Fish Stocks Research Articles

Mathematical approaches to fisheries quota management: ensuring sustainable practices in U.S. commercial fishing

Fisheries quota management plays a critical role in ensuring the sustainability of commercial fishing practices, particularly in the United States, where overfishing and resource depletion pose significant challenges to marine ecosystems. This review explores the mathematical approaches utilized to manage fisheries quotas effectively and sustainably. The paper examines key mathematical models, including population dynamics, bioeconomic models, game theory, and Catch-per-Unit-Effort (CPUE) models, highlighting their role in maintaining fish stock levels and regulating fishing activities. Through case studies from U.S. fisheries, such as the New England groundfish and Alaska pollock fisheries, the review assesses the effectiveness of these models in real-world applications. Additionally, it explores how advances in technology, such as satellite tracking, big data, and artificial intelligence, are enhancing the accuracy and adaptability of fisheries management models. The review concludes with insights into future directions for mathematical approaches in fisheries management, emphasizing the need for continuous innovation to support sustainable commercial fishing practices. By integrating advanced mathematical techniques and data-driven models, this paper aims to provide a pathway for policymakers and fisheries managers to achieve long-term sustainability in U.S. commercial fisheries.

No cascading negative effects of piscivorous fish stocking on phytoplankton biomass in subtropical shallow mesocosms: implications for lake restoration by biomanipulation

No cascading negative effects of piscivorous fish stocking on phytoplankton biomass in subtropical shallow mesocosms: implications for lake restoration by biomanipulation

Age structure of carp and catfish catch as a tool to assess ecological health of fished stocks from the Ganga River system with special reference to Mahseer Tor tor (Hamilton, 1822)

In the 20th centuary, the economically important carp species Labeo rohita, Tor tor, & Labeo calbasu and the catfishes Rita rita & Bagarius bagarius contributed substantially to the total fish catch from the Ganga River system in India. Samples were recorded between December 2003 and June 2004 from fish landing centers in the Ken, Paisuni, and Tons rivers for L. rohita, T. tor and L. calbasu. Rita rita and B. bagarius were sampled between September 2001 and September 2003 in the Ganga River system. The data were used to evaluate the growth and age structures of fish populations. Age classes varied 0+–5+ for L. rohita in the Ken & Paisuni rivers and 0+–8+ in the Tons River. For T. tor, the age classes varied 1+–6+ in the Ken & Paisuni rivers and 1+–8+ in the Tons. Age classes of L. calbasu varied 1+–6+ in the Ken River, 1+–5+ in the Paisuni River, and 1+–7+ in the Tons. In the Ganga River, age classes of R. rita & B. bagarius varied 0+–7+ and 0+–6+, respectively. The L. rohita, age pyramid showed a tendency for bell shape in Ken River, base tends to be broader through bell shape in Paisuni River, and bell-shaped age pyramid was slightly distorted in Tons River. In case of T. tor, tendency for bell shape in Ken River and bell-shaped age pyramid in Paisun River & Tons River were obtained. In case of L. calbasu, heavy bottom shaped age pyramid was recorded in Ken and Paisuni rivers, while base tends to be broader in the Tons River. Bell shaped age pyramid was recorded for B. bagarius in the Ganga River while heavy bottom shape for R. rita in the Ganga River. Overall, T. tor is facing heavy fishing pressure and also targeted fish species by fishermen from the Ganga River system.

Age, Growth, Sex Composition, and Diet of the Burbot, Lota lota, the Only Freshwater Species of the Family Lotidae in the Amur (Heilongjiang) River, Northeast China

