help fish fighting

Question
I need help i have a 75 gallon fish tank its been up for 3 weeks and 5 days !! Well i started with 9 Zebra Danios and they made it with out none dying for 3 weeks and 5 days ! Well today i bought home 5 Neon Tetras and 4 baby angel fish i left the bag for the angel fish flooding for 30 mins puting a cup of water every 10 mins and i left the Neon Tetra bag flooding for an hour putting a cup of water every 10 mins !! Well at first i put the angels in the tank and everything was find for 10 mins after that the danios started chasging the angels all over the tank biting at their fins !!! Than after that i put the  Neon Tetras in and the danios when crazy biting all 5 of the Neon Tetras and left the angel alone we all got scare so tryed to take of all the danios of the fish tank and put than in a 10 gallon by them selfs but after a hour of trying to catch them we only took out 5 out of the 9 !!! it was so hard trying to catch them in a 75 gallon tank !!  My question is if i leave the left over danios in the tank with the other fish will everything be ok ??
And i want to know why the danios atack all my over fish the min i put them in ??? I dont want my angels and Neon Tetras to die !!! PLZ help .....I DONT KNOW WHAT TO DO !!!!

Answer
Hi Sammy,

First of all, it's quite uncommon for issues to arise with Zebra Danios, but it's not unheard of. I recommend that you purchase an aquarium divider (a plastic divider with small holes in it, and will divide your aquarium into two sections). These are found at your local fish store, or on the internet.

Providing some plants will help. If your tank is just a wide-open space, it's easy to see why the Danios were chasing the others. Dense planting on the rear and sides is highly recommended for Angels and Neons - which brings me to the next topic:

Angelfish will NOT go well with Neon Tetras. Angelfish, as they grow, will become quite efficient at hunting and eating Neon Tetras. This is the classic example on how some 'community fish' are not compatible, despite the name. They may be OK for now, but I highly recommend that you return or give away either species.

The reason why your Danios were aggressive was that they were in the tank for the longest amount of time, and so they established their own 'territory', like what is commonly found in most species of Cichlids. By adding others, the other fish trespassed onto their 'area', and so they became protective. To reduce aggression, I recommend that you re-arrange any rock structures, driftwood or ornaments so that it creates a 'new' scene, and so that the Danios will no longer feel at home, effectively removing their territorial rights.

Once again, I highly recommend returning or giving away one or both species if they do not work out despite the suggestions given. Individual fish will act differently, and it's not uncommon for a peaceful fish to be quite aggressive. (A few of my Platy fish, which are normally extremely peaceful fish, literally control one of my tanks. They hold their own, and will even bully my Serpae Tetras, which are known for their fin-nipping and minor aggression!)

Monitor your fish carefully, if you cannot catch the remaining Danios. Chances are, they were extremely stressed from the net chasing them around, and will forget about the other fish for a little while.

So, better choices for your aggressive Danios would be:

-Serpae Tetras! (Keep these in a group of 5 or more, they can hold their own against your Danios, and make a colorful addition)

-Tiger Barbs! (If you find that your Danios are quite aggressive, adding these should be no problem. Remember to keep them in groups of at least 5-7, because they can be fin-nippers! They will not present a problem to your Danios, since Danios are among the fastest freshwater aquarium fish!

-Platy, Swordtail, or Molly
(These are livebearing fish, which means they give birth to babies rather than laying eggs. They are easy to breed, and don't be surprised if you find a batch of fry in your tank! Keep one male to every 3-4 females)

If the Danios damaged the fish's fins, then I recommend that you use a slime coat enhancer to help the fish's fins heal faster. A slime coat enhancer is actually part of your water conditioner, if you're using Aqua Plus, Aqua Safe, Stress Coat, or Sera aquatan.

Good Luck, and Happy Fishkeeping!