International Journal of Aquatic Biology

Macroinvertebrate distribution in relation to water and habitat quality changes in Lake Kuriftu, Ethiopia

2026-02-23T09:22:28+00:00

This study aimed to determine whether habitat or other environmental factors were critical for assessing the ecological condition and macroinvertebrate community structure of a shallow lake exposed to multiple human pressures. The fieldwork was conducted in 2023 during the dry season. The lakeshore was categorized into six distinct sampling sites (S1–S6) to capture the gradient of anthropogenic influence and habitat heterogeneity. The habplot quality assessment (HabQA), based on the Lake Habitat Survey (LHS) and Lake Habitat Quality Assessment (LHQA) methods, was used to evaluate hydromorphological characteristics. In the littoral zone, physicochemical data were gathered using measuring probes and standard sampling procedures. Thus, a total of fifteen taxa were identified and categorized as follows: Odonata (Calopterygidae, Coenagrionidae, and Aeshnidae, Cordulidae), Hemiptera (Corixidae, Belostomatidae, Gerridae, Naucoridae, and Notonoctidae), Ephemeroptera (Baetidae, and Caenidae), and Diptera (Chironomidae, and Ceratopogenidae). Using Bray-Curtis UPGMA analysis, the sample sites were grouped based on benthic macroinvertebrate distributions. The sites that were most similar to one another were 5 and 6, according to the UPGMA analysis. Sites 3 and 4 were found to be the second most similar to one another. The intricacy of these sites' habitats and their littoral substrate provide an explanation for this phenomenon. TP, water temperature, and HabQA score were shown to be important contributors to the variance observed in the macroinvertebrate data. In contrast to other physicochemical factors, this study elucidated the larger significance of habitat quality parameters on the abundance of macroinvertebrate communities. To better understand the attributes crucial to macroinvertebrate abundance, we strongly recommend using the HabQA scoring technique to examine the structure of macroinvertebrate communities. Management efforts should also assess various shoreline changes and prioritize preserving the littoral zone's morphological diversity.

Effect of different stocking densities on growth performance and gut villi histology of endemic ornamental fish (Betta rubra) in the biofloc technology

2026-04-08T16:08:26+00:00

The endemic ornamental fish Betta rubra, known locally as serban malem, is a high-value non-consumptive fishery product. This study aims to evaluate the growth performance and histological structure of gut villi of B. rubra fish maintained in a biofloc system with different stocking densities. This study used a completely randomized design with four treatments: 1 fish/liter (control, no biofloc system), 1 fish/liter (biofloc system), 2 fish/liter (biofloc system), and 4 fish/liter (biofloc system). Treatments showing significant differences were further evaluated using Duncan's test. The results showed that the survival rate, length increase, and feed conversion ratio in the biofloc system were significantly different from those of the control (P<0.05). In contrast, daily growth rate and weight gain were not significantly different between treatments. Fish intestinal villi in the biofloc system were significantly different compared to those in the control. In conclusion, the optimal rearing density of B. rubra is 2 fish/liter in the biofloc system (P2).

Exploring seaweed-associated microbiota as emerging probiotic candidates for aquaculture

2026-04-12T03:19:13+00:00

The rapid expansion of aquaculture has intensified the need for sustainable strategies to improve productivity and disease control, particularly amid growing concerns about antibiotic use. Probiotics have emerged as a promising alternative; however, conventional sources, primarily derived from aquatic animal guts, often exhibit inconsistent performance under field conditions. In this context, seaweed-associated microbiota represents a relatively underexplored but potentially valuable source of probiotic candidates. This review synthesizes current knowledge on the diversity and functional traits of seaweed-associated bacteria and evaluates their relevance to probiotic application in aquaculture. Key traits discussed include stress tolerance, antimicrobial activity, competitive exclusion and colonization ability, enzymatic capabilities, and the production of bioactive compounds linked to growth promotion and immunomodulation. Evidence indicates that these bacteria possess adaptive features suited to dynamic marine environments and exhibit multiple functions consistent with established probiotic mechanisms. However, most studies remain trait-specific, with limited in vivo validation and insufficient integration of functional assessments. Consequently, there is a need for more comprehensive and systematic evaluation of these microorganisms. Overall, seaweed-associated bacteria present a promising yet underutilized resource, and further research is essential to fully establish their role as next-generation probiotics in sustainable aquaculture systems.