Information about the population structure, including the age and sex composition, growth characteristics, and diet of fish, is essential for the conservation and sustainable exploitation of fish stock. The burbot, Lota lota, is the only freshwater species of the family Lotidae in the Amur (Heilongjiang) River catchment located in northeastern China. Information on the biological characteristics and data on the population structure of this fish from the Amur River are scarce. To study these factors in burbot, Lota lota, in the Amur River of China, 749 specimens from four sampling areas were taken and analyzed in October 2022, January 2023, and May 2023. The ages of the sampled fish ranged from 1+ to 7+ years. The female/male ratio was 1.04:1, and body length and mass varied from 175 to 595 mm and 73.5 to 1958.7 g, respectively. The length–weight regression parameter b value was estimated as 2.80. The parameters of the von Bertalanffy growth model were L∞ = 596, K = 0.221, and t0 = −0.771 for all sampled fish; L∞ = 625, K = 0.208, and t0 = −0.756 for females; and L∞ = 584, K = 0.219, and t0 = −0.980 for males. The analysis of the stomach contents showed fish to be the major source of nutrition across all areas and sampling periods. In January, the secondary prey of burbots in the Huma reach of the upper Amur River was aquatic insect larvae, while, in the Tongjiang and Fuyuan reaches of the middle Amur River, the secondary prey was shrimp. The mean stomach fullness index and rate of empty stomachs differed with the sampling area, with the greatest proportion of empty stomachs observed in the Luobei reach of the middle Amur River, and the lowest in the Tongjiang and Fuyuan reaches. The mean stomach fullness index showed the opposite trend. In the Huma reach, the contributions of fish to the diet and the mean stomach fullness index were significantly higher in May than in October and January. The study provides the first detailed information on the population age and sex structure, growth patterns, and feeding ecology of burbots from the Amur River, China. The results will aid in formulating management strategies and regulations for local populations of burbots in the Amur River, China.

ERMƏNİSTANIN AZƏRBAYCANA QARŞI EKOLOJİ TERRORU

Since 1988, 20% of Azerbaijan's lands have been occupied as a result of the war waged by Armenia to pursue its territorial claims against Azerbaijan. After a long occupation, during the 44-day Patriotic War and 24-hour local anti-terrorist operations, our lands, which had been in the hands of the enemy for almost 30 years, were liberated by our brave Army. However, in the territories we liberated from occupation, the enemy left behind ruins and an environmental disaster. For almost 30 years, Armenia deliberately tried to destroy our nature, carried out environmental terrorism against Azerbaijan, spontaneously exploited natural resources, including our occupied territories, polluted drinking water reservoirs with industrial waste, and disrupted the ecological balance of the environment. During the occupation, the enemy committed the great¬est acts of vandalism on our lands; the occupying forces destroyed forests, national parks, nature reserves, valuable trees and other rare examples of biodiversity. The rivers that are the source of Azerbaijan's drinking water are contaminated with chemical, biologi¬cal and other radioactive waste flowing from the territory of Armenia. Over the past years, contamination of water sources flowing from the occupied territories has led to the death of valuable fish species and the depletion of fish stocks. 7 ecologically important relic lakes and 10 reservoirs in the liberated territories of Azerbaijan were subject to serious anthropogenic impact from the occupying Armenia.

Enhancing Maritime Security: Challenges and Strategies in Indonesia's Natuna Sea

The Natuna Sea, a strategic region within Indonesia's exclusive economic zone, faces multifaceted maritime security challenges that threaten national sovereignty, economic interests, and regional stability. This abstract explores the key issues and strategic responses to enhance maritime security in this vital area. Indonesia's maritime security challenges in the Natuna Sea are driven by illegal, unreported, and unregulated (IUU) fishing, territorial disputes, and transnational crimes such as smuggling and human trafficking. The encroachment of foreign fishing vessels, particularly from neighboring countries, exacerbates the IUU fishing problem, undermining local economies and depleting fish stocks. Additionally, overlapping territorial claims, particularly with China, complicate Indonesia's efforts to assert its sovereignty and maintain peace in the region. To address these challenges, Indonesia has developed a comprehensive maritime security strategy that includes diplomatic, legal, and operational measures. Diplomatic efforts focus on strengthening regional cooperation through ASEAN and other multilateral forums to foster dialogue and build consensus on maritime security issues. Legal measures involve the enforcement of national and international laws, including the United Nations Convention on the Law of the Sea (UNCLOS), to uphold Indonesia's territorial rights and combat IUU fishing. Operationally, Indonesia has enhanced its maritime patrols, surveillance capabilities, and naval presence in the Natuna Sea. The establishment of the Maritime Security Agency (Bakamla) and the deployment of advanced technology, such as unmanned aerial vehicles (UAVs) and satellite monitoring, have improved the detection and interdiction of illegal activities. Despite these efforts, challenges persist due to resource constraints, coordination issues among agencies, and the complex geopolitical landscape. This abstract underscores the importance of a holistic and adaptive approach to maritime security, integrating diplomatic, legal, and operational strategies.

