Surviving in Freshwaters: How Ecological Variables Impact the Behaviour of Wild Zebrafish Shoals

Mukherjee, Ishani (2024) Surviving in Freshwaters: How Ecological Variables Impact the Behaviour of Wild Zebrafish Shoals. PhD thesis, Indian Institute of Science Education and Research Kolkata India.

Text (PhD thesis of Ishani Mukherjee (18RS098)) 18RS098.pdf - Submitted Version Restricted to Repository staff only Download (5MB)

Abstract

Animal behaviour is greatly shaped by the ecological variables of their habitats. Understanding how animals adapt their behaviour in response to these ecological variables is crucial for comprehending their survival strategies in changing environments. In the current thesis, we investigate the role of various ecological variables on the behaviour of zebrafish individuals, single-species zebrafish shoals and mixed-species shoals comprising zebrafish and co-occurring species. Our experiments involving conditioning zebrafish juveniles to nutrition regimes revealed that the interaction of testing age and early-life nutrition impacts activity in adult zebrafish. We observed interactions among zebrafish dyads and documented temporal and sex-specific patterns in their behavior We examined the impact of predation on shoaling behaviour among zebrafish and found that upon exposure to visual or olfactory predator cues, zebrafish increased shoal cohesion, polarization, and velocity. However, when both cues were present simultaneously, shoal cohesion, polarization, and velocity decreased, and individuals underwent freezing. This suggests that zebrafish rely comparably on vision and olfaction to respond to predators, and their anti-predator behavior varies based on the number of cues present. Additionally, we observed antipredator responses in presence of vegetation and found that a significantly higher proportion of individuals seek refuge under vegetation in presence of predator cues. Our experiments involving mixed-species shoals demonstrated that access to food, predator presence, and familiarity are key in driving zebrafish towards mixed-species shoaling. Information on predators and food sources is shared within and between mixed species shoals. Upon conditioning shoals to predicted high temperatures, we found species-specific responses in metabolism and reduced cohesion. This suggests mixed-species shoaling in freshwater systems may decline as water temperatures rise. Lastly, to validate our previous laboratory-based findings, we compared group behaviour observed in the field to that in the laboratory. We found that while cue use to perceive a predator and to detect food sources remains consistent across contexts; other behaviours may vary significantly between the laboratory and field conditions. Thus, the current thesis unravels the influence of predation, vegetation, temperature and co- occurring species on wild zebrafish shoaling. Our findings regarding the impact of rising water temperatures on mixed-species groups and the importance of vegetation in shoaling can aid in the formulation of conservation strategies.

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