Enjoying the dry season, visiting Kakadu National Park’s beautiful sites with a great bunch of people, it has been quite a while since I last found the time to write on this blog, not for want of topics…
I just added a new category to this blog which I named “Meet the Locals” as I think it’s time I introduced you to some of our amazing critters.
First up is a true Top End icon, the Barramundi (Lates calcarifer)!
There are a lot of keen fishermen (and women) out there, locals as well as visitors from interstate and overseas, who know how to catch our famous Barra – but there are quite a few interesting facts about this species that are little known. I actually spent the morning trying to find the answers to a few questions that came up on tour the other day.
Our group had just embarked on the boat trip down Twin Falls Creek after morning tea on the beach. The water was clear and calm, we could see quite a few decent sized Barramundi in the creek and the question was raised whether all Barramundi would migrate into saltwater sometime during their lives.
Mmmmh…I wasn’t sure.
I thought I knew our local Barramundi were migrating during the wet season – but not all of them…
I knew they were all born male, eventually undergoing a sex change – but what exactly happens?
I definitely had to do some homework and find out about the biology and life cycle of the Barramundi:
- Barramundi can live in both fresh and salt water. They are euryhaline (I learnt a new word today). Lates calcarifer can be found in coastal, estuarine and fresh waters of the Indo-Pacific region.
- In the wild Barramundi reach sexual maturity usually between 3 and 4 years of age. Yes, they initially mature as males and go through one or more spawning seasons before they eventually undergo a sexual inversion – this is called protandry (actually, I learnt two new words today!).
- By the following breeding season these fish will have become proper females, able to release many millions of eggs (the highest reported number is 40 million, no idea how long it took these poor researchers to count them…).
- As a rule of thumb, Barramundi less than 80cm in length are males and those exceeding 100cm are females.
- Barramundi breed during the wet season. The breeding season starts around late August, when the temperature in the Top End waterways is on the rise again and the large spring tides return.
- There does not appear to be a definite long range migration. Fish already in the river mouths and estuaries congregate locally for spawning.
- Other fish may arrive in the estuaries a little later, namely maturing male Barramundi, when the rain of the monsoon season causes the creeks and rivers to flood and allows the fish to travel downstream from places like Twin Falls Gorge – and there’s a good reason for making this long journey, keep reading!
- Barramundi eggs and larvae will only survive in salt water!
That’s why all breeding takes place in river mouths where the high tides wash the eggs and larvae into the mangrove swamps and floodplains. - Spawning seems to be related to the lunar circle, taking place at night around the slack tide, that short period in time when the flow of the water stops as the direction of the tidal current reverses.
- The breeding season is usually completed by late February or early March.
- The eggs are capable of being fertilised for a few minutes only, before they “water harden”. Fertilised eggs will then drift in the current for 12-15 hours until the larvae hatch.
- For the first 2 days or so the larvae will live on their yolk sac then move on to feeding on plankton which is plentiful in the mangrove swamps and floodplains.
- The juveniles feed ferociously (and are even cannibalistic) and grow fast.
- Towards the end of the wet season, the juveniles move from the floodplains into the rivers, many of them ready to migrate upstream, where they will spend the next 3 or 4 years as immature Barramundi boys.
It's a Boy!
Check out these links if you want to find out more:
The Department of Resources – Fisheries’ website has a lot of interesting information on Barramundi and other fishy locals: http://www.nt.gov.au/d/Fisheries/
All your Barra-questions answered: http://www.nt.gov.au/d/Fisheries/index.cfm?header=NT%20Fish%20-%20Barramundi
The diagram on the life cycle of Barramundi in this Fishnote is particularly helpful: http://www.nt.gov.au/d/Content/File/p/Fishnote/FN07.pdf
Boh boh!
Anja
