Walking Catfish Research Articles

Effect of cryoprotectant and concentration on the sperm quality of walking catfish, Clarias batrachus, post-cryopreservation

BACKGROUND: Walking catfish, Clarias batrachus is one of the native and most popular freshwater catfish species in Indonesia. However, cultivation faces challenges, particularly due to the scarcity of larvae resulting from underdeveloped breeding technologies. Cryopreservation is a method of storing sperm to maintain viability for a long period and support the breeding technology of the fish. Cryoprotectant, in this context, plays an important role in determining the success of sperm cryopreservation. OBJECTIVE: To determine the best type and concentration of cryoprotectant for cryopreservation of walking catfish sperm. MATERIALS AND METHODS: A total of five different types of cryoprotectants, namely DMSO, glycerol, ethyl glycol, ethanol, and methanol, were tested at four concentration levels namely 0%, 5%, 10%, 15%, and 20%, each with four replications. RESULTS: The type and concentration of cryoprotectant had a significant effect on sperm motility and viability (P<0.05). The best outcomes were obtained with 5% DMSO and ethyl glycol, 10% glycerol and methanol, as well as 15% ethanol. CONCLUSION: The highest motility and viability values were obtained with 5% DMSO, resulting in its recommendation for cryopreservation of walking catfish sperm.

An approach to optimizing dietary protein to growth and body composition in walking catfish, Clarias batrachus (Linneaeus, 1758).

Clarias batrachus is a commercially important food fish. In the present study, effect of varying dietary protein levels was evaluated on the survival, growth parameters and proximate composition of C. batrachus. Diets comprising 25%, 30%, 35%, 40%, 45%, and 50% crude protein (CP) were supplied to fish in T1, T2, T3, T4, T5, and T6, respectively, at the rate of 5% of fish body weight for the entire 90 days, twice daily. Size of each stocked C. batrachus was recorded after 15 days. Results revealed 100% survival rate of C. batrachus in all treatments. Significantly highest (P<0.001) mean value of weight gain (g/fish), percent weight gain, daily growth rate, specific growth rate and protein efficiency ratio (PER) in C. batrachus were recorded, reared in T4 by feeding 40% CP in diet. The best FCR value (1.90±0.02) for C. batrachus was obtained in T4 by feeding 40%CP in diet. Mean value of water, ash, fat and protein contents (wet mass) were ranged 74.10-79.23%, 3.12-4.68%, 3.90-4.43% and 13.09-16.79% for C. batrachus in the studied treatment groups. Water content (%) was found significantly (P<0.05) higher in the body of C. batrachus for T1, T2, T3 and T6 than for T4 and T5. Ash was found significantly (P<0.05) higher in the fish reared in T4 and T5. Fat content in the wet body mass of C. batrachus was found significantly higher in T4 and T1. While, significant higher (P<0.05) values of mean protein content was noted in C. batrachus reared in T4 and T5. Body composition of C. batrachus was also categorically affected by body size, however, condition factor showed non-significant correlation in most of the relationships in the present study. Overall, results indicated that feeding appropriate diet (containing 40% CP) to the fish resulted good growth performance, lower FCR and higher protein content in the fish. Present study provides valuable knowledge of optimal dietary protein level in C. batrachus which will help in commercial success of aquaculture.

Chronic toxicity of sediment-bound triclosan on freshwater walking catfish Clarias magur: Organ level accumulation and selected enzyme biomarker responses

