International Journal of Aquatic Biology

Light and electron microscopic study of Haematopoiesis in the spleen of two freshwater catfishes, Horabagrus brachysoma and Heteropneustes fossilis, of Kerala

Chandrabalan Vijayakumary Bobina — 2026-04-23

Haematopoiesis is the tissue-specific and developmentally regulated formation of mature blood cells from uncommitted stem cells through proliferation, commitment, and differentiation. In teleosts, blood cell formation occurs at more than one site: the head and trunk kidneys, spleen, thymus, and lymphoid tissue. In the present study, the characteristics of developing blood cells in the spleens of two indigenous freshwater catfishes in Kerala, Horabagrus brachysoma and Heteropneustes fossilis, were examined using imprint, scanning, and transmission electron microscopy. The spleen of the catfishes exhibited a few developmental stages of erythropoiesis, granulopoiesis, and lymphopoiesis, indicating the organ’s role in haematopoiesis. There was a dominance of erythroid and lymphoid cells and macrophages. Lymphoid cells were usually present as aggregates in the spleen of the catfishes. The study described the ultrastructural morphology of the splenic net and the associated cells in the sections of the studied catfishes’ spleen. The network of interconnected reticular cells and fibres form the meshwork for the proliferation of haematopoietic tissue and the pathway for senescent RBCs. The current work augments the available literature by providing an elaborate and complete description of the haematopoiesis in the spleen of H. brachysoma and H. fossilis.

Genetic diversity of populations of the endemic species Coptodon walteri from the Cavally River, Western Côte d’Ivoire

Ouangbo Yaya Ouattara — 2026-04-23

Coptodon walteri is a fish species of particular ecological importance due to its endemic status within the Cavally River basin. However, this hydrological basin is experiencing increasing environmental pressures, notably from gold mining, which may alter both the basin and the fish communities inhabiting it. Therefore, the objective of this study was to assess the genetic diversity of C. walteri populations, which to date have not been the subject of any genetic study in this region. A total of 120 individuals (30 per sampling station) were collected through experimental and artisanal fishing using gill nets. DNA from each specimen was extracted from a fragment of the caudal fin following a standard 2% CTAB protocol. To evaluate genetic diversity and population structure, seven microsatellite markers (GM005, UNH142, UNH146, UNH159, UNH174, UNH189, and UNH190) were analyzed. Genetic analyses were conducted using the software GenAlex, MEGA12, and STRUCTURE. The number of alleles per locus ranged from 2 to 9, with an average of 2. A total of 41 alleles were identified, corresponding to a mean polymorphism rate of 54% at a 95% confidence level. Despite this moderate level of polymorphism, the studied populations exhibited a pronounced heterozygote deficit (Ho = 0.01-0.10) and high inbreeding coefficients (Fis = 0.53-0.73), indicating strong genetic depression. High genetic differentiation across all analyzed loci was observed (Fst = 0.93), suggesting an almost complete absence of gene flow (Nm = 0.11) among sampling stations. Phylogenetic and population structure analyses revealed a clear separation of populations into three and four distinct groups, corresponding to their geographic locations. These results highlight severe genetic fragmentation and increased vulnerability in C. walteri, underscoring the urgent need to implement conservation measures.

Genetic Connectivity Analysis of Blue Swimming Crab (Portunus sp.) in Fisheries Management Areas (FMA) 713 and FMA 714 using a DNA Barcoding Approach: Implications for Blue Swimming Crab Resource Management in Indonesia

Yustika Intan Permatahati — 2026-04-25

Effective management of blue swimming crab (BSC) resources requires comprehensive understanding of their morphological and genetic characteristics. This study aimed to determine genetic distances, phylogenetic relationships, diversity, population structure, and connectivity of BSC populations in Fisheries Management Areas (FMA) 713 and 714, and to confirm their species identity. A total of 24 BSC samples (12 from each FMA; 6 males and 6 females) were collected from Poleang waters (FMA 713) and Lasongko Bay (FMA 714). DNA was extracted and amplified using mitochondrial COI gene with universal primers COIa and COIf. Results identified two Portunidae species: Portunus armatus and Portunus pelagicus, with P. armatus being dominant (83.33% in FMA 713; 91.67% in FMA 714). Phylogenetic analysis showed that P. armatus had closer genetic relationships among individuals than P. pelagicus. Both species exhibited high haplotype diversity with no significant difference (p = 0.4571), and very low genetic differentiation between regions (F_ST = -0.06164), indicating strong genetic connectivity. These findings suggest that BSC stocks in both FMAs are predominantly P. armatus. Consequently, resource management and conservation strategies should focus on P. armatus, since most past assessments referred to P. pelagicus, potentially misrepresenting population structure and stock dynamics.

