Search

A 30 years long data series on the infection dynamics of European eel (Anguilla anguilla L.) with the non-native invasive nematode Anguillicola crassus Kuwahara, Niimi & Hagaki, 1974 is presented. Parasite burden was evaluated for 30 years in inland and coastal waters in Mecklenburg-Western Pomerania from 1991 to 2020. The total prevalence, mean intensity and damage status of the swim bladders were very high during the first decade (1991–2000), and significantly decreased in both marine and freshwater eel populations in the following decades (2001–2010, 2011–2020). The parasite intensity of eels in coastal waters was significantly lower compared with the freshwater systems (61.3% vs 79.5% in the first decade), indicating the vulnerability of the parasites to brackish water conditions and the fact that the life cycle of A. crassus cannot be completed under high saline conditions. Eel caught in the western part of the Baltic Sea (west of Darss sill) had the lowest mean infection (51.8% in first decade) compared to the eastern part with 63.8%. Thus, besides different infection patterns caused by the environmental conditions, a temporal trend towards a reduced parasite intensity and a more balanced parasite–host relationship developed in the 30 years of interaction after the first invasion. Possible reasons and mechanisms for the observed trends in parasite–host interactions are discussed.

A 30 years long data series on the infection dynamics of European eel ( Anguilla anguilla L.) with the non-native invasive nematode Anguillicola crassus Kuwahara, Niimi & Hagaki, 1974 is presented. Parasite burden was evaluated for 30 years in inland and coastal waters in Mecklenburg-Western Pomerania from 1991 to 2020. The total prevalence, mean intensity and damage status of the swim bladders were very high during the first decade (1991–2000), and significantly decreased in both marine and freshwater eel populations in the following decades (2001–2010, 2011–2020). The parasite intensity of eels in coastal waters was significantly lower compared with the freshwater systems (61.3% vs 79.5% in the first decade), indicating the vulnerability of the parasites to brackish water conditions and the fact that the life cycle of A. crassus cannot be completed under high saline conditions. Eel caught in the western part of the Baltic Sea (west of Darss sill) had the lowest mean infection (51.8% in first decade) compared to the eastern part with 63.8%. Thus, besides different infection patterns caused by the environmental conditions, a temporal trend towards a reduced parasite intensity and a more balanced parasite–host relationship developed in the 30 years of interaction after the first invasion. Possible reasons and mechanisms for the observed trends in parasite–host interactions are discussed.

The European eel (Anguilla anguilla (L.)) is a unique catadromous euryhaline fish and the only anguillid eel species classified as 'critically endangered'. The Baltic Lakeland area contains naturally recruited and introduced eels. There is great uncertainty regarding a baseline for the location and number of naturally dispersed eels in the region. Little is known about the genetic structure of the European eel populations in Baltic countries. The estimation of population genetic structure is important for the efficient management of naturally recruited and introduced eels. Two mitochondrial regions were used to investigate the genetic structure within and between eel samples from 11 waterbodies. In this study, new, unique, and widely distributed haplotypes were revealed. The studied eel population in the Baltic Lakeland shows high genetic diversity, which is possibly a result of intensive restocking programs. Sequences characterized for Anguilla rostrata were revealed in both mitochondrial regions. Understanding the genetic structure of eel populations worldwide is crucial for conservation efforts. Eel restocking in waterbodies where natural migration is restricted contributes to diversity loss for the world gene pool of eels. [ABSTRACT FROM AUTHOR]

Diadromous fish such as the European eel (Anguilla anguilla L.) are hampered by a high density of barriers in estuaries and freshwater systems. Modified and fragmented waterbodies lack tidal flows, and habitat may be less accessible and underutilized compared to free-flowing rivers and estuaries. With rising sea levels and increased occurrence of droughts, the number of barriers may further increase, implying that the need to study migration in such areas may even become more urgent worldwide. To study glass eel migration and behaviour in such highly modified water systems, a mark-recapture study was carried out in the North Sea Canal (NSC) basin, which drains into the North Sea via a large sluice complex. In total, eight uniquely tagged groups (3,797 glass eels) were released near the sluice complex, and 11 groups (2,663 glass eels) were released at inland barriers upstream over a 28 km long stretch in the NSC in spring 2018. The sluice complex attracted 10.3 million glass eel and did not block or delay their immigration. The large and diurnally intensively used coastal ship locks and allowings some saltwater intrusion, efficiently facilitated glass eel migration. Once in the NSC, water outlets from adjacent polders attracted glass eels relative proportional to the discharge of pumping stations. In the NSC, average migration speeds of 0.7 km/day (max. 1.8 km/day) were measured, and this increased with higher temperatures. Redistribution of glass eel from accumulations at inland barriers to other outlet locations was observed in both upstream and downstream directions in the NSC. Passage success and residence time (‘delays’ of 4.1–13.7 days) varied between the different inland barriers. Most of the glass eel, however, appears to settle in the easily accessible habitats within the brackish NSC catchment. This study combined an integral assessment of successive bottlenecks in a modified inland water system. [ABSTRACT FROM AUTHOR]

The European and Japanese eel populations have declined significantly in recent decades. To effectively manage and conserve them, gaining a better understanding of their migratory life cycles is important. Previous research on the spawning ecology and larval dispersal of European and Japanese eels has led to many significant discoveries and advancements for their migratory life cycles. However, different scholars hold varying views on their migratory life cycles, especially concerning the European eel, therefore this article aims to provide a comprehensive review of research from multiple disciplines concerning the spawning ecology and larval dispersal of European and Japanese eels and to propose migratory life cycles of these two species. The migratory life cycle of the European eel is as follows: European silver eels undertake a year-long spawning migration from September to January to reach the Sargasso Sea for spawning before the next spawning season, typically between December and May. After hatching, European eel leptocephali are transported by the Gulf Stream, Frontal Countercurrents, North Atlantic Current, and Azores Current and return to Europe and North Africa for growth. Recruitment of European glass eels mainly occurs between October and June of the following year, and the recruiting season is more concentrated in countries closer to the spawning area and more dispersed in countries farther away. The consistent recruitment pattern and the growth rate of leptocephali suggest a larval transport period, also called larval duration, of around 1 year. Understanding the migratory life cycle of European eels can facilitate the evaluation or development of their conservation measures., (© 2024 Fisheries Society of the British Isles.)

Since the 1980s, the European eel (Anguilla anguilla) has declined by over 90% in recruitment across its European and North African distribution area. This diadromous fish spawns at sea and migrates into continental waters, where it grows for three to more than 30 years, depending on habitat conditions and location. During their growth, different habitat use tactics can locally influence the life-history traits of eels, including their survival rates. Thus, the spatio-temporal dimension of this species is crucial for management. Based on a rare Mediterranean long-term survey of more than 20 years (2001-2022) in an artificial drainage canal connected to a vast brackish lagoon (the Vaccarès lagoon), we aimed to study the dynamics of one subpopulation's life-history traits. We used Bayesian multistate capture-mark-recapture (CMR) models to assess the temporal variability in survival and abundance at both seasonal and inter-annual scales, considering life-stage structure. High survival rates and low detection probabilities were found for the undifferentiated and female yellow stages. In contrast, female silver eels exhibited lower survival rates and higher capture probabilities. Estimating detection probabilities and survival rates enabled accurate assessment of relative abundance across different life stages and time periods. Our findings indicated a substantial decrease in the abundance of undifferentiated and female yellow eels in the early 2000s, whereas the abundance of female silver eels remained consistently low yet stable throughout the study period. Considering the life stage seemed essential to study the dynamics of the eel during its continental growing period. The present results will provide key elements to propose and implement suitable sustainable environmental management strategies for eel conservation., (© 2024 Fisheries Society of the British Isles.)

