Fish Populations Research Articles

Redescription of Raphidascaris (Ichthyascaris) vicentei (Nematoda: Raphidascarididae) Parasitizing Lutjanid Fishes (Actinopterygii: Lutjanidae) from the Northeast Coast of Brazil, Including First Observation Using SEM.

In this study, 143 lutjanid fishes representing four different species from the Northeast coast off Brazil were analyzed for parasites. The aim of the present study is to provide a detailed redescription of R. (I.) vicentei, collected from lutjanid fishes in Brazil, including the first observation of the species using scanning electron microscopy (SEM). Nematodes found clarified in a crescent glycerin series, were photographed and measured (in mm), and some specimens destined for SEM. The Illustrations were made using an optical microscope with a drawing tube. Nematodes found were identified as Raphidascaris (Ichthyascaris) vicentei, infecting 6.29% of the examined fish. Detailed morphological analysis revealed the following characteristics observed for the first time in this species: labial papillae, narrow lateral alae and the detailed structure of male spicules. These contributions help filling the gaps in the literature and expand the knowledge of this parasite morphology. The presence of R. (I.) vicentei in four lutjanid species may indicates low host specificity, highlighting its adaptability to different hosts. Furthermore, new host records are given. This research provides the most comprehensive morphological description of R. (I.) vicentei to date, generating crucial insights for a better understanding of the parasitic biodiversity off the Brazilian Northeastern coast of Brazil, as well as establishing foundation for future investigations on the ecology and impacts of these parasites in fish populations from this region.

Predicting trawl catches using environmental DNA

Abstract Quantifying the biomass, or number of individuals, diversity, and distribution of marine species is a critical aspect of understanding and managing marine ecosystems. In recent years, there has been growing interest in using environmental DNA (eDNA) for marine ecosystem management and biodiversity assessment. However, the main challenge hindering eDNA applicability has been the inability to infer absolute species abundances from multispecies analysis (eDNA metabarcoding). In this study, we demonstrate a way forward by estimating the abundance of commercially important fish species in a Norwegian fjord using a joint Bayesian statistical model of traditional trawl-catch data and molecular data derived from eDNA. Using this model, we accurately predict out-of-sample trawl catches using eDNA alone. Moreover, our model provides empirical estimates for key processes linking marine eDNA concentration to the fish population abundance estimated from trawl observations, including trawl catchability, DNA shedding, degradation, dilution, transport, recovery rate, and isolation efficiency. These processes, including amplification efficiencies correcting for Polymerase Chain Reaction (PCR) bias, are species-specific and enable the translation of eDNA metabarcoding data into abundances. These findings have broad implications for the use of eDNA in marine ecosystem management and conservation efforts.

Half a century of citizen science tag-recapture data reveals stock delineation and cross-jurisdictional connectivity of an iconic pelagic fish

Tag-recapture programs to monitor the movements of fish populations are among some of the longest-running citizen-science datasets to date. Here, using half a century of yellowtail kingfish (Seriola lalandi, Carangidae) tag-recapture data collected through citizen-science projects, we report novel insights into population connectivity in Australia and New Zealand (NZ). Despite the importance of kingfish in commercial and recreational fisheries, substantial knowledge gaps about their stock structure and connectivity between jurisdictions hinder current management efforts. Between 1974 and 2022, 63,432 releases and 4636 recaptures (7.3%) of tagged kingfish were collected in Australia and NZ. Most tagged individuals (51.4%) were recaptured within 10 km of their original release location up to 14 years post-release (mean: 225 days), indicating some degree of site fidelity. However, 656 (14.2%) kingfish were recaptured over 100 km from their release location, with one fish travelling at least 2834 km in 702 days. Seasonal variability was evident for releases and recaptures, with more releases occurring in summer and autumn in most jurisdictions. Network analysis of recaptures revealed no connectivity between tagged kingfish from western and eastern Australia, supporting genetic delineation. By contrast, extensive connectivity exists across eastern Australia and NZ, with 87 kingfish moving between five Australian state jurisdictions, 316 individuals travelling across 15 bioregions and six kingfish moving between Australia and NZ. Our findings provide important new insights into the structure and connectivity of the eastern Australia kingfish stock and suggest increased collaboration between state and international fisheries jurisdictions may support improved stock assessment and management.