Triclosan (TCS) is a biocide widely used in personal care and medicinal products. TCS persists in sediments and has been detected worldwide, making sediments a vital route of TCS exposure to aquatic organisms. This experiment explored the bioaccumulation and toxicological effects of TCS-contaminated sediment. The study revealed that the half-life of TCS in the sediment-water system was 21.52 days. Exposure of Clarias magur juveniles to 0.4 and 0.8 mg kg−1 TCS-spiked sediment resulted in high Biota-Sediment Accumulation Factor (BSAF) with the highest bioaccumulation in the liver (29.62–73.61 mg kg−1), followed by gill (9.22–17.57 mg kg−1), kidney (5.04–9.76 mg kg−1), muscle (2.63–4.87 mg kg−1) and brain (1.53–3.20 mg kg−1). Furthermore, a concentration-dependent increase in oxidative stress biomarkers such as superoxide dismutase (SOD), catalase (CAT) and glutathione-S-transferase (GST) was documented during 45 days of exposure in gill, liver, kidney, muscle, and brain tissues of exposed fish. A similar increasing trend was also recorded for liver transaminase enzymes such as glutamic oxaloacetic transaminase (GOT) and glutamic pyruvic transaminase (GPT) during the experimental period compared to control. Serum biochemical analysis revealed a significant time and concentration-dependent increase in serum glucose, serum GOT, and serum GPT, while serum total protein and albumin decreased significantly during exposure. These findings demonstrate high bioaccumulative and toxic nature of TCS in fish, promoting multiple physiological and biochemical dysfunctions through sediment exposure. The study underscores the urgent need for strengthened regulations and robust monitoring of triclosan across various environmental matrices, including sediment, to mitigate the detrimental impacts of TCS effectively.

Molecular characterization of pathogenic Aeromonas jandaei bacteria isolated from cultured walking catfish (Clarias sp.)

Abstract. Mulia DS, Dwi NR, Suwarsito, Muslimin B. 2024. Molecular characterization of pathogenic Aeromonas jandaei bacteria isolated from cultured walking catfish (Clarias sp.). Biodiversitas 25: 1185-1193. Aeromonas spp. is pathogenic bacteria capable of causing fish disease, including walking catfish (Clarias sp.). In bacteria, virulence genes play a significant role in determining pathogenicity, while resistance genes influence resistivity. Therefore, this study aimed to determine molecular characterization of pathogenic Aeromonas jandaei bacteria isolated from walking catfish. The purposive sampling method was used to obtain diseased walking catfish from aquaculture ponds in Banyumas District, Central Java Province, Indonesia. The identification of bacteria was molecularly carried out based on 16S rDNA, followed by the detection of virulence genes on aer/haem, alt, ast, flaA, lafA, and fstA, as well as resistance genes on tet-A, strA-strB, and qnrA. The results of molecular analysis showed that three isolates from Singasari, namely BmSL-02, BmSL-04, and BmSL-07, were closely related to A. jandaei strain CDC0787-80 with a similarity rate and query coverage of 99.86% and 99%, respectively. Meanwhile, isolates from Cikawung, including BmCL-02, BmCL-05, and BmCL-07 were closely related to A. jandaei strain ATCC 49568. A total of six A. jandaei isolates had aer/haem virulence genes while alt, ast, and fstA were not found. BmSL-04 and BmCL-07 isolates had flaA gene, while four isolates including BmSL-02, BmSL-04, BmSL-07, and BmCL-07 had lafA gene. Additionally, BmCL-05 had tetA resistance gene, while the strA-strB and qnrA genes were not detected in all isolates. A. jandaei isolates were resistant to bacitracin, tetracycline, and gentamycin, but BmSL-04, BmSL-07, BmCL-02, and BmCL-05 were sensitive to chloramphenicol. This study provided valuable information on molecular characteristics of A. jandaei, serving as guidance in effective control and monitoring of isolates from Indonesia, specifically Banyumas, Central Java.

In silico study of myomere muscle proteins extracted from Indian walking catfish reveal Angiotensin Converting Enzyme (ACE) inhibitory activity – A potential bioactive peptide

Clarias magur (Hamilton, 1822), is an endemic Asian freshwater catfish known as the walking catfish is one of the most popular fish in India and Asian subcontinents due to its nutritional value and better taste. The fish has traditionally been used for medicinal purposes. The present study was undertaken to study the proteome profile through Liquid Chromatography based Mass spectroscopy (LC/MS) to elucidate the protein profile the catfish. In the present study muscle protein extract was prepared from C. magur, digested by trypsin for LC/MS analysis for peptide retrieval. Out of a total of 468 peptides retrieved from LCMS data, 23 peptides showed bioactivity for Angiotensin Converting Enzyme (ACE) inhibition using bioinformatic approaches. ACE enzyme is expressed on the surface of lung cells and acts as a receptor for SARS-CoV-2 spike protein to gain entry into host cells. ACE inhibitors can have implication in entry of virus into host cells and reduction of hypertension by effectively reducing vasoconstriction. Traditionally synthetic compounds used for ACE inhibition pose side effects. Fish derived ACE inhibitory bioactive peptides can prove to be a natural, less toxic therapeutic sources.