Estuaries exhibit high physicochemical variability and the properties of estuaries and the constituent segments are not yet systematically understood. This study aims to reveal the spatial heterogeneity of predominant organic sources using carbon and nitrogen stable isotope ratios (δ 13 C and δ 15 N, respectively) of Japanese eels (Anguilla japonica), one of the ideal natural samplers. In the Miyakoda River, Japan, our study site, the effectiveness of eel δ 13 C and δ 15 N values as standard indices of predominant organic sources was tested by employing the River Continuum Concept. This study then extended the application of these indices to the estuary, i.e., the Hamana Lake system, into which the Miyakoda River flows. Once in the upper estuary, eel δ 13 C and δ 15 N values became high, with the latter peaking in this river-estuary continuum, indicating that artificial labile subsidies (nutrients and organic matter) with high δ 15 N values were rapidly assimilated into the food web. Eel δ 15 N values decreased again in the middle estuary. Nevertheless, the influence of terrestrial organic subsidies extended into this segment, as evidenced by the low δ 13 C values of eels. These results suggest that refractory organic matter with low δ 15 N values, such as plant-derived ones, is slowly assimilated into the food web in the downstream estuarine segments. The higher δ 13 C values in the lower estuary suggested that the contribution of eelgrass or macroalgae occurred in addition to benthic microalgae. Thus, our results emphasize the need to consider the multiple energy flows to understand the estuary as a continuum., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

The European eel (Anguilla anguilla L.) is a critically endangered catadromous fish. Their inshore and in-river arrival as glass eel and elvers is an important stage of their life cycle, marking the transition from marine to freshwater habitats. Considerable knowledge gaps remain on the temporal and spatial patterns of this transition period to freshwater residency. Stable isotope (SI) analysis (δ13C, δ15N) was used to assess the timing and duration of the marine to freshwater transition among glass eels and elvers migrating upstream of the weirs at, or just upstream of, the tidal limit of four English rivers. (Parrett, Frome, Piddle, Chelmer). Variability in SI was low in the Parrett and Frome, resulting in narrow isotopic niches, but was high in the Piddle and Chelmer, resulting in wider niches. The Parrett and Frome data were then used to train a discriminant function analysis (DFA) model to classify eels as ‘marine’, ‘freshwater-established’ and ‘transitioning’. When applied to the Piddle and Chelmer eel SI data, only a small proportion of eels were classified as marine and transitioning, with most being freshwater established. These results suggest that most eels present in the lower reaches rivers have been present for sufficient time for their SI values to represent feeding on local prey resources, with relatively few eels being newly arrived from the marine environment. The transition of eels from marine to freshwater in this species can therefore be prolonged, with many ascending rivers at least one winter after their initial arrival. [ABSTRACT FROM AUTHOR]

European eel, Anguilla anguilla (Linnaeus) (Elopomorpha: Anguilliformes), is a critically endangered fish of ecological and economic importance, hosting numerous parasites, including myxozoans (Cnidaria). Since its initial discovery in the kidney of European eel, Myxidium giardi Cépède, 1906 has been reported with numerous spore sizes and shapes from various tissues of multiple anguillid species. Morphological variability, wide host and tissue spectrum, and lack of sequence data raised doubts about the conspecificity of reported isolates. Subsequent studies provided 18S rDNA sequences of several isolates from anguillids and other elopiform fish, and demonstrated a split of parasite data into two distinct phylogenetic lineages, one comprising the M. giardi sequence, and the other all species infecting elopiform fishes classified under the recently established genus Paramyxidium Freeman et Kristmundsson, 2018. Myxidium giardi was, however, transferred to this genus as Paramyxidium giardi n. comb. and designated as the type species of the genus. In line with this change, the sequence originally identified as M. giardi was considered to have been incorrectly associated with this species. To shed light on the status of M. giardi originally described by Cépède (1906), we conducted microscopic and molecular examinations of various organs of 24 individuals of European eel, originating from diverse Czech habitats. Through morphometric and molecular analyses, we demonstrated that spore and polar capsule morphology, morphometry and tissue tropism of our European eel kidney parasite isolates matched the features of the original M. giardi description. Our isolates clustered in the lineage encompassing the first published M. giardi sequence. Thus, the originally described M. giardi indeed represents an existing species within the genus Myxidium Bütschli, 1882, which we formally resurrect and redescribe. Due to the morphological and molecular differences between M. giardi and P. giardi of Freeman et Kristmundsson (2018), we additionally rename the latter species as Paramyxidium freemani nom. nov.

This study examined the presence of two heavy metals (Cd and Pb) in the sediments and Asian swamp eels (Monopterus albus) in the downstream area of Cisadane River. The average concentrations of Cd and Pb in the sediments from all sampling locations were 0.594 ± 0.230 mg/kg and 34.677 ± 24.406 mg/kg, respectively. These concentrations were above the natural background concentration and the recommended value of interim sediment quality guidelines (ISQG), suggesting an enrichment process and potential ecological risk of studied metals to the ecosystem of Cisadane River. The increase in contamination within this region may be attributed to point sources such as landfill areas, as well as the industrial and agricultural land activities in surrounding area, and experienced an increasing level leading towards the estuary of Cisadane River. Meanwhile, the average concentrations of Cd and Pb in the eels from all sampling locations were 0.775 ± 0.528 μg/g and 28.940 ± 12.921 μg/g, respectively. This study also discovered that gill tissues contained higher levels of Cd and Pb than the digestive organ and flesh of Asian swamp eels. These concentrations were higher than Indonesian and international standards, suggesting a potential human health risk and therefore the needs of limitations in the consumption of the eels. Based on the human health risk assessment, the eels from the downstream of Cisadane River are still considered safe to be consumed as long as they comply with the specified maximum consumption limits., (© 2024. The Author(s), under exclusive licence to Springer Nature Switzerland AG.)

Eel (Anguilla sp.) is an important freshwater-cultured species with high economic value in China. Anguillid herpesvirus 1 (AngHV-1) has been proven to be the pathogen of "mucus sloughing and haemorrhagic septicaemia disease" in eels, resulting in significant mortality and substantial losses to the eel industry. Current diagnostic methods for detecting AngHV-1 are limited to laboratory-based tests, for example, conventional end-point PCR and qPCR. Therefore, there is an urgent need to develop an accurate, rapid, and simple detection method for on-site diagnosis of AngHV-1. In this study, we developed a recombinase-aided amplification combined lateral flow dipstick (RAA-LFD) assay for the detection of AngHV-1. The RAA-LFD assay can be performed within a temperature range of 18-45°C, with a reaction time of just 10 min for amplification. Importantly, the established RAA-LFD assay exhibited no reactivity with other common aquatic viral pathogens, indicating its high specificity. The limit of detection for this method is 10 2 copies of AngHV-1, which is more sensitive than the established conventional end-point PCR method similarly targeting ORF95. Clinical detection of the diseased samples demonstrated that the accuracy of RAA-LFD was significantly higher than that of the conventional end-point PCR. In conclusion, the developed RAA-LFD assay has proven to be a convenient, rapid, sensitive, and reliable tool for on-site diagnosis of AngHV-1. This advancement will be invaluable for the prevention and control of AngHV-1 in the eel farming industry., (© 2023 John Wiley & Sons Ltd.)

