Betta died with ripped fins and red spot. Was it my pleco or tank mates?

Infection, old age, poor water quality or poor nutrition are all possible causes. The "wound" may have been post mortem, caused by being eaten by tankmates. Monitor tankmates for signs of illness or infection (red spots, fuzzy spots, swelling, lack of appetite/activity, etc.). Submit a water sample for quality testing or use a home kit to test for chemical imbalances. You may need to perform water changes, treat with chemicals or treat with antibiotics or antifungals depending on symptoms. You can request a consultation to discuss the situation in more detail.

Sorry for your loss. I would check water parameters for pH, ammonia, nitrites and nitrates. Sub-standard water quality can result in increased dermal mucous production and the white sheen. Neoplasia can also result in metabolic changes causing skin changes also.

Drop the water temperature to 80 F. Bettas do best between 78 F and 80 F. The higher temp likely did not cause her death, but warm water holds less oxygen than cooler water. She may have been ill or old. She does appear bloated in the image. It may have been dropsy or other infection. Monitor water chemistry using a liquid test kit. They are more accurate than the strips. Tou can also submit a water sample for testing. The local Petco may do this for free or for a small fee. Aim for 0 ppm ammonia and nitrites with nitrates at 20 ppm or less. Try to keep the pH as close to 7 as possible. Bettas can tolerate acidic water, but changes should be gradual to allow time for acclimation.

I am sorry for your loss. Without an exam, it can be difficult to determine the cause of death. Possibilities include constipation, severe swim bladder disease, dropsy (kidney failure), other infection or trauma. If you have other fish in the tank, monitor them for similar symptoms. You should also test the water using a home test kit or by submitting a water sample for testing. The local Petco may do this for free or for a small fee.

I recommend to start with having the water tested. Many times this is offered by the pet store. If all the fish have passed away, the culprit is most often poor water quality, a disease or the tank not being properly maintained for the species of fish. I do not recommend to get more fish until you know the water conditions are correct and that you know the environment (temperature...etc) is appropriate for the species of fish you want to have. I hope this helps.

Thank you for reaching out about your molly. Unfortunately, the fins are not very good at regenerating themselves completely, so your fish may always have a bit of a scar/missing parts of the fin. I also see that there is a potential scar/white area on the side of the body? These two together may be from this fish getting caught on something within the tank, or from trying to wedge himself into small areas where he can get caught. It would be less likely to be an infectious agent, such as a bacteria or parasite, or an environmental/water issue as the other fish appear to look okay in the photos from what I can tell. I would suggest trying to look very closely at the tank furniture and the fish's behavior to try to identify where it may be getting injured. Alternatively, you can partition out a portion of the tank for this fish to reside in for a period of time to allow the injuries to heal. This would also allow you to be able to rule out whether it is trauma from one of the other fish as well. I hope this gives you a place to start, and thanks for using Petco Pet Education Center, formerly Petcoach.

It is hard to tell from the picture if your fish has fungal plaques on the scales or if this is normal pigment. I would recommend taking your fish to a vet for a necropsy. That will allow for biopsies and cultures to be sent to the lab to determine the cause of death. IF it is fungal disease I would recommend treating the tank and cleaning the environment well.