How can I decipher how aggressive my Betta is?

Here are three different tests that you can do:

• Allow your beta to see himself. This can be through a mirror, or perhaps certain plastic tanks that are shiny. Watch how he reacts. Most male betas will become distressed and try to 'attack' the mirror-image. What you're watching for is how often and how vigorously he 'attacks' the mirror-image. Sometimes this is used as an indicator of beta health. If this is your first beta fish, it's hard to have something to compare to, so my best advice would be to watch some youtube videos (or watch other betas at the store) to get a general idea of where your fish stands in relation to other fish.

• Place the beta fish where he can 'see' other fish. Perhaps you put his clear tank next to a different tank, or perhaps you 'float' him in the tank as if he is getting acclimated to the water, like any other new tank-mate. Watch how he reacts, allowing for acceptable behaviors like trying to swim to the new places, or adjusting to new conditions (light, heat, etc).

• Carefully watching and with fish-net in hand, acclimate the beta into the larger environment and release him. It's worth noting that in general-disputes don't tend to happen right as the fish is released, but some time later, after he is used to it.

Tips:

• Having different tank mates with a beta works best when the tank is large enough to accommodate all the fish (the general rule is 1 gal / 1 inch of fish). Placing a new fish in a 1gal "tetra tank" has never ended well, even with the most docile of beta fish.

• Female beta fish can be aggressive, also. It is not only the males. I have had female beta fish more aggressive than average males.

• When the tank meets the needs of its occupants, everyone inside is calmer and more happy. For example, more than one of a schooling fish, places for fish to hide, acceptable pH and nitrogen levels.

Bettas are generally aggressive. Males are generally more aggressive than females. It is better to keep male bettas separately.

However, Male Bettas can be acclimatized to a community tank. Buy the male betta when it is young small as compared to the other fish in the tank.

This ensures that it does not become aggressive. As the fish grows, it get used to the presence of other fish.

Do not have aggressive fish such as tiger barbs and aquarium sharks. Avoid fish with big fins such as angelfish and gourami.

Bettas get distress and angry when they see large fins, which they associate with other male Bettas.

Bettas will attack male guppies mistaking them for other male Bettas. They will also attack angelfish.

If you are buying a Betta for a community tank, buy a young one which is small in size.

Some fish will be more fiercer than the others. This is due to individual temperament. Such fish should be isolated as soon as possible before they attack other fish or get injured themselves.

http://ericdockett.hubpages.com/hub/Tankmates-for-Bettas-and-Betta-Fish-in-a-Community-Tank http://www.petsnhobbies.com/2015/09/can-betta-live-in-community-aquarium.html

All of these answers help greatly, but you can also try putting your finger in front of the glass where your betta is and watch his behavior. If he backs away and seems uninterested he will most likely not harm any new fish in the tank, but if he seems to be irritated by your finger or stressed out, and protective he possibly will be aggressive to any other fish in the tank.

I posted an answer in the question you linked.

I have for a second time a male betta with other fish in a tank. The first time it was in a 15 gallon tank on the overstock side of things (after about 3 weeks I removed the betta because I was loosing fish, still not sure if he was the cause). Now I have one with the same fish in a 75gal tank, so they got plenty of space and it's going great. The betta doesn't attack other fish if they are close and most of the time just ignore them. Even at feeding time when all the fish are in a tiny space, no attack. This large tank has been up for over a month now with no fish lost due to the betta (the one I lost were due to an overflow not working correctly).

So from my observation from 2 different betta, I would say yes they can go in a community tank. I have read at many places to count 5 gallon of water for the betta than regular 1 inch per gallon for the rest. I would still have a plan B in case the betta doesn't want tank mates. As another answer suggest, while having him floating in the tank for acclimatization is a reasonable way to judge him.

If you try to have mates for your betta, be sure that you are ready to loose some, so don't try this with expensive fish at first. It's also recommended that you add the other fish first and than the betta last. If your doing this in the current tank of your betta, change the decoration, move stuff around so he doesn't feel like his mates have invaded his territory.

Well you need to pet same natural like fishes if your really want to. Ember tetras are easy to keep with bettas due to same nature plus you need a tank bigger than 10 gallon. I have 50 gallon tank and i am not facing any difficulty to pet them both together. You can research on probettafish.com for further queries. It has helped me a lot also