Aggressive Neon Tetra - Tropical Fish Keeping - Aquarium fish care and resources
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post #1 of 11 Old 09-10-2011, 02:22 PM Thread Starter
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Aggressive Neon Tetra

I've been stocking my first tank over the past few weeks, and I added a neon tetra yesterday. He seems to be nipping at the two bigger fish in the tank- a zebra danio and a tequila sunrise guppy. I thought that these guys were all community fish and would be happy together. I'm just really surprised that, since the tetra is the smallest, he's being the most aggressive.
Is this normal behavior? Can he hurt the others? He's really going after the guppy...
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post #2 of 11 Old 09-10-2011, 02:48 PM
This is unusual for a Neon Tetra, but they are supposed to be kept in groups of at least 6, more would be better. This may cut down on that behavior.
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post #3 of 11 Old 09-10-2011, 05:08 PM Thread Starter
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Hmm. The aquarium isn't ready for any more fish- the cycle isn't complete yet. I thought I'd take him back, because I can't get any buddies for him right now. I think they'd all die.
I don't have a net, so I reached in with a bag and my hands, but I couldn't get him. I think I scared him really bad though- he hasn't come out of the plants for about 3 hours. Maybe he won't bug the other guys anymore.
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post #4 of 11 Old 09-10-2011, 07:37 PM Thread Starter
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Well, he's since come out and is again bugging the other two. Every time I show him the bag (on the outside of the glass), however, he runs and hides for a while. I suppose that's good.

Anyway- should I return him? Or do you guys think that the aggressive behavior will subside, even without some others like him in the tank?
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post #5 of 11 Old 09-10-2011, 10:52 PM
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Originally Posted by Robanada View Post
Well, he's since come out and is again bugging the other two. Every time I show him the bag (on the outside of the glass), however, he runs and hides for a while. I suppose that's good.

Anyway- should I return him? Or do you guys think that the aggressive behavior will subside, even without some others like him in the tank?
I would advise not doing that. It might give the guppy some peace, but it is only stressing the neon each time you do it and could bring out Ich in him. Going through the cycling process is stress enough, as well as being by himself. Also having a net is one of the main/first pieces of equipment you should buy.

How long as he been doing this for and are you sure it is nipping and not just playing? Although, any tetra species, even the ones classed as peaceful can be aggressive/nippy at times and guppies are a prime target. The neon could be over-compensating due to being alone, they tend to become even timid and hide most of the time, or show more aggression. It may also just be his personality.

How long before your tank is cycled? I don't suppose you have a breeders net (that hangs inside the tank) or something along those lines that you can place the guppy or neon in for the time being, although if kept in them for a long period, that causes stress and may not be ideal. Maybe you could buy a divider for the tank, so that you could isolate the neon or guppy that way or add more plants. What size tank do you have btw?

If he is nipping/harassing the guppy and it is constant, it can damage him, cause added stress and possibly bring on fin rot if the fins get nipped and infection sets in, especially if your water quality isn't ideal yet due to still cycling.

It is a tough call, he may settle down or may not. I probably would return him if you can and wait until you can get a proper shoal of them. Neon's often aren't the best fish these days to use for cycling anyway, as they aren't as hardy and can be quite sensitive. Or if the cycle is very close to completion, you could wait it out. Zebra's also need to be in a group.
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post #6 of 11 Old 09-10-2011, 11:33 PM
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As has been mentioned continuing to send him in hiding by the bag will cause the fish a lot of undue stress, and can make him susceptible do diseases such as ich. Fish have a short memory and unlike a dog that you can train, fish are not really a trainable animal. They will eventually associate you with food, but in my opinion this is more of a natural instinct. You can kind of think of it as Polov's dog, were the fish sees a person, food drops into their tank and they are fed. Eventually they will associate human presence with food.

Also as mentioned both tetras and danios need to be kept in groups as they are a shoaling fish. There has been scientific proof that when shoaling fish are kept in smaller numbers than 6 that they will become stressed out. This stress can be displayed in actions of aggressiveness which may not be normally seen in that particular species.

Also answering the other questions such as tank size and how long your tank has been cycling for will help members in giving you advice.

Also I would suggest reading the profiles for the fish that you are interested in keeping. The profiles will give you information about the temperment of the fish, if they need to be kept in groups, the minimum size tank requirement for the species, and other helpful info. You can find the link for the profiles at the top of the page second tab from the left. You can also view the profiles for a particular fish by clicking on the shaded name when the common name or scientific name is used. Zebra Danio, Neon Tetra, Guppy
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post #7 of 11 Old 09-11-2011, 04:33 PM Thread Starter
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Thanks guys for all the advice- I've been watching him on and off for a few hours now, and it looks like the behavior has subsided somewhat. He still chases the others a little bit, but he doesn't seem to be nipping them so much. I only used the bag twice, haha. I see what you mean, the long term benefits don't outweigh the short term. The tank has been cycling for 2 weeks now, and the guy at the pet store said the ammonia levels were good, and that it'd probably be done in another week or so.

