Fisheries & Aquatic Life Feed

Length-weight relationship and condition factor of sea trout from the Słupia River (Poland), during the spawning migration

Sat, 14 Feb 2026 00:00:00 GMT

Ulcerative dermal necrosis (UDN) has been observed in sea trout (Salmo trutta L.) entering the Słupia River to spawn. During this time, various biotic and abiotic factors can disrupt homeostatic balance, leading to severe pathological changes, including those on the skin surface. The aim of the study was to determine whether the symptoms of ulcerative dermal necrosis affect the growth and condition of sea trout migrating to spawning areas in the Słupia River. Between 2021 and 2024, 63 fish ascending the fish ladder in the Słupia River were tested. The length-weight relationship (LWR) and Fulton’s condition factor (Kc) were estimated. A comparison of the slopes and intercepts of the LWR regressions for both healthy and diseased males and females indicated no statistically significant differences among the groups examined. Consequently, this suggests that UDN infection does not have a relevant impact on linear regression. Additionally, a comparison of Kc values between the studied groups did not reveal a statistically significant effect of UDN in sea trout. The current study provides basic biometric data on spawning stocks of sea trout in the Słupia River, where UDN is observed, thereby expanding knowledge on this subject.

Assessing the potential for introducing resident brackish-water pike (Esox lucius) to restore depleted Baltic Sea populations

Sat, 14 Feb 2026 00:00:00 GMT

The northern pike (Esox lucius L.) inhabits the Baltic Sea and has two reproductive strategies: spawning in freshwater wetlands (anadromous populations) and direct spawning in coastal marine waters (resident brackish populations). Resident brackish populations do not occur in Polish marine waters, and anadromous pike populations in Puck Bay are virtually extinct. This study assessed whether reproductive material from resident brackish pike populations could be used to obtain larvae under hatchery conditions for population restoration. Eggs were collected from resident brackish pike spawners in the coastal waters of Rügen (Germany) and transported 600 km (9 h) to a hatchery in Poland. The eggs were incubated in artificially prepared saline water at 0, 5, 7, and 8.5 PSU. In the 2023 trial, hatching success was 0% at 0 PSU, 0.7% at 5 PSU, 8.3% at 7 PSU, and 8.0% at 8.5 PSU. Larval survival to 18 days post hatching in salinities of 5–8.5 PSU was high (approximately 90%), and growth rates at 14°C ranged from 0.26 to 0.31 mm d−1.No eggs hatched in 2024. The results indicate that this strategy is feasible, particularly given the high larval survival; however, the low and variable hatching success requires further optimization before application in restoration programs.

Fish lice (Argulidae: Argulus spp.) infestations detected on freshwater fish in Türkiye: Argulus foliaceus (Linnaeus, 1758) and Argulus japonicus Thiele, 1900

Sat, 14 Feb 2026 00:00:00 GMT

Argulus (Crustacea: Branchiura) species, also known as fish lice, are among the most important aquatic ectoparasites infesting fish in Türkiye and worldwide because of their low host specificity and widespread distribution. Approximately 130 species have been identified within this genus, which inhabit freshwater, marine, and estuarine environments. To date, only two species have been reported from Türkiye: Argulus foliaceus (Linnaeus, 1758) and A. japonicus Thiele, 1900. This study aimed to determine the host diversity of Argulus species reported in Türkiye through a literature review. Additionally, we aimed to report A. japonicus infestations detected in common carp (Cyprinus carpio L.) and Amur carp (Cyprinus rubrofuscus LacepPde) (ornamental form; koi) during routine parasitological surveys conducted at the Mediterranean Fisheries Research, Production, and Training Institute (Antalya, Türkiye). Argulus japonicus, a parasite found on common carp (C. carpio), represents a new host–parasite association for the parasitic fauna of Türkiye.

