GENETIC SELECTIOM
dear angler,
pls catch n release all the big sized fish coz
when u kill the big sized ones.. olny the small sized are left to breed… so in the course of time only smaller ones will be found yah!!!
think twice before u take the big ones!!!
TIGHT LINES N ADIOS AMIGOS
quote:
Originally posted by kumar
GENETIC SELECTIOMdear angler,
pls catch n release all the big sized fish coz
when u kill the big sized ones.. olny the small sized are left to breed… so in the course of time only smaller ones will be found yah!!!
think twice before u take the big ones!!!TIGHT LINES N ADIOS AMIGOS
Too true Kumar,
Its like when you kill all those above 6 feet tall… in time their genes disappear and you cannot put up a basketball team anymore.[:)]
Seriously, this may have happened to the big Tomans and Sebaraus we used to find in places like Kenyir and Temenggor where the biggies were taken out without any thought for the future. So in the generations that followed, them babies cannot grow very big anymore because no more biggie genes left in them…Sad lah.[xx(]
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Not sure I buy into this logic. Fish are not like humans. As long as there is food, fish continue to grow throughout their lives. Fishing pressure obviously reduces their life span which means they do not have the time to grow to a large size. Another natural adaption to fishing pressure is that a population of fishes will become sexually mature and breed at an earlier age and a smaller size. Nature always tries to find a way. There is evidence that Tuna of various species and even Marlin are becoming sexually mature and breeding at a smaller size due to fishing pressure and reduced size range in the remaining population. Unfortunately, the biggest fish produce the most young, so an early maturing population cannot reproduce the same numbers as a balanced population, resulting in further decline in the population.
However, there is every reason to believe that with proper management and size and bag limits, the process is reverseable almost immediately and fish populations bounce back in both quantity and size in quite a short period of time. They also quickly repopulate areas that previously were devoid of fish. The net ban in inshore waters of the Gulf of Mexico resulted in a Redfish and Trout “boom” within 2 years of the ban.
Marlin,
Can’t remember where I picked it up … must be one of the studies reported in one of the American Fly Fishing Mags… sounded plausible to me, tho’ I do not know nuts about fish genetics.
I agree with you tho’, that given time their rehabilitation process can be very fast, esp. keeping in mind that it is at least one generation a year. And on a good diet, I guess the recovery rate, both in size and numbers, can be relatively fast.
In Malaysian conditions, its been proven that closing rivers do result in numbers coming back in 2 to 3 years…the Kelah in Sg. Cacing is a case in point … another sure thing is that the snakeheads will come back in numbers within 12 months if their habitat is left undisturbed …not sure about size though, as we hardly seem to get the sizes we see in the 60s and 70s anymore.
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The genetics argument regarding removal of the larger fish has been proven without a doubt on inland lakes. It is now common knowledge. However, those fish populations are very restricted being stuck in lakes. So, in river and sea environments, it is not proven.
Still natural evolution take eons to established itself, I tend to agree with Marlin, I don’t think a few generations of breeding among smaller population will drastically affect the future generation when it comes to size. Nature works in a myterious way…
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Anyone can point us to any studies regarding this interesting subject? … would really appreciate it…tks.
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Tony, you can check with AYAAK, he works for FISH WORLD .This organisation does research on fishes.I remember he told me once about GIFT TILAPIA.They are a result of selective breeding and how they go about it is that all larger size are isolated and left to cross(making sure no intercrossing ie.brother n sister) and their larger offspring are also isolated and the whole procedure are repeated until you get a larger than normal tilapis..That is your GIFT TILAPIA. So your posting makes sense…
quote:
Originally posted by culky
Tony, you can check with AYAAK, he works for FISH WORLD .This organisation does research on fishes.I remember he told me once about GIFT TILAPIA.They are a result of selective breeding and how they go about it is that all larger size are isolated and left to cross(making sure no intercrossing ie.brother n sister) and their larger offspring are also isolated and the whole procedure are repeated until you get a larger than normal tilapis..That is your GIFT TILAPIA. So your posting makes sense...
