The Courtship of the Coral Trout
I managed to make a few minor changes to the www.skippermeggs.com site last week with another sensational Weipa fishing article added to the “Links” section.
I also travelled to Tasmania and believe it or not was caught in a huge dust storm half way between Hobart and Devonport.
When I finally reached my destination it was pouring with rain and the wind was still howling so I gave all thought of trying out a local seafood restaurant on behalf of readers and decided to eat in at the Motel. Great decision! I will update the site’s “Recommended Fish Restaurants” link with the results next week.
Ok, the Northern Australian fish life cycle stories continue and this week we’ll take a look at the coral trout which is actually related to the Cod and Grouper family known as Serranidae.
There is not one Coral Trout but several different species.
The most common is the Leopard Trout or Plectropomus Leopardus.
These fish have a blue ring around their eye and are generally found around the inner to outer shelf reefs in Northern Australia where the visibility in the water is around 5-10m. Interestingly where the visibility in the water is between 15-20 metres on the outer mid shelf you will find the highest density of Leopard Trout. They can grow to 70cm and weigh in at 6kg and live to 16 years of age.
The Bar Cheeked coral trout or Plectropomus Maculatus is mainly caught in the turbid surrounds of the coastal to mid reef areas (visibility less than 5 metres) and these fish are characterised by the fact that their spots turn into “bars” at the side of their heads. Bar Cheeks can grow to 80cm in length and weigh 8kg.
The Blue Spot or Footballer coral trout Plectropomus Laevis are all but exclusively outer reef and Coral Sea dwellers (where the visibility is between 25-30 metres) and these can be identified by the blue spots with dark edges on their head, body and fins. These are relatively large coral trout and can grow to 120cm and weigh upwards of 25kg and live to the ripe old age of 18 years.
Finally, the Passionfruit coral trout or Plectropomus Areolatus has large blue spots everywhere - and it is the only coral trout to have the spots under its belly. These fish are relatively scarce but can grow to 70cm and weigh 6kg.
Being protogynous hermaphrodites coral trout are the opposite to Barramundi.
What the??
This basically means that they begin their lives as females and change sex later in life to become males (as discussed in a previous post, barramundi begin life as a male and change later to become females). It therefore follows that small fish are generally female, whilst large fish tend to be males. It could also be extrapolated that the male of the species is best able to provide the necessary survival traits and genes to pass on to future generations.
Sex change happens between 23-62cm in length and on average at 42cm and most often after spawning.
Spawning itself is more to do with water temperature change than seasons or months of the year and generally occurs when the water reaches 25-26.5 degrees (September - December in the north and October - February in the south Great Barrier Reef regions).
What is interesting is that the coral trout aggregate in huge numbers to spawn. In the past I have fished in various waters where large sizes and numbers of either nannygai, morwong or even leatherjackets have appeared in plague proportions and I now wonder whether this was due to their spawning activity. Future posts will tell.
Anyway, aggregations of coral trout peak during the new moon when the tidal flow is strong (especially the ebb tide) particularly at dusk. It’s thought that this allows the eggs to be transported far and wide away from the reef and the lack of light prevents likely predators from getting in the way.
Ok, so what’s so special about the coral trout spawning? Well by the sounds of things it would be an event well worth the watching.
Aggregations of fish cluster around reef slopes in depths of 10-15 metres and individual males stake out their territory and begin to attract females by flashing the darkened edges of their fins on and off. In turn, the females lay close to the ocean floor and the schmoozing male virtually lies down next to it on its side with its head on a 45 or 90 degree angle.
Although it doesn’t quite have a beer and a smoke in its fin, the male shakes its body and head from side to side and with its underbelly rubs the female’s head or body. It continues this many times until finally a phenomenan known as a “spawning rush” occurs.
If the female agrees (complies?) the pair will swim really fast to the surface and once they turn they release sperm and eggs. Some fish, mainly males (wouldn’t you know it!), spawn a few times throughout the night.
As for the eggs, these are carried away by the currents and float below the surface. They are incubated for probably up to 45 hours and then the larvae lives off the yolk for awhile until it is completely absorbed. The young can then start to catch its own prey.
Juvenile coral trout are around 14cm in 6 months and reach 22cm by year one. At 2 years they are around 30cm, at 3 years 35cm and 40cm at 4 years of age.
Fish over the 60cm mark are at least 15 years old.
Next week I will continue with yet another post on the life cycle of a northern Australian reef fish.
Until then…
Sea you later,
Skipper Meggs
April 11th, 2008 at 1:01 am
Seemed like a long story this time.