Willingness to pay for farmed salmon: Balancing sustainability and safety perceptions

Given pressure on wild fish stocks, aquaculture has worked to develop farmed seafood markets. While farmed seafood should be more sustainable, consumers may lack confidence in its sustainability and may have food safety concerns. Using a sample of 266 seafood consumers in the US state of Maine, the study examined preferences for wild-caught and farmed salmon based on safety perceptions of the latter. Most preferred wild-caught, but this declined with lower food safety concerns. Additionally, willingness to pay for certified sustainably farmed versus non-certified farmed salmon was compared, revealing higher premiums with greater confidence in food safety. The industry should improve food safety perceptions and promote its benefits as a sustainable seafood source.

A review of the global use of fishmeal and fish oil and the Fish In:Fish Out metric.

Aquacultured carnivorous species consume most of the world's fishmeal and fish oil (FMFO), which itself is primarily derived from small pelagic fish. This has raised concerns about the practice's impact on wild fish stocks, ecosystems, and coastal communities that rely on these fish. The aquaculture industry claims a decreasing dependence on wild fish, relying on the Fish In:Fish Out (FIFO) metric as a ratio of the quantity of wild fish required for farmed fish production. This is misleading because it usually assumes constant FM or FO yields, inclusion rates and feed conversion ratios, which vary widely. Thus, a constant FIFO value for a given species cannot be assumed. Furthermore, low FIFO values resulting from averaging carnivores and herbivores conceal the high feed requirements of carnivore species. The increasing use of FMFO from by-products does not demonstrate a decreased use of wild fish but rather reflects a growing demand for FMFO, particularly for the fast growing and valuable salmon and shrimp farming industries.

Evaluation of post-stocking re-encounters of an endangered fish using a large, multi-agency database to inform recovery

Managers frequently rely on conservation hatcheries to maintain declining fish populations in the wild, which is the case for bonytail Gila elegans, an endangered species endemic to the Colorado River basin, USA. We used a multi-agency database of stocking, capture, and PIT-tag detections during 2013-2021 across the upper Colorado River basin to assess if re-encounter probability of bonytail varied among seasons, stocking habitats (mainstem, tributary, and off-channel), and with length-at-stocking. Because of previous observations of recaptured bonytail in poor body condition, we tested for differences in condition among stocking habitats. Of 325054 stocked bonytail examined, 90% were never re-encountered. Most re-encounters (93%) were PIT-tag detections near stocking locations. Re-encounter probability was low regardless of stocking habitat, and 95% of fish were at large for <195 d. The effect of length-at-stocking on re-encounter probability varied among habitats and was positive in mainstem and tributary and negative in off-channel habitats. Slopes of length-weight relationships of recaptured fish differed among stocking habitats. Given consistently low re-encounters of stocked bonytail in all habitats regardless of length-at-stocking or stocking season, we recommend managers consider refining the stocking program to better identify specific factors that affect survival, including stocking fish into intensively managed off-channel habitats which afford greater control of abiotic and biotic conditions than riverine habitats. If stocking continues among multiple habitat types, at a minimum we suggest stocking fish at consistent locations over time to better allow for quantitative assessment and to ensure fish are stocked into water temperatures that align with optimums for growth, recovery-from-handling, and survival.

