Project number: 2005-200
Project Status:
Completed
Budget expenditure: $561,434.00
Principal Investigator: Roger S. Seymour
Organisation: University of Adelaide
Project start/end date: 13 Mar 2005 - 28 Feb 2008
Contact:
FRDC

Need

Any further expansion of the SBT aquaculture industry must come from greater or more efficient growth of the quota-limited supply of fish. To support and facilitate this goal an improved basic knowledge and understanding of SBT metabolic physiology is required. Metabolic physiology data are essential for any bio-energetic approach to improve our understanding of SBT nutrition. These data will underpin models that describe or predict the nutritional needs of growing or fattening SBT, helping to formulate baitfish and/or formulated diet matrices that deliver these nutritional needs, and improving our understanding of ingredient digestibilities, feed conversion ratios and the effects of differing feeding strategies. Furthermore, metabolic physiology data will increase our understanding of how SBT aquaculture affects the environment (eg. predicting cage- and regional-scale dissolved oxygen demands, and thus carrying capacities), and, conversely, how the environment affects the growth and health of SBT in culture conditions (eg. changes in water flow through cages due to net fouling, critical limits for minimum dissolved oxygen levels). Answers to both aspects of this question will assist in making this industry even more environmentally sustainable, more productive and enhance the perception of farmed SBT as a high quality, high value product in an increasingly competitive marketplace.
Thus, this application addresses the several of the research priorities identified in the Tuna Aquaculture Strategic Plan (2001-2006):
· nutritional studies;
· maintaining a healthy environment;
· improved farm husbandry and management practices resulting in increased production and product quality at reduced cost;
· SBT health.

Objectives

1. To examine the metabolic cost of specific dynamic action in SBT
2. To determine the relationship between visceral warming and metabolic rate associated to specific dynamic action in SBT
3. To assess the metabolic cost and behavioural responses of SBT to hypoxia
4. To evaluate the critical limits of dissolved oxygen for SBT
5. To investigate the effects of stage of farming season on the metabolism of SBT
6. To develop an archival tag for the in-situ monitoring of heart rate of free swimming SBT under aquaculture conditions
7. To evaluate the relationship between heart rate and metabolic rate of SBT in response to feeding and low dissolved oxygen levels

Final report

ISBN: 978-0-7308-5389-3
Author: Roger Seymour
Final Report • 2008-08-14
2005-200-DLD.pdf

Summary

Bluefin tuna have a variety of anatomical and physiological adaptations that enhance performance and make them distinctive among fish.  This unique physiology means that many common aquacultural beliefs are not applicable to this fish.  However, due to the logistical difficulties of studying these large pelagic fish, our understanding of tuna physiology lags far behind that of other aquaculture fish species.  In this study, some critical aspects of southern bluefin tuna (SBT) physiology (principally metabolic and cardio-respiratory physiology) are examined with the aim of supplying information that is beneficial for the SBT aquaculture industry in South Australia.  Metabolism data is essential for the bioenergetic study of tuna nutrition, potentially allowing the development of models that optimize feeding for growth or fattening of farmed SBT.  This study provides new information on the oxygen consumption rates of farmed SBT and their minimum dissolved oxygen requirements.  Basic information such as this is critical for farm managers to make husbandry decisions that ensure the health of farmed fish and maximize farm productivity, and is important for assessing environmental impacts of tuna aquaculture.  This study also examines SBT visceral warming and heart rate with the aim of evaluating if these physiological parameters could be used to assess the metabolic and health status of farmed fish, potentially providing a valuable tool for accessing this information in real time.

This study follows on from the Aquafin CRC 2003/228 project where technologies and procedures allowing the first measurements of SBT metabolic rate (oxygen consumption rate) were developed.  This largely involved the development of a novel respirometer (mesocosm respirometer) that can be installed in-situ into a marine farm research pontoon.  Initial studies in the current project used the mesocosm respirometer to make the first recording of the post-feeding metabolic rate and energetic cost of food digestion and assimilation of a tuna species.  These measurements offer a significant advance in our understanding of tuna energetics and has been internationally recognised, being published in a highly regarded biological journal.  It was found that in the period following feeding, the oxygen consumption  rate of SBT could be as great as 1 200 mg kg-1 h-1 and the energetic cost of food processing is twice that recorded for any other fish species, accounting for 35% of total ingested energy.  In a subsequent experiment, it was shown that the lipid/energy content of the baitfish ingested had little influence on the energetic cost of processing.  This confirmed the aquacultural and ecological relevance of the high cost of food processing in SBT.  It is hypothesized that tuna are not less efficient in processing food, but high cost of food processing is representative of their fast growth rates and high performance life style.  Data from these trials have already been adopted by other projects within the Aquafin CRC and incorporated into bioenergetic and environmental models, improving our knowledge of tuna nutrition and how tuna aquaculture interacts with the environment. 

Keywords: Tuna, metabolism, specific dynamic action, oxygen, hypoxia, endothermy, cardiovascular physiology, heart rate.

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