Overcoming taxonomic challenges in DNA barcoding for improvement of identification and preservation of clariid catfish species.

DNA barcoding without assessing reliability and validity causes taxonomic errors of species identification, which is responsible for disruptions of their conservation and aquaculture industry. Although DNA barcoding facilitates molecular identification and phylogenetic analysis of species, its availability in clariid catfish lineage remains uncertain. In this study, DNA barcoding was developed and validated for clariid catfish. 2,970 barcode sequences from mitochondrial cytochrome c oxidase I (COI) and cytochrome b (Cytb) genes and D-loop sequences were analyzed for 37 clariid catfish species. The highest intraspecific nearest neighbor distances were 85.47%, 98.03%, and 89.10% for COI, Cytb, and D-loop sequences, respectively. This suggests that the Cytb gene is the most appropriate for identifying clariid catfish and can serve as a standard region for DNA barcoding. A positive barcoding gap between interspecific and intraspecific sequence divergence was observed in the Cytb dataset but not in the COI and D-loop datasets. Intraspecific variation was typically less than 4.4%, whereas interspecific variation was generally more than 66.9%. However, a species complex was detected in walking catfish and significant intraspecific sequence divergence was observed in North African catfish. These findings suggest the need to focus on developing a DNA barcoding system for classifying clariid catfish properly and to validate its efficacy for a wider range of clariid catfish. With an enriched database of multiple sequences from a target species and its genus, species identification can be more accurate and biodiversity assessment of the species can be facilitated.

Effects of dietary Cu nanoparticles on growth performance, physiology and bioaccumulation in Asian walking catfish (Clarias batrachus)

The present investigation was conducted to determine the optimal dietary Cu-NPs requirement of Asian walking catfish, Clarias batrachus (7.46 ± 0.15 cm; 5.28 ± 0.10 g) by feeding with diets supplemented with different concentrations of Cu-NPs (10, 20, 30, 40 and 50 mg/kg) and control group. Each experimental diet was hand-fed to triplicate groups of fish for 60 days in glass aquarium. Results showed that fish group fed with 20 mg/kg Cu-NPs in feed exhibited highest (P &lt; 0.05) growth performance and feed utilization compared to the control group. However, increased level of Cu-NPs from 30 to 50 mg/kg in feed significantly reduced the growth performance. Significantly higher protein and lipid were also recorded at 20 mg/kg Cu-NPs supplemented group. Haematological parameters, serum lipid and enzymatic profile were found to influence significantly with the addition of Cu-NPs in feed compared to the control group. Based on the polynomial regression analysis between FW, WG and SGRW against dietary Cu-NPs levels, the optimal dietary supplementation of Cu-NPs for C. batrachus were estimated to be ranged between 19.98 to 20.05 mg/kg per diet, respectively. Bioaccumulation of Cu was the highest in liver compared to muscle and serum, whereas the highest Cu accumulation was observed at 50 mg/kg Cu-NPs supplemented group. The findings of the present study will be helpful for formulating nutrient rich low cost catfish feed.

Probiotics potential of lactic acid bacteria isolated from Slender Walking Catfish (Clarias nieuhofii)