Early fry performance of swamp eel (Monopterus albus) fed diets containing black soldier fly (Hermetia illucens) pupa meal

2026-04-13T14:01:58+00:00

The swamp eel (Monopterus albus) is an economically important freshwater species in Asia. However, its early life stage is constrained by high mortality and strong dependence on high-quality diets in intensive farming. This study evaluated the effects of dietary black soldier fly (Hermetia illucens) pupa meal (DBSFPM) on the growth performance, feed utilization, and survival of swamp eel fry during a 45-day rearing period. Five diets were formulated with graded DBSFPM levels (0, 5, 10, 15, and 20 g kg?¹), and 675 fry were reared in a completely randomized design with triplicate treatments. Growth performance improved significantly with increasing DBSFPM supplementation during the rearing period (P?0.05). At day 45, weight-related parameters exhibited a threshold response, with no significant difference between 0 and 5 g kg?¹ (P?0.05), whereas higher supplementation levels (10-20 g kg?¹) significantly enhanced growth (P?0.05). In contrast, length-related parameters responded at lower supplementation levels, with all supplemented groups outperforming the control (P?0.05). The feed conversion ratio was significantly improved at 15-20 g kg?¹ (P?0.05). Survival rates remained high (>93%) in all treatments. Although survival did not differ between supplemental groups and the control (P?0.05), the 20 g kg?¹ group showed a significantly higher survival rate than lower supplemental treatments (5-15 g kg?¹) (P?0.05). There was no significant difference in size uniformity among treatments (P?0.05). Overall, DBSFPM supplementation enhanced growth performance and feed efficiency, with optimal results observed at 15-20 g kg?¹. These findings support the use of DBSFPM as a functional dietary ingredient for improving early-stage aquaculture performance in swamp eels.

Genetic homogeneity across geographically isolated populations of Coptodon guineensis in Southern Morocco: Insights from the mitochondrial Cytochrome b gene

2026-04-22T16:48:25+00:00

This study examined the genetic differentiation of the Guinean tilapia, Coptodon guineensis, from two geographically isolated localities in southern Morocco: the arid-zone watercourse Oued Aabar (Smara Region) and the hypersaline Sebkha Imlili (Dakhla City), using the mitochondrial cytochrome b gene (1140 bp) as a molecular marker. Our results showed low genetic diversity and homogeneity between the two populations, indicating a lack of significant genetic differentiation and supporting the treatment of the two populations as a single conservation management unit. The neighbor-joining phylogenetic analysis, including other conspecific sequences and the haplotype network, confirmed this pattern. The observed genetic homogeneity may be attributed to the species’ euryhaline dispersal ability and tolerance to extreme environments, which can facilitate gene flow or reflect historical connectivity among fragmented habitats. Further research should involve more comprehensive sampling with broader spatial and ecological coverage to address the overall genetic structure of Coptodon guineensis across its full distribution range in Morocco.

Effect of human chorionic gonadotropin (hCG) and salinity on growth, reproductive indexes, and hormonal profiles of male short-finned eel (Anguilla bicolor)

2026-05-03T07:26:14+00:00

Anguilla bicolor is a catadromous teleost with high aquaculture potential; however, captive reproduction is constrained by males failing to mature spontaneously in captivity. This study evaluated the factorial effects of salinity manipulation (0 or 30 ppt) and with and without human chorionic gonadotropin (hCG) induction on growth performance, reproductive indices, and hormonal profiles of male A. bicolor. The experiment was conducted for 7 weeks. Findings reveal that survival was 100% across all treatment groups, while seawater at 30 ppt combined with hCG significantly enhanced the gonadosomatic index (GSI: 0.47%), hepatosomatic index (HSI: 1.54%), and plasma testosterone (66.91 ng/mL) compared with freshwater groups. Histological analysis confirmed more advanced spermatogenic progression in males reared in 30 ppt with hCG, including the presence of spermatocytes and early spermatozoa. Eye index, body coloration, and condition factor remained relatively similar across all groups (P>0.05), indicating that external silvering indicators were not initiated under the experimental conditions. These findings demonstrate a synergistic interaction between salinity and hCG in captive male A. bicolor, providing a scientific basis for broodstock conditioning in eel aquaculture.

