Journal of fish biology最新文献

Migrating silver European eels Anguilla anguilla are reported from the inland waters of the island of Cyprus for the first time, expanding the known geographic range in the Eastern Mediterranean of emigrating adults of this critically endangered, catadromous species. Silver eels were captured attempting to migrate to sea from two separate locations. This is important, as Cyprus was previously exempt from European eel management plans due to a presumed absence of significant eel populations, especially of the silver life stage. This now requires urgent review to ensure these populations are managed appropriately.

Intensive multigenerational size-selective mortality has been found to alter collective properties like shoaling via evolutionary adaptations of individual-level behavioural traits. For example, experimental populations of zebrafish (Danio rerio) experiencing intensive large size-selective mortality over multiple generations developed less cohesive shoaling in the laboratory, presumably because these fish were more attentive to environmental rather than social cues. By contrast, zebrafish exposed to small size-selective mortality evolved increased group cohesion. However, these studies were conducted in the absence of explicit predation risk by a live predator. In this study, we examined if size-selective mortality led to divergent responses in shoaling behaviour in the same zebrafish selection lines in the presence and absence of a live predator. The large line generated via size-selective harvest of smaller fish over five generations formed significantly more cohesive shoals than the control line, independent of whether a live predator was present or not. By contrast, the small line generated by size-selective mortality of large fish over five generations did not differ from controls in their shoaling behaviour in the presence or absence of a live predator. All zebrafish groups generally formed more cohesive shoals in the presence of a predator and became more dispersive over a 2-week experimental period. We conclude that the systematic removal of smallest individuals, thereby saving the largest fish from harvest, evolutionarily fosters increased group cohesiveness. These evolutionary adaptations might affect natural predation mortality and catchability by fishing gears.

Aquatic ectotherms are vulnerable to heatwave-induced physiological stress, which arises from increased energy demands and reduced dissolved oxygen content in warmer waters. Understanding thermal physiology is critical for predicting how commercially and ecologically important populations could be affected by the increasing risk of rising temperatures. Heatwave risk assessments often examine extremities of time scales: immediate impacts or long-term consequences. However, little is known about how consistently increasing mid-term thermal stress shapes aerobic performance in commercially important species such as Atlantic salmon (Salmo salar), which may face heat stress in rivers, especially at juvenile life stages. By measuring how salmon juveniles manage their aerobic capacity at 16, 19 and 22°C using intermittent flow respirometry, we test if their thermal performance curve declines at temperatures commonly occurring during heatwaves. Whole-animal metabolism was measured from control individuals kept at 16°C before and after the heatwave, and after 4-5 days exposure at 19 and 22°C during the heatwave. We show standard metabolic rate increases with temperature, but maximum metabolic rate and aerobic scope do not change between these temperatures. These findings suggest that juvenile Atlantic salmon may have limited capacity to increase aerobic performance during moderate heatwaves, leaving them vulnerable to cumulative effects of oxygen limitation to vital functions such as growth and stress responses. As climate change intensifies, incorporating thermal performance curves into conservation strategies can be used for predicting population resilience and informing effective management.

Comprehending a species' life-history strategies is crucial to inform effective conservation efforts. Commercial fishing impacts icefish (family: Channichthyidae) in the Scotia Sea, but detailed information on species-specific life histories remains largely unknown. In this study, the demographic characteristics of mackerel icefish (Champsocephalus gunnari), blackfin icefish (Chaenocephalus aceratus) and South Georgia icefish (Pseudochaenichthys georgianus) were examined and used to compare inferred life-history strategies, using long-term data from demersal and plankton trawl surveys conducted across the South Georgia and the Shag Rocks continental shelves. The results indicated that C. gunnari may exhibit alternative reproductive tactics, as they appear to spawn multiple times in a single year and mature at varying sizes. Conversely, C. aceratus and P. georgianus reproduced once per annum and appeared to favour investing in somatic growth, resulting in them consistently maturing at a larger size. Seasonal sex ratios demonstrated a reduction in captured mature males for C. aceratus and P. georgianus during the suspected spawning period, supporting the hypothesis of sex-specific behavioural patterns during the reproductive period. These findings highlight the variation in the life-history strategies among these three icefish species, which should be considered during the development of future management measures.