Abstract. Lingga R, Adibrata S, Roanisca O, Sipriyadi, Wibowo RH, Arsyadi. 2023. Probiotics potential of lactic acid bacteria isolated from Slender Walking Catfish (Clarias nieuhofii). Biodiversitas 24: 4572-4580. Probiotics are living microorganisms or bioactive agents that positively impact animal digestion. They have successfully isolated from various sources. Recently, we isolated and characterized lactic acid bacteria (LAB) from slender walking fish (Clarias nieuhofii Valenciennes, 1840). The fish sample was obtained from Batu Rusa and Paya Benua Rivers in Bangka Island, Indonesia. LAB was isolated from the fish intestine using the pour plate method. The isolated LAB was then characterized based on their phenotypic traits, biochemical properties, and the 16S rRNA gene identification. The chosen isolates were tested to determine their ability to produce lactic acid, hemolytic and antibacterial activity, and antibiotic resistance. All isolates have the characteristic of rod-shaped and short rod-shaped cells with Gram-positive properties. Isolate KP1 showed the number of populations (2.89 x 107 CFU/mL) and lactic acid production with a concentration of 1.85%. All isolates exhibited no hemolysis activity and displayed sensitivity to antibiotics. The twelve lactic acid bacteria formed clear zones against Staphylococcus aureus and Escherichia coli. The results of the 16S rRNA gene identification indicated that isolates KB4, KB7, KB8, and KP1 belong to Lactobacillus vaginalis, Lactobacillus fermentum, Limosilactobacillus fermentum, and Levilactobacillus brevis, respectively. Lactic acid bacteria isolated from slender walking fish exhibited potential probiotic traits.

Investigations of hemato-biochemical and histopathological parameters, and growth performance of walking catfish (Clarias batrachus) exposed to PET and LDPE microplastics

Fish inhabiting various trophic levels are affected differently as the presence of microplastic (MP) in the water column and their ingestion by fish varies. Walking catfish (Clarias batrachus) inhabits the bottom of the water bodies. To understand the effects of MP, we exposed C. batrachus to two types of MP – polyethylene terephthalate (PET) and low-density polyethylene (LDPE) for 60 days. After exposure, hematological indices, mainly red blood cells and hemoglobin levels decreased, and white blood cells increased significantly compared to the control group (p < 0.05). A significant increase in the levels of blood urea and glucose was observed, and serum glutamic pyruvate transaminase and serum glutamyl oxaloacetic transaminase activity remained elevated (p < 0.05). Histopathological examination of the liver, kidney, intestine, and gills showed morphological alterations. Moreover, MP exposure caused growth retardation (p < 0.05) in C. batrachus. Widespread pollution of water bodies by MP may impose serious ecological risks to bottom-feeding fish in Bangladesh.

Exploration of The Natural Extender for Dilution of Walking Catfish Clarias batrachus Sperm in Refrigerated Storage

Walking catfish Clarias batrachus is a freshwaterr fish that has high economic value. Currently, the culture of this local catfish has been initiated in Indonesia, but the breeding technology has not been well developed. Therefore, this study aims to explore the type of natural extender for sperm preservation of local catfish C. batrachus so that it can support the development of its breeding technology, especially in remote areas. The research was conducted at the Hatchery Laboratory of the Faculty of Marine and Fisheries, Universitas Syiahh Kuala, Banda Aceh, Indonesia.. Four types of natural extenders were tested in this study, namely young coconut water, nira water, sugarcane water, and old coconut water. Completely randomized design method consisting of five treatments and three replications were used in this study. Sperm were diluted with each tested extender with a sperm dilution rate of 1:20 (sperm: extender, v/v), then stored at 4 °C. The motility and viability were monitored every 24 h interval for 6 days. The results showed that the natural extender significantly affected the motility, viability, and sperm fertility of walking catfish (P<0.05). Young coconut water produced higher motility and viability on all observation days. The higher sperm motility, viability, and egg fertility on the last day of the experiment were also found in sperm diluted in young coconut water, with values of 45.83%, 43.83%, and 41.50%, respectively. These values were significantly different from other types of extenders. Therefore, it is concluded that young coconut water is the most suitable natural extender for sperm preservation of local catfish at 4 °C.

Observation of morphometric characteristics in fish Clarias batrachus (Linnaeus, 1758) from Lucknow, Uttar Pradesh

The walking catfish (Clarias batrachus Linnaeus, 1758) is an omnivorous bottom feeder, incorporating various food sources in its diet, such as insects, insect larvae, crustaceans, and vegetable matter. It is primarily nocturnal. However, it can adapt to pond conditions and readily switch to a more carnivorous diet. During observation, the main focus is to examine the morphometric relationship of Clarias batrachus for that total ten morphometric characters were measured for each specimen. Notably, a linear relationship was observed between the total length and other morphometric characters. The results highlight a strong correlation between most morphometric parameters and the total length of the catfish. However, it was found that the anal length does not show a significant correlation with the total length.