First record of the genus Hoplisoma (Siluriformes: Callichthyidae) with an extension of its distribution to the Andean–Cuyan region, San Juan, Argentina

Agustina Daniela Valenzuela Gomez — 2026-04-25

Knowledge of the geographical distribution of the ichthyofauna is key, as it provides the information needed for inventory and monitoring studies that detect endemism and/or introduced exotic species. Within Siluriformes, the family Callichthyidae, which comprises the subfamilies Corydoradinae and Callichthyinae, is recognized as the third largest family within the order. The Callichthyidae family, especially the subfamily Corydoradinae, comprises more than 200 species distributed throughout South America, showing notable morphological diversity and a range of habitats, from fast-flowing piedmont streams with sandy or rocky bottoms to lowland pools with muddy bottoms. In this work, the presence of a Callichthyidae species is reported and confirmed for the first time, with a voucher specimen, in the province of San Juan, and the geographical distribution range of the genus Hoplisoma is expanded to the Andean–Cuyan region of Argentina. The collected specimens were captured at the outflow of the José Ignacio de la Roza dam in San Juan province for taxonomic identification. The methodology proposed by Díaz et al. (2024) was followed. It was determined that these specimens correspond to the genus Hoplisoma, with diagnostic features similar to those of species such as H. osvaldoi and H. paleatus.

Spatial and temporal variabilities in abundance and size structure of Caspian sand smelt, Atherina caspia (Pisces: Atherinidae) in a coastal plain estuary of the southeast Caspian Sea, Iran

Khadijeh Maramaei — 2026-05-07

To investigate seasonal and habitat trends in the community structure of Atherina caspia, a total of 14791 specimens caught in four habitats from the eastern part of Gorgan Bay (southeast Caspian Sea) were examined to test variability in intrapopulation and inter-habitat abundance. Fish in four coastal habitats, including a sea-coast habitat (SC), a strait-zone habitat (SZ), a bay-zone habitat (BZ), and an old canal of Khozeini habitat (CZ). The largest specimen was observed in the SZ, with a total length of 135 mm, and the heaviest was in the BZ, weighing 14.20 g. The relative abundance of the fish was the highest in CZ (33.4%) and the lowest in BZ (14.75%). All habitats except KZ showed the highest abundance of this fish in summer, while KZ had the highest abundance of this species in spring. A comparison of fish size showed significant differences between habitats. Although females were dominant in all habitats, the intensity of female dominance varied across habitats. Analysis of age composition revealed inter-population and in-habitat variability. Age 1+ was dominant in SC and KZ habitats, whereas age 2+ dominated in SZ and BZ habitats. The results suggest that A. caspia populations may largely differ among habitats, indicating high interpopulation variability that may contribute to its dominance across habitats in the southern Caspian Sea.

Macrophytes' presence alters zooplankton composition and abiotic conditions in a reservoir in Northeastern Brazil

Natália dos Santos Mendes — 2026-05-13

Our objective was to analyze the composition of zooplankton in areas with and without macrophytes in the Rio Preto do Criciúma Reservoir, Jequié-BA, and to associate it with different water conditions (physical and chemical parameters) and changes in zooplankton species composition. The physical-chemical parameters of water (water temperature, pH, electrical conductivity, redox potential, turbidity, dissolved oxygen and dissolved solids, water transparency, chlorophyll-a, and suspended material) and the zooplankton community were sampled at four points in a single campaign in June 2022 at the Rio Preto do Criciúma Reservoir, in the municipality of Jequié, Bahia, Brazil. Two samples were collected in the central region (without macrophytes), and one sample was collected on each of the left and right margins of the reservoir (with macrophyte banks). We observed that the presence of macrophytes on reservoir margins was associated with distinct water parameters and altered zooplankton composition. We observed five species exclusive to the limnetic region (without macrophytes) and seven exclusives to the littoral region (with macrophytes). Chlorophyll-a and temperature were associated with the presence of macrophytes, while dissolved oxygen, electrical conductivity, pH, and redox potential were associated with the absence of macrophytes. The Rio Preto do Criciúma Reservoir is suffering from uncontrolled anthropic activities on its margins, activities that have the potential to alter water conditions, species establishment, and biological interactions. Therefore, our study contributes to a better understanding of the relationships among macrophytes, water conditions, and zooplankton composition in reservoirs before these activities worsen and alter these relationships.

