No abstract

The decline of freshwater fish biodiversity corroborates the trends of unsustainable pesticide usage and increase of disease incidence in the last few decades. Little is known about the role of nonlethal exposure to pesticide, which is not uncommon, and concurrent infection of opportunistic pathogens in species decline. Moreover, preventative measures based on current knowledge of stress biology and an emerging role for epigenetic (especially methylation) dysregulation in toxicity in fish are lacking. We herein report the protective role of lipotropes/methyl donors (like choline, betaine and lecithin) in eliciting primary (endocrine), secondary (cellular and hemato-immunological and histoarchitectural changes) and tertiary (whole animal) stress responses including mortality (50%) in pesticide-exposed (nonlethal dose) and pathogen-challenged fish. The relative survival with betaine and lecithin was 10 and 20 percent higher. This proof of cause-and-effect relation and physiological basis under simulated controlled conditions indicate that sustained stress even due to nonlethal exposure to single pollutant enhances pathogenic infectivity in already nutritionally-stressed fish, which may be a driver for freshwater aquatic species decline in nature. Dietary lipotropes can be used as one of the tools in resurrecting the aquatic species decline.

Aquaculture Nutrition. 2020;26:921-935. wileyonlinelibrary.com/journal/anu | 921

A 2-month preliminary study was conducted to delineate the effect of dietary methyl donors (choline, betaine, and lecithin) on the growth performance and metabolic status of Labeo rohita fingerlings subjected to endosulfan alone and in combination with elevated temperature. Four iso-caloric and iso-nitrogenous diets viz. basal diet, betaine-supplemented diet, choline-supplemented diet and lecithin-supplemented diet were prepared and fed to the different experimental groups throughout the experimental period as per the design. Two hundred and seventy fingerlings (average weight 7.95 ± 0.04 g) were randomly distributed in six treatment groups each having three replicates. The experimental groups were as follows: fish subjected to normal water (without endosulfan) and fed with control diet (control group T(0)), fish subjected to endosulfan-treated water and fed with control diet (T(1)), fish subjected to concurrent exposure of endosulfan and elevated temperature and fed with control diet (T(2)), fish subjected to endosulfan and elevated temperature and fed with choline-supplemented diet (T(3)), fish subjected to endosulfan and temperature and fed with betaine-supplemented feed (T(4)), and fish subjected to endosulfan and temperature and fed with lecithin-supplemented feed (T(5)). The result shows that in both the groups, that is, endosulfan exposed and concurrent exposure to endosulfan and elevated temperature group of L. rohita the growth performance like percentage weight gain, feed conversion ratio and specific growth rates were significantly different (P < 0.01) when fed with supplemented diet compared with control fed group. The liver LDH and MDH activity were significantly lower in lecithin, betaine, and choline fed groups. The muscle AST as well as G6PDH, AST, and ALT did not vary but liver ALT, gill and liver ATPase, intestine ALP, muscle and liver glycogen varied significantly with dietary supplementation. The liver and gill glutathione-S-transferase (GST) activities were significantly lower in methyl donors-supplemented groups and brain AChE activity showed lower inhibition in supplemented groups in both endosulfan alone and concurrently exposed endosulfan and temperature groups. The result obtained in this study concludes that inclusion of methyl donors, particularly lecithin and betaine in feed as nutritional supplements have potential to improve growth and stress mitigating effect in L. rohita fingerlings.

Aquaculture has been globally recognized as the fastest growing food production sector which plays a major role in meeting the increasing demand for animal protein requirement. A consensus is growing that a dramatic increase in aquaculture is needed to supply future aquatic food needs. However, there are sustained problems with the aquaculture like disease outbreaks, chemical pollution, the environmental destruction, and inefficient feed utilization. These altogether raise question mark on sustainability of aquaculture. In spite of the several strategy adopted on national and international level, as improved laboratory facilities, diagnostic expertise, and control and therapeutic strategies in order to handle disease outbreaks more effectively. Aquaculture industry is under uncertainty and the progress has not matched that of the rapidly developing aquaculture sector. In order to control disease prevalence and ensure better health of system and sustainable production, the sector demand more technical innovation for the drug use, disease treatment, water quality management, production of tailored fish for suiting better health, productivity drive by epigenetic and nutrigenomic interaction, better breeding success by efficient delivery of maturation and spawning inducing agent, nutraceutical delivery for rapid growth promotion and culture time reduction, successful use of autotransgenic, and effective vaccine. Nanotechnology has a tremendous potential to revolutionize agriculture and allied fields including aquaculture and fisheries. For these multiple purposes effort, importance of nanotechnology and nanodelivery of drugs, vaccine, nutraceutical, inducing hormones, and growth-promoting anabolics open tremendous opportunity. The paper has been targeted to delineate the possible future application of nanodelivery for the aquaculture development.