Unusual development of an accessory otolith in herring (Clupea harengus) larva

Sat, 14 Feb 2026 00:00:00 GMT

Otoliths are key to reconstructing fish life history, as their structure records individual and environmental information. These inner ear structures grow incrementally, revealing growth rates, migration patterns, and environmental conditions. However, internal factors (e.g., genetic mutations and stress) and external factors (e.g., temperature changes and pollution) can cause structural anomalies, such as shape deformities, asymmetry, and altered composition. This study describes a unique anomaly, an unusual accessory otolith, in the sagittal otolith of an Atlantic herring (Clupea harengus L.) larva collected from the Vistula Lagoon in the southern Baltic Sea, a vital spawning area. A 40 mm larva exhibited a rare otolith anomaly (found in only one of ~2000 specimens analyzed) characterized by a main otolith measuring 0.47 × 0.39 mm with an average of 64 daily increments, and an attached accessory measuring 0.20 × 0.10 mm with an average of 25 daily increments. This anomaly, previously unreported in Baltic herring larvae, may reflect environmental stressors and is significant for understanding developmental abnormalities in fish.

Age and growth of invasive alien fish species, Perccottus glenii and Lepomis gibbosus, in water bodies of Transcarpathia (Ukraine)

Sat, 14 Feb 2026 00:00:00 GMT

The Transcarpathia region of Ukraine is one of the most vulnerable regions for bioinvasions. There are five invasive and nine native species in the artificial water bodies of plain Transcarpathia. This study focused on the life-history traits of the Chinese sleeper Perccottus glenii Dybowski and pumpkinseed Lepomis gibbosus (L.). The standard length of the Chinese sleeper varied from 14.40 to 94.85 mm, and the total weight varied from 0.11 to 20.05 g. The standard length of pumpkinseed varied from 12.31 to 75.81 mm, and the total weight varied from 0.04 to 17.26 g. Both species form five age group populations dominated by young individuals and reach sexual maturity in their second year of life with a standard length of more than 40 mm. The combination of early maturation, rapid population turnover, and a broad size structure likely enhances the invasive success of both species under local conditions. These findings highlight the high adaptive potential of P. glenii and L. gibbosus and emphasize their capacity to establish stable populations, posing a long-term threat to native fish assemblages in artificial freshwater ecosystems of Transcarpathia.

Effect of different stocking densities on growth performance, feed utilization, and survival of Labeo angra (Hamilton) fry in aquaria

Sun, 18 Jan 2026 00:00:00 GMT

This study was conducted to assess the effect of stocking density on the growth performance, feed utilization, and survival of Labeo angra (Hamilton) in nine glass aquaria each containing 30 l of water for 45 days. Three different stocking densities of 1, 1.5, and 2 fry l−1 of water (T1,T2 and T3, respectively) were assessed in three replicates each. L. angra fry of approximately 0.32 ± 0.10 g weight were stocked and fed with a commercial feed four times daily at a rate of 15–30% body weight. Growth performance in terms of final weight (2.53 ± 0.22 g), weight gain (2.20 ± 0.05 g), percentage of weight gain (567.68 ± 15.25%), average daily gain (4.90 ± 0.11% day−1), and specific growth rate (4.54 ± 0.04% day−1) showed significantly higher values in T2 compared to the other treatments. Significantly lower feed conversion ratios and the highest protein efficiency ratio were noted in T2 (1.5 fry l−1) diets. Significantly higher survival was observed in T2 compared to T1 and T3. However, the results indicated that T2 (1.5 fry l−1) had more positive influence on the enhancement of growth performance, feed utilization, and survival of L. angra fry nursing in aquaria.

The use of biofilters with different types of fillers in recirculation aquatic system (RAS)

Sun, 18 Jan 2026 00:00:00 GMT

The aim of this study was to evaluate the effectiveness of using highly porous materials as fillers for biofilters in RAS, such as those with a much higher specific surface area than classical polymer floating bioload, and to determine the optimal proportion of biofilter with these fillers to the total volume of fish tanks. During the experiment, additional nitrogen in the form of ammonium chloride was added to the water of the RAS with different filler types. The effectiveness of biofiltration systems with different fillers was evaluated by the oxidation time of NH3/NH4+ to NO2− and the physiological condition of sterlet fry (Acipenser ruthenus L.), which was used as a test organism. It was proven that highly porous fillers oxidized ammonium compounds in RAS water 1-3 hours faster than polymer floating bioloading. The optimal proportions of the volumes of highly porous fillers to the total volume of fish tanks were determined to be 1:100 for foamed glass and 1:50 for porous ceramics. Under the experimental conditions, the survival of the test object corresponded to current technological standards. Observations of the physiological state and behavioral responses of young sterlets did not reveal any adverse effects of nitrogen compounds on fish.

