treated with sodium heparin, where minor variations in cell counts were observed. Morphological analysis of the blood cells revealed typical characteristics of various leukocytes, erythrocytes and thrombocytes. Lithium heparin is the anticoagulant of choice for processing blood samples from D. hypostigma, although sodium heparin may also be used. EDTA and citrate should not be used for this species. Samples should be processed as promptly as possible. To the best of our knowledge, this is the first study to describe the blood cell morphology of D. hypostigma.

This study reports the first record of the endemic Lutz's stingray, Hypanus berthalutzae, from Brazil, at the upwelling ecosystem of Cabo Frio, southeastern Brazil. A mature female (2.44 m of total length) was incidentally captured by artisanal fisheries at 7 m depth in January 2025. Molecular identification (COI, Cytb), based on DNA barcoding and maximum likelihood phylogenetic analyses, confirmed similarity with H. berthalutzae sequences deposited in GenBank and supported its monophyly. Although the species is distributed from the mouth of the Amazon River to São Paulo, the large size of the specimen documented in this study suggests marked growth associated with highly productive upwelling zones. This record represents the first occurrence for the area, including Cabo Frio, and extends the genetic analysis of the species in southeastern Brazil. These results highlight the importance of integrating morphological analyses with molecular tools to accurately identify species and support conservation actions for endemic species in regions where their populations are vulnerable, enabling a more precise evaluation of species threats and conservation status.

Atlantic salmon (Salmo salar L.) populations in Scotland are subject to active management and conservation practices which require biological reference points (BRPs), specifically conservation limits, defined at the level of the stock. Acquiring the data necessary to independently derive these BRPs for all managed populations in Scotland is prohibitive, motivating the use of Bayesian hierarchical stock-recruitment models. These models provide a framework for the joint analysis of multiple monitored stocks, and the transportation of BRPs to non-monitored stocks. This framework was adapted to introduce nationally relevant and available covariates that might explain variation in recruitment dynamics among stocks and reduce uncertainty in posterior predictions of BRPs. Model selection was designed to maximise the prediction of BRPs for new stocks via leave-one-group-out cross-validation. Out-of-sample predictive performance was maximised by including information on latitude, land usage within the catchment and historic catch per area of salmon habitat in the model. The extensions to Bayesian hierarchical stock-recruitment methods presented here, when applied at a national scale, result in more locally discriminative posterior predictions compared to existing methods and are readily applicable to other stocks and species.

Poeciliid fishes show diverse courtship displays. Building on recent work in Alfaro cultratus, we document mating behaviours in its only congener, Alfaro huberi. In both species, males adopt a unique posture above females and initiate physical contact. A. cultratus males rub the tops of females' heads with their pelvic fins, whereas A. huberi males touch females' chins with the gonopodium, a modified anal fin used in copulation. We compare these behaviours and discuss how differences may relate to the distribution of female sensory organs.

Triplophysa nayongensis sp. nov., a new blind stygobitic fish, is described here assisted by voucher specimens collected from an underground cave in Zhangjiawan Town, Nayong County, Bijie City, Guizhou Province, China. This species can be distinguished from all its known congeners, which are cave-restricted, based on morphological (eyes either reduced to discernible black dots or entirely absent; anterior nasal flaps not elongated into barbel-like processes; dorsal-fin origin anterior to pelvic-fin insertions; pectoral-fin tips failing to reach pelvic-fin origins; hindmost parts of pelvic fins extending beyond anus but not reaching anal-fin insertion; colourless body; and distal margin of dorsal fin truncate), geographic (upper basin of the Wujiang River vs. other sites) and phylogenetic (monophyletic with respect to close relatives) evidence. The finding elevates the number of cave-dwelling plateau-loach species from 42 to 43 and expands their spatial range to further upper drainage of the Wujiang River, a primary tributary of the Yangtze River.

Sex is an important driver of variation in behaviour, ecology and physiology. Sex identification in the Critically Endangered European eel (Anguilla anguilla) currently requires fish sacrifice, or the use of morphological differences such as body length, which can be inaccurate in certain habitats and at intermediate body lengths. Non-lethal tools for accurate sex identification in this species are therefore required. Here, we test the efficacy of two minimally invasive methods of sex identification: (1) ultrasonography and (2) molecular markers taken from pectoral fin clips. Both methodologies were applied to riverine European silver eel and compared to histological sex identification. Ultrasonography accurately identified the gonads in female eel, with males identified by the absence of detectable gonadal structures. The level of expression of three molecular markers (dcn, LOC111853410, kera) previously used to identify sex in Japanese eel (Anguilla japonica) were evaluated. There was no significant differential expression of the three molecular markers between sexes, suggesting that these markers cannot be accurately used to identify sex in European eel. Our findings suggest that minimally invasive imaging using ultrasonography can be a reliable tool for identifying sex in early-stage adult migratory European eels, with particular use at intermediate sizes (400-500 mm) and animals in habitats where migration potential is limited and may regularly exceed typical growth sizes. This technique can be highly valuable for studies that address ecological, behavioural, conservation and management issues in this Critically Endangered species.

To investigate the impact of tea polyphenols on the health of Pelteobagrus fulvidraco under ammonia stress, a total of 480 juvenile P. fulvidraco were divided into four groups receiving tea polyphenols supplemented diets at 0 mg kg^-1 (C group), 200 mg kg^-1 (L group), 400 mg kg^-1 (M group) and 600 mg kg^-1 (H group) for 56 days. Ammonia stress was applied from days 28 to 56. The results showed that intestinal histological damage was alleviated in the L and M groups under ammonia stress. In the M group, the levels of total antioxidant capacity and Nrf2, HO-1 and Occludin were the highest. Regarding ferroptosis-related genes, DMT1, FTM and FPN1 exhibited their highest expression in the L group, while TF, TFR1, FTL, SLC7A11 and GPX4 showed their highest expression in the M group. FTH demonstrated its highest expression in the H group. Furthermore, the expression of ACSL4 in the L and M groups was significantly lower than that in the C group. Intestinal microbiome analysis revealed enhanced microbial diversity in the tea polyphenol-added groups, accompanied by reduced relative abundance of dominant phylum Fusobacteriota and genus Cetobacterium compared to the C group. These results suggested that dietary supplementation of 200-400 mg kg^-1 tea polyphenols could alleviate ammonia-induced intestinal ferroptosis and histological damage, as well as protect intestinal health by regulating the compositional structure and diversity of the intestinal microflora. Specifically, the 400 mg kg^-1 dose exerted the most comprehensive protective effects. This study provides mechanistic insights into the development of tea polyphenol-based anti-ammonia feed additives for P. fulvidraco aquaculture.