Species authentication and conservation challenges in Chinese fish maw market using Mini-DNA barcoding

Fish maws, derived from the swim bladders of fish, are valued for their high collagen content and nutritional benefits, leading to significant market demand, especially in Asia. This study investigates the species authenticity of fish maw products using mini-DNA barcoding technology to address issues of mislabeling and substitution. Out of 350 samples, 347 were successfully sequenced, revealing a high mislabeling rate of 51.01% among identified species. Species such as Diodon liturosus and Diodon hystrix were found, posing significant health risks due to the presence of tetrodotoxin, a potent neurotoxin. The study also highlights the conservation implications of this market, with endangered species like Totoaba macdonaldi being illicitly traded. These findings underscore the urgent need for accurate species identification, stringent labeling regulations, and enhanced fishery management to protect endangered species and ensure consumer safety. This research advocates for robust international cooperation and reporting to combat illegal fishing and trade, promoting the sustainable development of fish populations and marine ecosystem health.

Leveraging ecological indicators to improve short term forecasts of fish recruitment

AbstractForecasting the recruitment of fish populations with skill has been a challenge in fisheries for over a century. Previous large‐scale meta‐analyses have suggested linkages between environmental or ecosystem drivers and recruitment; however, applying this information in a management setting remains underutilized. Here, we use a well‐studied database of groundfish assessments from the West Coast of the USA to ask whether environmental variables or ecosystem indicators derived from long‐term monitoring datasets offer an improvement in our ability to skilfully forecast fish recruitment. A secondary question is which types of modelling approaches (ranging from linear models to non‐parametric methods) yield the best forecast skill. Third, we examine whether simultaneous forecasting of multiple species offers an advantage over generating species‐specific forecasts. We find that for approximately one third of the 29 assessed stocks, ecosystem indicators from juvenile surveys yields the highest out of sample predictive skill compared to other covariates (including environmental variables from Regional Ocean Modeling System output) or null models. Across modelling approaches, our results suggest that simpler linear modelling approaches do as well or better than more complicated approaches (reducing out of sample Root Mean Square Error by ~40% compared to null models), and that there appears to be little benefit to performing multispecies forecasts instead of single‐species forecasts. Our results provide a general framework for generating recruitment forecasts in other species and ecosystems, as well as a benchmark for future analyses to evaluate skill. The most promising applications are likely for species that are short lived, have relatively high recruitment variability, and moderate amounts of age or length data. Forecasts using our approach may be useful in identifying covariates or mechanisms to include in operational assessments but also provide qualitative advice to managers implementing ecosystem based fisheries management.

Impacts of the High-Pressure Bratsk Hydroelectric Power Station on Fish Population of the Bratsk Reservoir

Environmental and ecological effects of the dam of the high-pressure Bratsk Hydroelectric Power Station (HPS) on the fish population and the probability of fish downstream migration from the Bratsk Reservoir have been studied. It has been revealed that thermal stratification of the water column is a significant factor in the ecological differentiation of the fish population in the upper reaches of high-pressure hydroelectric plants. According to hydroacoustics data, most of the ichthyomass, consisting of “warm-water” representatives of the Percidae (65%) and Cyprinidae (22%) families, is concentrated in the relatively warm layer of the epilimnion. Juvenile fish from 30 to 50 mm in size (up to 70% of the total fish number in this layer) are also concentrated here. In the cold-water hypolimnion, the fish population is represented by large single individuals of whitefish (Coregoninae). The data on distribution of fish in the lower and upper reaches of the dam, fish nutrition patterns, growth rate, and the presence of injuries that occur when fish pass downstream through hydroelectric plant dams are presented. Revealed differences in the growth rate of perches from the upper and lower reaches are associated with their constant inhabiting of water masses with contrasting temperatures. Net catches in the lower reaches over the four seasons of research lack injured individuals. These facts prove the absence of mass downstream passage of fish through the Bratsk HPS dam. Juveniles of cyprinids and perches accumulate in the upper warm layer of 0–10 m, i.e. outside the zone of the intake flow formation, which makes their entrance to intake openings at a depth of more than 20 m hardly possible.