Gonadal sensitivity of Barbus balcanicus Kotlik, Tsigenopoulos, Rab & Berberi, 2002 (Actinopterygii: Cypriniformes) to aquatic pollution in Bosnia and Herzegovina

Renata Besta-Gajevic — 2026-05-13

Growing pressures from aquatic pollution and the increasing vulnerability of aquatic organisms lead to frequent disturbances in the health of aquatic ecosystems. This study aimed to investigate the gonadal tissue of the fish Barbus balcanicus as a tool to identify the effects of water contamination on freshwater organisms. Within this context, quantitative analyses of the elements Cd, Pb, Ni, Fe, Mn, Zn, and Cu in water, sediment, and gonads, microbiological analyses of water, and histopathological evaluations of gonad tissue were performed. Two different areas (S1 and S2) of the Miljacka River in Bosnia and Herzegovina were investigated. The results from Colilert-18 and Enterolert revealed that the water quality at S2 poses extremely high risks of total and fecal coliform contamination. The results also showed significant differences in heavy metal levels in the water, sediment, and inside fish gonads. Importantly, average concentrations of toxic heavy metals Cd and Pb in water at S2 were higher than the permissible values, respectively. As a result, higher values of metals in gonadal tissues and the metal pollution index were determined at site S2 in addition to severe histopathological alterations. Higher values of Cu, Fe, Zn, Cd, Ni, and Pb were recorded in both locations in testicle tissue compared to the ovaries. Nearly all bioaccumulation values in the testes are higher than in the ovary. Lastly, histopathological alterations were slightly higher in individuals from S2 than in those from S1. From the perspective of these findings, fish gonad sensitivity to pollutants and environmental disturbances could be useful indicators of environmental health.

Optimization of safe transport conditions for hatchery-reared golden rabbitfish (Siganus guttatus) juveniles: Effects of loading density and transport duration on survival and water quality

Michael B. Andam — 2026-05-13

The golden rabbitfish (Siganus guttatus) is increasingly recognized as a promising aquaculture species in the Indo-Pacific region due to its rapid growth, tolerance to salinity fluctuations, high market demand, and consumer preference. However, one critical bottleneck in its culture is the safe and efficient transport of juveniles from hatcheries to grow-out facilities. Grow-out farms are often located far from hatcheries, making the transport of rabbitfish juveniles to grow-out rearing facilities a critical process. Establishing optimal transport conditions of this species for grow-out culture is essential to minimize stress and enhance survival. This study evaluated the effects of three loading densities (300, 400, and 500 fish?bag^-1, corresponding to 13.53, 18.06, and 22.59 g?L^-1) and two transport durations (10 and 15 h) on the survival and water quality of S. guttatus juveniles. Both loading density and travel duration significantly influenced the survival and water quality of rabbitfish juveniles. Dissolved oxygen (DO), pH, and total ammonia nitrogen (TAN) were critical factors that significantly affected survival, with positive correlations for DO and pH and a negative correlation for TAN. The optimal loading densities identified were 400 fish?bag?¹ for 10-h and 300 fish?bag?¹ for 15-h transport, respectively. These results provide valuable insights for optimizing transport protocols to reduce stress and unnecessary mortalities of S. guttatus juveniles during transfer from nursery facilities to grow-out production sites.

The effect of guava leaves (Psidium guajava L.) in feed with different extraction methods on the immunity of vaname shrimp (Litopenaeus vannamei) challenged by Vibrio parahaemolyticus

Andre Rachmat Scabra — 2026-05-13

Diseases in vaname shrimp can cause economic losses, reduced production, and, in extreme cases, crop failure due to mass mortality. One disease that frequently occurs in intensive ponds of Litopenaeus vannamei is vibriosis, caused by Vibrio parahaemolyticus. Efforts to enhance shrimp immune responses by administering immunostimulants aim to prevent disease. One natural ingredient that can act as an immunostimulant is guava leaves (Psidium guajava L.). Common methods for producing guava leaf extract include maceration, Soxhlet extraction, and ultrasonics, but these methods are expensive. One solution is conventional extraction methods, such as flouring, boiling, and blending. The purpose of this study was to evaluate the effect of adding guava leaf extract to feed, using different extraction methods, on the immune response of whiteleg shrimp and to test it against V. parahaemolyticus. The method used was a randomized design with 5 treatments and 3 replications. The measured parameters in this study consisted of SR, FCR, SLGR, SWGR, media TVCs, THC, DHC, PA, and water quality. The results showed that P5 (blender method) with an SR value of 80%, FCR 1.1, SLGR 3 %/day, SWGR 8,2 %/day, media TVCs 20x10² CFU/mL, THC 16x10⁶ cells/mL, hyaline cells 63.3%, and PA 68% showed the highest value compared to other treatments.

