Coping with life in aquatic habitats: can fish use hydrostatic pressure to orient through volumetric environments?

Unlike most terrestrial environments, aquatic systems are volumes through which animals can move in all directions; up and down as well as side to side. Aquatic animals need to orient efficiently through their volumetric habitats to exploit resources and avoid adverse conditions or predators. Indeed, being able to learn, remember and re-use information about local environments is key to their success. Despite this, we do not know how aquatic animals such as fish, or in fact how any animal learns and remembers information about volumetric environments. In comparison to a surface, the amount of information contained in a volume is massively increased. Artificial intelligence systems and humans find orienting through volumes extremely difficult, how then do animals such as fish cope? In relation to terrestrial habitats, aquatic environments have an extra available cue that could aid three-dimensional orientation - hydrostatic pressure. This cue could provide information about the vertical axis of space, either by allowing a fish to work out exactly where it is in the water column, or by giving compass-like information - telling a fish which way is up and down. We aim to discover whether fish can use hydrostatic pressure to orient, and what type of information it gives. Fish are known to be able to perceive small incremental changes in hydrostatic pressure, and a number of potential receptive mechanisms have been found. It therefore seems highly likely that fish have adapted to use this cue that is unique to aquatic systems as a way of coping with the unique problems associated with finding their way around a volumetric environment. In this project, we aim to find out whether fish use hydrostatic pressure to orient vertically, and if so how this cue is used. We will test whether fish use other potential vertical cues such as light, and distance to the surface, to determine whether one cue type is preferred (maybe pressure, as it is ever-present and usable at night or in conditions where visibility is poor), and whether there is redundancy in the cue-use system. We will build on this to consider orientation through three-dimensions, and whether fish orient using different mechanisms when in landmark-rich versus landmark-poor environments. Is pressure always the preferred cue as it is always available, or can the use of landmarks improve precision in orientation? Finally, we will consider orientation through a full volume, and whether fish can encode distance and direction within such a complex 3D space, or whether errors occur in either the horizontal or vertical dimensions. In other words, we aim to work out how fish learn and remember the features and cues of their volumetric habitat, so as to make the correct directional choices when they have to get somewhere in a hurry.

We aim to test what information fish learn and remember in the vertical axis of space, and how this interrelates with cues in the horizontal axis to allow efficient orientation through local environments. Aquatic animals, such as fish, must orient through volumes through which they can swim with three degrees of freedom of movement. This leads to a potential information-processing problem in comparison to animals that orient over surfaces. These environments have a unique vertical cue that could potentially aid fish in this task - hydrostatic pressure. Using three new behavioural paradigms we aim to test whether fish make use of this ever-present cue to aid orientation. We will test the nature of the hydrostatic pressure cue - whether it allows fish to pinpoint their vertical position, or whether it gives directional information. We will then explore other potential vertical cues to test whether there is a hierarchy in vertical cue use and redundancy in the system. Building from this we will explore the mechanisms and processes that underlie the ability of fish to orient through volumes by manipulating the intensity and type of cues in both the vertical and horizontal axes of space and by putting these in conflict. In particular we will test whether fish in landmark poor or landmark rich environments use different mechanisms to orient - are global pressure cues more salient, and more heavily weighted in an internal representation of space than other cues? Finally, we will introduce a newly developed 3D tracking system to test how fish swim through a volume when they are first restricted to a 3D Y-maze and then unconstrained and allowed to swim free. Can fish accurately encode distance and directional information in 3D, and if so how? In summary, we aim to discover whether fish are able to use hydrostatic pressure, a cue that is unique to aquatic systems, to cope with the unique complexities embedded in the problem of orienting through volumetric environments.

While the communication of the main results of this project will be via conference presentations and scientific journals, we believe that further benefits can be achieved through a programme developed to target communities that would not usually keep up with this field of research. We have already produced a webpage on our group's work, but aim to enhance this with a section that will be specifically set up for school and college users. We are already involved in a number of outreach initiatives to impart information to these groups. For example, I recently participated in two workshops at the Royal Institute of Navigation (composed of all levels of the public with a general interest in navigation) where I reported on our work to date. I also participated at the 2009 Cheltenham Science Festival, giving a presentation on our group's work to children between the ages of 7 and 11. I will give a similar talk at the Royal Society Summer Exhibition in 2009, again aimed at school-age children, and also at the Brighton Science Festival 2010. I regularly give presentations on our work to local schools, aimed at specific parts of the curriculum. Our work has been widely disseminated to the general public through radio and television (including BBC World Service and the ABC Science Programme), and has also been featured in national and international newspapers and popular science magazines. We will continue to develop these outreach activities to children of all ages. I am also involved in the support of Women in Science at a broad level, and have given interviews to the media, and helped organise workshops to stimulate discussion and also to encourage young women who are starting their careers in all fields of science. This is an area that I feel very strongly about, and will continue to support via workshops, interviews, talks, and mentoring groups. We will pursue collaborations with scientists in other fields to cross over data and research findings. For example, we have recently contacted Huosheng Hu from the University of Essex, with a view to collaborating on his robotic fish, that he has designed to detect pollution in aquatic systems. We will also indentify policy-makers involved in fish welfare and aquaculture, and will disseminate our results with a view to increasing the spread of knowledge on fish cognition to those involved in the care and keeping of fish at all levels. We believe that it is important for scientists to engage with the public, and with policy makes to ensure that data and research results have the widest impact possible. Our impact plan reflects this belief, and indicates the wide-ranging work we have been involved with in our outreach activities, and how we plan to expand and develop upon this broad base.