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View Full Version : Flathead fans a MUST READ!!!



Lovey80
21-01-2008, 11:48 PM
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
22-01-2008, 07:44 AM
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
22-01-2008, 07:53 AM
Reference??? Just a letter to the editor of November 2007 Modern fishing magazine.

Cheers Chris

DICER
22-01-2008, 07:55 AM
a scientific reference to a paper/publication?

Lovey80
22-01-2008, 08:02 AM
As he said in the post he is currently finishing his PHD on the subject.

Cheers Chris

plaztix
22-01-2008, 08:22 AM
Interesting, so in plain speak, big female duskies were never males.

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

Jeremy87
22-01-2008, 09:12 AM
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
22-01-2008, 04:25 PM
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
22-01-2008, 05:17 PM
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
22-01-2008, 05:17 PM
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
22-01-2008, 05:43 PM
Dan you are right that the big ones are female and should be thrown back...... It's also the law:D 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
22-01-2008, 05:55 PM
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
22-01-2008, 08:47 PM
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;D

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


cheers

Lovey80
22-01-2008, 09:13 PM
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
22-01-2008, 09:18 PM
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

Jeremy87
22-01-2008, 09:54 PM
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

I have a theory based on head shape, but thats for my honours project. If you run with the big ones are girls and the others go nicely with a bit of butter in the pan then it's enough for most.

Yeh Chris you've summed it up well. It's just an assumption alot of people have made and run with, though if you flick through the forums and magazines you'll find that there have been a few who have questioned the belief due to lack of evidence. I think starlo might be one. Clever bloke ,while he does all the usual fishing personality things he also seems to have a good scientific knowledge of alot of fish aswell. Anyway the next time someone says to me they swap sex over i'll be saying that the evidence suggests otherwise.

jackson4300
22-01-2008, 10:37 PM
yea thats an eye opener, have had more people tell me they change sex then those who say they don't. Hes done his research and written it up in a good way for all to read and understand which shows that he actually does know a thing or too (as he should if hes doing a PHD)

Even though its not going to change or affect what we do as we already do realese the larger flatties which are females it is still something interesting to know.

RayDeR
23-01-2008, 10:27 AM
G'day!

Just a thought: If we assumed that all "survivors" became females after a certain size, and were wrong in that assumption, do we need to work out a way to protect smaller females? That is, those in the 40 to 70cm range?

Ray De R

Jeremy87
23-01-2008, 12:52 PM
G'day!

Just a thought: If we assumed that all "survivors" became females after a certain size, and were wrong in that assumption, do we need to work out a way to protect smaller females? That is, those in the 40 to 70cm range?

Ray De R

Not a bad point but if you look at it from the new perspective it also means that you know have a higher proportion of the population being females than previously assumed, while the big girls are the major contributors to recruitment you'd have to think the plain numbers of smaller specimens would have to also make a significant imput.

I suppose idealy you would try to limit the removal of females but unfortunatly atm the only way you can tell the difference between the 2 sexes in similar sized specimens is to open them up and have a look inside (possibly leading to higher release mortality rate;D ).

Lovey80
23-01-2008, 07:08 PM
G'day!

Just a thought: If we assumed that all "survivors" became females after a certain size, and were wrong in that assumption, do we need to work out a way to protect smaller females? That is, those in the 40 to 70cm range?

Ray De R

I think Jeremy has a good answer to that one but I think we have it right as far as protection is concerned. These big girls must be doing something right. There is pleantly of Flatties around in most area's. While they aren't as prolific as bream I don't think they ever could be. The amount of times Iv'e thrown a cast net and caught reall small ones lets me know they are breeding fine. (Before the green brigade get on thier horses, the baby flatties go back before I worry about the live bait).

At the end of the day the flatty definitely has made a resurgance and am glad fisheries brought in the rules about the big flatties.

Cheers Chris

RayDeR
23-01-2008, 08:52 PM
G'day!

If it takes a PhD candidate to tell us that flathead do not change sex, I was really wondering if anyone has really looked for sex differences in the physical appearance of flathead.

Jeremy alluded to head shape in a previous post.

Ray De R

Jeremy87
23-01-2008, 10:59 PM
G'day!

If it takes a PhD candidate to tell us that flathead do not change sex, I was really wondering if anyone has really looked for sex differences in the physical appearance of flathead.

Jeremy alluded to head shape in a previous post.

