NT Fish - Barramundi

Your Questions Answered 

Authors: Q. Allsop, P. de Lestang, R. Griffin and G. White, Fisheries Research, Darwin

Barramundi, the fishing icon of the Top End, draws local, interstate and international anglers to the Northern Territory in droves every year. Barramundi is the most targeted fish by recreational anglers in the Northern Territory (Coleman, 1998). Although many of us know how to catch barramundi, what do we actually know about the fish? Many questions are fielded by fisheries staff every year, including some common ones such as, how old or what sex is my barra, when do barra migrate to fresh water and what do they eat? This Fishnote aims to give you a better understanding of the biology and ecology of the barramundi and should answer some of the most often asked questions.

What is the barramundi life cycle?

1. Spawning around the river mouths early in the Wet season.
2. High tides wash eggs and larvae into coastal swamps.
3. Juveniles migrate upstream at the end of the Wet season.
4. Maturing males move downstream at the beginning of the Wet season.

Barramundi spawn (produce eggs) between the months of September and March, with the build up period from October to December, being the most important. Barramundi eggs and larvae require salt water and spawning is in marine bays and river mouths. Juvenile barramundi (5-50 mm) move with the high spring tides into mangrove and wetland habitats, which offer both protection and a wide variety of foods. As the wet season comes to an end and the flood plains begin to dry, the juvenile barramundi (now 200-300 mm) migrate up the rivers into the freshwater billabongs. If fish do not have access to fresh water, they will probably remain in coastal and estuarine areas. After three to five years, most of the freshwater barramundi migrate back to the ocean to spawn.

How old is my Barra?

We determine the age of barramundi by counting growth rings on their scales or their earbones (otoliths), much like counting the growth rings found on a tree. There are many factors that can affect the growth of a fish. For example, fish from an early spawning have a head start on those fish that are spawned late and will generally be larger by the end of their first year. Food availability and water conditions also affect the rate of growth.

Examples of length to age: one year old barra are between 30-40 cm long, two year old are 50-60 cm long, three year old are 60-80 cm and 100 cm barra are around eight years old.

Is it Male or Female?

Barramundi change sex from male to female, but did you know that the size of the barramundi you catch maybe a good indicator of the sex of the fish? Studies by Davis (1982) show that there is a relationship between size and sex. Most barra mature as males, at about 50-60 cm and, they start changing sex at around 90 cm, but only if they are living in salt water. Of course there are exceptions; some barramundi over 100 cm are male and a very small number under 70 cm are female.

This can be due to insufficient food stunting growth, or it may be that a barra has been in fresh water for an extended period and has remained male. This is the case with fresh water impoundments such as Manton Dam here in the Northern Territory and Tinaroo Dam in Queensland, which are stocked with barramundi. Barra over 20 kg in weight and measuring over 100 cm that are regularly captured at Tinaroo, are all males. Restocking therefore, is the only way of replenishing the barramundi population in fresh water impoundments. Barra probably have to be sexually active as a male before changing to a female and can only do this in salt water.

Figure 1 [Right] shows, for example, that there is a 60% chance that a barramundi of 100 cm in length is female. Next time you catch a barra measure it and see if it is a male or a female.

What do barra eat?

Barra are voracious opportunistic predators. They eat just about anything that lives in or around water, including insects, spiders, crocodiles, prawns, fish and each other (Davis 1984). The size of the prey is largely determined by the size of the barra. The diet of a larger barramundi consists of 60% fish and 40% crustaceans, (mainly prawns) while smaller barra eat mostly small or large prawns. This will vary according to where the fish is living. One fish that stands out in a barra's diet is catfish. It has been found in the stomachs of barra with the spines protruding through the stomach and into the body cavity! Tough fish! Barra can take prey that is up to 60% their own total length.

As water temperatures cool during the dry season (May - August), barramundi slow down and eat less frequently. Catch rates are usually very low at this time of year. During the build-up and wet season (September - April) water temperatures can be up to 100C higher than the dry season. Barramundi activity increases with the warmer temperatures and catch rates are generally higher.

How much can barra see in dirty water?

Vision is probably limited in dirty water. Barramundi, like other fish, utilise what is called a lateral line. This is a sensory organ, which runs down both sides of the body. The lateral line enables fish to detect vibrations in the water and so be able to locate prey and avoid predators. A barra fisherman once caught a barramundi with no eyes, possibly the result of an old injury. On inspection by research staff it was found the fish was in excellent condition and was at least three years old. This shows that even a barra without eyes can survive.

It also raises the question of whether it is the colour or the action of a lure that attracts the fish? It is probably a combination of both. Brightly coloured lures with a tight action and a rattle have become very popular over the last few years.