Multi-decadal warming alters predator's effect on prey community composition.

Predator responses to warming can occur via phenotypic plasticity, evolutionary adaptation or a combination of both, changing their top-down effects on prey communities. However, we lack evidence of how warming-induced evolutionary changes in predators may influence natural food webs. Here, we ask whether wild fish subject to warming across multiple generations differ in their impacts on prey communities compared with their nearby conspecifics experiencing a natural thermal regime. We carried out a common garden mesocosm experiment with larval perch (Perca fluviatilis), originating from a heated or reference coastal environment, feeding on zooplankton communities under a gradient of experimental temperatures. Overall, in the presence of fish of heated origin, zooplankton abundance was higher and did not change with experimental warming, whereas in the presence of fish of unheated origin, it declined with experimental temperature. Responses in zooplankton taxonomic and size composition suggest that larvae of heated origin consume more large-sized taxa as the temperature increases. Our findings show that differences between fish populations, potentially representing adaptation to their long-term thermal environments, can affect the abundance, biomass, size and species composition of their prey communities. This suggests that rapid microevolution in predators to ongoing climate warming might have indirect cross-generational ecological consequences propagating through food webs.

Twenty-five emerging questions when detecting, understanding, and predicting future fish distributions in a changing climate.

The 2023 Annual Symposium of the Fisheries Society of the British Isles hosted opportunities for researchers, scientists, and policy makers to reflect on the state of art of predicting fish distributions and consider the implications to the marine and aquatic environments of a changing climate. The outcome of one special interest group at the Symposium was a collection of questions, organized under five themes, which begin to capture the state of the field and identify priorities for research and management over the coming years. The five themes were Physiology, Mechanisms, Detect and Measure, Manage, and Wider Ecosystems. The questions, 25 of them, addressed concepts which remain poorly understood, are data deficient, and/or are likely to be impacted in measurable or profound ways by climate change. Moving from the first to the last theme, the questions expanded in the scope of their considerations, from specific processes within the individual to ecosystem-wide impacts, but no one question is bigger than any other: each is important in detecting, understanding, and predicting fish distributions, and each will be impacted by an aspect of climate change. In this way, our questions, particularly those concerning unknown mechanisms and data deficiencies, aimed to offer a guide to other researchers, managers, and policy makers in the prioritization of future work as a changing climate is expected to have complex and disperse impacts on fish populations and distributions that will require a coordinated effort to address.

Small pelagic fish: new frontiers in science and sustainable management

Small pelagic fishes occupy an important trophic role in every global aquatic ecosystem, and many species are heavily exploited by fisheries, including some of the largest and most valuable capture fisheries in the world. In November 2022, a symposium on small pelagic fish titled “ Small Pelagic Fish: New Frontiers in Science and Sustainable Management” was cohosted by PICES, ICES, and FAO in Lisbon, Portugal. This special issue contains a collection of research manuscripts that explore approaches currently being used and developed to assess and manage small pelagic fishes. In particular, this issue covers topics on novel approaches to surveying small pelagic fishes, incorporating environmental covariates into management, management strategy evaluation, and aspects of the economics of small pelagic fisheries. The conclusions highlight the importance of new approaches that seek to enhance small pelagic fish surveys and ecosystem monitoring, incorporate that ecosystem information into management strategy evaluation, and predict the potential impacts of ecosystem changes on outcomes for economies and communities that rely on sustainable populations of small pelagic fishes.

Creation of complex reef structures through coral restoration does not affect associated fish populations on a remote, well-protected, Caribbean reef

Creation of complex reef structures through coral restoration does not affect associated fish populations on a remote, well-protected, Caribbean reef

Effect of Global Warming on Fish Population Parameters in Upper Volga Reservoirs

Effect of Global Warming on Fish Population Parameters in Upper Volga Reservoirs

Impacts of participation in Environmental Education projects on the evaluation of public services: an analysis of traditional artisanal fishing populations

Impacts of participation in Environmental Education projects on the evaluation of public services: an analysis of traditional artisanal fishing populations

Assessing genotype-environment interactions in Atlantic salmon reared in freshwater loch and recirculating systems.

