PhD Studentships: The effects of Different Beta-Glucans on fish microflora: Immunomodulation and disease protection

Sarah Harris

Keele University

Supervisor(s): Dave Hoole, Mark Skidmore and Dieter Steinhagen

There is ever increasing pressure on fish populations to meet the demands placed on them both as a food source and an economic commodity. Aquaculture plays a significant role in reducing the need to rely on wild populations, thus helping species that have been pushed dangerously close to extinction to start recovering and, additionally, lessening the strain on wild cohorts of more stable species. As with any farmed population keeping large numbers together can drastically increase the spread of pathogenic disease which may result in high mortality rates and economic losses.

Since the immune protection induced by vaccination tends to be specific to the target pathogen and there is a movement away from more traditional methods of coping with disease outbreaks, such as antibiotic treatments, there is an increased interest in the concept of improving overall health by increasing general immunity. Immunomodulants act by enhancing the general immune defence which can result in a higher rate of survival during infection. Immunomodulative compounds, such as β-glucans, are already widely used within the farming industry and are known to have a positive impact on fish health although the mechanisms behind their actions are still mostly unknown. Additionally, commercial products undergo several stages of processing before reaching the target organism therefore the physical structure of the final immunomodulative components have yet to be fully elucidated.

One of the simplest, least stressful means of exposing fish to β-glucans is to incorporate the compound into the fish feed. Upon consumption, the β-glucans come into contact with the commensal microflora population within the gut. There is an important symbiotic relationship between a host fish and its commensal bacterial population which, if disturbed, may have both positive and negative effects on gut functions and general health. In addition to having immunomodulatory properties upon the host fish, β-glucans can also be utilised as a food source by certain bacterial species. The aim of my research is therefore to establish how immunomodulants affect both the immune response of the host and the ecology of the microflora of the intestine. Whilst there are many publications related to either the host or the microflora as separate entities, there is very little on bridging the gap between the two within ichthyology. Using the common carp (Cyprinus carpio) as a model host and a range of known β-glucan structures, in vitro studies will determine the effects of β-glucans on individual bacterial species and in vivo trials will establish effects on the resident microflora population and the innate immune responses in the gut of the host fish.

Another mode of exposing fish to β-glucans is to add them as a bathing agent. This has been shown to have positive health benefits including increasing the rate of wound healing in carp, but the effect this has on the environmental microflora has not yet been studied. In order to establish the extent the inclusion of known β-glucan structures are able to alter waterborne microflora populations, molecular microbiological methods will be employed to analyse closed circulation systems both with and without the presence of the selected host fish.

This project is a development of the work undertaken under the auspices of the EU ITN “Nemo” which established the effect of MacroGard®, a commercially available β-1,3/1,6-glucan, on the immune status and health of common carp.


School of Life Sciences
Keele University

LinkedIn: Sarah Harris