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Miss Bettina Schelkle 


Supervisors: Dr Jo Cable, Prof David Lloyd (Cardiff University), Dr Cock van Oosterhout (University of East Anglia) and Dr Donna Snellgrove (WALTHAM Centre for Pet Nutrition).

I am investigating the behavioural, environmental and transmission implications of botanical treatments on gyrodactylid infections. Gyrodactylids are ubiquitous on teleost fish and they represent a significant evolutionary force acting on their hosts in natural fish populations. In the aquarium industry gyrodactylids are also a major problem due to high fish densities and increased handling stress, both of which contributes to the spread of these directly transmitted pathogens. High parasite burdens commonly cause death in infected fish: this may be due to impaired physiological (e.g. low oxygen uptake if high parasite prevalence in gills) and physical (e.g. swimming due to fin clamping; Fig. 1) abilities of the host or due to exposure to secondary infections of obligate and opportunistic microparasites through wounds left in the epidermis of the fish by the gyrodactylids’ attachment organs.

guppy

Fig. 1. Guppy with high gyrodactylid burdens. Note the clamping of the fins.

My work focuses on gyrodactylid presence in artificially kept fish populations, particular those in the ornamental fish industry. Including non-exported products, retail sales, wages and associated materials this industry has been estimated to be worth around US$15 billion per year. Hence, there is strong demand for effective treatments against fish parasites some of which could potentially also be effective in the food fish industry. The current control methods employed in aquaculture against gyrodactylids include chemicals such as formaldehyde, rotenone and malachite green. All these compounds do not act against gyrodactylids specifically: (1) they are toxic to host, humans and environment; (2) due to their broad anti-parasitic properties they are low in efficacy; and (3) application of treatment is difficult since the treatment concentration for 100% efficacy often crosses the toxicity threshold for the host.

I aim to investigate alternative methods to treat gyrodactylids using the model system Gyrodactylus turnbulli infecting ornamental and wild guppies (Poecilia reticulata) (Fig. 1). Currently, I am focussing on three main areas:

1. Assessing the efficacy of various botanicals, traditional freshwater fish disease remedies and extreme environmental conditions against Gyrodactylus turnbulli in vitro and in vivo.

Bettina Schelkle

Fig. 2. Field work at the Pitch Lake in Trinidad

Due to the problems associated with many of the commonly used treatments against helminths infections in fish, there is strong interest in finding alternatives. I am testing various plant extracts, assess established traditional remedies and extreme environmental conditions (e.g. pitch, Fig. 2) in vitro, but also in vivo by initially maintaining fish individually throughout treatments and later on testing efficacy of treatments on an aquarium level.

2. Assessing hybridisation rates and hybrid fitness of Gyrodactylus strains

Gyrodactylids are thought to reproduce asexually, parthenogenetically and sexually, but it is not known which of these reproductive modes prevails and whether external factors (such as the application of treatments) favours a particular reproductive mode. Assessing hybridisation rates between different strains of the same Gyrodactylus sp. will provide further insights into the hyperviviparous reproduction of gyrodactylids. Furthermore, we are aiming to assess hybrid fitness by interbreeding G. turnbulli strains of different age. Offspring fitness will be observed over several generations to detect possible fitness effects.

In conclusion, my work aims to support further knowledge on the controlled application of anti-helminthic compounds in the aquarium industry through an increased understanding of host-parasite interactions and parasite biology.

Collaborators:

Hybrid fitness in Gyrodactylus turnbulli strains

Dr Mireille Johnson, Cardiff University, UK

Dr Patricia Faria, Brazil

Ecology of guppies in the Pitch Lake, Trinidad

Dr Mark McMullan, University of East Anglia, UK

Dr Mike Coogan, Cardiff University, UK

Ryan S. Mohammed, University of the West Indies, Trinidad and Tobago

Gyrodactylid morphology

Dr Andrew Shinn, Stirling University, UK

Giuseppe Paladini, Stirling University, UK

Dr Stanley King, Dalhousie University, Canada