The interest in recirculating aquaculture systems (RAS) is growing due to their benefits such as increased productivity, better control over animal care, reduced environmental effects, and less water consumption. However, in some regions of the world, traditional aquaculture methods remain prevalent, and selective breeding has often been designed for performance within these systems. Therefore, it is important to evaluate how current fish populations fare in RAS to guide future breeding choices. In a commercial setting, we explore the genetic structure of growth characteristics, measure genotype-environment interactions (GxE) in salmon smolts, and examine genetic markers related to growth in freshwater lochs and RAS. Young salmon were raised together until they reached the parr stage, after which they were divided equally between freshwater net-pens and RAS. After an 8-week period, we sampled fish from each environment and genotyped them. Our findings revealed that fish reared in RAS were generally smaller in weight and length but exhibited a higher condition factor and uniformity. We found a notably smaller component of unexplained variance in the RAS, leading to higher heritability estimates. We observed a low GxE effect for length and condition factor, but significant re-ranking for whole-body weight, as well as noticeable differences in trait associations across environments. Specifically, a segment of chromosome 22 was found to be linked with the condition factor in the RAS population only. Results suggests that if the use of RAS continues to expand, the efficiency of existing commercial populations may not reach its full potential unless breeding programs specific to RAS are implemented.

Modulation of toxic effects of ammonia on growth, pathology of liver and kidney tissues and relative expression of GH and IGF-1 Genes by CoQ10 Supplementation in Oncorhynchus mykiss.

Reducing the negative impact of environmental and stressful factors is a crucial step in achieving sustainable aquaculture. Therefore, a study was aimed at evaluating the impacts of Coenzyme Q10 (CoQ10) supplementation on growth, relative gene expression of Growth Hormone (GH) and Insulin-like growth factor-1 (IGF-1), liver and kidney histopathology against stress induced by ammonia in Rainbow trout (Oncorhynchus mykiss). The fish were given feed containing different levels of CoQ10 for 8 weeks: Control - CoQ10 0%, G1 - CoQ10 0.1%, G2 - CoQ10 0.5% and G3 - CoQ10 1%. At the end of the experiment, fish were exposed to ammonia stress concentration at 0.6mg/L for 24 h to assess liver and kidney tissue damage. Results showed that there was a significant activity increase in GH and IGF-1 genes due to supplementation with CoQ10 alone (p < 0.05). Gene expression for GH increased about two-fold whereas that for IGF-1 experienced a four-fold upregulation compared to controls (p < 0.05). CoQ10's-related antioxidant effects probably minimized liver and kidney cellular injuries, as significant decreases were observed in ammonia-induced mortality (p < 0.05). In summary, adding CoQ10 to the diet is a potential way to improve fish production through controlling the gene expression of GH and IGF-1, as well as making fish populations more resistant to possible future stress caused by ammonia in intensive or super-intensive aquaculture systems.

Effect of an invasive species Mnemiopsis leidyi on the zooplankton community structure in the Caspian Sea

During the past three decades, the Caspian Sea (CS) ecosystem has undergone striking changes due to anthropogenic activities, particularly following the invasion of comb jelly Mnemiopsis leidyi that overfed on zooplankton in the late 1990 s. This study investigated the temporal and spatial patterns of the zooplankton community in CS over 25-year intervals using univariate and multivariate analyses. The objective was to assess the status of the zooplankton community through a comparison of the pre-invasion (1994–96) and post-invasion (2009–11 and 2018–19) of M. leidyi in the CS. The study revealed more zooplankton taxa for the pre-invasion period and fewer for the post-invasion period of 2018–19. Several key species such as Eurytemora grimmi, Polyphemus exicus, Synchaeta sp., and Calanipeda aquae dulcis disappeared post-invasion, and more than 50 taxa decreased to one-third in the post-invasion period. The abundance and diversity indices significantly declined following the invasion. The visualization of non-metric multidimensional scaling (nMDS) showed that periodic variations were more explanatory than assessments based on subareas and seasonal intervals. Significant differences were observed in the zooplankton assemblages across the three periods. In addition to highly affecting the zooplankton community, certain pelagic fish populations, notably those belonging to the kilka genus (Clupenella), have experienced significant decline as a result of M. leidyi invasion. In conclusion, the invasion of M. leidyi has caused major changes to the abundance and diversity of tropic levels in the CS, possibly through a combination of bottom-up and top-down forces at work in the ecosystem.