Fish marking is an essential tool for fisheries management, especially for evaluating the stocking of endangered fish species to support conservation and sustainable use of fish stocks. Batch marking of young European eels Anguilla anguilla (L.) prior to stocking is recommended as the benefits of stocking for the spawning stock can be evaluated by recapturing marked fish over time, therefore mass marking of young eels with substances such as alizarin red S (ARS) is becoming increasingly important. To improve the marking method and reduce marking costs when immersing glass eels in an ARS solution, eight laboratory experiments under varying conditions (e.g., temperature, ARS concentration, immersion time, osmotic induction, fish density) and with ARS from different suppliers were carried out. The results show that optimal marking of glass eels can be carried out in the field or during transport by putting approximately 50 g of glass eels per liter in 150 mg L -1 ARS solution for 3 h at 10-15°C. Lower concentrations did not result in reliable marking. Water temperatures of 5°C and below can have a stunning effect on the eels and increase mortality significantly, regardless of the concentration of ARS. Glass eel densities below 50 g L -1 in the marking bath increase marking costs unnecessarily, while a higher density of 100 g L -1 resulted in significantly higher mortality and lower marking success. A somewhat more difficult but less expensive alternative is to bathe the fish in a saline solution of 1% (10 PSU) of 80 mg L -1 ARS for 3 h at 10°C. Costs can also be significantly reduced by choice of supplier for ARS, but care should be taken as the quality of the powder appears to vary (mean percentage of sufficiently marked eels ranged from 59% to 91% among suppliers in the present study) and can lead to marking failure. The optimal marking conditions can help ensure that stocked glass eels can be reliably identified in future studies to assess stocking benefits while reducing costs., (© 2024 The Authors. Journal of Fish Biology published by John Wiley & Sons Ltd on behalf of Fisheries Society of the British Isles.)

The construction of less damaging (here called fish-friendly) pumping stations has taken place in recent years, but it is unknown if they provide efficient and timely passage to migratory fish, such as European eel (Anguilla anguilla (L.)). The pump is often the only downstream passage route and operation, i.e., fish passage opportunity, is temporally variable depending on precipitation and prevailing river levels. Once the pumps are operating, eels must also consider the pumping station an attractive downstream passage route. Here, the movement of seaward migrating silver European eel (n = 59) upstream of a fish-friendly shrouded Archimedean Screw Pump (ASP) was assessed during three migrations (December–March in 2018/19, 2019/20 and 2020/21) with highly contrasting hydrology using acoustic telemetry. The overall passage rate was low (36.8 %) and minimum passage time was 65.2 days during a year with very little pump operation (2018/19), with seven eels tagged with long-life transmitters passing the pumping station the following year (2019/20). Furthermore, the median number of approaches to the pumping station was seven, with 36.8 % (n = 7) approaching more than 10 times. By contrast, passage rate was high (95.0 %), maximum passage time was 2.7 and 34.0 days (minimum = 3 min in both years) and all but one eel passed during the first approach during the two wettest years (2019/20 and 2020/21). Eels were almost exclusively nocturnal, regardless of pump operation, with 96.1 % of total approaches occurring between sunset and sunrise and no eels passed downstream during the day. Ultimately, limited eel passage opportunity during dry periods and a reluctance to pass when operational curtailed the effectiveness of these pumps to provide efficient and timely passage. Thus, measures are required to align pump operation with the timing of eel migration, especially in dry years, and reasons for retreat from the pumping station during operation must be identified and alleviated. • Fish-friendly pumps, if safe for fish, must provide efficient and timely passage. • Passage rate varied greatly between years with low and high precipitation. • Eels were almost exclusively nocturnal, and no passage occurred during daylight. • Individual eels retreated from the pumping station up to 38 times. • Pumps should operate when eels migrate and reasons for retreat should be remediated. [ABSTRACT FROM AUTHOR]

High survival of the nematode Contracaecum rudolphii in European eel, Anguilla anguilla L. despite an extensive recruitment of immune cells in granulomas is described. A total of 39 eel specimens captured in Canneviè lagoon (Northern Adriatic Sea, Italy) was obtained from local fishermen. The fish were examined for the presence of endoparasitic helminths. Twenty-six eels (67%) harbored third-stage larvae (L3) of Contracaecum rudolphii A and the intensity of infection ranged from 1 to 100 parasites per fish (mean 11.4). A total of 296 larvae were counted and 293 were alive and encysted in the serosa (primarily on external surface of the rectum) as conspicuous granulomas, appearing as white nodules. Histological sections showed a granuloma formed around an individual larva and consisted of three concentric cell layers, containing numerous mast cells (MCs), fibroblasts, macrophages, and epithelioid cells. Encysted larvae were also present in other layers of the intestinal wall, including the mucosa, where recruitment of macrophage aggregates in lamina propria was documented. Immunohistochemical investigations, applying eight antibodies raised against immune cell markers, revealed histamine and serotonin in MCs and inducible-nitric oxide synthase and toll-like receptor-2 in macrophages surrounding the parasite larvae. The study indicates that this innate cellular response in the eel has a chronic inflammatory character and keeps the nematode larvae arrested in a state allowing both host tolerance and parasite survival. The European eel serves as prey for birds and the high survival of C. rudolphii A larvae in the eel indicates that this fish species is a good paratenic host for the parasite allowing completion of its life cycle in birds. [Display omitted] • High prevalence of Contracaecum rudolphii A larvae in eels from lagoon in North Italy. • Encysted larvae are present in the serosa and other layers of the intestinal wall. • Mast cells and macrophages express molecules involved in cellular immunity pathway. • The eel innate immune system isolates the parasite in a chronic inflammatory reaction. • There is a high rate of survival of larvae in the granulomas. [ABSTRACT FROM AUTHOR]

The aquaculture industry is suffering from significant financial setbacks due to an increasing frequency of disease outbreaks, posing a threat to the sector's sustainability. Various bacterial, viral, parasitic, and fungal pathogens have led to massive mortalities in farmed fish worldwide. Throughout the years, the management of fish diseases has predominantly centered around the utilization of conventional antibiotics and chemicals. Nevertheless, their indiscriminate use has given rise to serious implications, including an increase in resistant pathogens, disruptions in the metabolic processes of fish, degradation of the aquatic environment, the presence of drug residues in aquatic products, and a potential threat to human health. Various effective bio-based and immunoprophylaxis alternative therapies have been developed to overcome these impediments. Recent alternative therapeutic approaches to fish diseases encompass a range of strategies, including phytotherapeutics, nanotherapeutics, probiotics, prebiotics, synbiotics, phage therapy, vaccination, quorum quenching, antimicrobial peptides, biosurfactants, bacteriocins, stem cells, and diagnostic-based therapy. Advancements in biotechnology have significantly enhanced the efficacy of these therapies. However, additional research is essential to refine the utilization of these therapeutic approaches. Critical concerns, such as efficacy, cost, risks, availability, and adverse effects on fish and the ecosystem, need to be addressed to establish guidelines for their sustainable application in aquaculture. This review will increase aquaculturists' awareness of recent therapies used in fish farming, their mechanisms, challenges, and impacts while promoting the sustainability of commercial aquaculture. [ABSTRACT FROM AUTHOR]

