Outwelling of nutrients into the Pasur River estuary from the Sundarbans mangrove creeks.

The Pasur River estuary (PRE), the largest estuary in the Sundarbans mangrove area, provides vital fishery resources and supports millions of livelihoods in the southwestern coastal region of Bangladesh. This study focused on the tidal and run-off effects on the outwelling of nutrients from the Sundarbans mangrove creeks to the PRE. Spatial and temporal variations of nutrient and chlorophyll-a concentrations were assessed by water sampling at 11 stations in the study area from January to December 2019. Dissolved inorganic nutrients and chlorophyll-a were analyzed by standard methods using a spectrophotometer. In the tidal mangrove creeks, dissolved inorganic nitrogen, phosphate, and silica concentrations were significantly higher (p < 0.05) during the spring tide than those during the neap tide, suggesting that these nutrients were flushed from the mangrove area by the inundation and tidal mixing of the spring tide. In general, chlorophyll-a (mean ± SD) concentrations in the PRE and the tidal mangrove creeks were 5.62 ± 1.30 µg/L and 9.03 ± 0.59 µg/L in the wet season, respectively. During the dry season, the chlorophyll-a decreased to 4.37 µg/L ± 0.68 and 4.94 ± 1.52 µg/L in the PRE and the tidal mangrove creek, respectively. The amount of nutrients outwelled from the mangrove creeks to the estuary was 1.53 ± 0.67 mg/L DIP, 0.001 ± 0.0004 mg/L DIN, and 1.38 ± 0.48 mg/L dissolved silica. DIP, silica, and chlorophyll-a concentrations were significantly higher (p < 0.05) during the spring tide compared to the neap tide, but salinity was not significantly (p > 0.05) different between the two tidal levels. This study showed that the mangrove creeks formed an important link in transporting nutrients from the mangrove forest to the estuary.

Application of fenitrothion on Heteropneustes fossilis causes alteration in morphology of erythrocytes via modifying hematological parameters.

In Bangladesh, the extensive use of fenitrothion on crops and in aquaculture ponds inevitably threatens a range of aquaculture species, including fish, owing to stress responses and physiological disturbances. The present study elucidated the potential toxic effects of fenitrothion on the blood biomarkers (haemato-biochemistry and structure of erythrocytes) of stinging catfish (Heteropneustes fossilis), a commercially significant aquaculture species. Fish were exposed to four sub-lethal concentrations (0%, 10%, 20%, and 40% of the 96-h LC50 value) of fenitrothion in triplicate and observed on the 7th, 14th, 21st, and 28th day following exposure. With increasing fenitrothion concentration, blood glucose and white blood cell levels increased significantly; in contrast, hemoglobin, red blood cell, and packed cell volume substantially decreased. However, the mean corpuscular volume and mean corpuscular hemoglobin did not change significantly during the exordial period (0-7 d); although, at a later stage, changes were observed. Frequencies of observed erythrocytic nuclear abnormalities, such as degeneration, bi-nucleus, micronucleus, notch nucleus, and nuclear bridge and erythrocytic cellular abnormalities, such as echinocytes, fusion, elongation, and tear drop morphology increased significantly in a concentration-dependent manner. Differences between the control individuals and those individuals under treatment were considered insignificant for twin cells on the 14th day of exposure. The study showed the pernicious impact of the effects of fenitrothion on H. fossilis through physiological alteration, which is likely to pose challenges for aquaculture production.

Screening of antibiotic residue in transported live fish and water collected from different fish markets in Mymensingh district of Bangladesh.

Objectives: The objective of this study was to evaluate the persistence of oxytetracycline (OTC) residue in common fish species (Catla, Rui, Mrigal, and Pangas) available in local fish markets and the corresponding transport water of the Mymensingh region. Materials and Methods: Live fish and corresponding transport water samples were analyzed by thin layer chromatography (TLC) and high-performance liquid chromatography for qualitative and quantitative detection of OTC residue, respectively. A total of 240 fish samples and 60 water samples were randomly collected from three local fish markets during the summer and winter seasons. Results: OTC residues were detected in 18 samples (13 fish and 5 water samples) in the summer and 8 samples (only fish samples) in the winter. The overall percentage of antibiotic residue positive in fish samples was 5.42%, and in water samples, it was 8.33%. In fish, OTC concentrations of TLC-positive samples ranged from 34.7 to 56.85 parts per billion (ppb) in Catla, 23.45-35.37 in Rui, 11.02-26.80 in Mrigal, and 10.80-77.55 in Pangas during summer. The concentrations were 18.5 ppb in Catla, 15-16.09 in Rui, 10-14.63 in Mrigal, and 21.02-40.11 in Pangas during the winter season. On the other hand, the range of OTC concentrations of TLC-positive samples for water was 12.9-59.18 ppb during summer and below the detection level during winter. The highest prevalence of antibiotic residues among fish samples was found in Pangas (16.67%). The highest percentage of samples (15% in the fish sample and 30% in the water sample) found to be positive were collected from Mechua Bazar. The comparison between the summer and winter seasons showed that the percentage of positive antibiotic residue in the summer season (10.38% for fish and 16.67% for water) is higher than that of the winter season (6.67% for fish samples only). This variation indicates that fish transporters use more antibiotics during the summer than in the winter season. The difference between the means of fish species and water samples was not statistically significant (p > 0.05). In addition, no samples exceeded the maximum residue limits (MRL) of OTC (100 ppb) in fish set by the European Commission. Conclusion: Although the concentrations of antibiotic residues in fish edible tissues are below MRL values, the presence of antibiotic residues in transported water may lead to the development of antimicrobial resistance bacteria that are detrimental to humans, animals, and aquatic animals.

Variation in toxin compositions of two harmful raphidophytes, Chattonella antiqua and Chattonella marina, at different salinities.

Toxin compositions of the two species of raphidophytes, Chattonella antiqua (Hada) Ono and Chattonella marina (Subrahmanyan) Hara et Chihara, were investigated at different salinities under laboratory conditions. C. antiqua contained toxin components CaTx-I, CaTx-II, CaTx-III, and CaTx-IV, which corresponded to brevetoxin components PbTx-1, PbTx-2, PbTx-3, and oxidized PbTx-2. Similarly, C. marina included CmTx-I, CmTx-II, CmTx-III, and CmTx-IV corresponding to PbTx-2, PbTx-9, PbTx-3, and oxidized PbTx-2. Toxin yields in both species varied markedly with a change in salinity concentration. In C. antiqua CaTx-I, CaTx-II, and CaTx-III peaked at 25 P.P.t. with yields of 0.99, 0.42, and 2.90 pg/cell, but the highest yield (2.35 pg/cell) of CaTx-IV was attained at 30 P.P.t. The yields of all CaTx components decreased sharply at salinities exceeding 30 P.P.t. On the other hand, C. marina yielded higher proportions of CmTx-I (0.55 pg/cell) and CmTx-III (2.50 pg/cell) at 25 P.P.t. However, CmTx-IV was present in its highest amount (1.65 pg/cell) at 30 P.P.t., as seen in C. antiqua. A small amount of CmTx-II was also detected at 20 P.P.t.-35 P.P.t. Both species showed the highest ichthyotoxicities at 25 P.P.t., at which the maximum cell division rate was obtained.