Research on the critically endangered European eel (Anguilla anguilla L.) has long been focused on the continental part of the species' wide distribution. Comparatively, we know very little about its ecology in the small stream habitats of the oceanic Macaronesian islands and whether it differs from that of continental estuaries, rivers and lakes. We used acoustic telemetry to investigate the movements of 36 yellow-staged eels for 1 year at a typical Azorean stream, with small pools below waterfalls interchanged by riffles and runs. Tagged eels had a restricted movement range and mostly stayed in a given pool. Such limited movements render this part of the population particularly susceptible to changes in the stream, which can seasonally run dry at some parts. These findings likely reflect the extreme habitat limitation in Azorean streams, and possibly an evolutionary adaptation to ensure growth under limited food supply and high competitive pressure. These specificities should be taken into account in future management plans for the European eel and its Azorean habitats.

This study investigates the ecological structure of an ichthyofaunal assemblage within the Galmal Oya-Heel Oya stream network on the southern flank of the Knuckles Mountain Range, Sri Lanka. We examined how species composition and spatial distribution vary along an elevational gradient and assessed the influence of environmental factors - including substrate type, water velocity, habitat dimensions, turbidity, shading, canopy cover and physicochemical parameters - on assemblage structure. Species richness increased downstream, with Garra ceylonensis and Schistura notostigma dominating high-elevation reaches (~1000 m above sea level, asl), whereas Devario malabaricus and Dawkinsia filamentosa were more abundant at lower elevations (500-1000 m asl). Species within the assemblage exhibited clear differentiation in macrohabitat associations and microhabitat selectivity, reflecting distinct ecological preferences and adaptive strategies. Our results suggest that this co-evolved structure plays a critical role in resource partitioning within Sri Lankan highland stream assemblages, thereby minimizing niche overlap. This pattern is evident in both identified feeding guilds, where species with similar feeding strategies avoid direct competition through spatial-ecological segregation, as observed in the 'benthic feeders' - the loach duo Lepidocephalichthys thermalis and S. notostigma, and the pair Mastacembelus armatus and Channa kelaartii - and in the surface feeders, D. malabaricus and Rasbora dandia. In contrast, co-occurring species further reduce competitive interactions through dietary differentiation, exploitation of different relative depths (e.g., D. filamentosa and D. malabaricus), or fine-scale feeding behavioural specialization, as observed between G. ceylonensis and Plesiopuntius bimaculatus. The study also highlights the importance of biological interactions among benthic cyprinids in shaping assemblage structure. Overall, our findings provide baseline ecological information essential for understanding and conserving Sri Lanka's highland stream fish assemblages.

The invasion of the North Atlantic by pink salmon Oncorhynchus gorbuscha has raised concerns regarding their impact on coastal rivers. Although the influence of marine-derived nutrients from returning adult O. gorbuscha on rivers in their native range has received much attention, the ecological consequences of invasive O. gorbuscha for ecosystems outside the native range are largely unknown. To investigate the impact on the density and community structure of benthic macroinvertebrates, O. gorbuscha carcasses were added to 12 experimental channels for 60 days at three treatment levels (control, no carcass; low and high, loading rates). Stable isotopes of carbon (δ¹³C) and nitrogen (δ¹⁵N) were used to determine if nutrients from carcasses were incorporated into native biota. The density of macroinvertebrates increased close to the carcasses in the high-addition treatment, suggesting aggregation. Furthermore, macroinvertebrates had a higher δ¹⁵N near to the carcasses in the low- and high-addition treatments after 30 days, indicating uptake from the carcasses. The higher δ¹⁵N of willow moss Fontinalis antipyretica in carcass-addition treatments indicated that primary producers could also assimilate nutrients from the decomposition of carcasses. Whilst the addition of carcasses resulted in the increased density of small individuals of macroinvertebrates, this did not propagate to changes in community composition in this relatively short experiment. Overall, the results suggest that native biota might benefit from the marine-derived nutrients transported to streams by invasive O. gorbuscha, however, the long-term effects of such nutrient/energy subsidies on receiving ecosystems require further investigation.