Разработка мер по сохранению биологического разнообразия рыб, предложений по организации системы мониторинга состояния популяций редких видов рыб западного региона Республики Казахстан

The purpose of the work is to develop measures to ensure the development of fisheries, the conservation of fish resources and the biological diversity of the ichthyofauna of Western Kazakhstan (Mangystau, Atyrau, Aktobe and West Kazakhstan regions), improving the principles and methods of management and protection of fish stocks. The research was carried out both according to the methods generally accepted in the post-Soviet space, and according to the methods developed by the authors (a temporary method of accounting for the number of fish, withdrawal coefficients for populations of fish with undermined stocks) and methods of foresight research. The monitoring system for rare and endangered fish species should include both in-life research methods and the capture of a minimum necessary number of individuals in order to further domesticate and form breeding herds, artificially reproduce and release the resulting juveniles into those reservoirs. The continued decline in populations of rare and endangered fish species indicates the low effectiveness of the measures taken to preserve them. In order to prevent the loss of the gene pool, it is necessary to select sexual products for cryopreservation during the monitoring process. In addition to monitoring the condition of rare species of fish and other animals conducted by scientific organizations, it is necessary to create a geoinformation system for monitoring rare species, which any resident can replenish by sending experts photos of samples of flora or fauna with observation coordinates. The results of the work are supposed to be used to determine further ways of developing reservoirs in the context of “green growth”.

Small pelagic fish: new frontiers in ecological research

Populations of small pelagic fish (SPF), such as sardines, anchovies and herrings, support some of the largest marine fisheries globally and are critical for trophic transfer in large marine ecosystems and food security, particularly in low- to medium-income countries. Marked changes in population size, shifts in distribution on multiple time scales, and impacts on their populations from other pressures (e.g. overfishing, climate change) pose large challenges to sustainably manage these resources to avoid the serious socioeconomic and ecological impacts of population collapses. The ecology and management of SPF was discussed in an international symposium in Lisbon, Portugal, attracting participants from 38 countries and 6 continents. This Theme Section includes 18 research contributions examining SPF from 6 different ecological regions alongside 3 global analyses. These studies, including a wide range of topics from parasitology, behavior and trophodynamics to growth and spawning, provide important new knowledge that will improve science-based advice and tools needed for sustainable, ecosystem-based management of these resources. This symposium was an important milestone for a global working group and sowed the seeds for continued, globally coordinated research efforts on the role of SPF in complex socio-ecological systems.

POTENTIAL OF BIOFLOC TECHNOLOGY IN AQUACULTURE WASTEWATER TREATMENT

The increasing global demand for aquatic products and decline in wild fisheries pose a challenge in achieving the United Nations’ Sustainable Development Goal 14, which is to conserve and sustainably use marine resources. The depletion of fish populations due to overfishing, destruction of aquatic habitats as well as climate change has adversely affected aquatic ecosystems, which leads to further pressure in establishing food security. To meet the rising demand for fish products, countries have turned to aquaculture, but the industry itself faces many environmental challenges, particularly in wastewater management. This review explores the potential of using biofloc technology (BFT) to treat wastewater. BFT utilises microbial ecosystem processes to remove excess nutrients and acts as a natural “cleaning” mechanism. It transforms organic waste into valuable microbial biomass, which enhances water quality and minimises the ecological footprint of aquaculture. In this way, BFT reduces the amount of solid waste generated, increases the level of dissolved oxygen and creates an environment that is less conducive for the growth of harmful bacteria, thus reducing the need for chemical treatments. This paper also discusses the role of BFT in toxic remediation by analysing the nature and composition of aquaculture wastewater. This study provides a comprehensive overview of the mean values for various water quality parameters in aquaculture and biofloc water, and compares them with aquaculture standards.