Feeding trials with Anguilla marmorata during the nursery culture were conducted to establish optimized protocols for transitioning from live to formulated diets. This study evaluated different weaning schemes over three phases of the nursery culture: from live feed (Artemia) to raw fish meat-based mash (FMT), from FMT to dry fish meal-based mash (FML), and from FML to dry formulated crumble diet. Specific growth rate (SGR), percent weight gain (%WG) and survival of A. marmorata elvers were assessed across treatments. The optimized weaning scheme for transitioning A. marmorata glass eel feeding from Artemia to FMT requires a 6.25% reduction of live feed daily for 16 days, resulting in the highest growth performance (SGR=4.49, %WG=109.25%) and survival (98.37%). Dietary transition from FMT to FML feeding, a 5% daily reduction of FMT with FML, over 20 days was found optimal. This treatment yielded superior growth performance with an SGR of 1.59, %WG of 68.80%, and survival of 62.00% (p<0.05). The final phase, transitioning from FML to a formulated crumble diet, was optimized with a 25% daily reduction of FML over 4 days. Elvers on this feeding regime exhibited the highest growth (SGR=2.49, %WG=41.81%) and survival (100.00%). These weaning protocols effectively facilitated the dietary transition of A. marmorata during the nursery stage from live feed to dry-formulated diets within a 40-day period, enhancing the growth and survival of A. marmorata cultured in the brackish water nursery system. [ABSTRACT FROM AUTHOR]

Few studies have documented the biology, demography, and ecology of eels in deep and large riverine ecosystems, which nevertheless contain important growing areas for this endangered species. Using an original eel sampling technique, this 6-year study, started in 2018, aims to characterise the bioecology and demography parameters of eels in a deep and wide riverine ecosystem, the Meuse in Belgium. It was performed over a 125.8 km stretch and included four sampling sites. This technique, never previously used in the Meuse, trapped the eels in fyke nets when they swam back upstream, swimming against the current, after an avoidance reaction generated by the screens of hydropower facilities. Results revealed a high performance in catching eels as well as their sympatric biodiversity. The inter-site growth of eels was good. Yellow eels were mostly caught in the spring and summer under the influence of rising water temperatures, and silver eels were caught during autumn in October–December when flow and turbidity were high. A down-to-upstream decreasing demographic gradient was observed, but this pattern was not found for entry rate, catchability, survival, and immigration and emigration nets. Survival was low, and net emigration was high at a site experiencing noise pollution and hydraulic disturbance due to the work of expanding the ship lock to facilitate the passage of large boats. Effective strategies for the local eel stock and habitat management have been provided for deep and large riverine ecosystems. [ABSTRACT FROM AUTHOR]

The common occurrence of dams is a major threat to riverine fish communities globally and a common remediation technique for fragmented fish communities is fishway construction. Demonstrating the effectiveness of this technique on impacted species is required to rationalise or improve management practices. This study investigates the effects of the installation of a fishway complex on the catadromous common galaxias (Galaxias maculatus) population at a catchment scale. We used electrofishing in a before-after-control-impact design to investigate the effects of the installation of a rock-ramp and a vertical-slot fishway complex on this species. This study demonstrated an increase in the relative abundance of common galaxias of 7.6–28.1 times and a shift to higher proportions of small fish in tributaries upstream of the fishway complex (as far as 90 km upstream). These findings provide strong evidence for the efficacy of the installation of fishways to increase the number of catadromous fishes in rivers where fish migrations have been blocked by dams. [ABSTRACT FROM AUTHOR]

Lumpfish (Cyclopterus lumpus) are raised as cleaner fish for controlling sea lice. Intensive rearing is complicated by fin nipping that occurs between juvenile conspecifics. Lumpfish density‐dependent interactions are not well understood; therefore, the effects of rearing density for different fish size classes warranted evaluation. Two size classes (2‐ and 13‐g) of juvenile lumpfish were stocked at four different rearing densities (40, 60, 70, and 90 g/L) with growth, survival, and fish aggression assessed over 8 weeks. Mean weight gain and specific growth rates ranged from 170% to 307% and 1.77% to 2.50%, respectively, depending on density treatments, for the 2‐g fish, and from 286% to 471% and 2.42% to 3.10% for the 13‐g fish. Growth was negatively correlated with density, with faster growth linked to lower densities. No mortality occurred in any treatment and significant fish aggression only occurred among the larger lumpfish in the higher rearing densities. Based on these findings, growth of 2‐g lumpfish can be increased if reared at 40 g/L or slowed at 70 g/L without impacting aggression. For grow out of 13‐g fish to ~70 g with minimal aggression, a 40 g/L rearing density is recommended for faster growth and 60 g/L for slower growth. [ABSTRACT FROM AUTHOR]

The color pattern of fish is formed/manifested by the distribution and combination of different pigments such as melanophore, xanthophore, erythrophore, iridophore, leucophore, and cyanophore. Coloration is the key factor for ornamental fish and also plays a very significant role in the life history and behavior of fishes, such as in mimicry or predator avoidance, mate selection, etc. The major players of coloration in fish are: melanophore found in melanosome (for black and brown); xanthophore pigment found in xanthosome and carotenoid (for yellow and orange); erythrophore present in erythrosome (for orange and red); iridophore present in platelets (for iridescence); leucophores present in leucosome (for white); and cyanophore present in cyanosome (for blue color). The main sources of carotenoid in fish are dietary or synthetic to achieve the carotenoid pigment in fish body. There is an established molecular signalling pathway through which carotenoids regulate coloration in fish. Besides these, the addition or supplementation of prospective source of carotenoids through diet may also increase the color intensity in fish body. However, interference of several factors may negatively influence the pigmentation in ornamental fish. The present review has covered all these aspects and consulted possible up to date publications to forward a comprehensive understanding on the topic. [ABSTRACT FROM AUTHOR]

Fish movement into large, deep lakes has been rarely investigated due to the complexity and extent of such ecosystems. Among the different monitoring methods available, acoustic telemetry enables the study of the spatial ecology and behavior of aquatic organisms in lentic environments. In this study, the movement of 69 hatchery-reared adult brown trout (size 43–61 cm) marked with acoustic transmitters was monitored in the large and deep subalpine Lake Lugano (Switzerland and Italy). Trout were tracked for six consecutive months by seven acoustic receivers (March–August 2022), positioned in a non-overlapping array. Trout movement was reconstructed using R packages specific for acoustic telemetry (actel and RSP), which also allowed us to translate tracking information into utilization distribution (UD) areas for each fish. The effects of different environmental variables (rainfall, water discharge of the two main tributaries of Lake Lugano, atmospheric pressure, cloud coverage, and moon phases) on trout movement were tested, but none of these variables seemed to significantly correlate with fish movement. After release, most of the tagged fish exhibited reiterative movements during the initial month, with some maintaining this behavior throughout the entire study period. This spatial behavior can be particularly evident in hatchery-reared fish due to their aggressive and bold attitude. The association of these behavioral traits, shaped by domestication, could expose hatchery-reared fish to high risks and post-release mortality in the wild. Indeed, within a few months after the release, most of the tagged fish were no longer detected by the acoustic receivers. In addition, 26% of the total tagged fish were caught by recreational or professional fishermen. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Hydrobiology / Shuisheng Shengwu Xuebao is the property of Editorial Department of Journal of Hydrobiology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The Northern snakehead (Channa argus) is a significant economic aquaculture species in China. Exhibiting sexual dimorphism in the growth rate between females and males, mono-sex breeding holds substantial value for aquaculture. This study employed GWAS and transcriptome analysis were applied to identify sex determination genomic regions and develop sex-specific markers. A total of 270 single-nucleotide polymorphisms (SNPs) and 31 insertion-deletions (InDels) were identified as being sexually dimorphic through GWAS and fixation index (Fst) scanning. Based on GWAS results, two sex-specific InDel markers were developed, effectively distinguishing genetic sex for XX females, XY males, and YY super-males via (polymerase chain reaction) PCR amplification. A major genomic segment of approximately 115 kb on chromosome 3 (Chr 03) was identified as the sex-determination region. A comparative transcriptome analysis of gonads for three sexes identified 158 overlapping differentially expressed genes (DEGs). Additionally, three sex-related candidate genes were identified near the sex determination region, including id2, sox11, and rnf144a. Further studies are required to elucidate the functions of these genes. Overall, two sex-specific InDel markers support a male heterogametic XX/XY sex-determination system in Northern snakeheads and three candidate genes offer new insights into sex determination and the evolution of sex chromosomes in teleost fish. [ABSTRACT FROM AUTHOR]

