Thermal biology of zebrafish (Danio rerio)

Abstract

Zebrafish has become one of the most important animal models in research. Most of the variables studied using zebrafish are influenced by water temperature. The objective of this review was to analyze the published data on the thermal biology of the zebrafish. The paper first provides a brief introduction to zebrafish ecology and thermal tolerance, and continues with a review of the influence of temperature on several physiological variables, including development, growth, metabolism, reproduction, behavior, circadian biology and toxicology. Although a number of papers have already studied the effects of temperature on the zebrafish biology, knowledge in this field is still scarce, especially compared with other model organisms such as the rat, and therefore further research should be encouraged.

Introduction

Zebrafish (Danio rerio Hamilton, 1822) has become one of the most important model organisms in many fields of research, including genetics, neuroscience, development, physiology, toxicology and biomedicine, and it is frequently used as a model of many human diseases (Vascotto et al., 1997, Fishman, 2001, Grunwald and Eisen, 2002). A number of attributes have contributed to the scientific importance to this species, among them its small size, rapid development, optical transparency during early development, tractability in forward genetic screens and genetic similarity to humans (Lawrence, 2007). In addition, it is a robust fish and large numbers can be kept easily and cheaply in the laboratory. Females can spawn every 2–3 days and a single spawn may contain several hundred eggs (Spence et al., 2008). Fertilization is external, which makes live embryos accessible to manipulation throughout all developmental stages (Kimmel et al., 1995).

Temperature is considered as the “abiotic master factor” in aquatic ectotherms, influencing the behavior, physiology and distribution of organisms (Brett, 1971). In view of its importance as a model organism, it is essential to have a thorough understanding of the thermal biology of zebrafish. In other model organisms such as the rat, thermal biology has been extensively reviewed, emphasizing the influence of temperature on a great variety of physiological processes (Gordon, 1990). The objective of the present report was to provide a thorough review on the thermal biology of the zebrafish.

Zebrafish belongs to the family of freshwater fishes Cyprinidae. In the wild, zebrafish is located mainly around the Ganges and Brahmaputra basins in north-eastern India, Bangladesh and Nepal. In addition, zebrafish has also been reported in rivers throughout India, as well as in Pakistan, Myanmar, Sri Lanka and river basins draining into the Arabian Sea (Engeszer et al., 2007; Spence et al., 2008). While the basic biology of zebrafish is well understood, knowledge of its ecology and natural history is relatively limited (Engeszer et al., 2007; Spence et al., 2008).

The areas where zebrafish occurs in the wild have a typical monsoon climate with marked seasonal variations. The major rivers inhabited by zebrafish run through low-lying areas that flood during the monsoon season (Spence et al., 2008). A wide variation in temperatures can be observed in these waters, with both daily and seasonal variations being reported (Payne and Temple, 1996). For example, in a fishery study by Payne and Temple (1996), water temperatures were recorded at several points in the Ganges basin for a year and daily variations ranging from a lowest difference of 0.1 °C to a highest difference of 5.6 °C were reported. Wide seasonal variations in water temperature in these locations were also reported, with a mean seasonal difference of 15.0±0.4 °C. The lowest water temperature recorded was 14.2 °C and the highest was 33 °C. Furthermore, some authors have reported water temperatures as low as 6 °C in winter to as high as 38 °C in summer (Spence et al., 2008).

Temperatures in waters where zebrafish has been collected in the wild are shown in Table 1. As can be observed, these temperatures are within the usual ranges of waters in these geographical areas (see above). The lowest temperature recorded in the places where zebrafish was found was 16.5 °C and the highest was 38.6 °C (Table 1). It should be noted that the maximum temperature of 38.6 °C is close to the thermal limits of zebrafish (see Section 2). This is likely an exception and does not seem to be common in the natural habitat of zebrafish, as the second highest recorded temperature was 34 °C (Engeszer et al., 2007).

Zebrafish has mainly been found to inhabit slow-moving or standing waters and have also been reported in the slower reaches of streams and even rice-paddies (McClelland et al., 2006, Spence et al., 2008). Zebrafish is usually found in shallow waters with high transparency, frequently in shaded locations with aquatic vegetation and a silty substratum (McClelland et al., 2006, Spence et al., 2006; Engeszer et al., 2007). In these habitats, zebrafish feeds mostly on zooplankton and insects, although phytoplankton, algae, vascular plants and detritus can also be found in their digestive system (McClelland et al., 2006, Spence et al., 2007). With regards to reproduction, zebrafish seems to be an annual species, spawning mainly during the monsoon season (Engeszer et al., 2007). In the wild, adult fish rarely achieve a second reproductive season. On the other hand, under laboratory conditions, zebrafish shows a mean lifespan of 42 months, the longest living individual reported surviving for 66 months (Gerhard et al., 2002).