Developmental toxicity and teratogenic effects of phytic acid on zebrafish (Danio rerio) embryos

Dewi Puspita Sari — 2026-05-14

Phytic acid (myo-inositol-1,2,3,4,5,6-hexakis-dihydrogen phosphate) is a common constituent of oilseeds, legumes, and cereals and is ubiquitously present in plant-based foods. While its antinutritional effects in vertebrates have been well documented, its potential impacts on early embryonic development remain poorly understood. Therefore, this study aimed to investigate the developmental toxicity of phytic acid in zebrafish (Danio rerio, ZF) embryos. Developmental toxicity testing was conducted in accordance with OECD Test Guideline 236, in which ZF embryos were exposed to various concentrations of phytic acid and a control treatment. Embryo mortality and developmental abnormalities were evaluated at different hours post-fertilization (hpf). Phytic acid exhibited moderate toxicity to ZF embryos, with an estimated median lethal concentration (LC??) at 96 hpf of 5.0±1.0 ppm. Furthermore, phytic acid-treated embryos and larvae exhibited various developmental deformities, including reduced heart rate, shortened body length, yolk sac edema, tail malformations, delayed hatching, and spinal curvature. Cardiac-related abnormalities, such as pericardial edema and impaired blood circulation, were also observed. Overall, these findings indicate that phytic acid exerts teratogenic effects on zebrafish embryos at certain exposure levels.

Optimization of broodstock culture and larval quality of Scylla serrata in a modified recirculating aquaculture system incorporating a polychaete-assisted biofilter

Derly Nemeño — 2026-05-18

This study evaluated the performance of two culture systems: a recirculating aquaculture system (RAS) incorporating a polychaete-assisted biofilter, and a conventional non-recirculating aquaculture system (NRAS, control) with regular water replacement. Both systems were equipped with individual compartments to minimize cannibalism. The survival, spawning success, hatching rates, and larval quality of Scylla serrata broodstock were assessed. Broodstock maintained in the RAS exhibited significantly higher survival (70.37±6.41%), spawning (61.11±4.80%), and hatching (55.55±4.81%) rates compared to those in the NRAS (51.85±5.78%, 35.18±10.14%, and 20.37±8.01%, respectively), indicating that the RAS provided more favorable conditions for broodstock conditioning. Larvae from broodstock in both systems were subjected to salinity (0, 10, 15, 20, 25, and 30 ppt) and formalin (0, 10, 20, 30, 40, and 50 ppm) stress tolerance tests. Larvae produced from RAS-held broodstock displayed significantly higher LT?? values under both stressors, suggesting greater resilience. Overall, these results demonstrate that the RAS with a polychaete-assisted biofilter not only enhances the reproductive performance of S. serrata broodstock but also improves larval quality, providing a promising approach for sustainable and reliable hatchery production.

Salt stress-driven bioorganic biorefinery of Monoraphidium contortum algae: Lipid transformation and starch valorization for integrated biodiesel and bioplastic production

Muntaha Mahmoud Al-Rashidy — 2026-06-12

This study aimed to collect and identify Monoraphidium contortum from local water bodies in Mosul, Iraq, using morphological and molecular characteristics. Furthermore, after cultivation in multiple media (modified NPK and modified CH10) and exposure to saline stress, lipid transformation and starch valorization were estimated to support the integrated production of biodiesel and bioplastics. Based on the results, the best medium for growth was M4 (CaCO3 + (NPK20:20:20) + CH10). On the twelfth day, the light absorption reached 650 nm with an optical density of 1.742 in this medium. The extracted oil yield was 9.6%, and polyunsaturated fatty acids increased to 22.7%, which were used to produce biodiesel. The transesterification process successfully converted the crude oil into diesel in two stages: an acidic and a basic stage. GC-MS analyses revealed that the salt stress stimulated the algae to accumulate polyunsaturated fatty acids. FTIR showed the success of the reaction through the appearance of a peak. The carbonyl group of methyl esters at 1728 cm^-1 and the disappearance of the glycerol and water fractions indicate the product's purity. HPLC results revealed that glucose was the main starch component at 55.48%, with 32.18% fructose and 12.34% sucrose. Furthermore, bioplastics were manufactured from the extracted starch, with glycerin added as a plasticizer. The results showed the high biodegradability of the manufactured plastic in soil, reaching a decomposition rate of 68.2% within 120 days, ASTM D6400, making it a successful, environmentally friendly product that conforms to international standards.

