I wasn't sure where to post this, but I figured that since it's about a spawn I had just over two months ago, here would be okay :)
When do bettas develop their ventral fins? I've googled it a few times and haven't come up with an answer. My finned babies turned 2 months recently, and still no ventrals :/ they all have all of their other fins, are growing very quickly, and have full color. I keep the bottom of their tanks very clean and stopped BBS quite awhile ago.. Any help is appreciated!
I usually see ventral fins in my fish at around 2-4 weeks old if that helps at all. Rosetails sometimes have stubby ventrals, missing ventrals, or ventral fins that come in later. A picture of the fish in question would help so much.
Some breeders on my tropical site were talking about how some fish are genetically prone to having no vetrals.
I know that there are lots of people who blame microworms on the missing ventrals, and although there may be some related factoring, I highly doubt it is the major influence.
In my experience, I usually have missing ventrals (or half ventrals) in the same spawns. So, for example my red/gold dragon spawn... of 6 survivors, 4 have no ventrals, one has half ventrals and the sixth has ventrals. All 6 of them have other major fin malformations that are definitely genetic. In other spawns where I have seen missing ventrals, usually 25-50% of the spawn is affected. Basically, if there are missing ventrals, there are many missing ventrals.
All of my fry are raised similarly. Fed VE first, then mw after a few days, then BBS after a week. The VE and mw are continued even after I move onto the larger food until I'm sure that all the fry are eating the larger foods. Cleaning I am slack... I've been known to clean fry tanks as infrequently as once weekly and still not have ventral issues. Other times I've been meticulous in cleaning them and had ventral issues.
So, my personal opinion is that missing ventrals is a genetic condition. Since I've never had two survivors of missing ventrals from two different spawns at the same time, I've never done a F1 out cross of missing ventrals to see if the F1 has ventrals and if so, what percentage show the trait.
I do not know betta's specifically, however i do know it has been proven that the same gene that produces the pelvic fins in fish controls rear leg growth in animals. Also this gene has a genetic switch or trait that will cause them not too grow, it's been found too exist in some fish species, as well as animals like whales, manatees ect.
Amazingly it's all the same gene persistent through various animal families , it's completely possible and very likely that this same genetic switch exists and can cause the loss of pelvic/ventral fins in betta fish.
These are some of the responses from a breeder and someone with lots of experience with fish.
:( darn.. I was really hoping they still had a chance of coming in. Thank you both so much for your responses though. This makes me sad, the daddy has the longest, most beautiful ventrals I've seen, I was hoping the babies would get that trait. Do you know if not having ventral fins will have any negative effects? I know they're used for balance, but all five babies swim just fine and have no other deformities.