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Yo Ah Pek Dato’
Thanks for the input. Lets hope AYAAK reads this and enlighten us somore. I guess the way the GIFT Tilapia was “engineered” is all about saving the ‘biggy’ genes and passing them on… so in time you get only the big fellas around… similarly, if only the tall boys marry the tall girls and this goes on a few generations, we’ll get all tall fellas in the population, right?..unless there’s a throwback, of course.[:)]… now who was it that started playing with black and white rabbits?[:)].. old brain cannot remember anymore liao.[:D]
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Aiyaa, Atuk Culky, it’s World Fish Centre lah… Fish World, you make it sounds like Aquarium store, heheheh… [:D]
Anyway, If I’m not mistaken, what Ayaak is doing is “artificial” selection and also in optimum growing condition. Yet, again, I’m no expert in genetics…[;)]
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Just received sms from ayaak. He said that he has read this issue but no time yet to post… why… hahahahh because his tilapias are very busy ‘mau kahwin’ So I think he is busy nursing them to ‘do it’.
Chheerrss, T2
Be Happy Go Fisshing
Guys,
sorry ler, pretty busy right now observing the mating behaviour of Gift fish, currently i’m running some small experiment, trying to convert female to male heh heh…no chemical or hormone use eh…no genetic modification has been made, just selective breeding..
later..[:)]
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Well, IMHO, removing the big one will not 100% degenerate the genetic variation within that sp/population. But off-course we will lose a potential fish that may produce good milt or large number of eggs. But if this kinda of thing happen frequently on that sp, the same population and location, genetics bottleneck will develope slowly.
Say for example, people harvesting ikan Tengalan that is on the way for spawning (usually spawners have good eating size), we will lose one batch of good spawners and also a batch of tengalan fries. Not everyday they spawn, just at a particular time. I’ve experienced in just one night, the “org kita” harvest more than 200 kilos of Tengalan from Sg. Tiang, Temengor, just in one sampan…and a lot more sampan coming. So just imagine what happened next year, the number of Tengalan spawning decline terribally…they the “org kita” mumbling about the catch was bad, even during the spawning season…and the bad situation prolonged 2 to 4 years after that. When the big one was removed, what was left is the small unmature tengalan that won’t be able to spawn, but yet they are still being caught..so the population recovery will take more time. The same thing applied to few other freshwater sp, especially those seasonal spawner. Some freshwater fish takes 2 to 3 years to mature…not tilapia, within 3 months they can kawin already[:D].
Genetics variation can be increased easily by hybridization within the same spesies but from different population/location. For example, sebarau from Kenyir cross with that of Temengor…we may get…sebarau also lah but maybe better shape, good fighting skill, or maybe not a good sebarau[:D]. In case of GIFT-Genetic Improvement of Farmed Tilapia, it is more like a keeping the good one and remove the bad one through selective breeding. The base population of GIFT is made of 4 wild strains from Africa-Ghana, Kenya, Senegal, Egypt and 4 commercial strains namely Thailand, Taiwan, S’pore and one more. The cross within the wild and commercial strains, culture in many ways of aquaculture practices, polyculture…with ducks and chicken oso, home backyard oso, monoculture, in ponds, cages …produced the GIFT fish. The selection was in general in term of weight and most important..the level of inbreeding (calculate using some statistical software).The fish that will continue to produce new generation normally have very low level of inbreeding, means that they show genetic gain during the study and their genetic variation is relatively in good condition..
Huh, i’ve never write so long, hope u guys can understand my english yah ha ha…got to go now[xx(]
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Thanks ayaak for the detailed explaination on how selective breeding was done to produce GIFT tilapia. If I’m not mistaken, this is also refers to as “genetic strengtening” or “genetic vigor” or something like that…[xx(] it’s been a while since my Uni days…[:D]
But the question still remains whether a species will be smaller and weaker just after a few generation of “influence” selection caused by human because the lost of big healthy parent fish stock? We might see reduction in avg size of the fish population as a sign of overfishing but does that means the future genaration of that species won’t be able to attain the maximum size even if when the human factor been reduced?? I admit the lost of big size parent fish as a stock will reduce the gene pool of desirable gene being introduced for making it more suited to live in it’s current environment. But I stil have doubts that smaller size parent stock won’t be able to produce off springs that can grow bigger than ther average parent stock provided they live in ideal condition.
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Found this article which supports this theory… goto
www.conbio.org/cip/article63poi.cfm …based on a study done by Prof. David Conover of the Marine Science Research Centre of Stony Brook Uni. in N.Y.
