Foraging Behaviour of the Ruffe (Gymnocephalus cernuus) and Predator Avoidance by the Freshwater Isopod Asellus aquaticus: Implications for Predator-Prey Interactions

Hay, Alexandra Morag (1999) Foraging Behaviour of the Ruffe (Gymnocephalus cernuus) and Predator Avoidance by the Freshwater Isopod Asellus aquaticus: Implications for Predator-Prey Interactions. PhD thesis, University of Glasgow.

Abstract

This thesis describes a study of aspects of the foraging behaviour of ruffe (Gymnocephalus cernuus), anti-predator responses in an important prey species (Asellus aquaticus), and the interactions between them. A pilot study was conducted to examine use of shelter by small groups of A. aquaticus. This showed that A. aquaticus aggregated in shelter, and formed the basis for later experimental design (chapter 2). To examine the trade-off between use of shelter and feeding, 53 groups of 10 individually marked A. aquaticus were observed over 1 day in tanks containing food and sterile, food free shelter (in the form of artificial plants), separated by a brightly lit section of bare sand. The proportion of time spent foraging and in shelter was compared in different reproductive categories of A. aquaticus. Brooding females spent more time in shelter than other groups (chapter 2). Behavioural changes within the brooding cycle were examined; the trade-off that females made between seeking shelter and food was influenced by stage in this cycle, with females in early stages spending more time in shelter and females at the end spending more time feeding (chapter 2). A similar experimental set up was used to examine possible effects of chemical cues from a potential predator on shelter seeking and foraging in A. aquaticus. Shelter use and activity of A. aquaticus was quantified on 2 successive days, one with 'clean' water straight from Loch Lomond pumped through the tanks, and the second with water pumped from a fish tank containing several brown trout (Salmo truttd). This experimental protocol was used, because only one tank was available in which to carry out these experiments. A control was conducted with 'clean' water provided on both of the 2 days. In males use of shelter was greater when predator cues were introduced than they had been prior to introduction. However this could not be clearly ascribed to the cues themselves, since shelter use also increased (albeit less strongly) in a control study, where water was added on a second day. Possible improvements to experimental design are discussed (chapter 3). Previous studies of ruffe have indicated that the lateral line is important in foraging. The behaviour of ruffe was therefore studied while foraging for live concealed prey in the dark. Individual fish were trained over several weeks to forage in the dark for a few hours a day, in an arena with an array of pots, some of which contained live bloodworm buried in gravel and others which contained gravel alone. Foraging was recorded using a video camera under infrared light, and the tapes analysed to show general foraging responses and the frequency and duration of foraging visits to all pots during sessions lasting two hours. Seven sessions were recorded in this way, and the first 2 hours of foraging analysed in detail. In general from early on in the foraging sessions ruffe made more frequent visits to pots with food; this is interpreted as evidence that they can use non-visual cues to detect concealed prey. Foraging behaviour of some fish indicated that they leam the location of profitable food patches during each session (chapter 4). To examine anti-predator responses of A. aquaticus and their effects on foraging attempts by ruffe, predatory behaviour of ruffe towards A. aquaticus were observed in the presence and absence of sheher, in well lit tanks. Use of shelter by A. aquaticus conferred strong protection against ruffe. In the absence of shelter, different predator avoidance tactics were used, based largely on immobility, exploiting the dependence of ruffe on prey movements. Selection of prey by ruffe was examined, and in these feeding conditions no preferences according to size and gender were found (chapter 5). A sample of ruffe from Loch Lomond was examined for morphological status and the presence of macroparasties. Age was determined using a relatively new technique based on rings in the dorsal fm rays. Ages ranged from 0 to 6 years and sizes from 5 to 10 cm. Females were larger and heavier than males, had slightly larger gonadosomatic indices, but did not differ from males in body condition. A small proportion of fish were infected with the nematode Camallanus lacustris, but most of them had Diplostomum infection in one or both eyes; in some cases more than a hundred flukes were found per fish. Intensity of Diplostomum infection was similar in males and females, and increased significantly with fish age. No adverse effects on condition were observed, even in fish with very heavy infections. These findings can be related to the diet and foraging behaviour of ruffe (chapter 6). The results described in this thesis are discussed in relation to existing literature on foraging behaviour in ruffe and their status as a newly introduced species in Loch Lomond. Possible improvements to the design of this study are discussed and future areas for further research identified (chapter 7).

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Additional Information: Adviser: Felicity Huntingford
• Keywords: Ecology, Zoology, Evolution & development
• Date of Award: 1999
• Depositing User: Enlighten Team
• Unique ID: glathesis:1999-75912
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 19 Nov 2019 17:37
• Last Modified: 19 Nov 2019 17:37
• URI: https://theses.gla.ac.uk/id/eprint/75912