A novel approach for rapidly determining the reproductive status of walleye pollock (Gadus chalcogrammus) using Raman spectroscopy

Knowledge of the reproductive biology of fishes is essential for effective fisheries management. Information derived from an understanding of fish reproduction, such as size and age at maturity, is used in models to assess fish stocks and can affect estimates of important ecological processes such as recruitment, abundance, and trophic interactions. Common practices for determining the reproductive status of teleost fishes include macroscopic evaluation of gonads as well as histological analysis. However, macroscopic evaluation can be biased and histological analysis is time-consuming, resulting in limitations to spatial and temporal data availability. Here, we explore Raman spectroscopy of ovaries as a novel approach to rapidly determine the reproductive status of walleye pollock (Gadus chalcogrammus), a commercially and ecologically important species in the North Pacific. We used a two-stage partial least-squares (PLS) regression analysis followed by a linear discriminant analysis (LDA) to classify walleye pollock ovary samples as physiologically mature or immature and to subsequently predict their histologically-determined reproductive stage based on the Raman spectra. Biologically mature samples with visible yolk differentiated from mature and immature samples (non-yolked; 99% accuracy). Non-yolked ovaries that were physiologically mature (either mature non-developing or previously spawned) were further differentiated from physiologically immature ovaries (93% accuracy). In addition, detailed, histologically-determined reproductive stages of yolked samples also differentiated via Raman spectroscopy, but with reduced accuracy (79% - 86% accuracy). Our results indicate that accurate identification of maturity status and the reproductive staging of oocytes of walleye pollock based on spectral data from ovaries is possible. This can provide a fast and efficient way to increase the availability of a key component of reproductive data to inform fisheries research and management.

Advances in understanding physical and biological controls on eggs and larval distribution in Pacific fisheries: A review

The early stages of fish, comprising eggs and larvae, are exceptionally fragile and sensitive to environmental dynamics and climate change. Pacific Ocean (PO) currents play an important role in shaping the distribution of marine organisms, influencing global climate patterns, heat distribution, coastal temperatures, and nutrient redistribution. These currents reveal significant changes within the climate system. Their variability across different timescales can be attributed to the complex interplay of physical forces. These currents are subjected to diverse anthropogenic factors, exerting detrimental effects on the dispersal of fish larvae. Furthermore, climate change variables, including alterations in tropical PO temperature associated with the ENSO cycle, Atlantic Nino modes influencing equatorial Atlantic temperature, changes in ocean salinity, polar ice cap melting, increasing greenhouse gases, marine heatwaves, and fluctuations in subsurface flows, directly impact the distribution, abundance, and species composition of early life stages. Major Pacific fisheries, such as those targeting Pacific sardines, saury, and anchovies, undergo population booms and declines due to significant alterations in the current dynamics of currents and fronts within the PO. The anticipated intensification of the ENSO cycle, characterized by more frequent and severe El Niño (warm) and La Niña (cold) events as a result of climate change, is expected to significantly impact the early developmental stages of important commercial fish stocks regularly. This review synthesizes the current understanding of the physical and biological parameters driving changes in ocean currents and their implications for early fish dispersion, emphasizing the critical need for research in this area to inform global conservation efforts, fisheries management, and food security.

Estimates of life-history and growth parameters of exploited fish species in lakes Edward and George: Implications on exploitation status, population dynamics, management, and conservation of native species.