Quantifying the effect of trolling speeds on catch composition, CPUE, and fuel consumption in Teluk Tamiang, Indonesia

Ahmadi Ahmadi — 2026-06-12

Trolling speed is an operational factor that can influence catch performance and fuel use in small-scale pelagic fisheries, yet its quantitative effects remain insufficiently documented in Indonesian waters. This study evaluated the influence of towing speed on catch composition, catch per unit effort (CPUE), and fuel consumption during trolling operations in Teluk Tamiang, Indonesia. A total of 32 fishing operations were conducted at two towing speeds (4 and 8 knots), each repeated 16 times, resulting in 264 fish dominated by narrow-barred Spanish mackerel (Scomberomorus commerson), trevally (Caranx tille), and barracuda (Sphyraena jello). Although total biomass did not differ significantly between speeds, species-specific responses were evident: faster towing favored highly active predators such as mackerel, whereas slower speeds attracted opportunistic feeders, including trevally and barracuda. Mean CPUE at 8 knots (5.45 kg trip?¹) was approximately 1.5 times higher than at 4 knots (3.62 kg trip?¹) and improved distance-based fuel efficiency; however, it required 35-40% higher hourly fuel consumption. Conversely, the lower speed produced smaller catches but greater catch-per-liter efficiency, indicating clear trade-offs between fishing performance and fuel use. These findings highlight towing-speed optimization as a practical operational strategy for balancing catch productivity and energy efficiency in small-scale trolling fisheries.

Efficient removal of heavy metals and nutrients from wastewater using dried Cladophora biomass: Effect of environmental parameters

Asaad Abbood Aldhalimy — 2026-06-12

This study investigated the efficiency of dried algal biomass for removing selected pollutants from wastewater, including chromium (Cr), nickel (Ni), lead (Pb), nitrate (NO?), and phosphate (PO?). The experiments were conducted under different pH levels (5.5, 7, and 10), temperatures (15, 25, and 35°C), and contact times (2, 6, and 24 hours). The results showed that the removal efficiency of heavy metals increased significantly with increasing pH and contact time. The highest removal efficiencies were recorded at pH 10 after 24 hours, reaching 99.56% for Cr, 92.27% for Ni, and 95.72% for Pb. In contrast, NO? removal efficiency ranged from ?40.21 to 86.83%, while PO? removal ranged from ?11.57 to 78.50% under different experimental conditions, indicating variable behavior and possible release under certain conditions. The results revealed that dried algal biomass is an effective biosorbent for heavy metal removal, particularly under alkaline conditions, whereas its efficiency for nutrient removal is less stable and highly dependent on environmental factors. These findings highlight the potential of algal biomass for wastewater treatment and emphasize the importance of optimizing operational conditions to improve removal efficiency.

First record of the monogenic Gyrodactylus Magadiensis Dos Santos, Maina & Avenant-Oldewage, 2019 from the gills of the red belly cichlid fish Coptodon Zillii in Iraq

Aisha Sulaiman Obaid — 2026-06-14

This study reports the first record of the monogenean parasite Gyrodactylus magadiensis Dos Santos, Maina, and Avenant-Oldewage )2019) in the gills of the redbelly cichlid, Coptodon zillii, in Iraq. A total of 37 fish were collected from the Tigris River from July to November 2024. Then, the examined specimens yielded a prevalence of 13.5%. The morphological measurements and description of Gyrodactylus are based on the opisthaptor or the haptor, which is a posterior attachment apparatus. The hamulus was narrow and long; the ventral bar had small, rounded processes, with a distinct, tongue-shaped membrane. The marginal hooks, where the slender sickles are angled forward. Morphological analysis of the haptoral sclerites matched the original description of G. magadiensis. Despite notable variations in the lengths of the anchor shaft and ventral bar, these differences suggest morphological plasticity in both host and parasite. These findings expand the known host fish range and geographic distribution of G. magadiensis, contributing to the understanding of monogenean diversity among cichlids in Iraq.