J D Thomas

School of Biological Sciences, University of Sussex, Falmer, Brighton, East Sussex, BN1 9QG, UK

Abstract 2

1. Introduction 4

2. Ecological Background 6

2.1. Topography 6

2.2. Physicochemical characteristics of study sites 8

2.3. Methods used for investigating the helminth parasites and their fish hosts 10

2.4. Methods used for investigating the invertebrate fauna including intermediate hosts 11

2.5. Species of helminth parasites 12

2.6. The life history strategies of the parasites 12

3. Dispersion Patterns of the Helminth Parasites 19

4. Spatiotemporal Aspects of the Parasitic Fauna 22

4.1. Quantitative data 22

4.2. Physicochemical factors that may influence the distribution and abundance of the parasites and their fish hosts 32

4.2.1 Water flows and water types 32

4.2.2. Water temperature and photoperiod 35

4.2.3. Water chemistry 43

5. The Relationships between Parasite Abundance and the Age and Size of the Fish Hosts 45

5.1. Quantitative data 45

5.2. Causative mechanisms 50

5.3. Ecological relevance and density dependence 54

6. Relationships between Parasite Abundance and the Wellbeing of the

Fish Hosts 59

6.1. Introduction 59

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