Therapeutic impact of biopesticide neem oil on health status of walking catfish Clarias batrachus for replacing synthetic organophosphorus pesticides

Pesticides are widely used in agricultural purposes and indiscriminate use of pesticides resulted in unintentional harming of the environment. Lack of consciousness and education coupled with indifferent attitude also contributed to indiscriminate use of pesticides. Enormous amount of these toxic pesticides and other chemicals reaches in the aquatic environment by the runoff and other sources and polluted the water, air and soil for any living organisms. One of the fastest growing food producing sectors is aquaculture, supplying approximately 40% of the world’s fish food. Pesticides may be used in aquatic ecosystem to control the fish parasites, diseases, and other pests that have also adversely affected the aquatic ecosystem. Nuvan is an organophosphorus pesticide is widely used due to low persistence in environment but also affects the non-targeted organisms including fish. Synthetic chemicals generate environmental problems; researchers have been leaning towards pest control with natural or plant based substances. Protection of water quality is possible when rationalize the use of natural pesticides and promote biopesticides. Neem oil is a natural or mixtures of chemicals obtained from neem plant (Azadirachta indica) which has many significant benefits to overcome from the chemicals or synthetic pesticides. By making the health beneficial uses of neem oil accessible to the farmers in the society, the use of chemicals in agriculture can be reduced. The aim of the current study is to observe the impacts of nuvan and neem oil on the survival and health status of fishes which also affected the other animals by the food chain. Changes in blood parameters of fish are related to the response of the whole animal, which affect on survival, reproduction and growth of fish. Some alterations in cholesterol and triglycerides in serum of treated fish Clarias batrachus with 1/20 and 1/10 LC50 concentrations of nuvan and neem oil separately compared with non-treated one after 7, 15, 30 and 60 days of exposure were recorded and discussed. Also, this assessment may be essential for encourage suitable methods of application in aquatic organism production facilities to be fully explored in future.

Isolation of a Novel Mosquitocidal Bacterium &lt;i&gt;Bacillus cereus&lt;/i&gt; VCRC-641 from Fresh Water Fish &lt;i&gt;Clarias batrachus&lt;/i&gt;

In this study, search for new mosquitocidal bacterium was attempted from the gut content of the fresh water fish Clarias batrachus (walking cat fish) which resulted in the isolation of a highly potential mosquitocidal bacterium. The isolate was identified as Bacillus cereus VCRC 641 by Bacillus species specific molecular markers ilvD, pur and pycA gene sequence analysis. Laboratory mosquito larval toxicity assay (bioassay) against mosquito larvae revealed that this new isolate was highly potent against Culex quinquefasciatus followed by Aedes aegypti and Anopheles stephensi. The lethal concentration values at LC50 for these three mosquito species were 0.001, 0.004 and 0.007mg/ L respectively. Therefore, in the present study, this is the first report that a highly potential mosquitocidal bacteria of B. cereus VCRC 641 was isolated from the gut content of Clarias batrachus and suggested that it can be used for mosquito vector control program.

Mitochondrial DNA Corroborates the Genetic Variability of Clarias Catfishes (Siluriformes, Clariidae) from Cameroon.