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In-Fisherman magazine based out of Brainere Minnesota has published or mentioned many an article on this topic. Not only that, but I have talked with DNR personnel regarding this topic on several occassions. All the muskie and bass trophy hunters take this factor into consideration when choosing which bodies of waters to fish. That’s one of the reasons that In-Fisherman has been promoting selective harvest of smaller members of the gene pool for more than a decade. Editor-in-chief Doug Stange is a good guy and should be happy to lightly discuss this matter with any of you interested but please remember the guy is very busy.
It is for this reason that lakes that we fish tournaments in, I make it a point not to keep any large bass at all except for during the tournament for weight. Trophy lakes such as Lake Mendota for walleyes, mot anglers keep walleyes less than 22 inches and have been doing so for two decades due to this common knowledge based on proven scientific fact. The huge runs of fish between 24 inches up to over 30 inches are almost eclusively released. Only a few giants taken through the ice and accidentally killed in the summer from unrecoverable stress due to the high energy exertion in the hot water are taken. Another example is the raising of muskie size limits in lakes such as Lac Courte Oreilles to 53" from what started years ago statewide as 32 inches. The lakes near me started at 32 inches but have been continuously raised in the major muskie lakes such as Waubesa, Wingra, and Monona. Regular stocking of new fish stocks with the increased size limits are used to combat this effect. All this based on this proven information. Again, this idea has never been proven in rivers. I don’t recall seeing anything about this in oceans or seas. But small little bodies of water that are confined are susceptible to this. I don’t know of that many waters in Malaysia that would be affected as the floods from monsoons and such constantly allow things to change if the fish wish to swim over and check out a new spot. For sure the major dams in Malaysia would probably be unaffected.
I think we have to be very careful about some of the so called “irrefutable” evidence since all science has to make certain assumptions before conclusions are drawn. Managed fisheries with farmed stock in isolated lakes are not representative of what might happen in a wild gene pool. I think we must also differentiate what species of fish we refer to when speculating on genetic effects.
Yellowfin Tuna only live for about 5 years and in that time, under ideal conditions they can reach 300lbs or more maximum size potential. With commercial fishing pressure reducing their effective lifespan, not only does the population numbers diminish, but we notice an overall reduction in the size of the fish caught. This happens very quickly, within the space of a few years. There is no way that genetic variation can operate this quickly and the gene pool is likely uneffected by commercial fishing since all the fish either caught or remaining in the population have all the genes they need to reach 300lb’s if they live long enough.
The only way you’d really know if the genetic effect was responsible for a reduction in overall size would be to study growth rates, longivity and ultimate size of two comparable fish populations under identical conditions. A fish with a smaller maximum size potential would have a slower growth rate than one with normal genes. Unfortunately, there are other variables that prevent scientists from completely isolating the parameter they wish to study. Other variables that can effect the outcome include availability of food, water temperature, water chemistry and condition, climate, etc etc etc…
I would suggest that unless a control population could be isolated in completely unchanging conditions, free from climatic variation, good years and bad, free from pollution and everything else that effects a fishes maximum size potential, we’d never really know. We can’t extract the genes and read the code, that’s for sure. The likelyhood of genetic variation also requires isolation. If genes are constantly mixed from a wild and uneffected population, the gene pool remains the same. Isolated lakes and ponds are more likely to experience this than open water bodies, but with everything else that’s changed in the world over the length of time required for genetic change, it’s a tough call to say its all in the genes.
So all this science doesn’t exactly convince me. What does convince me is the effect of a net ban on an inshore fishery which had been all but decimated by commercial overfishing. Rod and line anglers catch rates had diminished to the point it wasn’t worth wetting a line. Any fish that were caught were typically undersized. Yet now the population is healthy, fish are prolific and record weight fish are caught on a regular basis. No sign of genetic damage by years of overfishing here.
Another example of other variables aside from the gene pool effecting the outcome would be the change I noticed in Indonesian school children in just a few short years in the 90’s. With McDonalds and fast food freely available in Indonesia now, school children tower above their parents. They always had it in them, they just needed McD to bring it out!
This is certainly an interesting topic, but I think one thing which can be considered fact and that I think no-one here would dispute, releasing the big breeding fish that are the cornerstone of population regeneration is a smart thing to do in any fishery.