The aim of the present study was to evaluate propofol as an anesthetic and its effects on physiology and histology in Ictalurus punctatus. To determine the ideal concentration, juvenile of I. punctatus (96.60 ± 27.70 g) were used, submitted to different concentrations of the anesthetic: 1.5, 2.0, 2.5, 3.0, 4.0, 5.0, and 6.0 mg L−1. The concentration evaluated as ideal was 2.5 mg L−1. To evaluate the physiological and histological effects of propofol exposure, juvenile of I. punctatus (99.71 ± 26.38 g) were sampled immediately (T0) and 30 min after anesthesia (T30) with 2.5 mg L−1, had blood, liver, and gill samples collected. The exposure of the animals to propofol in both treatments (T0 and T30) caused increases in plasma glucose and lactate levels (p < 0.05) but prevented an increase in cortisol (p > 0.05). The histological study showed mild to moderate changes in the gills (congestion in the lamellar vessels and central vein and epithelial elevation) and moderate and severe changes in the liver (congestion and degeneration). This study concludes that the concentration of 2.5 mg L−1 of propofol provides safe anesthesia for I. punctatus and prevents increased plasma cortisol levels. [ABSTRACT FROM AUTHOR]

Aquaculture and the production of aquatic goods are rapidly growing industries in the world. These industries involve the cultivation of various saltwater and freshwater fish as well as shellfish species, and they undergo regular updates in their manufacturing processes. The increasing popularity of aquaculture is driven by the desire to achieve long-term sustainability in food production. However, the intensification of farming techniques can lead to economic losses due to fish mortality, which is often caused by infectious and stressful conditions. To address this challenge, it is crucial to enhance the immune response of fish as part of sustainable intensification and aquaculture management. Recently, there has been growing interest in eco-friendly and natural bioactive solutions as potential alternatives to synthetic compounds used for disease prevention in aquaculture. Medicinal plants, available as whole plants, plant extracts, or synthetic analogues of natural substances known as phytomedicines or phytopharmaceuticals, have shown high efficacy in disease prevention for humans and animals. One such medicinal plant is Saussurea lappa, which is extensively utilized in various forms of medicine for treating multiple diseases. The bioactive chemicals derived from S. lappa exhibit a wide range of biological activities, including anti-inflammatory, antioxidant, antimicrobial, and anticancer properties, along with immunostimulatory effects. Given the diverse biological activities of S. lappa and its potential to enhance the immune responses of aquatic species, this review focuses on exploring its contributions in this area. By examining the numerous benefits and applications of S. lappa, we aim to shed light on its potential role in improving the immune response of aquatic species. [ABSTRACT FROM AUTHOR]

Simple Summary: The European barracuda (Sphyraena sphyraena) is a wild fish species that is both commercially and ecologically valuable and is found in the Adriatic Sea. To better understand its distribution and physiology, this study examined the digestive enzymes in various parts of the barracuda's gastrointestinal system using histochemical analyses. This is the first known study to evaluate the activity of aminopeptidase, alkaline phosphatase, acid phosphatase, and non-specific esterase in the pyloric caeca and the anterior, middle, and posterior segments of the European barracuda's gastrointestinal tract. In this study, we examined the gastrointestinal tract of the European barracuda (Sphyraena sphyraena) living in the Adriatic Sea near Dubrovnik, Croatia. The study aimed to identify the presence and distribution of four digestive enzymes: alkaline phosphatase, aminopeptidase, acid phosphatase, and non-specific esterase. We found that alkaline phosphatase activity was present in the brush border of the enterocytes in all the investigated intestinal segments. The activity of the alkaline phosphatase was the strongest in the pyloric caeca but strong only in the basal part of the intestinal villi in the anterior and middle intestinal segments. In the posterior intestinal segment, alkaline phosphatase had strong activity along the entire villi. The activity of acid phosphatase was weak in all the investigated parts of the intestine, except in the posterior part, where it was moderate. Aminopeptidase was detected in the brush border of the intestinal epithelium, with stronger activity in the pyloric caeca and anterior part of the intestine and weaker activity posteriorly. The activity of the non-specific esterase was moderate in the pyloric caeca and anterior part of the intestine, while it was weak in the posterior segment and the lamina propria in all parts of the digestive tract. Weak acid phosphatase activity was observed only in the lamina propria of the posterior part of the intestine. This study is the first to evaluate the activity of digestive enzymes in the European barracuda. [ABSTRACT FROM AUTHOR]

The importance of fish as a component of healthy nutrition and as a high-quality source of nutrients in the human diet has increased in recent years. To assess the nutritional value of the six main commercial fish species (common roach Rutilus rutilus, common bream Abramis brama, crucian carp Carassius carassius, crucian carp Carassius carassius, common carp Cyprinus carpio, European perch Perca fluviatilis, and northern pike Esox lucius) from the Barguzin River (Eastern Cisbaikalia), the FA composition and lipid quality indices of the muscle tissues have been determined. The FA composition of the dorsal muscle tissue of fish has been analyzed by direct methanolysis. The total content of SFAs ranges from 26 rel. % in carp to 37 rel. % in bream, MUFAs from 17 rel. % in perch to 32 rel. % in carp, and PUFAs from 42 rel. % in bream and carp to 54 rel. % in pike. The dominant FAs are palmitic 16:0 (17.5–29.2 rel. %), oleic 18:1(n-9) (17.5–29.2 rel. %), and stearic 18:0 (5.0–8.0 rel. %) acids, as well as PUFAs, including essential docosahexaenoic 22:6(n-3) (9.7–24.9 rel. %), eicosapentaenoic 20:5(n-3) (9.2–19.1 rel. %), and arachidonic 20:4(n-6) (6.9–10.1 rel. %) acids. The Σ(n-3)/Σ(n-6) ratio of PUFAs is 2.8–4.6, which is typical for freshwater fish. Relatively high nutritive value index (NVI), values of the health-promoting index (HPI), and ratio of hypercholesterolemic to hypocholesterolemic FAs (HH), the as well as the atherogenicity and thrombogenicity indices (<1), indicate the high nutritional value of the muscle tissue of the studied fish species. According to the content of (n-3) PUFAs and high total ratio of eicosapentaenoic and docosahexaenoic acids, the most valuable species are European perch and northern pike. [ABSTRACT FROM AUTHOR]