The airbreathing walking catfish (Clariidae: Clarias) comprises 32 species that are endemic to African freshwater systems. The species-level identification of this group is challenging due to their complex taxonomy and polymorphism. Prior to this study, the biological and ecological studies were restricted to a single species, Clarias gariepinus, resulting in a biased view of their genetic diversity in African waters. Here, we generated the 63-mitochondrial Cytochrome c oxidase subunit 1 (COI) gene sequences of Clarias camerunensis and Clarias gariepinus from the Nyong River in Cameroon. Both C. camerunensis and C. gariepinus species maintained adequate intra-species (2.7% and 2.31%) and inter-species (6.9% to 16.8% and 11.4% to 15.1%) genetic distances with other Clarias congeners distributed in African and Asian/Southeast Asian drainages. The mtCOI sequences revealed 13 and 20 unique haplotypes of C. camerunensis and C. gariepinus, respectively. The TCS networks revealed distinct haplotypes of C. camerunensis and shared haplotypes of C. gariepinus in African waters. The multiple species delimitation approaches (ABGD and PTP) revealed a total of 20 and 22 molecular operational taxonomic units (MOTUs), respectively. Among the two Clarias species examined, we found more than one MOTU in C. camerunensis, which is consistent with population structure and tree topology results. The phylogeny generated through Bayesian Inference analysis clearly separated C. camerunensis and C. gariepinus from other Clarias species with high posterior probability supports. The present study elucidates the occurrence of possible cryptic diversity and allopatric speciation of C. camerunensis in African drainages. Further, the present study confirms the reduced genetic diversity of C. gariepinus across its native and introduced range, which might have been induced by unscientific aquaculture practices. The study recommends a similar approach to the same and related species from different river basins to illuminate the true diversity of Clarias species in Africa and other countries.

Identification and Characterization of Mosquitocidal Toxins From &lt;i&gt;Bacillus cereus&lt;/i&gt; VCRC-641

Bacillus cereus VCRC 641 was found to be an alternate larvicidal bacterial agent which was newly isolated from fresh water fish, Clarias batrachus (walking cat fish). The protein responsible for mosquito toxic effect was separated and purified by Sephacryl S-200 column chromatography and NATIVE PAGE. It was observed that a unique protein with molecular weight of 70kDa was the responsible factor for mosquito killing effect. Further analysis of the protein by liquid chromatography-mass spectrometry (LC-MS) it was identified as “Uncharacterized Protein”. The length of the uncharacterized protein was around 158bp. The uncharacterized protein was expected to have a molecular mass of 70 kDa, 51 amino acids, confidence score of 78.45 and mass of 206772.57. Therefore, in the present study we report for the first time that uncharacterized protein (70kDa) was the responsible factor for the mosquito killing effect.

Prospecting of Anti-Cancer Peptides (ACPs) from proteome of muscle tissue from Indian walking catfish, Clarias magur (Hamilton 1822) by Mass spectrometry and in silico approaches

The freshwater walking catfish Clarias magur (Hamilton, 1822) is one of the most popular aquaculture fishes in Indian and the Asian subcontinent because of its nutritional value and great taste. Muscle proteome of C. magur was studied. Muscle tissue is of significance in fishes due to presence of high protein content and poly unsaturated fatty acids (PUFA) proved to have medicinal and therapeutic value. Fishes procured were acclimatised and muscle tissue was studied. Briefly, muscle protein extract prepared from C. magur, by homogenizing muscle tissue in 50 mMTris buffer with protease inhibitor for downstream processing, digested with trypsin in solution, reduced with dithiothreitol (DTT) and alkylated with iodoacetamide (IAA) for LC/MS analysis. The peptides were separated on Waters Synapt G2 Q-TOF equipped with Electro-Spray ionisation (ESI) for DATA independent acquisition for MS analysis. The raw data was processed by Protein Lynx Global Server (PLGS) software. Peptide tolerance limit was set at 50 ppm with minimum fragment match of 2 peptides for proteins. In silico approach was used to retrieve ACPs from muscle proteome derived from LC/MS by BIOPEP, Anti-CP and iDACP online servers. Out of a total of 468 peptides, 60 peptides showed anti-cancer peptide (ACPs) activity. Out of 19 non-allergenic peptides as analysed by AlerPred software, one peptide was toxic as revealed by ToxinPred software. The peptides were ranked with 0.9884 being highest and 0.0341 being the lowest by Peptide Ranker tool. This study reports C. magur derived anti-cancer bioactive peptides as a natural, less toxic anti-cancer therapeutic source exhibiting anti-cancer activity by activating apoptosis in mitochondria slaying cancer cells.

