In commercial aquaculture operations, the temperature to maximise growth is around 27-30°C. But what’s their tolerance limits? And what happens in their natural settings?
In this handbook – Schipp, G, Bosmans, J & Humphrey J (2007) Northern Territory Barramundi Farming Handbook. Third revision. Northern Territory Government. – under 2.5 Environmental requirements, it states that “Barramundi fingerlings are known to survive in water… temperatures up to 35°C. They can also survive temperatures as low as 16°C.”
In this factsheet – Q. Allsop, P. de Lestang, R. Griffin and G. White, (2006) Barramundi – Your Questions Answered. Fishnote, No 27, DPIFM – it states that “Barramundi inhabit areas where the water temperature ranges between 23°C to 35°C, from the Ashburton River in the west to the Mary River in Queensland.”
In a dry season day, the ambient temperature in Northern Territory can fall to 15°C and the water temperature in barramundi farms in can drop to around 20°C.
I have had a case where a client with aquaponics setup saw their fish become sick in the middle of May in Perth, when water temperature ranges dropped to as low as 13-17°C. In another case, a barramundi in an outdoor aquarium became ill during the month of July in an unheated outdoor tank.
My colleague’s experience is that the water temperatures in barramundi farms get down to 15°C most years without mass mortality. Two years ago, in dams located in Queensland, water temperatures dropped to 11°C (which was extreme), and it was then that it caused mass mortality.
So, based on a combination of literature reviews of natural occurrences, experimental data and professional experience, the optimal temperature range for barramundi is between 25-30°C. The tolerance range for them would 16-35°C.
Here we should make a distinction that tolerance range means that they can survive this, but only for short periods and only if exposed to the extremes gradually.