Heavy metals contamination is a serious threat for the toxicity and bioaccumulation in food chain. Aquatic environment contamination has become a global concern because they have toxic effects on fishes. The concentration of heavy metals like arsenic (As), chromium (Cr), cadmium (Cd) and lead (Pb) in commercially fishes (Tenualosa ilisha, Gudusia chapra, Otolithoides pama, Setipinna phasa, Harpadon nehereus, Polynemus paradiseus, Sillaginopsis panijus and Pampus chinensis) collected from Karnaphuli River in Bangladesh were (fish muscles) assessed with health risk during summer and winter season. These heavy metals are toxic in nature and can come to human food chain through fish consumption. The mean concentration of As, Cr, Cd and Pb was found 1.59, 0.73, 0.41 and 1.13 mg/kg in summer and 1.81, 0.92, 0.52 and 1.45 mg/kg in winter, respectively. Cr and Pb concentration of all fish species were found to be higher than Food and Agriculture Organization (FAO)/(WHO) tolerable concentration assuming these metal pose risk to human. The hazard quotients value of heavy metals in Harpadon nehereus was found higher than one resulting non-carcinogenic risk for consumption of this fishes. Carcinogenic risk value for As and Pb were remaining 10⁻⁶ to 10⁻⁴ indicating continuously consumption of studied fish samples may cause cancer risk.

Seaweeds can play an essential role in controlling antibiotic resistance for bacterial diseases. Three extracts of two brown seaweeds Padina tetrastromatica and Sargassum ilicifolium were investigated as growth promoters and to provide immune protection against Vibrio parahaemolyticus. Extracts of the two seaweeds were administered at 2.5 and 5 g kg⁻¹ with food for 45 days to Penaeus monodon juveniles. The maximum weight gain (6.28 and 7.08 g), specific growth rate (3.39 and 3.32%), and survival rate (78.45 and 82.45%) of the juvenile tiger shrimp were obtained at a dose of 5 g kg⁻¹ with P. tetrastromatica extracted by methanol and ethanol, respectively; which was significantly higher than the other solvents and control group (p < .01). On the other hand, methanol extract of both seaweeds had maximal antibacterial activity against V. parahaemolyticus with zones of inhibition ranging between 20.25 ± 1.00 and 22.00 ± 0.50 mm. The minimal time required for haemolymph clotting was with methanol extracted of P. tetrastromatica at 5 g kg⁻¹, which was significantly lower than the other groups (p < .05). After challenging with V. parahaemolyticus, the total haemocyte count (THC) in P. monodon treated with methanol-extract of P. tetrastromatica diet at 5 g kg⁻¹ was higher (5.42 × 10⁵ cells mL⁻¹) but not significantly different than the other diets (p > .05). However, the administration of 5 g kg⁻¹ methanol and ethanol extract of P. tetrastromatica improved growth performance and the immune capacity of P. monodon by increasing their phenoloxidase activity, superoxide anion concentration, and resistance against V. parahaemolyticus.

In this study, elemental abundances of As, Cd, Cr, Co, Cu, Pb, and Zn in the 30 composite sediment samples from Jamuna River, Bangladesh were measured by atomic absorption spectrophotometer to assess their contamination level, toxicity, and ecological risks in both summer and winter season. In the summer season, mean concentrations of As, Cd, Cr, Co, Cu, Pb, and Zn in sediment samples were 2.82, 1.13, 25.30, 8.63, 22.01, 4.58, and 68.82 mg/kg, respectively. In the winter season, mean concentrations of As, Cd, Cr, Co, Cu, Pb, and Zn were 3.83, 1.48, 43.22, 13.86, 35.63, 8.48, and 100.27 mg/kg, respectively. The mean concentrations of all elements were found lower than the sediment quality guidelines values of probable effect level (PEL), effect range medium (ERM), and toxic effect thresholds (TET) in both seasons. There was a significant variation in elemental concentrations between wet and dry seasons and also between upstream and downstream sites (P < 0.05). Principal component analysis showed Zn, Cr, and Pb; As and Cu; and Cd and Co might have originated from the same geogenic source. The pollution evaluation indices showed consistent outcomes of almost no pollution for As, Cr, Co, Cu, Pb, and Zn, but moderately to strongly polluted for Cd in all seasons. The contamination level of elements follows the decreasing order of Cd > Zn > Cu > As > Co > Cr > Pb for both seasons. The elemental toxicity in the sediments follows the order of Cd > Cr > Zn > As > Cu > Pb, with a very high risk for Cd while a minimal risk for other elements. The ecological threats of the toxic elements were found moderate to very high. Therefore, the findings of our study concluded that the ecological condition of the Jamuna River posed a considerable risk for human health and living organisms.