Metabolic scaling in adult white-spotted pygmy filefish (Rudarius ercodes) from a wild population in Japan

2026-03-10T15:23:03+00:00

Metabolic rate is a critical determinant of energy flux in organisms, influencing both physiological and ecological performance. Despite its importance, intraspecific metabolic scaling in wild adult populations remains poorly understood. This study measured whole-animal metabolic rate in wild-caught adult white-spotted pygmy filefish (Rudarius ercodes) to assess metabolic scaling under natural conditions. The results indicated that whole-animal metabolic rate increased with body mass, following a pattern of negative allometry. This suggests that larger individuals have a lower metabolic demand relative to their body mass compared to smaller individuals. Consistent with this observation, mass-specific metabolic rate decreased with increasing body size. Although body mass explained some of the variation in metabolic rate, significant inter-individual heterogeneity was observed among individuals of similar size, highlighting substantial physiological diversity beyond the effects of body size. These findings provide population-level evidence for size-dependent metabolic structuring in a natural adult fish population and support a context-dependent interpretation of metabolic scaling exponents. By incorporating individual-level variation observed under ecologically realistic conditions, this study offers empirically grounded insights that refine metabolic scaling theory beyond idealized interspecific comparisons or captive-derived datasets.

Growth of milkfish (Chanos chanos) under stocking density gradients: Implications for efficiency and environmental stability in aquaculture

2026-04-02T03:58:42+00:00

Aquaculture is a rapidly growing food production sector, and milkfish (Chanos chanos) is a key species in tropical aquaculture due to its high economic value and broad environmental tolerance. However, identifying an optimal stocking density remains a critical challenge, as excessive fish biomass can disrupt the pond's ecological balance and reduce production efficiency. This study evaluated the effects of different stocking densities on milkfish growth performance, survival, feed efficiency, and environmental conditions in pond aquaculture systems. A 60-day experiment was conducted in a semi-intensive brackishwater pond using a completely randomized design with three stocking densities (10, 20, and 30 individuals m?²), each with three replicates. Growth, survival rate, and feed conversion ratio (FCR) were recorded, while water quality parameters—including temperature, pH, dissolved oxygen, salinity, transparency, and sediment redox potential—were monitored weekly. The results showed that stocking density significantly affected fish performance. The lowest density (10 individuals m?²) produced the highest growth (7.83 cm in length and 14.73 g in weight gain), survival (100%), and feed efficiency (FCR 0.68). Increasing density reduced growth and survival while increasing FCR. Higher densities were also associated with lower DO, salinity, transparency, and sediment redox potential, although temperature and pH remained relatively stable. Correlation and regression analyses indicated that DO and water transparency were the main environmental factors influencing milkfish growth, survival, and feed efficiency. These findings highlight the importance of maintaining moderate stocking densities to balance productivity and environmental stability in milkfish pond aquaculture.

Toxicity effect of the combined salinity and nitrite on biochemical indices, digestive enzymes, histopathology, and cytochrome P450 gene expression responses in fingerlings of stellate sturgeon, Acipenser stellatus Pallas, 1771

