PhD Studentship: Using Integrative Physiology to Reassess Optimal Foraging Theory & Aquaculture Diets

University of Exeter - Biosciences Department

The University of Exeter and the University of Queensland are seeking exceptional students to join a world-leading, cross-continental research team tackling major challenges facing the world’s population in global sustainability and wellbeing as part of the recently launched QUEX Institute.

The student will have the chance to study in the UK and Australia, and will graduate with a double degree from the University of Exeter and the University of Queensland.

Find out more about the PhD Studentship via

Lead Academic Supervisors

Prof. Rod W. Wilson (University of Exeter)

Prof. Craig Franklin

Project description

Optimal foraging theory (food selection based on calorie/nutrient value) has not previously considered dietary acid-buffering capacity (which is not linked to calorific/nutrient content). Carnivorous fish commonly ingest whole prey, and hard skeletal parts (calcium phosphate in fish bone, calcium carbonate in invertebrate shells) are often entirely dissolved by gastric acid secretion. This process has an energetic cost, and in turn it induces an alkaline tide (rise in blood pH and bicarbonate during digestion) which we were the first to discover in teleost fish (Cooper & Wilson, 2008). Recovering post-feeding acid-base balance can take up to 3 days in fish, and has energetic costs (gill, intestinal and kidney ion transport), as well as physiological consequences for blood oxygen transport by haemoglobin.

Experiments at Exeter used rainbow trout fed on isocaloric pellet diets that differed only in the calcium salt added (calcium carbonate, calcium phosphate, or calcium chloride in equimolar quantities that mimic the skeletal calcium content of crustacean/mollusc or fish prey). These experiments demonstrated that acid-buffering minerals can have major energetic consequences during digestion. This raises hypotheses that dietary buffer capacity should influence: a) prey selection and hence optimal foraging theory in nature, and b) efficiency of growth in aquaculture.

Several species are amenable to test these hypotheses. For aquaculture this includes trout, salmon, sea bass and barramundi (providing both UK and Australian relevance). In nature, freshwater tench and sticklebacks consume whole snails (with calcium carbonate shells) as well as bony fish and soft-bodied invertebrates. A study of invasive lionfish (of marine conservation relevance) found they ate 78% teleosts and 14% crustaceans by volume (Morris and Akins, 2009).

This integrative ecophysiology project will apply automated respirometry to characterise energetic costs, and assess physiological consequences (ion/acid-base balance, blood oxygen transport) of consuming different artificial and natural diets across a realistic range of acid-buffering capacities. The supervisory team (Rod Wilson & Steve Simpson at Exeter, Craig Franklin at UQ, and Al Harborne at Florida) provides ideal physiological (RW/CF), behavioural (RW/SS/AH) and ecological/conservation expertise (CF/AH/SS), as well as current aquaculture collaborations within UK (RW) and Australia (CF). We can also use our existing collaborations with field stations (e.g. Lizard & Heron Island, Australia; CEI, Bahamas) to run mesocosm- and field-based studies of prey selection to further evaluate this novel idea regarding our understanding of optimal foraging theory.

Cooper CA, Wilson RW. 2008. Post-prandial alkaline tide in freshwater rainbow trout: effects of meal anticipation on recovery from acid-base and ion regulatory disturbances. Journal of Experimental Biology 211: 2542–2550

Morris JA, Akins JL. 2009. Feeding ecology of invasive lionfish (Pterois volitans) in the Bahamian archipelago. Environmental Biology of Fishes 86: 389–398

Full tuition fees, stipend of £15,000 p.a, travel funds of up to £15,000, and RTSG of £3,000 are available over the 3 year programme.

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