Boom & bust strategies of the spangled grunter

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Above: A mega-feast for blow flies in the Todd. This and photo below by MIKE GILLAM. 

 

The spangled grunter – expiring in such great number in the presently drying Todd – is not only the most widespread fish species in arid Australia, it’s the most widespread Australian freshwater fish species of all.

 

One reason for this is that it is very hardy, able to withstand widely varying water temperatures, quality and salinity, says Dr Steve Morton, an expert in the ecology of arid Australia. This means it can occupy not only the arid zone, but monsoonal and tropical regions as well.

 

Another reason is its fertility. Summer is the breeding season and a single large female will spawn in the order of 100,000 eggs. They turn into larvae after just two days and are fully grown within their first year.

 

p2310-Spangled-grunters-livThey don’t needs floods to breed although the output will be higher in big flows of rivers and streams. But they can swim for kilometres in “the water of a wheel track”, seeking out new opportunities to feed and breed. The consequence is that they quickly fall victim of receding waters and die, as we have seen recently in the Todd.

 

Right: These guys were swimming in the Todd last week.

 

They are omnivores. The young eat mainly fungal matter but as they grow they become more carnivorous – eating mosquito larvae, diving beetles, aquatic bugs and even one another.

 

Mike Gillam, who has tried keeping them in an aquarium, warns says that “even if you feed them regularly, you will end up with the largest grunter swimming around with the tail of the second largest protruding out its mouth!”

 

In dry times populations survive in the tiniest of waterholes, ready to explode as the opportunity arises. It’s an evolutionary strategy that allows the spangled grunter to make the most of the ephemeral resources that characterise arid Australia, says Dr Morton.

 

Retired now from full-time work with the CSIRO, including as Chief of Division and on the Executive Team, Dr Morton is writing a book on desert ecology for the general reader: what scientists have learned about inland Australia in terms that everyone can understand. Photography will be by Mike Gillam, who so wowed locals last year with his Maximo of Mparntwe exhibition. The book, which will take two years to complete, promises to be a landmark publication for The Centre.

 

– Kieran Finnane

 

 

 

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3 Comments (starting with the most recent)

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  1. Ian Sharp
    Posted April 2, 2016 at 10:48 am

    Good read, thanks Kieran. Looking forward to Steve Morton’s book, I’m sure the Alice Springs News Online will do a story on it when published.

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  2. Monty
    Posted April 1, 2016 at 4:48 pm

    Steve, another example of the big fish in a small pond. Let’s not forget that even if they die they provide nutrient for the next rain event.
    Assume the Lake Eyre system would benefit from the deposited nutrients to initially feed the explosion of brine shrimp which allows a massive explosion in fish numbers and if big enough a significant pelican breeding event.

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  3. Pete
    Posted February 10, 2016 at 8:22 am

    You’ve gotta love spangled grunter (or spangled perch, same dude). Apart from a few tiny, isolated patches of introduced things, they are the only real angling target we have in Central Australia which is good for those of us who break out in hives if we can’t play with our food occasionally.
    Sure, they only grow to about 30cm in permanent waterholes but in the right conditions they are super aggressive, taking lures and flies quite happily.
    A hot afternoon with a thunderstorm rolling in is perfect and in those conditions, I have caught them on barra lures much bigger than they are.
    For a freshwater fish, they don’t go too bad on a plate either – in fact, they are very sweet. It just takes a few to make a feed.
    They are a really important part of the Red Centre environment (and traditional life) in more ways than one.

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