Danios Acting Strangely

Question
QUESTION: I have a 29 gallon aquarium, just set up at the start of the year. It has cycled, although it took two months. Water tests zero for nitrites,and safe for nitrates. I keep several male guppies,two dwarf sunset platties, two hatchets, two long finned tetras, a few neons, and four zebra danios. They are not behaving as they had been. Suddenly they are staying in a corner bunched up. Occasionally one will swim away, but no fast swimming and darting around like they did. Supposedly, all my fish are male, but if one is female could that be what is causing the unusual behavior? All the rest of the fish look healthy and are lively. The danios seem all depressed. Any idea what could be going on?

ANSWER: Hi Shirley

The best way to sex Zebra Danios is that females are usually larger and have a rounded belly, and the males are more of a streamline shape.

Having 2 different sexes would not cause this behavior. A group of 4 is minimal, but they are at their best in groups of 6-10. They are adaptable to most water conditions, and are very tolerant of cooler water. However your other fish are not as tolerant. Ammonia/nitrite/nitrate should all be at or near 0. Temperature should be about 75, pH 6.5-7.5

Make sure you are doing your weekly tank maintenance.

Usually I would say there is a larger tank mate harassing them, but there is no tankmate you mentioned that would bother the Zebras. Although Guppies and Neons are not the best tankmates for them.

If they appear healthy otherwise, I wouldn't worry about them. You could try adding one or two more, but remember, an active school of Zebras may nip the Guppies and harass the Neons.

Hope this helps you, good luck!

Richard

---------- FOLLOW-UP ----------

QUESTION: Thanks Richard for your help. Actually, one of the Danios died yesterday. Of the three remaining, one has gone back to acting normally, one is still hiding, and the other swims out occasionally. Two are eating well, one not. I have not noticed them being harassed. If there was a disease, wouldn't some of the others be affected? I may bring home two or three to get the school number back up. As long as I stick to small thin fish, do I have to worry about overstocking, yet? There are about 20 little fish, the neons being smallest, and the hatchets the largest. I am doing weekly 25% water changes.

ANSWER: Hi Shirley

This is really hard to say. If one of them died, there is a problem somewhere. However, the Guppies and Neons are more prone to disease than the Zebras. You could simply have old fish. The life span of Zebras is only 2 years. You certainly don't want to treat the tank if the other fish look healthy and are acting normally.

You could move the Zebras to a 10 gallon quarantine tank and treat them with some Aquarium Salt and a broad antibiotic like Maracyn and see if they improve. I wouldn't add anymore to the tank.

In the 29 gallon, you are overstocked. Based on the size of the adult fish, you have about 36 gallons worth of fish. Not really a major concern in a larger tank with smaller fish, but as I said, I wouldn't add anymore right now. I don't usually worry about overstocking in larger tanks with smaller fish. In a 55 gallon, I have about 100 small fish. However in this tank I also have 3 large power filters, 2 designed for 75 gallon tanks and 1 designed for 55 gallon tanks and a sponge filter in the bottom. I've also been at this awhile, so I never recommend overstocking to beginners.

Other than treating the Zebras as mentioned above, what I would do in your case is complete tank maintenance. 30% water change, change the carbon cartridge in your filter, and clean the gravel thoroughly. Check the ammonia/nitrite/nitrate and pH levels. Add some StressCoat and a small amount of Aquarium Salt to the tank. 1tsp per 5 gallons of water. Aquarium Salt, not table salt. The salt relieves stress and fights parasites. The salt will tell you to add 1-2 tbsp per 5 gallons, but I don't recommend adding that much to a tank when the fish aren't used to it. Also, I must emphasize again, DON'T add any medications to your main tank if all of the other fish look and act healthy.

Hope this helps you and they get better!

Richard

---------- FOLLOW-UP ----------

QUESTION: Thanks again. I'll hold off on adding any new danios. I was hoping you would say I still had some room, but I knew better! I have been doing just about what you advise for maintenance. I keep up with vacuuming and use Stress Coat and Zyme. I already have salt in the aquarium at about the amount you recommend. I have been adding back some for the new gallons replaced when doing water changes. Should I do that each time? Don't want to pickle them. If I get a small tank for quarantine, does it have to be kept up and running even when there is nothing in it? Sorry for so many questions and hope they aren't too dumb.

Shirley

Answer
Hi Shirley

If you maintain salt in your tank, then you should always replace the amount you remove with water changes. For example, if you maintain 1tbsp per 5 gallons, and you remove 5 gallons, then you add 1tbsp to the new water. I don't keep salt in many of my aquariums, only with my Bettas, Brichardi and a few other Cichlids. I use it occasionally when fish seem stressed, but it is rare.

I do keep a small 10 gallon quarantine tank that I use to watch new fish prior to adding them to one of my tanks. This tank must be kept full of water and filter running to keep it cycled. And lol, I keep Zebras in it. When I put a large fish in it, I move the Zebras to another tank then put them back when the tank is empty.

No problem on the questions, the only dumb one is the one that isn't asked. Hope I've been able to help you, good luck!

Richard