Fish behavioural response to static visual cues

Abstract

Fish have been shown to associate with visual cues, whereas flying animals tend to avoid areas of visual complexity, but the reasons for this difference in reaction remain unclear. For fish, visual cues provide reliable information on their position in space and help them align with hydrodynamic flow. Vision is also vital to maintain cohesion in schools and for communication. This thesis aims to improve fundamental knowledge regarding how European freshwater fish behave in relation to static abiotic visual cues (patterns on surfaces) by answering two main research questions; how (1) flowing water, and (2) group size, affects the response of fish to visual cues?
Affiliation with visual cues was greater in flowing than static water. It is hypothesised that the higher level of association with visual cues in flow provides fish with reliable reference points, which may improve swimming performance (the ‘Station Holding Hypothesis’). However, the lack of correlation between association with visual cues and flow velocity and the short duration of visits to the visual cues for both common minnow (Phoxinus phoxinus) and brown trout (Salmo trutta) implies that controlling swimming is not a primary reason for the observed behaviour. The association with visual cues continued under static water suggesting that visual cues may provide other benefits such as physical refuge from predators or an opportunity for crypsis. Both individuals and groups of minnow exhibited a positive affiliation for the visual cues, travelling at a slower speed and spending more time closer to the striped walls. Individual fish tended to show a stronger association with visual cues when they came across them. However, larger groups responded to the presence of stripes more quickly due to enhanced detection efficiency and information transfer between group members. The greater association with the striped walls exhibited by individuals may reflect a greater dependence on environmental information or anti-predator behaviour (the ‘Predator Refuge Hypothesis’) when separate from a group.
Groups of minnow aligned more side-by-side when associating with visual cues in flowing water compared with a control in which visual cues were absent. However, the sub-structure (distance to nearest neighbour and polarisation) of groups was unaffected. Although the whole group responded by associating with visual cues, members continued to maintain cohesiveness and align with one another, presumably to benefit from energetically advantageous formations, suggesting that the equivalent benefits could not be gained by aligning with environmental visual cues. The findings of this thesis enhance fundamental understanding of fish behavioural response to stimuli and demonstrate the importance of visual cues in dictating behaviour. This research may give rise to some useful applications, for example in fish guidance technology and improving animal welfare in aquaculture.

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Identifiers

ORCID for James Miles: orcid.org/0000-0001-6448-6343

ORCID for Paul Kemp: orcid.org/0000-0003-4470-0589

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