The invasion and impacts of the African sharptooth catfish (Clariidae: Clarias gariepinus) in the Malay Peninsula

Abstract The African sharptooth catfish, Clarias gariepinus, is a globally invasive species with known severe impacts, including native species declines through ecological (e.g., competition, predation) and genetic interactions (e.g., hybridisation, introgression). The species was introduced to the Malay Peninsula in the late 1980s, and has since become widely established. In this study, we used structural equation models (SEMs) (habitat analyses) and stable isotope analyses (dietary analyses) to elucidate the determinants of C. gariepinus invasion success in streams of the Malay Peninsula and investigate potential impacts on native counterparts. Our SEMs indicate that C. gariepinus invasions were mediated by greater anthropogenic influences as well as environmental conditions associated with open streams (large channels, higher temperatures and lower canopy cover). Additionally, on the one hand, we find that invasions by C. gariepinus have led to substantial negative impacts on the native Asian walking catfish, Clarias batrachus, with the latter being displaced, or in some areas extirpated, from its characteristic open‐stream habitats. On the other hand, C. gariepinus invasions did not appear to impact the native forest specialist, Clarias leiacanthus. Stable isotope analyses showed that all three Clarias species were opportunistic, generalist feeders. There was substantial overlap in the diets of C. gariepinus and C. batrachus. However, C. leiacanthus generally assimilated comparatively greater volumes of aquatic macroinvertebrate prey, therefore reducing dietary overlap with introduced C. gariepinus. Our findings indicate that propagule pressure and exaptations probably have played a major role in facilitating C. gariepinus invasions in the Malay Peninsula. Furthermore, our results suggest that habitat competition may have acted synergistically with trophic competition to drive C. gariepinus impacts on native species, although this was mitigated by differentiation in ecological preferences. Our results help shed light on the general characteristics of invasive species, the mechanisms facilitating their proliferation, and the potential outcomes of biological invasions. These highlight the urgent need to manage the introduction, spread and impacts of invasive C. gariepinus in the Malay Peninsula and elsewhere in its invaded range.

Antioxidant enzyme activity and pathophysiological responses in the freshwater walking catfish, Clarias batrachus Linn under sub-chronic and chronic exposures to the neonicotinoid, Thiamethoxam®.

The hydrophilic nature and resultant persistence of neonicotinoids in aquatic systems increase the exposure duration for non-target organisms. The sublethal toxicity of the neonicotinoid Thiamethoxam® spanning sub-chronic and chronic durations was investigated in Clarias batrachus, a non-target freshwater fish species. 96 h LC50 value of Thiamethoxam® on Clarias batrachus was 138.60 mg L-1. Pre-determined exposure concentrations of Thiamethoxam® (6.93 and 13.86 mg L-1) were used and effects were assessed at days 15, 30, and 45 exposure intervals. Biomarker effects were evaluated using antioxidant enzyme responses (CAT, SOD) neurotransmission (acetylcholinesterase activity), haematological and serum biochemistry changes (including haemoglobin content, total erythrocyte count, and serum albumin total leukocyte count, total serum protein, serum globulin, triglyceride, cholesterol, high-density lipoprotein, very low-density lipoprotein, low-density lipoprotein, phospholipid, and total serum glucose), histopathological alterations (gill and liver). Thiamethoxam®-exposed fish showed a marked reduction in haemoglobin content, total erythrocyte count, and serum albumin levels compared to control fish. Similarly, gill and liver antioxidant enzyme activity (CAT, SOD) and neurotransmission (acetylcholinesterase) also showed altered responses between sub-chronic exposure on day-15 and chronic responses on day-45. Histopathological observations in gill tissue revealed alterations ranging from vacuolation, hypertrophy, disruption of primary lamellar architecture, haemorrhage, the fusion of secondary lamella, and sloughing of outer epithelia. For liver tissue of exposed fish histopathological observations included increased sinusoidal spaces (ISS), necrosis of hepatocytes (NOH), nuclear degeneration (ND), disruption of architecture (DOA), macrophage infiltration of the central vein, vacuolation (V), hypertrophied hepatocytes, and haemorrhages. The gradients of toxic responses across exposure concentrations and depictions of impaired fish health with increasing thiamethoxam® exposure duration portend lowered physiological capacity for survival in the wild.

