Barramundi (Lates calcarifer – also known as the Asian sea bass or the Giant sea perch) is a commonly angled, native Australian fish. Within Australia, Barramundi can be found along the northern coasts and inland rivers in Queensland, Western Australia, and Northern Territory.

Looking globally, Barramundi have also left their mark as an introduced species in some countries like Saudi Arabia, French Polynesia and Israel, whilst also being native to other countries in the Pacific and South-east Asia.

Barramundi have an interesting lifecycle; individuals can inhabit both freshwater and saltwater habitats, as well as change their sex based on their surrounding environment and age. At around 3-4 years old, Barramundi become reproductively mature males. At 5-6 years old, Barramundi then turn into reproductively mature females, however, this change is dependent on the fish being typically around 80cm long.  in some rare instances Barramundi can be born female. During the wet season in Australia’s tropical regions, juvenile Barramundi are known to migrate upstream into freshwater rivers and wetlands, whilst adult Barramundi migrate downstream into estuaries where they spawn.  

The habitat Barramundi live in have a huge impact on the species’ ability to reproduce, as they benefit from healthy freshwater for their early years to develop and grow, and then require unregulated migration paths into seawater to be able to reproduce as females in their later years.  

Unfortunately, in some parts of Australia, river regulation has prevented this ecologically important migration.  The love of the Barramundi as a recreational fish has, since the 1980s, led to it being stocked in inland weirs and dams that would otherwise contain little/no fish.  This situation is different to other native fish species in Australia, as Barramundi stocking is not carried out to maintain a healthy wild population, it is instead carried out to create freshwater fisheries in locations far enough upstream that Barramundi would be unable to get there naturally.    So we now have populations of Barramundi that have never migrated between freshwater and seawater – is this a problem?

Learning more about Barramundi

A 2022 study by scientists at the Queensland Department of Fisheries and Agriculture found that by measuring mineral composition of Barramundi otoliths, they are able to learn where the fish has spent different stages of its life.  Otoliths are fish ear bones, used for hearing and balance, and are made up of mineral deposits that reflect the environment where a fish has lived, and they grow continuously throughout a fish’s life.

The study found that Barramundi that spend more time in their younger years in freshwater, are more likely to grow faster and larger than those who spend their whole lives in salt water. The study reported that there are little/no effects of upstream stocking on downstream saltwater fisheries. The study noted that upstream stocking of Barramundi supports recreational fishing in dams and weirs that would otherwise not contain the fish, and that stocking is not needed to maintain the sustainability of the marine fishery.

As explained by Dr Susannah Leahy, a senior scientist at the Department of Agriculture and Fisheries::

work shows that the biggest benefit to the wild barramundi population comes from juvenile fish—wild or stocked—getting access to healthy freshwater habitats.

In conjunction with freshwater habitat rehabilitation and fishways, it is hoped more Barramundi will be able to migrate to upstream freshwater. The study found that that stocking of upstream areas should continue in order to support recreational fishing activities in dams and weirs.

The main finding of the report is that there is little/no impact of freshwater stocking on marine fisheries. This is good news for anglers, as it means spawning season fishing is permitted in a very small number of dams because those fish are known to be completely isolated from the downstream population and therefore are not part of the wild stock’s spawning activities.

For our wild populations of Barramundi, however, we need to continue to work to enable the fish to migrate between healthy habitats.  Fishways are becoming an increasingly important adaptation for native fish species to enable fish to navigate through river regulation structures, like dams and weirs, that enhance fish migration. Some recent examples in other states include the Koondrook fishway at Cohuna and the Homestead Dam fishway in Toorale National Park.

Another recent fishway by OzFish and Greening Australia is at the Palm Creek weir in Queensland, which has recorded Barramundi, amongst 15 other native fish species, using the fishway to migrate. Palm Creek is an important waterway, connecting the Herbert River during high flow and the Great Barrier Reef lagoon near Forrest Beach.  

Overall, native fish species across Australia benefit from healthy and natural waterway systems, as well as connectivity to allow their migration, especially with a changing climate impacting on their habitats. We need to look after our rivers and native fish to ensure their best chance at survival.  

Main photo: Barramundi swimming in freshwater. Source: Sarah Jane Duran.

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