Prediction of reproductive performance in wintering females of Siberian sturgeon (Acipenser baerii, Brandt) based on in vitro ovulation rate of isolated follicles

Early prediction of the reproductive success of sturgeon females is important both for artificial breeding conditions in sturgeon farms and for monitoring wild fish populations approaching spawning. This study demonstrated that ovarian follicles removed from wintering Acipenser baerii females can undergo in vitro ovulation when exposed to 17α,20β-dihydroxy-4-pregnen-3-one. The research was conducted from 2015 to 2021 and involved the examination of 110 wintering Siberian sturgeon females (A. baerii), with an average weight of 8–11 kg and an age range of 8–10 years. Selection of females for spawning was based on the polarization index (PI) at the time when the river temperature dropped to +8 °C. The selected females were overwintered in concrete flow-through tanks with water from the Volga River for approximately two months. At the end of this period, oocyte samples were collected for in vitro incubation. An increase in water temperature to 15 °C, which precedes spawning, was achieved by mixing with warm effluent from a regional power station. The reproductive success of females was evaluated based on fertilization and embryonic survival rates. High reproductive success was characterized by females with fertilization rates above 70% and hatching rates above 60%. We identified a positive correlation between the percentage of in vitro ovulated follicles and the in vivo fertilization and embryo survival rates, with correlation coefficients of Rsp = 0.60 and Rsp = 0.48, respectively. Statistical analysis showed that females whose in vitro ovulation rate of follicles exceeded 30% displayed high reproductive performance compared to those with an in vitro ovulation rate below 30%. The predictive accuracy of this criterion was determined by calculating the ratio of ranks between females with high and low reproductive performance, averaging 80.9% for fertilization and 77% for embryonic survival. Therefore, we propose a new criterion to select females of A. baerii for spawning based on the in vitro oocyte ovulation rate obtained from wintering individuals.

Impacts of estuarine habitat degradation on the modeled life history of marine estuarine-dependent and resident fish species.

Shallow coastal and estuarine habitats play an essential role in the life cycles of many fish species, providing spawning, nursery, feeding, and migration areas. However, these ecologically valuable habitats are increasingly threatened by anthropogenic activities, causing substantial changes in both habitat availability and quality. Fish species use these shallow coastal habitats and estuaries during various life stages, leading to their categorization into guilds based on how and when they rely on these areas. This differential functional use of estuaries means that changes to these habitats may affect each guild differently. To understand the impact of estuarine habitat degradation on fish populations, it is therefore necessary to consider the full life cycle of fish and when they rely on these coastal habitats. Here, we use conceptual size-structured population models to study how estuarine habitat degradation affects two functionally different guilds. We use these models to predict how reduced food productivity in the estuary affects the demographic rates and population dynamics of these groups. Specifically, we model estuarine residents, which complete their entire life cycle in estuaries, and marine estuarine-dependent species, which inhabit estuaries during early life before transitioning offshore. We find that total fish biomass for both guilds decreases with decreasing food productivity. However, the density of juveniles of the marine estuarine-dependent guild can, under certain conditions, increase in the estuary. This occurs due to a shift in the population biomass distribution over different life stages and a simultaneous shift in which life stage is most limited by food. At the individual level, somatic growth of juveniles belonging to the estuarine-dependent guild decreased with lower food supply in the estuary, due to increased competition for food. The somatic growth rates of fish belonging to the resident guild were largely unaffected by low food supply, as the total fish density decreased at the same time and therefore the per-capita food availability was similar. These outcomes challenge the assumption that responses to habitat degradation are similar between fish guilds. Our study highlights the need to assess not only fish biomass but also size distributions, survival, and somatic growth rates for a comprehensive understanding of the effects of habitat degradation on fish populations. This understanding is crucial not only for estuary fish communities but also for successful conservation and management of commercially harvested offshore population components.