Modification of fish behaviour by parasites under variable flow conditions

• Main Author: Hockley, Frances Anne
• Format: Thesis
• Language: English
• Published: 2014
• Subjects: QH301 Biology; Anguilla anguilla
• Online Access: https://orca.cardiff.ac.uk/id/eprint/69706/; https://orca.cardiff.ac.uk/id/eprint/69706/1/2014HockleyFAphd.pdf; https://orca.cardiff.ac.uk/id/eprint/69706/7/HockleyFA.pdf

Fish populations are increasingly under threat by anthropogenic habitat modification. As demands on rivers have increased through increased human activity, resultant watercourse manipulations have altered the natural flow regime. However, it is unclear how diseased fish react to variable flow conditions in terms of their behaviour and swimming ability. This thesis addresses fundamental questions about the interaction between flow hydraulics and fish behaviour using two popular model systems: Trinidadian guppies (Poecilia reticulata) and three-spined sticklebacks (Gasterosteus aculeatus). Firstly it was found that guppies shoaled less when a member was infected with Gyrodactylus turnbulli but the magnitude of this effect was greater in the absence of flow (Chapter 2). Over time, the shoaling behaviour of guppies in the static flow condition reduced as parasite prevalence increased. In the flow condition, however, this effect was not observed, which resulted in higher peak prevalence of the parasite (Chapter 3). Sticklebacks utilised the lower flow velocities near the bed boundary layer to improve anaerobic and aerobic swimming performance but their natural parasite fauna had little effect on their swimming ability (Chapters 4 and 5). Guppies of different size, sex and parasite load utilised different regions around boulders to refuge from undesirable hydraulic conditions (Chapter 6). Finally, the impact of an invasive nematode Anguillicoloides crassus on the swimming behaviour of downstream migrating European eels (Anguilla anguilla) was investigated (Chapter 7). The parasite reduced burst swimming ability of the eels, which may have a knock-on effect for migration. In summary, this thesis demonstrates the importance of flow heterogeneity within a river system to provide shelter for smaller or weaker fish in poor health. River managers need to carefully consider any adaptation of flow regimes to provide appropriate flow conditions for resident species displaying a range of microhabitat requirements.