Adequate knowledge is essential for responsible inland fisheries. However, many inland fisheries lack monitoring, and therefore, decision-making for fisheries management is not reliable. In this paper, we used data from surveys and literature to estimate the life-history and growth parameters of 16 exploited fish stocks in the Ugandan part of Lake Edward and Lake George (East Africa). The estimated parameters are pivotal indicators of fish stock status, particularly in data-poor fisheries. The estimated parameters included maximum length (Lmax) and mean length (Lmean) as indicators of size structure in experimental and commercial catches, coefficients of length-weight relationships, length at 50% maturity (Lm50), fecundity, von Bertalanffy parameters, total mortality (Z), and natural mortality (M). These parameters were estimated using empirical formulae, statistical methods, and analyses of length frequencies. Only two stocks of semutundu Bagrus docmak exhibited significant and increasing trends in Lmax (Lake Edward) and Lmean (Lake George). The estimates for the remaining parameters were consistent with those in FishBase and other literature resources, either for the same species or related species. This consistency indicates their reliability for application in decision-making and further assessments. Some parameters showed evidence of unsustainable fishing. For example, estimates of Lm50 for four of the assessed stocks belonging to two species (Nile tilapia Oreochromis niloticus and marbled lungfish Protopterus aethiopicus) were lower than baseline estimates in the studied waterbodies. Furthermore, the Lmean in catches for all the stocks were less than the optimum lengths (Lopt), which maximize catches with a minimal impact on biomass and size structure. No significant changes in Lmean, length-frequency distributions, and size at maturity could be attributed to the management changes implemented in 2018, probably because it is too early to observe changes in these parameters. However, there are positive signs attributable to the changes in management as shown by a high proportion of mature individuals in commercial catches for most of the stocks for which the proportion was calculated, and an increase in Lmean and Lmax for some stocks, such as B. docmak, in commercial or experimental catches. New estimates from this study will enhance decision-making and further assessments of fisheries. Routine monitoring is recommended to update and improve the estimates.

Climate change undermines seafood micronutrient supply from wild-capture fisheries in Southeast Asia and Pacific Island countries

Marine ecosystem functions are affected by climate change impacts such as ocean warming, deoxygenation and acidification. These impacts drive changes in distributions and body size of fish species and directly affect fisheries. Wild-capture fisheries are crucial for providing nutrients, livelihoods, and employment in tropical Southeast Asia and Pacific Island countries, where coastal communities are highly vulnerable to climate change. We examined the impacts of climate change on fish stocks and nutrient availability of seven key micronutrients (calcium, Omega-3 fatty acids, iodine, iron, vitamin A, vitamin B12 and zinc) in Southeast Asia, Pacific Islands, and Oceania (Australia and New Zealand). We combined micronutrient demands by local human populations with Sea Around Us reconstructed catch time series and catch projections from a dynamic bioclimate envelope model for the 21st century. The model predicted a decline in the Maximum Catch Potential (MCP) within Exclusive Economic Zones for Oceania, Pacific Islands, and Southeast Asian countries. Under the ‘strong mitigation’ scenario, catch potential reductions ranged from a decline of 54–66 % in Oceania, 58–92 % in Pacific Islands, and 65–86 % in Southeast Asia by the mid to the end of the 21st century relative to the historical period, respectively. Under the ‘no-mitigation’ climate scenario, reductions were more severe, with a decline of 55–70 % in Oceania, 66–92 % in Pacific Islands, and 70–86 % in Southeast Asia for the same time periods. Our findings indicate that Australia and New Zealand are unlikely to meet the recommended nutrient intake demand for most micronutrients through their fisheries (not considering trade or aquaculture production), except for iodine and vitamin B12. Pacific Island countries will likely follow the same pattern while Southeast Asia is expected to face worsening deficits, except for iodine and vitamin B12. This study highlights the importance of incorporating nutritional considerations of seafood into national food, trade and economic policies.

Early warning indicators of decadal shifts in the planktonic assemblage of the Cabo Frio upwelling ecosystem

Long-term monitoring of coupled environmental and biological components in upwelling ecosystems is critical for early warning under the global warming context. Temperature, salinity, nutrients, and plankton populations are promising indicators of the ecosystem state that help us to address the current status of the oceans and construct better predictions for the future. The Cabo Frio Upwelling System (CFUS) is a regionally productive wind-driven coastal upwelling ecosystem on the northern boundary of the South Brazilian Shelf sustaining diverse marine life including large stocks of fish and squid. Like other cold marine ecosystems, most of its functioning is likely threatened by ocean warming which emphasizes the need for ecological indicators. This study aimed to analyze the causal relationships between the temporal changes in the physical and chemical properties and the dominant planktonic communities leveraging long-term observations (20 years). The results suggested a link between the temporal changes in the ecosystem conditions and the composition of the plankton assemblage, notably an increasing proportion of dinoflagellates relative to diatoms and cladocerans relative to copepods. This increase in the proportional abundance of dinoflagellates and cladocerans over time suggests a regime shift in the plankton assemblages during the 2000s, highlighting some large phytoplankton and zooplankton groups as early indicators of productivity shifts in upwelling ecosystems.