New multiplex PCR assays for estimating genetic diversity in European grayling (Thymallus thymallus) by polymorphism of microsatellite DNA

Sun, 18 Jan 2026 00:00:00 GMT

The European grayling (Thymallus thymallus L.) is a vulnerable freshwater fish that plays an important role in the conservation of the biodiversity of European ichthyofauna and is a key species in recreational fishing. Multiplex PCR is a technique used to estimate genetic diversity that saves both time and money. This paper presents three multiplex PCR assays for amplifying 11 microsatellite markers from European grayling DNA. The steps necessary for constructing multiplex assays and verifying genotyping results are described. The compositions of the PCR mixture and the characteristics of the PCR thermal profile recommended for amplification in multiplex mode, and protocols used in genotyping them by using automatic DNA sequences are also described. Consequently, our method enables a near four-fold reduction in time and costs of the PCR stage of studies on genetic variation. Moreover, the next step of analysis (measuring the length of DNA fragments) can be done faster and easier without decreasing the precision or quality of genotyping results. This method was tested by assessing the genetic variation in a grayling stock kept under aquaculture conditions, and it has proved useful in the management of the genetic variation of this species.

New sites of the invasive signal crayfish, Pacifastacus leniusculus (Dana, 1852), from the Lutynia and Prosna rivers in Poland

Sun, 18 Jan 2026 00:00:00 GMT

This article presents new observations of the invasive signal crayfish, Pacifastacus leniusculus, in Poland. The species was detected for the first time in the Lutynia and Prosna rivers in southwest Poland. In total 59 and 50 individuals were captured. The population examined probably came from illegal releases, while the presence of juvenile specimens may suggest that the population is capable of reproduction. This species could continue to spread and expand its range to include additional aquatic ecosystems. Therefore, it is recommended to monitor the environment regularly and take appropriate remedial actions against this population.

Ecological role and importance of oysters for environmental sustainability: a mini review

Sun, 18 Jan 2026 00:00:00 GMT

Oysters, a bivalve species, play an important role in balancing aquatic ecosystems. However, the role of oysters in environmental sustainability is poorly understood. Here, we answer the question of how oysters contribute to ecological health and environmental sustainability in coastal and marine ecosystems. We reviewed published articles and technical reports. We found that oysters contribute to minimizing eutrophication and provide habitat for many species. Moreover, oysters serve as a good source of food for many invertebrates and vertebrates, including fishes and birds. Additionally, oysters help prevent soil erosion and increase species diversity in aquatic ecosystems. Our research provides basic information about oysters’ contributions to the sustainability of nature; however, more detailed research is needed to better understand how oysters and their environment work together to support and maintain healthy aquatic ecosystems.

Relative growth and morphometry of otolith sagittae of Pseudotolithus senegalensis (Val.) along the coastline of Cameroon

Mon, 22 Sep 2025 00:00:00 GMT

Pseudotolithus senegalensis is among the most important commercial fishes in Cameroon. However, data on the life history of P. senegalensis are limited. This study analyzed the length-weight relationship (LWR) and condition factor of the fish, the relationship between the length and weight of fish and the length and weight of otolith sagittae. The fish (123) were collected for a period of three months (March-May) from the coastline region of Down Beach, Limbé, Cameroon. There was a significant (P<0.05) positive allometric relationship between the length and weight of the fish. However, no significant (P>0.05) relationship between the length class frequency of males and females was noted. Relationships between fish length and weight and otolith length and weight were described by linear regression models and significant correlations were obtained for all relationships. The highest correlation (r2 = 0.55) was between otolith length and fish weight and the lowest correlation (r2 = 0.14) was between otolith weight and fish weight. The results of this study demonstrate that fish length and weight and otolith dimensions have a positive allometric relationship; therefore, they could be a useful instrument for the assessment and evaluation of fish growth in stock and fisheries management.