Swimming performance is important for fish migration, habitat selection, and predator-prey interaction, as well as for fish passage design. Procedural choices made when experimentally estimating it may influence the results. Systematic experiments were conducted to study the effect of different in-flume habituation times, habituation behaviour, and the use of external encouragement on burst swimming performance of Rutilus aula, a small-sized cyprinid, in a fixed velocity testing protocol. Increasing habituation times from 30 s to 5 or 20 min substantially increased the success proportion of swimming trials and estimated fish swimming performance, with no difference between the latter two habituation times. Fish resting on the downstream grid before the start of testing velocity outperformed those who swam during habituation and transition periods. Fish swimming volitionally in response to flow at testing velocity showed a significantly improved performance compared to fish motivated by external poking. The results of this study highlight that in-flume habituation time is important, and fish behaviour before actual testing may influence the outcomes of swimming performance results. [ABSTRACT FROM AUTHOR]

A survey was conducted to identify fish fauna related to the dominant habitats, viz., (i) Honduwa Lake (stagnate water), (ii) estuarine area with mangroves, (iii) freshwater marshy area with floating aquatic vegetation, (iv) canals, and (v) river, in the Dedduwa estuary of southern Sri Lanka. Thirty-nine species of fish including two endemics (to the island) were identified, including members of major migratory families such as Anguillidae and Megalopidae. Based on the abundance of species, the Bray-Curtis similarity index indicated a clear separation of the canal and freshwater marsh, with other studied areas. Similarly, the taxonomic diversity of the canal and freshwater marsh was high, indicating high variation and diversity of the species and genera. Protection of mangroves and related habitats is important to maintain the stability and long-term existence of fish fauna in the estuary. Effective monitoring is proposed for detecting and eliminating illegal encroachments, mangrove clearance, and illegal fishing activities. Moreover, improving the knowledge and awareness among members of the local community, politicians, and environment officers about the importance of the region's biodiversity implementing strong policies, and creating a strong responsible stakeholder bond are required to ensure the long-term sustainability of the estuary. [ABSTRACT FROM AUTHOR]

Fyke nets are the preferred type of equipment used for platypus (Ornithorhynchus anatinus) live-trapping surveys in shallow watercourses. However, numerous factors other than abundance may affect the frequency of platypus captures, including when, where and how nets are set, stream discharge and entry into nets by rakali (Hydromys chrysogaster), which create exit holes that are then also available to a platypus. A threefold difference in the mean monthly frequency of platypus captures in fyke nets is also evident across the year. To limit net evasion, it makes sense to reduce net visibility and minimise opportunities for animals to squeeze under, climb over or walk around nets. Time-lapse cameras can also be deployed at fyke-netting sites to estimate how many individuals evade capture. To protect platypus welfare and the welfare of non-target species held in fyke nets, it is important to ensure that captured animals have access to air, to check nets frequently throughout the time they are set and to release bycatch when first encountered. Fyke-netting studies typically generate sparse platypus population data, so care is needed when selecting and interpreting platypus abundance metrics generated through mark–recapture modelling or use of indices. Fyke nets are commonly used for platypus survey or other research purposes in shallow water bodies. We discuss the wide range of factors influencing the frequency of platypus captures, identify issues affecting animal welfare in fyke nets and consider the options available for estimating platypus abundance from fyke-netting data. Photograph by G. Williams/APC. This article belongs to the collection: Recent research on the platypus. [ABSTRACT FROM AUTHOR]

The European hake (Merluccius merluccius) is a highly sought after, overfished commercial species with a high ecological value. Otolith morphometric characteristics were employed from 150 individuals captured from the Central Aegean Sea (Eastern Mediterranean) using a commercial trawler. Age reading was independently performed by three readers. A multivariate methodology identified the morphometric factors that significantly affect age estimation, and easy to use equations using limited morphological otolith characteristics with a high degree of accuracy were produced as a practical tool for fisheries management. A second tool using ML algorithms produced a highly accurate ML model with the ability to further predict European hake's age using limited otolith morphometric characteristics. Both tools are important for assessing fish population dynamics, managing sustainable fishing practices, and ensuring the long-term health of marine ecosystems. Practically, the models could be implemented by collecting fish otolith samples, measuring limited morphometric features using imaging techniques, and inputting these measurements into the machine learning model. Both model outputs will allow researchers and fisheries managers to obtain rapid and reliable age estimates without the need for labor-intensive traditional methods. By integrating these models into routine fisheries assessment workflows, stakeholders could make more informed decisions about fish stock assessments and conservation strategies. [ABSTRACT FROM AUTHOR]

This study aimed to describe and compare the morphological characteristics of saccular otoliths (sagittae) in the protandrous hermaphrodite Sarpa salpa and the synchronous hermaphrodite Serranus scriba collected from the Bizerte site located in northwestern Tunisia, and to examine the effect of hermaphroditism type on the otolith shape and size at the inter- and intraspecific levels, using elliptical Fourier analysis. At the interspecific level, a significant bilateral asymmetry in shape was observed between the left and right otoliths. At the intraspecific level, a significant bilateral asymmetry in shape was detected between the left and right otoliths only in S. scriba. Discriminant function analysis (DFA) produced two separate main groups corresponding to the two species, and intrasexually differentiated between left and right otoliths in S. salpa. In addition, a significant bilateral asymmetry was found in Lo, Wo, Ao, and Po in S. salpa and in Po only in synchronous S. scriba. Thus, protandrous hermaphroditism did not affect otolith shape in S. salpa, but showed an apparent bilateral asymmetry in otolith size. However, synchronous hermaphroditism exhibited a significant bilateral asymmetry in otolith shape and Po only in S. scriba. The causes of this significant inter- and intraspecific bilateral asymmetry observed in otolith shape and size were discussed. [ABSTRACT FROM AUTHOR]

Globally, catadromous freshwater eels of the genus Anguilla are of conservation concern, including critically endangered European eel (Anguilla anguilla). Pumping stations that move river water to a higher elevation severely impact eels during their seaward spawning migration. Fish-friendly pumps can mitigate fish injury and mortality but here we uniquely rethink a fish-friendly pump as a fish passage solution. In this pluriannual study, the seasonal timing of pump operation was misaligned with the typical silver eel migration period. Eels were almost exclusively nocturnal but night-time pumping represented as little as 5.6% a year. Night-time eel approaches were primarily influenced by pump duration and temperature, but did not align with lunar phase, unlike in unregulated rivers. After reaching the pumping station, eel passage was influenced by weedscreen aperture and increased when the aperture was increased. Passive sensor collision suggested non-pump infrastructure could cause injury and mortality to eels. It is therefore recommended pump operation should align with the timing of silver eel migration, weedscreen and pump entrance efficiencies should be maximised, and non-pump infrastructure must have low fish injury risk. Ultimately, considering the entire structure a fish passage solution will help ensure fish-friendly pumps have high conservation value for anguillid eels globally. [ABSTRACT FROM AUTHOR]