Yes, it’s difficult to say with certainty since there are so many variables involved. In my case, I am referring more to dams like Kenyir, rather than sea fishes, where the size of Tomans and Sebaraus caught today are much smaller than those 10 years ago. This may be due to overfishing itself … and unless controlled studies are undertaken, we can only speculate if genetics is involved.
As for the growth of Indonesian children, its the same with Malaysians … and the joke is that its due to the growth hormones in the beef they consume.[:D]. Seriously though, a high protein diet (and milk) certainly has a positive effect on human growth… Japan may be another case in point, where the pre-WW2 Japanese were generally thought to be short … but not today.
And yes, I agree that the application of an appropriate Bag & Size Limit regime is the way to go.
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Marlin,
I like your McD’s comparison, simple and right on. Now I’ll go get some McD, you are making me hungry…[:D]
IMHO, instead of worrying what genetic will affect the size of the fish that we’ll catch in the future, we should concentrate on educating the general angling community in Malaysia about benefits of CnR and bag limits, environmental awareness and issues regarding releasing alien species in our local waters. Malaysian still have a lot of catching up to do when it comes to dealing with these issues.
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Marlin,
You bring good arguments, but you failed to actually read my post. I actually strongly backed everything you said. If you read to the actual end of the post, you’ll see it in black and white. My last four sentences were: "Again, this idea has never been proven in rivers. I don’t recall seeing anything about this in oceans or seas. But small little bodies of water that are confined are susceptible to this. I don’t know of that many waters in Malaysia that would be affected as the floods from monsoons and such constantly allow things to change if the fish wish to swim over and check out a new spot. For sure the major dams in Malaysia would probably be unaffected. " I was talking about evidence gathered in decades of studies in small isolated freshwater environments. You gave an example of yellowfin tuna. Do apples grow from orange trees now? Your mention of the net ban in Florida then means almost nothing in this discussion. However, it is a very important event in conservation history. I would add that the longlining ban off of the same state revitalized the swordfish fishery. But again, in this discussion, those items are difficult at best to work in.
I highly respect your paraphrasing of my material when you wrote:“The likelyhood of genetic variation also requires isolation. If genes are constantly mixed from a wild and uneffected population, the gene pool remains the same. Isolated lakes and ponds are more likely to experience this than open water bodies, but with everything else that’s changed in the world over the length of time required for genetic change, it’s a tough call to say its all in the genes.” Like I had mentioned in my two posts, these studies were in isolated waters. Riverine systems went unaffected or were not studied. Either way, none of the anglers I know of speak of genetics in rivers. No point. Oceans are an even more mute point. There’s no way that human contact as of now can affect the genetics in the ocean regarding maximum fish growth. Maybe in a thousand years from now, but that’s a long haul!
Also, stunting and maximum growth as affected by genetics are two different events. Stunting occurs in, again, small isolated waters where a certain fish population overpopulates the waters severely limiting the amount of food and space available to the point that the fish are unable to grow any larger in that water. If you pull a specimen out and grow it individually, it exhibits the same growth rate as unstunted waters. No genetic influence there. However, if after many generations of larger specimens removed from a healthy system, the elite genetics of the larger fish in that population can and manytimes are removed. Something like removing all the people on the earth over the height of 6’5" tall. If you do this over ten generations, the average maximum height of humans would possibly be limited to below 6’5" tall. There would be plenty of people growing to their maximum heights if their genetic max is only 5’8" tall, but the gene that had previously existed of growiing to 6’5" would be severely reduced. That’s the actual theory, hypothesis, and proven outcome in many studies. However, those studies were in isolated populations. Impacts as simple ass fish eggs clinging to bird feet and being transported from one pond to the next can alter genetics. DNR biologists have only in the last 15 years or so published findings of different genetics between lacustrine and riverine populations of fish such as muskies. Actually the pike family is a great example. European pike have evolved beyond American pike for size capability. There are severeal subspeices of muskies that had previously not been identified so that what had previously been trophy populations of muskies were detroyed by stocking the incorrect subspecie leading to smaller max size of that fish.
For sure, fish genetics is a very complex issue. I’ve been keeping up with the studies since the early 1990s and I still say we have a long way to go. The breakthroughs prove this. So, before responding to posts, please read and digest them thoroughly. I respect and agree with everything you posted in your last post. Cheers dude! Let’s keep this discussion going as it appears that it will help everyone involved grow and learn in this area. Keep up the great work.