What is that red spot on that barramundi?

If you have ever fished at Corroboree Billabong, a popular waterway about an hour's drive from Darwin, you may have caught a barra with a few red spots or even sores on the body. This is probably epizootic ulcerative syndrome, better known as red spot disease. On barramundi, it is found mainly in fresh water. Similar conditions occur in other species of fish in fresh and salt water. The cause is still not completely understood but it is believed that as water temperature falls and food becomes scarce the condition of the fish and resistance to disease drop and it becomes more susceptible to infection. Research showed that a fungus was responsible for the primary infection (Roberts 1997). Open sores caused by the fungus are then infected by other pathogens such as bacteria and viruses.

It is not advisable to eat fish affected by red spots as microorganisms found in such lesions have the potential to cause disease in humans (Pearce 1990).

I thought all small barra swam upstream after the wet?

Not quite. Large numbers of small barra do swim upstream after the wet season. However, some barramundi do not have a freshwater phase in their life cycle and spend their entire lives in an estuarine habitat. (Pender and Griffin 1995). This is one reason why we can catch small barra all year round in areas like Darwin Harbour and some of the Gulf rivers such as the McArthur near Borroloola.

How heavy is my Barramundi?

Most barra anglers talk in length instead of weight these days, but there are still some of us who like to know how heavy that barra was. Weighing a large fish is generally not a good idea, due to the damage it may cause, if you intend to release it. Measuring your barra is the better option. Over the years researchers have collected a huge amount of data on barramundi including weights and lengths. The length / weight relationship of barramundi varies between individual fish and is due to habitat differences and times of year. Click here to view a table showing an approximate relationship between the length and weight of barramundi. So next time you catch a prize barramundi but want to release it with the least amount of stress, measure it carefully and use the table below to work out the approximate weight.

Fishbits - did you know?

• Barramundi have been recorded up to 150 cm long and weights in excess of 40 kg, but larger fish have been reported!
• Barramundi are thought to live to around 20 years of age.
• Large female barramundi can produce 32 million eggs a season; that's almost twice the human population of Australia
• Barramundi change sex, they generally mature as males in their third to fifth year and then change to females between four to eight years of age, but only in salt water.
• Barramundi inhabit areas where the water temperature ranges between 23C to 35C, from the Ashburton River in the west to the Mary River in Queensland.
• Barramundi can travel great distances in their life; one fish that was tagged and released had travelled 622 km when it was recaptured. Most fish however are recaptured close to where they were tagged. There is generally not much movement of barra between river systems.

References

• Coleman, A. P. M. (1998). Fishcount - A Survey of recreational fishing in the Northern Territory. Fishery Report No. 41. Department of Regional Development, Primary Industry, Fisheries and Resources.
• Davis, T.L.O. (1982). Maturity and sexuality in Barramundi Lates calcarifer (Bloch) in the Northern Territory and south-eastern Gulf of Carpentaria. Australian Journal of Marine and Freshwater Research 33, 529-545.
• Davis, T.L.O. (1984). Estimation of fecundity in barramundi Lates calcarifer (Bloch) using an automatic particle counter. Australian Journal of Marine and Freshwater Research, 35, 111-118.
• Pearce, M. (1990). Epizootic ulcerative syndrome (red- spot disease). Fishnote. No. 1 Department of Regional Development, Primary Industry, Fisheries and Resources.
• Pender, P.J. and Griffin, R.K. (1996). Habitat history of barramundi Lates calcarifer in a north Australian river system based on barium and strontium levels in scales. Transactions of the American Fisheries Society 125: 679- 689.
• Roberts, R.J. (1997). Epizootic ulcerative syndrome (EUS): Progress since 1985. In T.W. Flegal and I.H. MacRae (eds.), Diseases in Asian Aquaculture 111.Fish Health Section, Asian Fisheries Society, Manila.
• Schipp, G. (1991). Introduction to the life history and biology of barramundi. Fishnote No. 7 Department of Regional Development, Primary Industry, Fisheries and Resources.

Date: November 2003

Disclaimer:

While all care has been taken to ensure that information contained in this Fact Sheet is true and correct at the time of publication, the Northern Territory of Australia gives no warranty or assurance, and makes no representation as to the accuracy of any information or advice contained in this publication, or that it is suitable for your intended use. No serious, business or investment decisions should be made in reliance on this information without obtaining independent / or professional advice in relation to your particular situation.

Additional Information

• Fishnote: Anaesthesia of Barramundi
• Fishnote: Care of Newly Captured Barramundi Broodstock
• Fishnote: Diseases of Barramundi Broodstock
• Research: Barramundi