Fin Deformities - Temperature or Genetics

[tjd]

I have been breeding some double red aggies with considerable success. In the past with this strain I had maybe one or two fish from a brood that showed any deformities which I usually attributed to an injury of some kind -- 1 out of 50 to 100 seemed pretty reasonable. However, a recent brood had 5 out of about 60 with deformities, primarily of the fins: 1 had no ventral fins, 1 had deformed ventral fins, 2 had stout caudal peduncles, and 1 had a dorsal and anal fin that look like a trigger fish. Aside from the deformities the fish seemed healthy and happy. I also received a ratio of males to females of about 2.25 to 1.

I have obviously culled the deformed fish, but was concerned about using any of this brood for breeding stock or releasing them into the hobby as potential breeding stock. Is this stain starting to show signs of being too inbred or can the deformities be attributed to the higher temperatures and temperature fluctuations that they experienced the first couple months?

Tom

 

[Apistt_ed]

there could be many things that could lead to this, but I'd have to say that it was most likely the genetics of line breeding and selective breeding. The genetics for the finnage is probably already been in the parent fish and just didn't show itself outside of the one or two from the brood, and with time, it just probably came out in the recent brood. If you'd like to make the line stronger with less deformities, then it couldn't hurt to add some new genetics. best wishes. john.

 

[aspen]

ammonia can cause deformed fins too, fyi. ensure that your water quality is good before making any assumptions.

rick

 

[creedmore creek]

TJD,
Apistt ed and aspen are both right - the fin deformity could be cause by either environmental or genetic (or both) factors.

If what you are seeing is purely or mostly genetic in cause then you can go down a few paths all of which depend on your philosophy of fish breeding. If you plan on keeping the fish as close as possible to the specimen found in nature then you may opt to either discard your line or bring in fresh native (or wild caught) aggies to breed into your current bloodline.

If you the type of person who is just trying to perpetuate his own fish then I would not worry to much with the deformities. Just select against them as future breeders and continue breeding the viable/healthy offspring to one another. This will cause inbreeding to occur but that is not necessarily a bad thing. You will go through a period of what is called "inbreeding depression" where deleterious genes become paired with one another and lead to fish with reduced fitness. However, if you select against breeding these animals you ultimately will eliminate all the "bad" genes and develop an inbred line - this is where all the genes of fish within that line are exactly the same essentially identical twins. This has been done with many species: mice, rats, fruit flies and many species of fish (swordtails, mollies, zebra fish etc.).

It all depends on your goals.

 

[tjd]

Thanks everyone for your input. I was hoping there could have been an easy answer but guess things are never that clear.

Turns out the parents of the brood that I saw the deformities in spawned again a little over a month ago, this is what prompted my original post. While it was not my intention to raise another of their spawns, I am giving these fry pampered treatment. I left them in the 29g breeding tank and removed the parents after 4 weeks. Temp is being held steady at 79F and the ammonia and nitrates are kept at 0 in this tank even between water exchanges (the tank receives direct sunlight in the morning). The fry are about 18.5mm and so far I have not seen any of the deformities that the previous brood showed.

I would like the fry to make it to 22mm-25mm before I can more confidently say whether there are any of the previious deformities.

Thanks again,
Tom