Dactylogyrosis is caused by more than 900 reported species of Dactylogyrus (gill fluke), mostly in Cyprinoidei fish leading to low to severe mortality in different culture systems and also in rivers/lakes. Dactylogyrus has been reported worldwide where Cyprinoidei is endemic. In recent years, incidents of infection and infectivity of different species of Dactylogyrus have increased many-fold due to several predisposing factors like intensification of culture, environmental quality, climatic change, poor quality fish seed, etc. These parasites are host choosy, either generalist or specialist. Dactylogyrus infection causes major changes in the anatomy and physiology of gill function. Necrosis, hyperplasia and hypertrophy of gill lamellae are the common pathologies observed during infection, which in turn invites other secondary pathogens leading to heavy mortalities. Currently, very few drugs or chemicals are available for controlling dactylogyrosis. Very few attempts have been made to develop vaccines against this important parasite. Here, we review the innate and adaptive immune responses modulated by Dactylogyrus infection and a hypothetical immunological model has been proposed to understand host-pathogen interaction based on our findings. The information collected and analysed in this review on the biology and host-pathogen interaction will help in the development of prophylactic and other sustainable management measures to reduce the loss associated with dactylogyrosis. [ABSTRACT FROM AUTHOR]

During field surveys and culture procedures, large growth disparities in Anguilla japonica have been observed. However, the potential causes are unknown. This study explored differences in digestive ability, metabolic levels, and transcriptomic profiles of appetite-related genes between growth-retarded eel (GRE) and normal-growing eel (NGE) under the same rearing conditions. The results showed that growth hormone (gh) mRNA expression in GREs was considerably lower than NGEs. The levels of total protein (TP), total cholesterol (T-CHO), triglyceride (TG), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), blood ammonia (BA), blood urea nitrogen (BUN), and alkaline phosphatase (ALP) in GREs were significantly lower than in NGEs. Conversely, levels of glucose (GLU), alanine aminotransferase (ALT), and aspartate transaminase (AST) were higher in GREs. The activities of SOD, CAT, and T-AOC levels were also significantly lower in GREs, as were the activities of glucose-related enzymes including hexokinase (HK), pyruvate kinase (PK), phosphoenolpyruvate carboxykinase (PEPCK), and glucose-6-phosphatase (G6PASE). Additionally, orexigenic genes (npy and ghrelin) were dramatically downregulated, whereas anorexigenic genes (crh and pyy) were significantly upregulated in GREs. These findings suggested that variances in growth hormone, metabolic activities, and appetite level could be associated with the different growth rates of A. japonica. The present research not only revealed the characteristics of the growth, metabolism, and appetite of GREs but also offered new perspectives into the substantial growth discrepancies in A. japonica, providing novel ideas for enhancing fish growth. [ABSTRACT FROM AUTHOR]

Copyright of South China Fisheries Science is the property of South China Fisheries Science Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Simple Summary: In marine coral reef ecosystems, anemonefish are a group with highly complex behavioral patterns and strict social hierarchies. However, there has been a paucity of research on the factors associated with stable hierarchical relationships or the behaviors performed during competitive interactions, especially in anemonefish in the growth phase before sexual differentiation. In the present study, we employed an observational approach to assess the personality type of each individual by observing the interactive behavior between unsexually differentiated Amphiprion clarkii. Our findings revealed that the personality of A. clarkii varied significantly between individuals, with two main types. Furthermore, our pairing experiments confirmed the impact of personality on the establishment of a stable social hierarchy. These personality-related behavioral traits are potentially important for both individual and population survival, and extend our understanding of the establishment and evolution of social hierarchies in anemonefish and their impact on population dispersal. Furthermore, they have the potential to guide aquaculture practices. In this study, the behavioral ethogram of Amphiprion clarkii during the growth phase prior to sexual differentiation was summarized based on behavioral observations in three social environments. These behaviors can be classified into four categories: in addition to normal behaviors, the other three categories of behaviors—threatening, agonistic, and appeasing behaviors—represent different intentions in interactions with other individuals. Subsequently, the personalities of each individual were assessed by testing their reactions to intruders. These individuals mainly exhibited two distinct personality types: bold-aggressive and shy-submissive. In pairing experiments, the interactive behaviors of the anemonefish were observed in pairing combinations of different body sizes and personalities. The impact of personality on the establishment of a stable social hierarchy was confirmed by significant differences in the success rates of different pairing combinations, with the frequency of appeasing behaviors being the main factor influencing the success rate. Our results suggested that in natural waters, when juvenile individuals migrate among host anemones, shy-submissive individuals are more likely to be accepted due to their appeasing behaviors towards larger individuals, thus avoiding the risk of being attacked and bitten, and benefiting the survival of the individual. Conversely, bold-aggressive individuals are more likely to be driven away to another host anemone due to their unwillingness to settle for a lower-ranked status, thereby contributing to population dispersal and increasing opportunities for gene exchange between populations. [ABSTRACT FROM AUTHOR]

Many organisms exhibit social behaviors and are part of some scheme of social structure. Zebrafish are highly social, shoaling fish and therefore, social isolation may have notable impacts on their physiology and behavior. The objective of this study was to evaluate the effects of social isolation on feed intake, monoaminergic system related gene expression, and intestinal health of juvenile zebrafish fed a high-inclusion soybean meal based diet. At 20 days post-fertilization zebrafish were randomly assigned to chronic isolation (1 fish per 1.5 L tank) or social housing (6 fish per 9 L tank) with 18 tanks per treatment group (n = 18). Dividers were placed between all tanks to prevent visual cues between fish. Zebrafish were fed a commercial fishmeal based diet until 35 days post-fertilization and then fed the experimental high-inclusion soybean meal based diet until 50 days post-fertilization. At the end of the experiment (51 days post-fertilization), the mean total length, weight, and weight gain were not significantly different between treatment groups. Feed intake and feed conversion ratio were significantly higher in chronic isolation fish than in social housing fish. Expression of monoaminergic and appetite-related genes were not significantly different between groups. The chronic isolation group showed higher expression of the inflammatory gene il-1b, however, average intestinal villi width was significantly smaller and average length-to-width ratio was significantly higher in chronic isolation fish, suggesting morphological signs of inflammation were not present at the time of sampling. These results indicate that chronic isolation positively affects feed intake of juvenile zebrafish and suggest that isolation may be useful in promoting feed intake of less-palatable diets such as those based on soybean meal. [ABSTRACT FROM AUTHOR]

Protecting ocean habitats is critical for international efforts to mitigate climate impacts and ensure food security, but the ecological data upon which policy makers base conservation and restoration targets often reflect ecosystems that have already been deeply impacted by anthropogenic change. The archaeological record is a biomolecular archive offering a temporal scope that cannot be gathered from historical records or contemporary fieldwork. Insights from biogeochemical and osteometric analyses of fish bones, combined with context from contemporary field studies, show how prehistoric fisheries in the western Baltic relied on seagrass meadows. European eels (Anguilla anguilla) harvested by Mesolithic and Neolithic peoples over millennia showed a strong fidelity for eelgrass foraging habitats, an ecological relationship that remains largely overlooked today, demonstrating the value of protecting these habitats. These data open new windows onto ecosystem- and species-level behaviours, highlighting the need for wider incorporation of archaeological data in strategies for protecting our oceans. [ABSTRACT FROM AUTHOR]

The article presents a study on the effect of sublethal and lethal concentrations of Cartap hydrochloride on the liver and kidney histopathology of freshwater fish, Cirrhinus mrigala exposed for 24 and 96 hours. Topics discussed include histological changes in the liver of the fish, findings on the kidney of the treated fish, and the need for regular monitoring programs to control pesticides contamination in aquatic environment.