Ray De R

Just a theory, not based on anything as yet. I just noticed out of personal experience that all the big girls have a characteristic round head, and yet in smaller specimens you get this squarer more even tapered head shape. I always assumed that this was a male female thing and when the mature their heads change into this rounder head shape. But since this thread was brought up it doesn't make sense and reflecting i can also recall smaller specimens with the rounder head shapes. It might be nothing but if it turns out to be females have a round head and males have a square head then just remember who came up with it.

anyway heres 2 photo's one is of a 45cm job i caught a couple of days ago and the other is of a 61cm fish that my mate caught a few years ago which sought of show what i'm going on about, please tell me you see it aswell and i'm not just going crazy.

reidy
24-01-2008, 09:51 AM
Good day Jeremy87,
Good call about head shape.Do alot of off shore flattie fishing in Tas. and have noticed a similar trend,Smaller flatties on the Bell Bay mud flats (1000s of 100-250mm models) have the same rounded head shape as the larger (much larger) off shore critters.The exeption appears to be tigers who all have the narrower head.I do agree with the WA study that our flatties are not hermafradites (poor spelling David) as I have caught a number of large 700mm + models during the spawn that are def. males (they release their milk at the side off the boat).
A very interesting topic
Cheers
Reidy

Lovey80
17-10-2008, 10:07 PM
Bump for those reading the other flatty thread.

reel scream
18-10-2008, 12:56 AM
. The females and males of the Yellowtail Flathead attain a maximum length of 615mm and 374mm respectively.[/B]Cheers Chris


Thanks for the info Chris. Trawled off WA and would have to ?? those max lengths mate. Yellows out of 45mtrs go well over the 70.

Cheers Scott

rando
18-10-2008, 12:39 PM
How many of you have filleted a maximum legal size male.Something to look out for when you are at the filleting table in future.

Lovey80
18-10-2008, 02:35 PM
Scott, I think they were only refering to the estuary version of the fish. I'm guessing those figures were of ones caught inshore only. But going on those figures it would be safe again to assume that the ones offshore well over the 70cm mark are also females.

Cheers

Chris

Lovey80
10-07-2010, 08:53 PM
bump again for another flatty sex change thread

gr hilly
10-07-2010, 09:26 PM
yea and if we take all the males there will be nothing to bang the females and you know how stroppy a sheila gets when she gets nothing,hahaha
Hilly

bondy99
10-07-2010, 10:23 PM
G'day Jeremy87,

Maybe run this via Ian Tibbetts back at CMS, it would be interesting to see if a project could be done on this but dont think anyone would be giving up a nice tasty flattie for science.

Off topic.

From what I gather from a researcher there appears to be two species of snapper on the coast. DNA is to be done but Fisheries are not keen.

The two species of snapper have slightly different morphometrics at the head and another section from what was said. I cant eloborate any further as that's all I Know of.

Happy fishing, Peter

wayno60
10-07-2010, 10:55 PM
so what it boils down to is that any yellowtail flatty over 374mm is a female..?!?!
where do you draw the line??

split-shot
12-07-2010, 08:48 AM
A search on Google, produced the following result;
Peter Coulson

Email: p.coulson@murdoch.edu.au (p.coulson@murdoch.edu.au)
Phone: 9360 2256
Position: DSE PhD candidate
Thesis title: Size and age compositions, growth and reproductive biology of the western blue groper, queen snapper and bar-tailed flathead on the south coast of Western Australia
Supervisors: Ian Potter and Norm Hall (DSE)

This was taken from Murdoch uni web site www.cffr.murdoch.edu.au/postgrads.html

baffleo_bill
15-07-2010, 07:36 PM
I posted this over on Nugget's site several months ago. The paper I've linked to is well worth a read for anyone interested in flathead.

*-----*

Hi all,

Gray and Barnes conducted a study on flathead growth rates and reproduction. They sampled around 8000 flathead from nsw waters. In regards to the belief that flathead undergo sex change, they had this to say:

"No hermaphroditic fish were observed in this study or in previous studies in NSW (Gray et al. 2002, West 1993), suggesting that dusky flathead do not change sex, but rather male fish do not grow as large or as fast as females."

The entire report is an interesting read and can be found at: http://www.dpi.nsw.gov.au/__data/assets/pdf_file/0005/237794/WF-2008_Output-1053_Gray-et-al_Dusky-Flathead-Final-Report_REPORT.pdf (http://www.dpi.nsw.gov.au/__data/assets/pdf_file/0005/237794/WF-2008_Output-1053_Gray-et-al_Dusky-Flathead-Final-Report_REPORT.pdf)

*-----*