On the Observation of Wild Zebrafish (Danio rerio) in India.

Zebrafish is one of the world's most widely used laboratory species, and it is utilized to answer important research questions in disparate fields such as biomedicine, genetics, developmental biology, pharmacology, toxicology, physiology, and evolution. Despite their popularity, very little is known about the biology of zebrafish in their natural habitat. This may, in part, be due to the difficulties associated with undertaking field trips to the remote areas of northern India, Nepal, and Bangladesh, which is the natural distribution range of zebrafish. Here, we present a field report describing a recent trip where we, together with local collaborators, visited several rivers in West Bengal, India, to observe wild zebrafish and their habitat. We present an overview of our observations on the biology of wild zebrafish, and the great variability of the different environments where they were found. We also include data collected on water chemistry parameters at 12 zebrafish sites, and weight data and photos of fish from these sites. We present extensive underwater videos of wild zebrafish and photographs of the sites, including video footage of courtship behavior. We show that the breeding period of wild zebrafish can be extended from the previous record of April-August to April-October. In addition, we provide practical advice for future zebrafish expeditions to this rural and inaccessible area. The goals of this article are to shed some light on the ecology of wild zebrafish, and to facilitate scientists in their future research trips. We hope that by observing zebrafish in the wild, we can increase our understanding of the natural ecology of this important model organism.

Are model organisms representative for climate change research? Testing thermal tolerance in wild and laboratory zebrafish populations.

Model organisms can be useful for studying climate change impacts, but it is unclear whether domestication to laboratory conditions has altered their thermal tolerance and therefore how representative of wild populations they are. Zebrafish in the wild live in fluctuating thermal environments that potentially reach harmful temperatures. In the laboratory, zebrafish have gone through four decades of domestication and adaptation to stable optimal temperatures with few thermal extremes. If maintaining thermal tolerance is costly or if genetic traits promoting laboratory fitness at optimal temperature differ from genetic traits for high thermal tolerance, the thermal tolerance of laboratory zebrafish could be hypothesized to be lower than that of wild zebrafish. Furthermore, very little is known about the thermal environment of wild zebrafish and how close to their thermal limits they live. Here, we compared the acute upper thermal tolerance (critical thermal maxima; CTmax) of wild zebrafish measured on-site in West Bengal, India, to zebrafish at three laboratory acclimation/domestication levels: wild-caught, F1 generation wild-caught and domesticated laboratory AB-WT line. We found that in the wild, CTmax increased with increasing site temperature. Yet at the warmest site, zebrafish lived very close to their thermal limit, suggesting that they may currently encounter lethal temperatures. In the laboratory, acclimation temperature appeared to have a stronger effect on CTmax than it did in the wild. The fish in the wild also had a 0.85-1.01°C lower CTmax compared to all laboratory populations. This difference between laboratory-held and wild populations shows that environmental conditions can affect zebrafish's thermal tolerance. However, there was no difference in CTmax between the laboratory-held populations regardless of the domestication duration. This suggests that thermal tolerance is maintained during domestication and highlights that experiments using domesticated laboratory-reared model species can be appropriate for addressing certain questions on thermal tolerance and global warming impacts.