Journal of fish biology最新文献

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.

This study reports three cases of pigmentation disorders in Squalus acanthias from the Gulf of Venice. Two specimens exhibited spotless phenotypes, whereas one exhibited hypermelanism. Morphological assessments were conducted for two individuals, alongside genetic analysis of mitochondrial genes to determine phylogeographic relationships. Both specimens belonged to the South Pacific/Atlantic/Mediterranean haplogroup, with the first one associated with the main haplotype and the second one linked to a rarer haplotype. This study emphasizes the need for proper identification based on morphology and genetics when pigment disorders hinder a clear-cut species assignment.

This study evaluated the effects of the controlled flood pulse on diet composition, trophic niche breadth and feeding intensity of Archolaemus janeae, an electric knifefish species with a restricted distribution in the Amazon Basin. Monthly samples were collected from December 2020 to November 2021 in the Volta Grande stretch of the Xingu River, and stomach contents of 134 specimens were analysed. The diet was predominantly composed of aquatic insect larvae, with a notable occurrence of terrestrial plant fragments. Hydrological variation affected diet composition, trophic niche breadth and feeding intensity, indicating temporal shifts in resource use associated with changes in river flow. Feeding intensity was higher during filling and flood periods than during the ebb phase, suggesting that the reduction and regulation of the flood pulse by the Belo Monte Hydropower Plant influenced the diet composition by A. janeae. This study provides the first data on the feeding ecology of this species, highlighting the role of habitat heterogeneity in sustaining fish populations and underscoring the potential impacts of hydropower development on the feeding ecology of Amazonian fishes. Such information is essential for the conservation of A. janeae populations in the Xingu River Basin.

Host functional traits are widely used to explain patterns of parasite diversity and community structure; however, their predictive power in species-rich Neotropical freshwater systems remains poorly understood. We examined whether host traits predict helminth parasite community composition in the Lacantún River (southern Mexico), using presence/absence data for 74 helminth genera recorded from 58 fish species. We evaluated a suite of host traits related to body size, spatial ecology, migration and trophic position, together with a proxy for host phylogenetic relatedness. Multivariate analyses revealed that the first axis explained 17.9% of the total variation in parasite assemblage composition. Trophic level was the strongest contributor to this axis (23.8% of its explained variance), followed by host total length (21.3%) and position in the water column (20.6%). Notably, piscivorous hosts harboured distinct parasite communities. Nevertheless, the overall proportion of explained variation was low, reflecting the complex, multicausal nature of host-parasite systems and the influence of unmeasured factors such as host density, sampling effort and parasite life-history diversity. Consistent with this interpretation, univariate analyses showed no significant linear relationship between helminth genus richness and either host total length or trophic level. Together, these results indicate that host traits act primarily as ecological filters shaping which parasite genera occur, rather than determining the total number of parasite genera per host. Our findings highlight the importance of multivariate, trait-based approaches for understanding parasite community assembly in Neotropical rivers and caution against relying on simple richness-based predictors in highly complex host-parasite networks.

Some studies have shown phylogenetic proximity between the scorpionfish species Scorpaena plumieri and Scorpaena mystes, despite having inhabited different oceans for millions of years. The former occurs in the Western Atlantic Ocean, including the Caribbean Sea, and the latter inhabits the Eastern Pacific. The venom of S. plumieri from tropical Atlantic reefs has been widely studied, whereas that from S. mystes has not been characterized. To determine whether the venom of S. mystes reflects the previously shown phylogenetic proximity between these species, we performed a proteomics study and analysed its biochemical activities. We identified proteins with similarity to the characteristic cytolysin α- and β-subunits of S. plumieri, as well as putative pore-forming toxins from the venom of other scorpionfish species. As in many scorpaenoid taxa, several of the identified components are coming from the epidermal mucus, produced by mucus glands, leukocytes or other potential organisms living on their skin. This is the case of the mucus B- and C-type lectins identified in S. mystes, which are homologues to those from S. plumieri. The analysed venom also displays hyaluronidase and proteolytic activities, and can induce hemolysis, hemagglutination and nerve membrane permeabilization. In conclusion, regarding their venoms, S. mystes and S. plumieri appear to be closely related lineages inhabiting different marine ecosystems.