2025-05-01T02:54:42+00:00

Reactive nitrogen compounds, such as nitrite (NaNO₂), are highly toxic to aquatic animals. In some fish species, low levels of sodium chloride significantly reduce the toxicity of nitrite. Acipenser stellatus, one of the sturgeon species in the Caspian Sea, can tolerate the salinity of Caspian Sea water (12 g.L^-1), and chloride ions are predicted to compete with nitrite. Therefore, we conducted this research to determine whether salinity can decrease the effects of nitrite in stellate sturgeon fingerlings. This research was conducted in two stages: the first step involved determining the median lethal concentration (LC₅₀) of sodium nitrite at salinities of 0, 4, 8, and 12 g.L^-1over a period of 4 days. The LC50-96h values for sodium nitrite (NaNO₂) at salinities of 0 to 12 g.L^-1were found to be 75.11, 93.54, 241.60, and 353.31 mg.L^-1, respectively. In the second stage, 240 fish (19.1±1.7 cm and 15.23±2.17 g) were exposed to 50% of the LC50-96h of sodium nitrite (at salinities of 0 to 12 g.L^-1: 37.56, 46.77, 120.80, and 176.579 mg.L^-1, respectively) for 4 days, with 4 controls and 4 experimental groups in triplicate. In this stage, as salinity and nitrite concentration increased, the activity of superoxide dismutase, alanine aminotransferase, and aspartate aminotransferase in blood serum increased significantly (P?0.05). Conversely, the levels of catalase, alkaline phosphatase, and lactate dehydrogenase in blood serum, as well as amylase, alkaline protease, and lipase in the intestine, decreased significantly (P?0.05). High nitrite concentrations associated with salinity had damaged the fish's gills, kidneys, liver, and intestine. The highest expression of the cytochrome P450 gene was observed in the liver of A. stellatus exposed to a salinity of 12 g.L^-1and a nitrite concentration of 176.579 mg.L^-1 (P?0.05). The results indicated that the toxic effects of nitrite on blood indices, intestinal digestive enzymes, tissues, and gene expression did not decrease as salinity increased.

Evaluating insect-based feeds as sustainable alternatives to trash fish for spiny lobster (Panulirus sp.): Implications for growth efficiency and feeding behavior

2026-02-20T05:14:01+00:00

The rapid increase in global demand for spiny lobster (Panulirus sp.) has intensified pressure on wild stocks and highlighted the urgent need for sustainable aquaculture development. In Indonesia, lobster farming remains heavily dependent on trash fish as the primary feed source, despite associated challenges related to sustainability, biosecurity, and environmental degradation. This study evaluated the potential of insect-based feeds—Black soldier fly (Hermetia illucens) maggots and mealworms (Tenebrio molitor)—as sustainable alternatives to trash fish by examining their effects on growth performance and feeding behavior of spiny lobster under controlled conditions. A 30-day experiment was conducted using a Completely Randomized Design with three feed treatments (trash fish, BSF maggots, and mealworms), each replicated three times. Lobsters were fed daily at 5% of body weight, and growth parameters, feeding response, feed utilization, and water quality were monitored. The results showed that lobsters fed trash fish achieved significantly higher absolute weight gain (6.47 g) and length increment (0.39 cm) compared with those fed mealworms (1.67 g; 0.09 cm) and BSF maggots (0.93 g; 0.13 cm). Feeding behavior analysis revealed faster approach times and longer consumption durations in the trash fish treatment, indicating higher palatability and stronger chemosensory stimulation. Water quality remained within optimal ranges across all treatments, confirming that growth differences were primarily feed-driven. Although insect-based feeds demonstrated nutritional potential and supported positive growth and survival, their performance was inferior to that of trash fish. These findings suggest that successful replacement of trash fish requires improved formulation strategies, including attractant supplementation, enhanced digestibility, and adaptation periods, to optimize the effectiveness of insect-based feeds for sustainable lobster aquaculture.

Molecular identification and plant-extract antifungal susceptibility of skin and gill mycoses in common carp (Cyprinus carpio) from Wasit Ponds, Iraq

