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    Why is betta fish missing ventral fin?

    One of the most frustrating things with Siamese fighting fish I have experienced is being excited about a spawn, only to have them reach 3-4 weeks of age and… the fry are missing ventrals. I thought it might be worth discussing the possible causes in hopes of helping other breeders since the discussions are rather decentralized around the web.


    1.Feeding nematodes: banana worms, microworms, walter worms and vinegar eels
    2.Medications – especially those for treating velvet
    3.Water Quality
    4.Other factors?

    Betta splendens

    Feeding nematodes: banana worms, microworms, walter worms and vinegar eels

    This is complicated. The general belief is that the longer any nematode is fed to betta fish fry, espeically as the bulk of the diet, the fry will not have ventral fins. The fry in the photo was fed only banana worms for 3 weeks before adding in baby brine shrimp and other things. I’ve had other spawns where this was true too. But I’ve also had a few that were fed many nematodes and they were fine. There is some other factor at play. It is also a common theory that more bacteria forms on the bottom of the aquarium and it can eat away at the ventrals as the fry rub against the bottom of the aquarium. There is a definite tie to it being more likely to occur if the fry are fed any of the nematodes for long periods. I have found that if I siphon a fry aquarium daily and wipe the bottom if feeding nematodes, that the missing ventral problem occurs less often.


    Medications – especially those for treating velvet

    There is also a definite connection with treating fry for velvet with copper based medications especially that result in no ventrals. Of course, it is better to risk treating the fry than to let them die from velvet so that is a gamble most breeders will take. I’ve found that using either almond leaf extract or almond leaves often keeps the fry from getting velvet (and they are prone to it with my water).


    Betta fish

    Water Quality

    No matter how frequently water changes are done or the bottom of the aquarium is wiped, bacteria or toxins can build if the fish are over crowded or food is left decaying in the aquarium for too long. This might possibly be a cause as well. Ideally it should be 2 fry per gallon when growing them out. Bacteria and parasites can definitely eat away fins, including ventrals.


    Other Factors

    I have been talking to an aquatic veterinarian about these issues and if water is too soft the fish cannot absorb enough calcium or magnesium to develop correctly. I will be conducting further tests to try to figure out the specific cause as my second spawn that came up missing ventrals only had vinegar eels for a week, then baby brine shrimp and I introduced pellets and gel foods at 3 weeks… still no ventrals. I’ve raised bettas in my water previously without missing ventrals so there is some other factor at work that I will have to figure out.




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