Dichlorodiphenyltrichloroethane (DDT) residues status in fishes and prawns of Chittagong chemical complex area, Bangladesh

Fourteen various fish samples i.e., rui Labeo rohita, catla Gibelion catla, striped dwarf catfish Mystus vittatus, stinging catfish Heteropneustes fossilis, walking catfish Clarias batrachus, Ganges river sprat Corica soborna, mola carplet Amblypharyngodon mola, common carp Cyprinus carpio, Nile tilapia Oreochromis niloticus, climbing perch Anabas testudineus, spotted snakehead Channa punctatus, striped snakehead Channa striata, bronze featherback Notopterus notopterus, wallago catfish Wallago attu and mixed juvenile prawns were collected from a pond of closed down DDT (Dichlorodiphenyltrichloroethane) factory area of Chittagong Chemical Complex (CCC) of Bangladesh to assess the concentrations of DDT and its metabolites (4,4'-DDD and 4,4'-DDE). The fish flesh and shell-free prawn muscle samples were extracted by QuEChERS method and these were cleaned up using H2SO4. The cleaned sample extracts were analyzed using a Gas Chromatograph coupled with Electron Capture Detector (GC-ECD). The cultured L. rohita was used as a control which was found to contain no detectable amount of DDTs. Recovery experiments with control samples were spiked with certified DDTs standard at three different concentrations (0.01 mg kg-1, 0.02 mg kg-1 and 0.05 mg kg-1) levels. The percent recoveries were 72-114 % (0.05 mg kg-1), 70-101 % (0.01 mg kg-1) and 87-105 % (0.02 mg kg-1). LOD and LOQ of the standards were found to be 0.0625 μg kg-1 and 0.2063 μg kg-1, respectively and R2 of 4'-DDE, 4,4'-DDD, 2,4'-DDT and 4,4'-DDT were found to be 0.999, 0.999, 0.999 and 0.998, respectively. The concentrations of total DDTs residue in fish and prawn samples ranged between 0.66 ng g-1 in W. attu to 8.90 ng g-1 in H. fossilis. The ratios of 4,4'-DDT/ΣDDTs in the studied fish samples indicated the historical use of DDTs in the adjacent region around the DDT factory of the CCC area. The concentrations of total DDTs in all the samples were within the permissible Maximum Residue Level (MRL) recommended by FAO-WHO. To assess human health risks, Health risk Indexes (HI) of fish and prawn samples were calculated. HIs&lt;1 in all fish and prawn samples indicated that the fish samples are safe to consume but the daily consumption of the fish together with other contaminated food may cause human health hazards. Bangladesh J. Zool. 49 (3): 381-391, 2021

Effects of Different Cooking Methods on the Vitamin D Content of Commonly Consumed Fish in Thailand.

This study determined vitamin D content in commonly consumed fish in Thailand and the effects of different cooking methods on vitamin D retention. Five species of freshwater fish and four species of marine fish were purchased from three representative markets. All of the fish were individually prepared according to common household practices. Vitamin D2 and D3 were determined using the HPLC standard method (AOAC method 995.05). The results indicated that vitamin D3 was the only detectable form of vitamin D in the fish. Vitamin D content of raw freshwater fish ranged from 2.42 to 48.5 µg per 100 g edible portion (EP), which was higher than that of raw marine fish (2.94 to 4.69 µg per 100 g EP). Common silver barb, Red Nile tilapia, and Nile tilapia (freshwater fish living in the limnetic zone) contained high levels of vitamin D (48.5 ± 26.5, 31.0 ± 7.7, and 19.8 ± 3.5 µg per 100 g EP, respectively). Boiled fish (except for Common silver barb), fried fish (except for Striped snakehead, Walking catfish, and Common silver barb), and grilled fish (except for Common silver barb, Giant sea perch, and Short-bodied mackerel) retained high levels of vitamin D, which were not significantly different (p > 0.05) from raw fish. Common silver barb, Red Nile tilapia, and Nile tilapia—cooked by boiling, frying, and grilling—are recommended for consumption as excellent sources of vitamin D.