Purpose: Intravenous narcotic agents, such as etomidate and metomidate, has been widely spread and abused in the world, including in Korea and China; thus, it is important to establish validated and sensitive analytical method for these compounds. Human hair as a biological sample has various advantages, including a wide detection window of drugs, compared to other typical samples, such as urine and blood in investigation. The purpose of this communication is to develop a reliable and useful method for the simultaneous detection and quantification of etomidate and metomidate in human hair samples by ultraperformance liquid chromatography combined with triple quadrupole mass spectrometry (UPLC–MS/MS), and to apply it for authentic samples in abuse cases. Methods: The hair samples were washed with a detergent solution, followed by with water and acetone. After drying, they were cut into approximately 2 mm sections and then ground to powder by a low-temperature grinder. The 20 mg of hair powder plus internal standard in 1 mL of methanol was vortexed and then centrifuged to obtain the supernatant layer, followed by subjecting to analysis. Results: The coefficient of determination (r2) values of the calibration curves of etomidate and metomidate in the hair samples were both more than 0.99 in the range of 1–500 ng/mg and 1–500 pg/mg, respectively. The limits of detection and lower limits of quantification were 0.5 and 1 pg/mg, respectively, for the both target compounds. Other tested validation data were all satisfactory. Etomidate and metomidate could be detected in the all hair samples and cigarette oil, which were seized by the police. The concentrations of etomidate and metomidate obtained from 10 samples from suspects were 5.48–45.7 ng/mg and 3.60–377 pg/mg, respectively. The concentrations of etomidate and metomidate in the cigarette oil were 95.8 μg/mg and 2.8 μg/mg, respectively. Conclusions: In this study, a simple and reliable analytical method for etomidate and metomidate in the human hair has been established. To the best of our knowledge, this is the first report to establish a method for the simultaneous detection and quantification of etomidate and metomidate in the human hair, and to apply it to authentic samples seized in authentic cases. [ABSTRACT FROM AUTHOR]

Engin, S.; Gurkan, S., and Taskavak, E., 2024. Cellular changes in liver tissue of adult common sole (Solea solea L. 1758) in the Aegean Sea, Turkey. Journal of Coastal Research, 40(4), 740–748. Charlotte (North Carolina), ISSN 0749-0208. In this study, cellular changes and biological indices in the liver tissue of the common sole, Solea solea (L. 1758), are investigated based on sex, size groups, and seasons. The specimens used in the study were obtained monthly between 2019 and 2020 from commercial trawlers and small scale–fishing operations in the fishing grounds of Izmir Bay, the Aegean Sea coast of Turkey. A total of 240 common sole fish (166 female, 66 male, 8 immature) were used in this study. In the obtained specimens, the male: female ratio was determined as 0.39:1 (χ2 = 33.19; p > 0.05), whereas the length–weight relationship was calculated as W = 0.009TL2.97 (R2 = 0.86) for females and W = 0.009TL3.27 (R2 = 0.91) for males. Four size groups (19–22, 23–26, 27–30, >30cm) were established in the study. Significant histological changes, such as macrovesicular steatosis degenerations, were observed in the liver tissue of the examined fish, especially in larger size groups. Females exhibited higher levels of condition and hepatosomatic index values compared with males, possibly because they are more susceptible to liver degeneration. During the summer months, liver degeneration is more striking due to hunger among common soles. Based on these results, 36.7% of the specimens caught from fishing grounds in Izmir Bay have normal liver tissues, whereas 11.3% have macrosteosis and 8.3% have a sinusoidal hemorrhage. [ABSTRACT FROM AUTHOR]

Simple Summary: Based on the differences in otolith morphology and skeletal morphology, this study presents an investigation of the evolution of three Schizothoracinae species from two major river systems in Northwest China. A total of 138 samples were collected, and the morphological factors, morphological indices and Fourier transform coefficients of the otoliths were measured and analyzed to compare the morphological differences between the otoliths and bones. Morphological analysis of the otoliths of the three Schizothoracinae species revealed significant differences and cluster analysis further confirmed this relationship. At the same time, their skeletal morphology showed significant differences in the number of tentacles, pharyngeal teeth and vertebrae, as well as in the shape of several key bone blocks. The unique morphological characteristics and skeletal differences of the three Schizothoracinae species during their evolution are closely related to the geological changes in and water system evolution of the Qinghai-Tibet Plateau. This study not only deepens our understanding of the evolution of plateau fishes and other species but also provides a scientific basis for understanding the conservation and evolutionary mechanism of plateau fishes, which is highly important for ecological protection and biodiversity conservation. Schizothoracinae species are the largest group of Cypriniformes that readily adapt to the natural conditions of the Qinghai-Tibet Plateau. This group has habitat characteristics and distribution patterns centered on the Qinghai-Tibet Plateau. To study the evolution of three Schizothoracinae species in Northwest China, the evolutionary characteristics of these species were explored based on differences in otolith morphology and skeletal morphology. From 2020 to 2022, 138 samples (63 Aspiorhynchus laticeps, 35 Diptychus maculatus and 40 Schizothorax pseudaksaiensis) were collected from the Tarim River and Ili River, 6 basic morphological parameters of otoliths were measured and converted into 6 morphological factors and 7 morphological indices. A total of 77 Fourier transform coefficients of each otolith were selected The first three principal components accounted for 92.834% of the total variation in 13 otolith morphological indices of the three Schizothoracinae species, and the overall discrimination rate was 94.20%. According to the principal component analysis of 77 Fourier harmonic values of otoliths, the first 20 principal components explained 97.233% of the total variation, and the overall discrimination rate was 100%. The results of the cluster analysis directly reflected the relationships between related species. The differences in the bone morphology of the three Schizothoracinae species were particularly reflected in the number of whiskers, pharyngeal teeth and vertebrae, and there were also significant differences in the shapes of the sphenotic (SP), pterotic (PTE), preoperculum (PO), branchiostegal ray (BRA) and basibranchial (BB) bones. Their unique morphological and skeletal characteristics are closely related to geological changes and water system evolutionary trends. This study contributes to the understanding of species identification and the evolutionary status of plateau fishes, provides a reference for further evolutionary classification and for assessing the evolutionary mechanisms of plateau fishes, and provides a scientific basis for phylogeny and germplasm resource protection. [ABSTRACT FROM AUTHOR]

The European eel encounters challenges in achieving sexual maturation in captivity, which has been a concern for researchers. This study explores surrogate broodstock technology as an alternative approach for eel production. The present study aimed to evaluate zebrafish and European sea bass as potential recipients for European eel spermatogonia transplantation, given the abundance of eel type A spermatogonia (SPGA). Immature European eel testes were dissected and maintained at 4 °C or cryopreserved. SPGA were obtained by dissociation of fresh or post-thawed tissue, employing an enzymatic solution, and then labelled with fluorescent membrane marker PKH26. SPGA from fresh tissue were transplanted into wild-type zebrafish larvae and triploid European sea bass larvae, while SPGA from cryopreserved testis were transplanted into vasa::egfp transgenic zebrafish larvae. One-and-a-half months post-transplantation (mpt), fluorescent donor cells were not detected in the gonads of zebrafish or European sea bass. Molecular qPCR analyses at 1.5 or 6 mpt did not reveal European eel-specific gene expression in the gonads of any transplanted fish. The findings suggest that the gonadal microenvironments of zebrafish and European sea bass are unsuitable for the development of European eel spermatogonia, highlighting distinctive spermatogonial stem cell migration mechanisms within teleost species [ABSTRACT FROM AUTHOR]