Role of water flow regime in the swimming behaviour and escape performance of a schooling fish

Abstract

Animals are exposed to variable and rapidly changing environmental flow conditions, such as wind in terrestrial habitats and currents in aquatic systems. For fishes, previous work suggests that individuals exhibit flow-induced changes in aerobic swimming performance. Yet, no one has examined whether similar plasticity is found in fast-start escape responses, which are modulated by anaerobic swimming performance, sensory stimuli and neural control. In this study, we used fish from wild schools of the tropical damselfish Chromis viridis from shallow reefs surrounding Lizard Island in the Great Barrier Reef, Australia. The flow regime at each site was measured to ascertain differences in mean water flow speed and its temporal variability. Swimming and escape behaviour in fish schools were video-recorded in a laminar-flow swim tunnel. Though each school's swimming behaviour (i.e. alignment and cohesion) was not associated with local flow conditions, traits linked with fast-start performance (particularly turning rate and the distance travelled with the response) were significantly greater in individuals from high-flow habitats. This stronger performance may occur due to a number of mechanisms, such as an in situ training effect or greater selection pressure for faster performance phenotypes in areas with high flow speed..

Group size, temperature and body size modulate the effects of social hierarchy on basal cortisol levels in fishes

“…stickleback Gasterosteus aculeatus (Ginnaw et al, 2020)), to highly organized schooling (e.g. a tropical damselfish Chromis viridis (Nadler et al, 2018)). Although this myriad of social organization systems might be an advantage in studying links between physiology and behavior, the fact that fish species greatly vary in their life history traits might also obscure any underlying patterns.…”

Social familiarity improves fast-start escape performance in schooling fish

“…1a), average turning rate (the ratio of the turning angle achieved during stage 1 to the stage 1 duration, Fig. 1b) and distance covered (distance moved by the centre of mass during the first 42 ms of the reaction, the mean time to achieve stages 1 and 2 in this species according to published data 54 , Fig. 1c).…”

“…School cohesion was assessed using nearest neighbour distance (NND; distance to the closest neighbour) and school area (horizontal spread of the school), while school alignment (length of the mean circular vector, a measure of the variation in fish orientations) was used as a proxy for spatial coordination of individuals within the school 56 . These school characteristics were measured at set time points throughout the escape response (time = 0,~20, and~100 ms after stimulus onset), representative of before, during, and after the escape response on average in this species 54 (complete model output detailed in Supplementary Table S5). Responder number Average Turning Rate ( /s) Familiarity: p>0.05 (first), p=0.01 (subsequent) Responder number Distance Covered (mm) Familiarity: p>0.05 (first), p=0.006 (subsequent) Fig.…”

“…School escape response was characterised through school cohesion (nearest neighbour distance and total school area) and spatial organisation (alignment of individuals). These school characteristics were measured at set time points throughout the escape response (0, 20.8 and 99.8 ms following the stimulus) 56 , as this short time frame following a predator attack is crucial for survival 30,31 and previous studies indicate that these time points represent the school's pre-stimulation behaviour as well as the latencies for 33% and 66% of C. viridis individuals, respectively 54 .…”

Adaptive effects of parental and developmental environments on offspring survival, growth and phenotype

“…The water flow in an environment may also require different performance and physiological traits which support more or less metabolically expensive swimming modes (Boisclair & Tang, 1993). For example, tropical reef fish living in high‐flow areas have higher maximum swimming speeds and aerobic scopes, and quicker fast‐start escape responses (Binning et al, 2014; Nadler et al, 2018), while those in lower flow areas have lower metabolic rates, aerobic scopes and maximum swimming speeds (Binning et al, 2014; Binning et al, 2015). Such differences in physiological (metabolism) and performance (swimming) capacities have rarely been shown in juveniles, making it difficult to know if observed differences come from developmental or parental environments.…”