Flathead fans a MUST READ!!!

[Lovey80]

Hi all, as many of you regular readers to this site will now there is often a topic of conversation concerning the Dusky Flathead and the 70cm no take limit. There seems to be many a theory/oldwivestale/misinformation/opinion(call it what you want) about the topic. I was one of those with the wrong idea. Below is close carbon copy of a letter to the editor of a Marine Biology PHD student on the matter. While the outcome is still the same as most of what we thought, I think this is some very interesting reading and mostly likely the right information.

Happy reading..... Oh the letter was published in November 2007, Modern Fishing Magazine. A bit long but a good read just the same.

Cheers Chris

" I was reading the July 2007 issue of Modern Fishing and came across the letter 'Lizard Lore', from a fellow reader (Anthony Willebrands-DL) and thought I may be able to provide a few answers in regards to the Flathead biology. I'm currently finishing my PHD through the centre for Fish and Fisheries Research at Murdoch University in Western Australia, in which I am investigating the biology of the Yellowtail Flathead and the Western Blue Groper and Blue Morwong.

During this study of the Yellowtail Flathead, (Platycephalus endrachtensis), in the Swan river estuary in Perth, we found several characteristics that Anthony Willebrands and other fellow Flathead lovers may like to know. Even though the Yellowtail Flathead can not reach the extraordinary lengths and weights to that of the Dusky Flathead, it does share the same characteristics of females and males having markedly different growth rates. The females and males of the Yellowtail Flathead attain a maximum length of 615mm and 374mm respectively. If you were only to see this result , you could be forgiven for assuming that this species is a protandrous hermaphrodite( male and female sex change). However, we also found that both sexes are present at all age classes from a age of one year old to the maximum of 9 years, recorded for both sexes.

Further investigation of the reproductive organs, overies and testes of Yellowtail flathead found no evidence of male and female reproductive tissue occurig together-a key indication of possible sex change. Our conclusion was that Yellowtail Flathead were dioecious ( Speparate sexes), with females and males possessing markedly different growth rates.

In other studies of Flatheads in the genus Platycephalis, including the Dusky (P.fuscus), Southern blue-spotted Flathead(P.speculator), Sand Flathead (P.Bassensis), Tiger Flathead(P.richardsoni) and the bar tailed flathead(P.indicus), similar results of femailes attaining a larger size have been found. Furthermore, none of these scientific studies found any evidence of sex change in these species.

The thought that Dusky Flathead may change sex may could have come about from literature describing the biology of other members of the Platcephalid family, including several species found in Japanese waters, such as the Lizard Flathead(Inegocia japonica). They do change sex from male to female. In species where the large fish are females not just in Flathead, it is imperative that we try to protect these large fish because it is these individuals that have the greatest reproductive output; they are able to produce hundreds of thousands or even millions of eggs.

To think that these large Dusky Flatheads are barren is not correct. Kind Regards Pete C.

Peter Coulson, Centre for Fish and Fisheries Research , South St. Murdoch, WA 6150.


There it is boys and girls a real scientific reason behind fish conservation. Maybe someone at the EPA could adopt the same. I doubt it .

Cheers Chris

[DICER]

great post - is there also a reference?

Did they check throughout the year to see if any changes occur abruptly, say within a particular season?

[Lovey80]

Reference??? Just a letter to the editor of November 2007 Modern fishing magazine.

Cheers Chris

[DICER]

a scientific reference to a paper/publication?

[Lovey80]

As he said in the post he is currently finishing his PHD on the subject.

Cheers Chris

[plaztix]

Interesting, so in plain speak, big female duskies were never males.

Well i'll be..........

[Jeremy87]

great post - is there also a reference?

Did they check throughout the year to see if any changes occur abruptly, say within a particular season?

Yeh good point

He's covered most bases there, considering he's openned up fish between 1-9 years of both sexes without finding any mixing of organs. The only thing i'd like to see is a survey of fish caught during the breeding season. He could have done all these things and we just don't know.

I did a quick search on scholar and nothing comes up under his name or using Platycephalus endrachtensisin the search box. They do host a species of eye fluke though (not relevant but just a little bit icky) . At a guess i'd say it hasn't been published yet.

It seems strange that nothing has been published on the subject and even still in the highly likely circumstance that yellow tail flathead are dioecous it still isn't confirmation that duskies are though its a pretty good indicator.