Morphological characteristics of smoothbelly sardinella, Amblygaster leiogaster (Val.) in the Bay of Bengal

Mon, 22 Sep 2025 00:00:00 GMT

Species identification, classification, and the genetic studies of fishes rely principally on meristic counts and morphometric characteristics. The current study was designed to provide the first comprehensive, instructive description of the meristic counts and morphometric relationships (length-weight relationship [LWR] and length-length relationship [LLR]) of Amblygaster leiogaster (Val.) from Bangladesh waters. Using various traditional fishing gears, 250 individuals were collected from the Bay of Bengal, Bangladesh between December 2019 and November 2020. A magnifying glass was used for the meristic counts, including several fin rays. Nine lengths were measured to the nearest 0.1 cm using a measurement board, and body weight (BW) was determined to the nearest 0.01 g with a digital electronic balance. The fin formula was: D. 17–18 (2/15–16); P. 15–16 (1/14–15); Pv. 8 (1/7); A. 18–20; C. 19–20 (2/17–18). Total length (TL) range was 13.3–20.0 cm, and BW range was 25.72–79.69 g. All LWRs demonstrated a high level of significance (P < 0.0001) with r2 values ≥ 0.946. The best fitted models were BW vs TL in LWRs, and TL vs FL in LLRs, as shown by the highest r2 values. This study serves as a baseline for identifying this species that will help fisheries scientists in further research.

Effects of active protection of the endangered fish lake minnow, Eupallasella (Rhynchocypris) percnurus (Pallas, 1814), on its occurrence in Mazowieckie Voivodeship in Poland

Mon, 22 Sep 2025 00:00:00 GMT

Mazowieckie Voivodeship was the first region in Poland to widely apply fish translocations for the active protection of the lake minnow, Eupallasella (Rhynchocypris) percnurus, a species of the family Leuciscidae at serious risk of extinction. These efforts began in 2002 and concluded in 2018, during which time over 21,000 juvenile fish from aquaculture were translocated to 13 water bodies. As a result, five new viable populations were established with the use of 17,000 fish. Three of these were confirmed to be viable in 2024, and one other probably also still exists. The failure of all the other translocations were habitat loss from drying up or population extinction caused by introductions of predatory fish species. The three or four new lake minnow populations contribute considerably to the present status of this species in the voivodeship, because the total number of all sites in 2024 did not exceed seven. These new populations also play a notable role in Poland, as there are likely not more than 80 lake minnow sites at present.

Length-weight relationship and condition factors of European perch, Perca fluviatilis, from 38 lakes in northeastern Poland

Mon, 22 Sep 2025 00:00:00 GMT

Length-weight relationships and condition factors of various fish species depend on food resources, habitat, season, water quality, and the size, age, and sexual maturity of fishes. The aim of this study was to determine the length-weight relationships (LWR) and the values of the Fulton condition factor (Kf), the allometric condition factor (Ka), and the relative condition factor (Kr) of European perch Perca fluvatilis from 38 lakes located in northeastern Poland. The total length (TL) of the perch ranged from 3.9 to 41.4 cm. The body weight of the fish caught ranged from 0.4 to 1,162.1 g. The linear regression coefficient of the LWR was highly significant (r2=0.99). Parameter b (3.1859) indicated positive allometric growth. The mean values of Kf (0.996 ± 0.154) and Kr (1.003 ± 0.121) indicated that the fish from the Polish lakes were in good condition. None of the condition coefficients differed significantly among the various maximum depth ranges of the lakes (P > 0.05). RDA analysis indicated a weak positive correlation between Kr and morphometric parameters of lakes. Ka was strongly correlated with lake surface area, while Kf was weakly correlated with the depth of the lakes studied. The results of this study are very important for updating data regarding the fish fauna of Polish lakes and for the management of commercial and recreational fisheries.

