Effects of biotic and physical stressors on fish swimming performance and behaviour

Abstract

Locomotion is essential for all aspects of a fish's ecology and directly influences individual fitness by facilitating reproduction, food acquisition and predator avoidance. The effect of environmental factors on swimming fundamentally shapes the distribution of species. The first five chapters of this thesis examine how biotic and abiotic stressors influence fish swimming performance and behaviour. Because data (not just fish!) are essential for answering these questions, the last chapter discusses public data archiving, and proposes improvements to this practice. Chapter 1 investigates the prevalence of a large ectoparasite, Anilocra nemipteri, and how it affects its fish host, Scolopsis bilineata, on the Great Barrier Reef. I show that A. nemipteri is common and appears to affect the population size structure of S. bilineata. I suggest that this system is ideal to answer questions about host-parasite interactions and co-evolution (Roche et al. 2013, Aust J Zool). In Chapter 2, I test whether A. nemipteri, which attaches asymmetrically on S. bilineata, affects lateralization (the preferential use of one side of the body for behavioural tasks). I show that parasitised fish are more lateralized than non-parasitized fish, and that removing the parasite from infected fish decreases the strength of lateralization to the level of uninfected fish. These results suggest that side-biased behaviours are more plastic than previously thought (Roche et al. 2013, Behav Ecol Sociobiol). Chapter 3 focuses on the host, S. bilineata, and compares two common respirometry methods for estimating metabolic rates in fishes. I argue that a single approach might not produce the most accurate parameter estimates for all fishes, and that researchers should carefully consider which apparatus and method are most appropriate for their species and question of interest (Roche et al. 2013, J Exp Biol). Chapter 4 examines how cyclic changes in water flow velocity influence the swimming performance and energetics of a pectoral-fin (labriform) swimming fish. The results suggest that the costs of swimming in wave-like, unsteady flow are context dependent, and are influenced by individual differences in the ability of fishes to adjust their fin beats to the flow environment (Roche et al. in press, J Exp Biol). Chapter 5 explores the effect of unsteady, wave-driven water motion on fast-start escape responses, a key behaviour fishes use to evade predators. I found that water motion had a very strong negative effect on juvenile fishes' response time to a threatening stimulus, with deeper-bodied species being less affected. Since response latency is a key determinant of escape success, I argue that postural disturbances from unsteady water motion might reduce the ability of some coral reef fishes to evade predation (Roche submitted, Funct Ecol). Despite benefits for the wider society, many scientists are reluctant to share their data publicly. In Chapter 6, I explain why. I then offer practical solutions to increase the net benefits for individual researchers and to encourage public data archiving (Roche et al. in press, PLoS Biology). I also argue against charging fees for researchers to archive their data in public repositories (Roche et al. 2013, Nature).