Thanks for posting that up for us Chris i think we can cautiously call australian flathead species dioecous now. When we see something published then we'll know for sure.

[Lovey80]

Yeh good point

He's covered most bases there, considering he's openned up fish between 1-9 years of both sexes without finding any mixing of organs. The only thing i'd like to see is a survey of fish caught during the breeding season. He could have done all these things and we just don't know.

I did a quick search on scholar and nothing comes up under his name or using Platycephalus endrachtensisin the search box. They do host a species of eye fluke though (not relevant but just a little bit icky) . At a guess i'd say it hasn't been published yet.

It seems strange that nothing has been published on the subject and even still in the highly likely circumstance that yellow tail flathead are dioecous it still isn't confirmation that duskies are though its a pretty good indicator.

Thanks for posting that up for us Chris i think we can cautiously call australian flathead species dioecous now. When we see something published then we'll know for sure.

He does make reference to "other studies" finding the same outcome but I am not aware of what he is refereing to as I don't run in Marine Biology circles. Just a question there Jezza. His point that both sexes are present from year 1 to year 9, wouldn't that be more of an indication that they don't change sex at a certain age/size as it is simply not a requirement if females are present at all ages?

So if there is no evidence of dual organs and females are found at all ages, is there any need to delve into it any further by catching them during breeding season? Just a thought.

Cheers Chris

[Dapper Dan]

thx for the post.

how can u tell whether its a male female (without cutting them up)? I always put the big ones back thinking they are females.

Dan

[dogsbody]

Is there a published doc that says they do change sex (ossie flathead). As i don't know, I think that the japanese flathead change sex maybe that's where the whole change sex thing comes from.

Please note i used words like " I don't know" and " I think"



Dave.

[Lovey80]

Dan you are right that the big ones are female and should be thrown back...... It's also the law It's just that those big ones you were throwing back were always female an didnt have a sex change so to speak. They are the most productive fish and still need to be returned.

Cheers Chris

[Jeremy87]

He does make reference to "other studies" finding the same outcome but I am not aware of what he is refereing to as I don't run in Marine Biology circles. Just a question there Jezza. His point that both sexes are present from year 1 to year 9, wouldn't that be more of an indication that they don't change sex at a certain age/size as it is simply not a requirement if females are present at all ages?

So if there is no evidence of dual organs and females are found at all ages, is there any need to delve into it any further by catching them during breeding season? Just a thought.

Cheers Chris

Don't get me wrong it all sounds pretty conclusive, i was just agreeing with dicer that to confirm it (as much as anything can be confirmed in science) then there are a few things that you'd want to include in your study and it would be good to actually view the paper when its released.

If someone was to say I believe all australian flathead species are dioceous and not hermaphroditic that would be a hypothesis, and in the world of science you can't actually prove anything so to speak, you can only aquire evidence that supports your hypothesis and dicredits others.

You normally gather evidence by looking at other sources or gathering your own data. In this case he seems to have done both and it looks pretty conclusive. But this is a pHD he's doing which is a big deal and all he's really talked about in the letter is stuff supporting his hypothesis. If he wanted to be really thorough then he'd look at flathead throughout the year and if nothing pops up then he has good evidence going against the hermaphroditic hypothesis. He might have already done all this but without going through his paper you don't actually know.

Anyway i'll be following this with interest as this time next year i might be thinking about an honours project and if no ones actually done anything with duskies it might be a good topic considering the recreational importance etc.

[oldboot]

Unfortunatly not all masters papers are published openly on the internet or they may not be easy to find.

I vsited a mate who is a lecturer at uni........ there in the waiting area of his department is this huge book case full of masters papers.......just in case someone shuld want some light reading while they are waiting

It's good to see that he thaught it worthwhile to write to the editor......


cheers

[Lovey80]

I totaly get what your saying there Jeremy and as we know all good scientific research isn't worth the paper it's written on until it is published and had the opportunity to be scruitinised by peers. ( A point the EPA obviously loves to ignore). Until there is the same level of research put into the subject (or any) and there is ANY evidence to support the sex change then this is how I beleive we should view it. Up until now (as far as I am aware) it was just assumed they had a sex change like Barra as only the big ones were female.

Just my thoughts. Do you agree?

Cheers Chris

[RayDeR]

G'day!

There is a chance that most of us who catch flathead would be able to tell a male from a female on the filleting table.

This should confirm that there are both males and females across the whole of the range of legal sizes.

Ray De R