2026-06-29T05:06:31+00:00

Fungal and fungus-like infections are important external diseases of freshwater fish, especially when skin and gill integrity are compromised and water quality is poor. This study investigated fungal and fungus-like pathogens associated with skin and gill lesions in common carp (Cyprinus carpio) and evaluated the in vitro antifungal activity of the ethanolic extracts of thyme (Thymus vulgaris), clove (Syzygium aromaticum), pomegranate peels (Punica granatum), and garlic (Allium sativum). During spring (March-April), 200 common carp from eight ponds in Wasit Governorate, Iraq, were clinically inspected. From 120 infected fish, 60 skin and 60 gill samples were collected. Isolates were examined using culture, morphology, molecular, and histopathological methods. Ethanolic extracts of thyme, clove, pomegranate peel, and garlic were tested by agar-well diffusion and MIC assays. Fungal or fungus-like growth was recovered from 55/120 specimens (45.8%). Skin samples showed a significantly higher positivity rate than gill samples (63.3% vs. 28.3%). Six taxa were identified: Saprolegnia parasitica, Aspergillus flavus, A. niger, Fusarium solani species complex, Penicillium chrysogenum, and Candida albicans. Histopathological examinations revealed epithelial erosion, inflammatory infiltrates, lamellar changes, and PAS-positive fungal- or oomycete-like elements, with more frequent tissue involvement in skin lesions. Thyme and clove extracts produced the largest inhibition zones and the lowest MIC values, followed by pomegranate peel extract, whereas garlic extract showed moderate activity. Integrating conventional mycology, ITS-based identification, histopathology, and antifungal testing improved diagnostic confidence. Thyme and clove extracts showed strong in vitro activity, but their aquaculture applications require standardized in vivo safety and efficacy evaluations.

Community structure, spatial distribution, and species–station association of Asian horseshoe crabs from North Kalimantan, Indonesian Borneo

2026-06-08T04:33:35+00:00

Asian horseshoe crabs are ecologically important coastal arthropods, but local community-level information from North Kalimantan, Indonesian Borneo, remains limited. This study assessed species composition, relative abundance, diversity, dominance, evenness, species-station association, occupancy, and inter-station similarity of Asian horseshoe crabs recorded from four coastal stations in North Kalimantan. A total of 205 individuals were documented through fisher-assisted bycatch records from traditional kelong trap-net fisheries and identified as Carcinoscorpius rotundicauda, Tachypleus gigas, and T. tridentatus. Community structure was analyzed using relative abundance, Shannon-Wiener diversity, Simpson dominance, Pielou evenness, chi-square species-station association, adjusted standardized residuals, occupancy, and Bray-Curtis similarity. Carcinoscorpius rotundicauda was the most abundant species, followed by T. gigas and T. tridentatus. Clear spatial differentiation was observed among stations. Bening Island was strongly dominated by T. gigas, whereas Karis Island and Mangkudulis Island were dominated by C. rotundicauda. Tanalia Island showed the most balanced community and the strongest positive association with T. tridentatus. Bray-Curtis similarity identified Karis Island and Mangkudulis Island as the most similar stations, while Bening Island was the most distinct. These findings provide baseline ecological information on protected horseshoe crab species in North Kalimantan and highlight the importance of habitat-based monitoring that accounts for station-specific community signatures, as well as the limitations of bycatch-derived data.

Immunostimulatory effects of octopus ink extract on the hematological and immune responses of catfish (Clarias sp.) challenged with Aeromonas hydrophila

2026-02-25T06:20:36+00:00

Catfish (Clarias sp.) cultivation is often challenged by bacterial infections caused by Aeromonas hydrophila, which can lead to Motile Aeromonas Septicemia (MAS). The excessive use of antibiotics can lead to antibiotic resistance and residues, creating a need for natural immunostimulants. Octopus ink, a byproduct of the fisheries industry rich in bioactive compounds, shows potential as a sustainable alternative. This study evaluated the effectiveness of octopus ink extract in enhancing the immune response and survival of catfish against A. hydrophila. The experiment used a Completely Randomized Design with four treatments: control (no extract) and feed supplemented with octopus ink extract at 50, 100, and 150 ml/kg, each replicated three times. A total of 240 catfish (6-7 cm) were reared for 28 days, fed according to treatment, and challenged with A. hydrophila (10⁸ CFU/ml) by immersion. Measured parameters included erythrocyte and leukocyte counts, leukocyte differential, hematocrit, and survival rate (SR). The results showed that octopus ink extract significantly improved hematological parameters and survival. The 150 ml/kg dose yielded the best results: erythrocytes 2.4×10⁶ cells/mm³, leukocytes 5.78×10⁴ cells/mm³, lymphocytes 89%, hematocrit 33.8%, and SR 88.3%. Thus, octopus ink extract effectively enhances catfish immunity and survival against A. hydrophila, supporting its use in sustainable aquaculture.