Topological analysis of the three-dimensional radiodensity distribution of fish otoliths: Point sampling effects on dimensionality reduction

Otoliths are calcified structures found in the inner ears of teleost fish, pivotal in marine biology for studies on metabolism, age, growth, and the identification of fish stocks, potentially leading to sustainable management practices. An important feature of this structure is its density, as it corresponds to modifications in the crystalline form of calcium carbonate during the fish's lifetime, resulting in variations in its final shape. The internal and external 3D radiodensity of otoliths from different species was obtained utilizing micro-computed tomography, however, an appropriate methodology for describing and conducting comparative studies on these data appears to be absent in the current body of literature. Therefore, we study otolith density variations from 3D computed tomography images, employing the Ball Mapper technique of Topological Data Analysis. We focus on reducing the computational cost of this analysis by applying probabilistic sampling and assessing its effects on the density variations provided by the Ball Mapper graph. To determine the sample size, we used the topology to establish what we term "Topological Sample Validation", which provided the minimum resolution with the same density information as raw data. Sample representativeness was validated through non-parametric statistical tests on the density variable. Based on the network's structural characteristics, network properties allowed for evaluating similarity between graphs. Besides the small sample size, remarkable correlations were obtained between age and network variables. Additionally, the Ball Mapper technique proved effective as a preprocessing algorithm for tomographic images, enabling the segmentation of undesired features in the object of interest.

Occurrence and Strength of Instantaneous and Intracohort Density-Dependence in Northeast Atlantic Fish Stocks.

Biological reference points (BRPs) used in fisheries management do not include density-dependent (DD) growth, with DD processes only considered in the stock recruitment relationship. Not accounting for DD on somatic growth has led to criticism that such BRPs underestimate the compensatory effects of DD at low stock size, and therefore risk foregone catch opportunities. Here, we analyse 81 stocks from the Northeast Atlantic for evidence of DD growth, defined as the process in which stock size affects somatic weight. We evaluate the following questions: (1) How many stocks have experienced instantaneous DD growth and do stocks of the same species display similar trends? (2) Is there a common instantaneous DD growth relationship shared by all stocks? (3) For stocks exhibiting significant instantaneous DD growth, can we quantify the strength of the relationship? (4) Is DD growth operating as an intra-cohort process as opposed to an instantaneous effect? Results reveal that only the weight of recruits exhibits a common instantaneous DD growth while the other responses analysed show a positive, noncompensatory effect, suggesting that other processes are at work. All responses examined showed significant temporal autocorrelation, which, when not accounted for, suggest apparent instantaneous DD growth in several stocks. Comparison of instantaneous against intracohort DD growth showed an increase in the number of stocks with significant DD growth, although, as for instantaneous DD growth, this declined greatly when temporal autocorrelation was accounted for. Our results counteract the a priori assumption that DD growth compensation is related only to stock biomass or density, suggesting that DD growth should be dealt case-by-case. Consequently, management practices that aim to fish down stock biomass with the anticipation of triggering DD growth will be associated with greater asymmetric risks than keeping biomass at levels where replacement yield does not rely on it.

On the problem of annual overfishing of the silver bream Blicca bjoerkna (Cyprinidae) in industrial fishing in the Astrakhan region

The silver bream Blicca bjoerkna and the small-sized common bream Abramis brama are characterized by external similarity, which contributes to manipulations with the substitution of one species (common bream) by another (silver bream) when taking into account the volume of industrial fishing in the Astrakhan region. This is due to the fact that in the period of spring fishing season during common bream spawning migration, the share of non-commercial common bream in commercial catches increases (to 20–30 %), the catch of which is limited in accordance with the Fishing Rules. In order not to exceed the allowable volume of by-catch of non-large common bream, fish producers register en masse catches of small-sized bream as a catch of silver bream, which causes significant damage to common bream fish stocks through oversampling of first-time maturing individuals of the population. In recent years, the share of non-commercial common bream recorded as a silver bream in May alone is 13–28% of its official catch during this period. In order to reduce the catch of first spawning common bream producers of non-commercial length on the water bodies of the Astrakhan region in the period from April 21 to May 20, it is recommended to introduce a ban on industrial fishing of silver bream.