The sustainability of Micropterus salmoides (largemouth bass) aquaculture is challenged by environmental stressors, prompting this study to investigate the antistress compounds Antistress Fish and antistress compounds A and B (AscA and AscB) through a two-phase experimental design. In the initial 30-day feeding trial, the effects on growth, antioxidant capacity, and immune function were evaluated. Subsequently, stress resistance was assessed through controlled challenges, including high temperature, hypoxia, simulated transport, and pathogen exposure. Results demonstrated that dietary AscA significantly enhanced growth performance, as evidenced by higher weight gain rate, specific growth rate, and average daily gain, along with a reduced feed conversion ratio, compared to the other groups. Both AscA and AscB supplementation increased serum and hepatic activities of alkaline phosphatase (AKP), total antioxidant capacity (T-AOC), lysozyme (LZM), superoxide dismutase (SOD), and acetylcholinesterase (AChE), while reducing malondialdehyde levels compared to the control group (NC). Hepatic analyses further revealed a significant up-regulation in the expression of immune-related genes (Cu/Zn SOD, LZM, immunoglobulin M [IgM]) and a down-regulation of stress biomarkers (heat shock protein 70, interleukin [IL]-8, IL-1β) in AscA-fed fish. Following exposure to multiple stress challenges-including high temperature, hypoxia, simulated transport, and Aeromonas veronii infection-the AscA group exhibited significantly elevated serum activities of AKP, T-AOC, SOD, LZM, and AChE, as well as increased hepatic activities of AKP, SOD, LZM, and corresponding gene (Cu/Zn SOD, LZM, IgM) expressions compared to the NC group. Notably, AscA supplementation resulted in the highest survival rates following hypoxia and pathogen challenges, outperforming all other treatments. These findings indicate that dietary AscA and AscB enhance antioxidant capacity, immune responses, and resilience to multiple stressors in largemouth bass, with AscA demonstrating superior efficacy in mitigating aquaculture-related stress.

Non-lethal biopsy is a valuable tool for gaining insight into the physiological status of fish in the wild and for predicting their subsequent behaviour and survival. However, linking the insights from biopsy to post-release behaviour relies on the assumption that the biopsy itself has no meaningful impact on post-release behaviour or survival (e.g. in animals tagged with electronic devices). This assumption is likely to be questioned by fishery managers, animal ethics committees, and other researchers. To date, there has been very little work to assess the sublethal (or lethal) effects of biopsies on fish, and no such studies have evaluated fine-scale behaviours. Here, muscle and gill tissue samples were taken (both individually and as a combined treatment) from hatchery-reared juvenile lake trout (Salvelinus namaycush) in captivity. Twenty-four hours after sampling, we used two behavioural assays (behaviour within a Z maze and flight initiation distance) and quantified exhaustive exercise performance to determine whether biopsies impacted behaviour or physiology when compared to non-sampled controls. We found no evidence that biopsies had any influence on exploratory and shelter-seeking behaviour in the maze, flight initiation distance, or time to exhaustion (as a proxy for swimming performance). Mortality during a 7-day monitoring period was very low (2% across treatments) and limited to fish that received either a gill biopsy or the combined biopsy treatment. This study provides empirical support for the use of non-lethal biopsy in juvenile salmonids as a means of collecting physiological data on individuals in behavioural studies and experiments.

Lates calcarifer, commonly known as barramundi perch, Asian sea bass or barramundi, is a significant aquaculture species across the Indo-Pacific. Barramundi typically exhibit a silver to bronze wild-type (WT) skin colour, with occasional golden (xanthic) variants of commercial interest. Although previous studies have identified gene expression differences between golden and WT variants, the genetic mechanism driving golden colouration remains elusive. By combining whole-genome enzymatic methylation sequencing (WGEMS) and RNA sequencing (RNA-seq), this study explores the molecular underpinnings of skin pigmentation within golden barramundi in an integrated approach. A total of 435 differentially methylated regions (DMR) were identified. Among 389 genes examined, an inverse relationship between expression ratio and promoter methylation levels was observed in 145 genes, suggesting a regulatory role of DNA methylation in gene expression. Notably, significant correlations between the changes in methylation and expression levels were identified in key pigment genes such as tyrp1 and pax7a, as well as potassium transmembrane transporter genes kir6.1 and kcnj3a. This suggests that barramundi colouration may result from complex molecular changes rather than the influence of a single or few genes. To further validate these observations, independent reverse transcription quantitative polymerase chain reaction (RT-qPCR) analysis was performed on representative genes, supporting the methylation-expression trends observed. This study is the first to characterize the whole-genome methylation landscape in barramundi, and one of the few to examine integrated methylome and transcriptome changes associated with pigmentation in teleost fish. By shedding light on the potential epigenetic mechanisms influencing rare skin colouration, this research contributes to the broader understanding of methylation-driven phenotypic variation in vertebrates and provides a foundation for future studies exploring environmental and developmental regulation of DNA methylation.