Fish communities in Baltic Sea coastal bays; using eDNA metabarcoding to assess vertical profile and traditional method comparison

Mon, 22 Sep 2025 00:00:00 GMT

Fish communities in the coastal Baltic Sea are currently monitored using passive fishing gears, such as gillnets. In recent years, eDNA approaches have gained popularity for fish detection thanks to their non-invasive nature, faster processing, and more precise identification, although such methods have been underutilized in comprehensive fish community assessments in the Baltic Sea. This study reports fish diversity using eDNA metabarcoding within different depth profiles for the first time in temperature-stratified coastal bays in the Baltic Sea, while also offering some comparison with traditional net-based approaches. Comparing samples above and below the thermocline revealed exclusivity in fish species at both depths, emphasizing the importance of vertical sampling in capturing a comprehensive understanding of fish distribution patterns in such systems. Results indicated that eDNA captured more fish taxa per sample compared to gillnet sampling, with similar or higher fish diversity, although variations occurred between bays. This study highlights the importance of incorporating eDNA metabarcoding, alongside traditional survey methods, to aid assessment of fish communities in aquatic environments.

Large water flea (Daphnia magna Straus) and mealworm (Tenebrio molitor L.) as potential food sources for rearing common carp (Cyprinus carpio L.) juveniles indoors

Fri, 23 May 2025 00:00:00 GMT

When rearing common carp fry using intensive technology, expensive rearing feeds can be replaced, or partially replaced, with economically produced live food organisms, which is a solution that is close to a natural one. Natural feeding conditions for common carp (Cyprinus carpio L.) juveniles were modeled in indoor studies 49 d in length in two consecutive years in Szeged, Hungary. In 2021, feeding Szeged mirror carp advanced fry with a nutritionally complete formulated feed was compared to feeding them large water fleas (Daphnia magna) and yellow mealworms (Tenebrio molitor) in rations that were adjusted for fish growth. In 2022, Szeged mirror carp and scaled landrace advanced fry fed water fleas and mealworms were compared with the same fish genotypes fed water fleas and complete feed in rations that were adjusted for fish growth. Feeding natural food resulted in significantly larger fish and better values for average daily gain, specific growth rate, feed conversion ratio, and final condition factor in both experiments, confirming that feeding live arthropods results in faster-growing carp fry with better feed utilization efficiency. The carp genotypes had different growth dynamics, with Szeged mirror carp exhibiting faster development and more efficient feed utilization compared to scaled landrace.

Impact of varying sodium bicarbonate concentrations on carp skin structure and carcass pH

Fri, 23 May 2025 00:00:00 GMT

This preliminary study investigated the effects of washing common carp (Cyprinus carpio) carcasses with different concentrations of sodium bicarbonate solution (0%, 2%, 5%, and 7%) on skin morphology and carcass pH levels, which could potentially affect shelf life for consumers. Skin biopsies were analyzed histologically using AB/PAS staining, and pH was measured during a seven-day storage period under refrigerated conditions. Results showed that increasing sodium bicarbonate concentrations led to progressive skin degeneration, with the 5% and 7% groups showing the most superficial loss of the epithelial layer. However, no statistically significant differences were observed among the groups. Washing fish carcasses with sodium bicarbonate solution is a promising way to reduce the amount of mucus on the surface and in the fish skin, which could potentially extend the storage life of carp meat. However, further microbiological studies are needed to confirm these preliminary findings and to investigate the optimal concentration and duration of washing with sodium bicarbonate for different fish species, as well as its impact on the product’s sensory qualities and nutritional value.

Exposure to cobalt chloride alters hemato-biochemical indices and erythrocyte morphology in stinging catfish, Heteropneustes fossilis