I'll pick up a net the next time I'm in- I just never really thought I'd use it that much. A breeder's net may not be a bad idea for this guy, if he acts up again.

The tank is a 6 gallon, I built it custom for a specific application (I'll make a thread on it once I get it stocked and cycled. And I still need to stain the canopy!) so I can't buy any partitions or anything that are pre-made for this tank. I could make one, though.
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post #8 of 11 Old 09-12-2011, 11:40 AM
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Robanada, welcome to Tropical Fish Keeping forum.

This is not what you will want to hear, but please understand it is solely aimed at the well-being of your fish.

A 6g tank is not sufficient space for any tetra species. All characins are shoaling fish, needing a group. They have many reasons for this, including security (they just feel "safe" with more of their own around them) and interactions whether it is social, a pecking order, or whatever. Keeping a lone tetra is frankly cruel; the fish is programmed by nature to live in groups of hundreds, and outside a group it is highly stressed. Stress weakens the immune system, causing health problems that would not otherwise occur, and always means a shorter lifespan than normal. It also brings out aggression; this is the fish's way of dealing with continual frustration, fighting back, even though contrary to its normal behaviour.

It is not only the other fish in the tank being picked on; it is the neon itself which is in no better state. As for the other fish, even though physical activity may have stopped, there is still the chemical signals in the water that fish release, and these cause stress to everything in the tank.

Please return the neon, since you do not have space for a group of them, and he will be unhealthy and die prematurely. Someone referred you to our profiles, please read the one for the Neon Tetra, click the shaded name. All this is explained there, along with minimum requirements for keeping this beautiful fish happy and thus healthy.


Byron Hosking, BMus, MA
Vancouver, BC, Canada

The aquarist is one who must learn the ways of the biologist, the chemist, and the veterinarian. [unknown source]

Something we all need to remember: The fish you've acquired was quite happy not being owned by you, minding its own business. If you’re going to take it under your wing then you’re responsible for it. Every aspect of its life is under your control, from water quality and temperature to swimming space. [Nathan Hill in PFK]
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post #9 of 11 Old 09-13-2011, 02:18 AM Thread Starter
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Thanks for the input. I have read the profiles, as well as a number of other articles. 5 was actually the magic number I had in my head, but a difference of one fish is probably negligible. I can't add 6 tetras to the tank at once, because the tank is not cycled yet, and, if my understanding is correct, they would all die. I figure that it's better to have one discomforted rather than to have all 5 or 6 dead.

The literature that I have read has suggested that the tank size be 1 gal per inch of fish. If the tetras are each 1 inch long, and there are 5 or 6 of them, then my tank should be 5-6 gallons- so I should be fine there.

I'd ultimately like to stock the tank with tetras, but the gentlemen at the LFS pointed me toward the danio as a starter because it's a bit hardier. I figure that, instead of stocking my tank with danios to get it started, and waiting for them to die, I should add the fish I like.

The bacteria need a certain level of ammonia to survive, so I can't stock it with other fish, and wait for them to die gradually, because the bacterial colonies will decrease in population proportional to the ammonia decrease. This means that, even if I cycle the tank with danios and add tetras later, I still can't add more than two at a time or so. I'm just not sure how i'm supposed to spontaneously have 6 tetras and happy bacteria all in one day.

I am really inclined to take him back- i just figure that, later on down the road I'll be adding tetras a few at a time anyway, so I might as well do it now, and have fewer fish die during the course of my tank-stocking.
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post #10 of 11 Old 09-13-2011, 10:14 AM
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As Byron has said, 6 gallons is not large enough for tetras or for danios. The one gallon per inch of fish is not really accurate. This does not take into account the swimming room that a fish will need. Some fish are more active swimmers than others and will need more room to be able to swim. The profiles will give you good information about the needs of different fish. As for what you can keep in a 6 gallon tank I would suggest looking at some of the dwarf species. Something like dwarf rasbora, would work depending on what your water parameters are. You could do a single dwarf puffer, or you could do a tank with some shrimp, or you could do some african dwarf frogs. A 6 gallon would also work well for a betta. With a 6 gallon you will be somewhat limited on what you can have, but with doing some research you could set up a nice tank. Look through the profiles and check the minimum tank requirement for the fish.
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