Vulnerability of elasmobranchs caught by artisanal fishery in the Southeastern Caribbean

The Caribbean is recognized as one of the regions with significant elasmobranch diversity; however, the lack of scientific data has made it difficult to conduct traditional fish stock assessments. A Productivity Susceptibility Analysis (PSA) was used to evaluate the vulnerability of the most important elasmobranch species caught by artisanal fishery carried out in the northeastern region of Venezuela. The fishing database created by the INIA and CIT was used as a starting point to obtain catch composition, and biological and fishing information. Of the 37 elasmobranch species captured in the study area, 12 were selected for the PSA. Analysis indicated that the selected species, most of them small-sized sharks, had medium and high productivity; while all species evaluated showed high susceptibility to artisanal fishing. Among the elasmobranch species with high vulnerability, seven of them comprised five sharks (C. limbatus, R. lalandii, R. porosus, C. brevipinna and C. acronotus) and two batoids (H. guttatus and A. narinari). Elasmobranchs species with medium vulnerability included two sharks (M. higmani and M. minicanis) and one batoid (H. americanus); while those with low vulnerability comprised two shark species (M canis and M. norrisi). In the study area, elasmobranch fishing has been carried out for decades without effective management strategies, and the artisanal fishery poses a potential threat to the populations of this group of fish. The species identified in this study as having high vulnerability or risk should be immediately prioritised for serious management by the national agencies responsible for fishing administration.

Status of the fish stocks and fisheries of the main commercial fish species of Lake Ladoga in the XXI century

In the 21st century, there has been decrease in stocks and catches of aquatic biological resources in Lake Ladoga as well as a change in the structure of the fish population in the Lake, primarily due to changes in the trophic capacity of the reservoir. Smelt dominates in the commercial catches. Stocks and catches of autumn-spawning whitefish and lakecisco show obvious downward trend. Biological and commercial indicators of the pike-perch population are at a low level. Stocks of bream, roach and perch are in good condition.

Study of Fungal Organisms Associated with Smoked and Dried Fish Sold in Awka Markets, Anambra State

Fungal contamination of fish is considered as the major cause of spoilage and it constitutes a significant public health problem. This study was carried out to determine the fungal organisms associated with smoked and dried fish samples: Scomber scombrus (Mackerel), Sardinella longiceps (Sardine), Oreochromis niloticus (Tilapia), Clarias gariepinus (catfish), Gadus morhua (Stock fish), Ethmalosa fimbriata (Bonga fish), and Citharinus citharus (Mangala) sold in Awka markets, Anambra State, Nigeria. A total of fifty (50) (25 smoked and 25 dried) fishes were obtained from three markets in Awka and examined microbiologically for viable fungal infestation using Potato Dextrose Agar (PDA) media. A total of 121 fungal organisms were isolated from 25 smoked and 25 dried fish samples and identified. The isolated fungi were Mucor spp, Aspergillus niger, Aspergillus flavus, Penicillium spp, Fusarium spp and Rhizopus spp. It was observed that all the fish samples harboured multiple fungal organisms. Aspergillus niger was the fungus with the highest mean fungal count of 9.00±5.568, followed by Mucor spp (8.00±1.732), while Aspergillus flavus was the lowest (3.67±1.528). In the dried fish samples, Gardus morhua (stock fish) had the highest infestation with fungi (1.08±1.083), while in smoked fish, Clarias gariepinus (catfish) had the highest infestation. The high level of fungal contamination can be attributed to poor handling of fish and the environment. Considering the danger to public health, food and safety authorities should intensify their monitoring efforts towards controlling fish contamination, and fish sellers should also be sensitized on hygienic fish handling techniques.