Fri, 23 May 2025 00:00:00 GMT

Higher amounts of cobalt chloride (CoCl2) released by industries are regarded as environmental pollutants. The goal of the current investigation was to assess the acute toxicity of CoCl2 from its effects on erythrocyte morphology and hemato-biochemical indicators in stinging catfish, Heteropneustes fossilis. The fish were subjected to CoCl2 at five different concentrations of 0, 50, 100, 200, and 300 mg L−l, which were referred to as control, CC50, CC100, CC200, and CC300, respectively. Red blood cell (RBC), hemoglobin (Hb), hematocrit (Hct), platelet counts, white blood cell (WBC), mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), mean corpuscular hemoglobin concentration (MCHC), lymphocytes, granulocytes, serum protein, and blood glucose level were among the hemato-biochemical parameters of stinging catfish that were measured following a 96 h exposure period. Additionally, erythrocytic nuclear abnormalities (ENA) and erythrocytic cellular abnormalities (ECA) were evaluated in the experimental fish. As the quantity of CoCl2 increased, there were notable reductions in RBC, Hb, Hct, WBC, platelet counts, MCH, MCV, MCHC, lymphocytes, granulocytes, serum protein, and blood glucose levels compared to the control. When the CoCl2 concentration increased, the frequencies of ECA and ENA also increased significantly (P < 0.05). This work demonstrated the significant toxicity of high CoCl2 concentrations caused alterations in hemato-biochemical indices and deformities in the erythrocytes of stinging catfish. Thus, it is imperative to take all necessary corrective action to guarantee that the amount of CoCl2 in the aquatic environment stays below permissible limits.

The first occurrence of halophyte Oryza coarctata in the mid-southern coast of Bangladesh

Fri, 23 May 2025 00:00:00 GMT

Salt marshes and other coastal habitats are essential for preserving ecological balance because they provide a habitat for a variety of species, prevent erosion, and mitigate climate change. The salt-tolerant wild species of rice Oryza coarctata is highly valuable because it may be used to develop crops that can withstand salt. It is a species that is well suited to coastal areas. This study documents the first recorded occurrence of O. coarctata along the mid-southern coast of Bangladesh, specifically in the intertidal zone of the Andharmanik River, Patuakhali, Bangladesh. The distribution and features of the species were evaluated by morphological studies and field surveys. The results show considerable variability of O. coarctata in shoot density (300 to 830 shoots m−2), plant height (5 to 152 cm), leaf length (2.7 to 29 cm), and biomass (48 to 71 g dry weight m−2), indicating the species’ phenotypic plasticity in response to environmental conditions. This finding highlights the potential expansion of O. coarctata’s known distribution area.

Role of β-glucans in reducing oxidative stress and improving muscle tissue health in European whitefish (Coregonus lavaretus L.)

Fri, 23 May 2025 00:00:00 GMT

β-glucans are currently a notable topic in research on enhancing immunity in fishes and their significant role in improving fish health and productivity in aquaculture. Phagocytic activity (PA), phagocytic index (PI), analyses of oxidative stress biomarkers (2-thiobarbituric acid reactive substances [TBARS] as biomarkers of lipid peroxidation, aldehyde and ketone derivatives of oxidatively modified proteins [OMP]), total antioxidant status (TAS), and lysosomal enzyme activity (alanyl aminopeptidase [AAP], leucyl aminopeptidase [LAP], acid phosphatase [AcP], and β-N-acetylglucosaminidase [NAG]) were used to assess the effects of dietary β-glucans on the skeletal muscle and heart tissues of European whitefish (Coregonus lavaretus L.). Our study showed that dietary β-glucan supplementation improved the immune system of European whitefish. Fifteen, 30, and 45 days after supplementing diets with β-glucans, the fish showed increased blood PA and PI, indicating improved immune response. β-Glucans also reduced lipid peroxidation and oxidatively modified protein levels and effectively managed the overall antioxidant status. We observed an increase in β-N-acetylglucosaminidase (NAG) activity in the skeletal muscle tissue on days 15 and 30 after β-glucan dietary supplementation and in the cardiac tissue on days 15 and 45 after β-glucan dietary supplementation. This highlights the role of NAG in the metabolic changes in muscle caused by the action of β-glucans. Furthermore, NAG activity was significantly associated with the tissue type and the duration of β-glucan dietary supplementation, as shown by regression analysis. MANOVA analysis confirmed that the long-term effect of β-glucans was more pronounced. β-glucan supplementation is an effective strategy for improving immune function and managing oxidative stress in the skeletal and cardiac muscles of European whitefish.