By identifying and measuring metabolic processes - used by Southern Bluefin Tuna (SBT) to swim, feed and grow - researchers are helping commercial farmers to maximise returns from their limited quota of fish.
Researchers from the University of Adelaide have been using giant air-tight bags as respirometers to measure the energy and oxygen requirements of large free-swimming tuna in the sea off Port Lincoln - a world-first achievement.
The new knowledge coming from this project is expected to contribute to reducing nutrient wastes, improving health and growth, and reducing mortalities, all of which will help to increase the productivity of tuna farming.
"Increased cost-efficiency of SBT aquaculture will come from improving the growth and quality of the limited number of fish", says Principal Investigator Professor Roger Seymour of the University of Adelaide's School of Earth and Environmental Sciences.
"Achieving this growth", he says, "requires insights into metabolic physiology - the tuna's internal organic functions".
A bio-energetics model will identify the energy that needs to be delivered through feed as appropriate to the SBT growth cycle and will allow farmers to predict the impact of a particular feeding strategy on the dissolved oxygen levels inside a pontoon of fish as the tuna eat and digest the feed.
Fish metabolism can be broken into three main components:
- A fasting routine rate to maintain minimal functions
- A second rate due to activity - mainly swimming
- A third attributed to food digestion and assimilation, often referred to as specific dynamic action
The study uses a mesocosm respirometer and temperature loggers that are implanted into the belly cavity of the tuna to examine the effect of feeding on the fish's metabolic rate. It also investigates the correlation between the feeding metabolic rate and visceral (internal) warming following feeding, during which, in other fish species, the oxygen consumption often reaches three times the resting levels.
Previously, no direct measure of metabolism had been made for SBT. Now, the metabolic costs of a wide range of feed rations have been recorded and the resulting data for different feed rations will be released soon.
This research will also throw new light on the way SBT aquaculture affects the marine environment, by predicting the oxygen demands of fish in pontoons to help determine optimum fish holding levels. In addition, remarkable new observations have already been made on the responses of tuna when oxygen levels in the water are low.
This work forms part of a project of Aquafin CRC, and receives funds from the Australian Government's CRCs Program, the Fisheries R&D Corporation and other CRC Participants.