Kusum Parajuli

Golden mahseer (Tor putitora) is an economically important but endangered fish species in many countries. Increasing pesticide application can possess a threat to this species but their sensitivity to pesticides, typically chlorpyrifos and dichlorvos, is unknown. We determined 96 h-LC50 of chlorpyrifos and dichlorvos to be 0.753 mg/L and 12.964 mg/L, respectively, indicating higher toxicity of chlorpyrifos than dichlorvos. Despite the same mode of action, their joint effect was antagonistic, with an additive index value of - 0.58 at 96 h-LC50. Moreover, to get insights in the temporal sub-lethal effects, fish were exposed to 10% and 50% of the 96 h-LC50 values of the respective pesticides. Aerobic metabolism, opercular movements, and feeding behavior were examined for sub-lethal end-points following 24 h, 48 h, 72 h and 96 h exposure. Both chlorpyrifos and dichlorvos in single exposures induced a significant drop in oxygen consumption rate; while it was significantly elevated in the mixed pesticide exposure. Accelerated opercular movements were observed in all pesticide treatment groups but were more persistent in chlorpyrifos treatments. Reduced feeding attempts were more pronounced in chlorpyrifos and mixture treatments wherein feeding attempts dropped to zero. Overall, the acute toxicity data reported in the present study can be used to assess the maximum tolerance level of golden mahseer to chlorpyrifos and dichlorvos, and their mixture. Furthermore, the sub-lethal end point responses can be applied in monitoring the environmental risk posed by these waterborne pesticides either individually or in combination to the aquatic life.

Toxicity imposed by organophosphate pesticides to the freshwater cultivable fish species mrigal (Cirrhinus mrigala) was assessed under laboratory conditions. Healthy juveniles were exposed to chlorpyrifos, dichlorvos, and their equitoxic mixture in geometric series. Median lethal concentrations of chlorpyrifos were found to be 0.906 (0.689-1.179), 0.527 (0.433-0.633), 0.435 (0.366-0.517) and 0.380 (0.319-0.450) mg/L and dichlorvos were found to be 38.432 (33.625-47.866), 22.477 (19.047-26.646), 12.442 (9.619-14.196) and 11.367 (9.496-13.536) mg/L after 24 h, 48 h, 72 h and 96 h of exposure respectively. Surprisingly, the joint toxicity of these organophosphates in the binary mixture was less than additive during most of the exposure periods. Behavioral changes exhibited by individual as well as mixture pesticide treatments were loss of schooling behavior, aggregating at corners of the test chamber, elevated opercular beatings, surplus mucus secretion, slight color changes and sudden and rapid body movements before death. Loss of fish equilibrium was noticed only in chlorpyrifos treated fish, whereas sluggish behavior was noticed only in mixture pesticide treatment. Such behavioral studies can be applied as a non-invasive bio-monitoring tool for water quality assessment for fish growth and development. Despite the same mode of action of both pesticides, the antagonistic action in the binary mixture is an interesting outcome of this research that requires further investigation for a lucid understanding of the joint toxicity mechanism of such pesticides.

As resistance to traditional antibiotics has become a major issue, it is essential to explore natural sources for new antimicrobial agents. The marine environment offers a variety of natural bioactive compounds. In this study, we examined the antibacterial potential of Luidia clathrata, a tropical sea star species. The experiment was conducted against both gram-positive (Bacillus subtilis, Enterococcus faecalis, Staphylococcus aureus, Bacillus cereus and Mycobacterium smegmatis) and gram-negative (Proteus mirabilis, Salmonella typhimurium, Escherichia coli, Pseudomonas aeruginosa and Klebsiella pneumoniae) bacteria using disk diffusion method. Specifically, we extracted the body wall and gonad using methanol, ethyl acetate, and hexane. Our findings show that the body wall extract using ethyl acetate (1.78μg/ml) was particularly effective against all tested pathogens, while the gonad extract (0.107μg/ml) showed activity against six out of ten selected pathogens. This is a crucial and new discovery that suggests L. clathrata may be a useful source for discovering antibiotics and more research is required to pinpoint and comprehend the active ingredients.