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I have often wondered how the fish that are stocked in a pond maintain healthy off spring. In other words, I have heard the initial first class fish are always the biggest healthy fish. Then when they spawn the second and third generation fish get smaller and smaller. I was told that this is due to "inbreeding" between the fish. Is this true? If so how is this avoided in the natural wild? I talked to hatcheries and they tell me the best way to get Brood fish is to get them from different places to avoid this “inbreeding” of the same class. I guess I thought of it as family members from the same blood line having children, if there is any other way to explain it..... I hope what I am saying makes sense. It is the only way I could explain it.

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big_pond, I think that what you are refering to are hybrids, particularily hybrid bluegills. While bluegills can hybridize with other species in the sunfish family, we normally think of the cross with green sunfish. If you do a search, you will find much information about this.

This first cross is normally called the F1 generation and it does indeed show hybrid vigor. Later crosses, the F2, F3 etc. generations show hybrid depression. If you're familiar with hybrid seed corn, you know that the companies that produce it must make this F1 cross every year.

Hybrid depression tends not to happen with pure species. Exceptions are with highly inbreed species or the extremely unlucky. Genetic problems in wild species usually cause the individuals with these problems die very quickly leaving only healthy individuals.

Again, there are many posts that get much more technical that this. Hopefully this helps.


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big_ pond :

I am also interested in the genetics topic and would be interested in any info .

There is some discussion about it on the topic " inbread" dated 6-14-05 on the page but dated 6-17 -05 on index , under the heading " Questions and Observations" . ewest
















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BP,

The reference that ewest mentions is:

http://www.pondboss.com/ubb/ultimatebb.php?ubb=get_topic;f=20;t=001725;p=

It isn't clear to me which is the best course of action: to get fish from many different sources to obtain more vigor or to selectively breed and raise your own with the best traits...the best of the best, so to speak.

I've been following the former approach, but that recent discussion has certainly given me cause to doubt that as the best approach.

In my cows, crosses seem to promote the best growth and I thought the same would apply to fish, but now I wonder.

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No Norm Kopecky, I am not really talking about Hybrids like you would in hybrid blue gills or Hybrid Striped bass.
Hybrids are the EXACT OPPOSIT of what I am talking about. In Hybrids you usually come up with offspring that are superior to both the parents!
But what I am talking about is something like brothers and sisters marrying and having kids. The children would come out deformed and have problems. Like the problem you would have with incest.
In a pond environment you would have sort of the same thing. The same year class of fish from the same parents would breed among them self’s and produce offspring. The offspring would be inferior to the parent fish.
How does this problem get avoided in hatcheries? Also, how does this problem get avoided in the wild??

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big_pond, many of your questions have been covered by the thread pointed out by Meadowlark. The most important answer is that individuals with genetic defects usually die before they can breed. This is what occurs with wild populations. Culling any individuals with genetic problems is how we handle this in domestic animals.

What is the magic number of individuals needed to avoid genetic problems? The answer is that it all depends on how many and what kind of genetic problems the the individual animal has. We can't just look at an animal and know that. So we use a larger number of individuals to minimalize the risks.

There is one other point to this. Just because some particular trait is considered "good" doesn't mean that it can't be "bad" at the same time. Taking asprin can be "good" in helping thin the blood thus preventing strokes and heart attacks. It can also be "bad" in that it helps promote bleeding ulcers.

One last point. Parent/sibling is the closest genetic relationship and is sometimes used to establish certain traits.


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big_pond, are we answering your question?

Inbreeding exposes recessive genes that might hurt the individual. If there are few "bad" genes or they aren't real "bad", this might not matter.

Genetic variability helps the species adapt to changing conditions. An example might be water temperature.

Another example is skin color in humans. Black or dark skin protects the skin from UV radiation. Skin damage can range from sun burn to cancer. With such an evolutionary advantage, why doesn't everyone have dark skin? Along with this advantage comes a disadvantage. Dark skin doesn't make vitamin D3 from sunlight as well as light skin does. So as humans moved away from the equator, the need to protect from UV radiation decreased allowing the skin to lighten to produce vitamin D3 better. What happens when light skinned people move back to areas with high UV radiation? As they've found out in Australia, the skin cancer rates rise dramatically.

When it comes to genetics, the answer is almost always the same. How does a particular trait help or hurt in a particular environment.


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yeah this is some what of something I am looking for. I went to the link and read that respones and it helped alot as well....I gues I sort of understand..

thanks

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Norm, your advice on genetics appears sound, something I have not spent much time considering. The Peacock Bass that I have in my pond were released from three different broods however would not be surprised if the bloodline is not awful narrow. Though you probably have not spent a lot of time on the subject of PB, for fish in general, would you suggest that I pay particular attention to any genetic irregularites and cull accordingly?
The PB have started spawning in May, should be catching their offspring in the next few months...thought a good chance to get the question in while the subject is HOT!!!


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Norm, went back and reread one of your earlier post on this thread...think the question was already answered!


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Don, it is so interesting to read about yours and Rad's experiences in Thailand.

I love giving interesting (at least to me) examples in genetics. There is an extremely small (3-4 acres) island off the coast of New Zealand. The Catham Island Black Robin has been isolated there for well over 100 years. When the population was found, it consisted of 4 males and 1 female, all highly inbreed. However, the deleterious (bad) genes had been removed from the population and they were able to increase the population.

This is an example of pure luck. In the vast majority of cases, this species would have gone extinct. Even now, this species has very little genetic ability to adapt to change.

Most populations have as much variability within their populations as they do between populations. You just have to watch and remove any individuals that look like they have problems.


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Norm :

Thanks for your efforts on this post . It is an interesting tpoic.

In line with the post referenced above I would appreciate any thoughts or references to papers or articles regarding the matters below as they apply to LMB , BG , RE or sport fish in general.

Like how many parent lines are enough to start with ? , how long should one expect an isolated population in a pond to stay vibrant without new genes added ? , how effective is adding a few new fish to an existing isolated population when pond carrying capicity won't allow large scale restocking ? .

I realize that a lucky pond owner may not have this { or a } problem because of natural selection . I am thinking about the unlucky one who has or may encounter the situation or , in trying to avoid it all together by some effective method. For example I question if 20 years down the line adding a few LMB to a population will make much difference if the original stockers were from to few parent lines. It seems that the % of new fish would not be enough to change the larger population genetics in a reasonable time. Do the hatcheries have guidelines on their methods which might be applicable or help?

Thanks in advance. ewest
















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ewest,
Try this site for starters, and there is a ton of info on fish genetics, more will follow as the aquaculture business continues to boom.
http://www.fao.org/documents/show_cdr.asp?url_file=/DOCREP/003/AB412E/ab412e03.htm
As an aside, the above article refered to wild fish changing in as little as one or two spawns when placed in ponds. I have nile tilapia in my pond and they are almost white, I neighbor caught one of mine on Sunday and released it in his pond and by Friday it was almost black a normal tilapia color.


1/4 & 3/4 acre ponds. A thousand miles from no where and there is no place I want to be...
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Nice job, Rad! Hadn't seen that one.


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Rad :

Great post , thanks for the reference . There is a lot in the article to think about , like the info on "genetic endg." . There is a lot there applicable to ponds but be sure to read the warnings and dangers . If you are a fourm member and are interested in CC or tilapia you should read Rad's referenced article on the results.Thanks again. ewest
















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Rad, this really is a great article! For anyone interested in the genetics of fish, this is a wonderful article. Rad, you really did a great favor for us by finding and putting this article where we could print it.


Norm Kopecky

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