Testing the rule: How many Endler's per gallon


It always drives me crazy when I hear people say something is "the exception that proves the rule." A better translation would be "the exception that tests the rule,"

As experienced fishkeepers know, the one inch of fish per gallon myth only holds water some of the time with smaller fish that have a low bioload and in at least 10 gallons. What happens when you go beyond that? Things can get strange to say the least in sometimes funny and at other times awful ways, I've had to go through periods of extreme Endler crowding while dealing with random crises, so I can tell you what numbers are reasonable and what will surely lead to craziness So if you're thinking of stuffing too many Endler's into a tank to see what happens, check here first because maybe I already was that foolish, and you don't have to follow in my foot steps.

Please note, I'm assuming that anyone who overstuffs Endler's will stay on top of the water parameters. I've never had any produce measurable quantities of ammonia. It's always about staying on top of the nitrates for me.

10 gallons:
1) 2 males and 4-5 females (if you intend to pull out about 100 babies per month)
2) 7 females (hopefully no boys will leap into the tank)
3) 14 boys (22 boys can work, if none of them are particularly aggressive, but 45 are definitely too much)

20 gallon tall:
1) 10 males and 15 females (again, pulling fry continuously)
2) 30 females
3) 35 males (got up to 86 juveniles for a bit, but they really got desperate when their colors came in)

29 gallons:
1) 12 males and 24 females (don't forget to net those fry)
2) 65 females (depends on the group in particular as one group of 80 has been fine)
3) 45 males

These are the only sizes that I've had Endler's in so far. As you can see, the numbers do not correspond exactly to the numbers of gallons per fish. It just hasn't worked out that way. Unpredictable groupings of aggressive and passive individuals come together and will make one tank max out at a lower number of fish than another.

I would think that a 20-gallon long would allow for more males because then they could really scoot out of each other's ways. They won't have as much room vertically, and I don't know if that would make them want to jump out more. Again, lids are necessary.

The 65 females that I had in a 29-gal were the most violent Endler's I've ever seen, eating all but a few fry and attacking and devouring a girl who was a couple of months old. The 29-gal of 80 girls (sister and daughters of the first group) were much mellower and ate no fry at all even though they were just as obsessed with food. They simply did not develop a hunting obsession.

Mixed gender tanks are mellow because the boys have girls to chase instead of each other. More fry survive because the males get in the way of the females' hunting, giving the babies a chance to swim away.

I had an emergency last year when I had to stuff fry into a male tank, and they were fine. No one was eaten. The boys eat about 1/4 as much as the girls. They get so caught up in dancing. For this reason, food such as Repashy Community Plus works well because they can graze when they want in between dance routines.

Lately, I've had to back off on feeding Repashy Community Plus to the girls because they're so violent that some have been hurting their mouths on the eco complete as they push and shove.

Definitely be sure to cover every possible escape route when dealing with 2+ Endler's per gallon. Their instinct in the wild is to leap and end up in another pool of water. This is how wild guppies get upstream. And believe me, some do make it. I'm still amazed at the boy who got into my 3rd-generation girl tank. He was one of a group that apparently leaped into their HOB filter and then straight up and down toward the 10-gallon on the shelf below. It wasn't a straight drop, so the successful boy must have bounced off the wall, landed on top of the HOB filter below, and rolled into the return. Both tanks have Versatop lids. The other boys didn't make it--I found their little dried up remains over the course of several days. I now have plastic fabric at every conceivable spot.

And then there are the people on Fishlore whom I sure have hundreds in plastic wading pools. Pics anyone?


I've never kept that many endlers. That is an incredible amount of investigation that you have done to figure out how many endlers you can safely keep in your tanks. Thank you for sharing your findings.

Claire Bear

Hi,endlercollector and that, to me, seems like a lot of fish in one tank. Not disagreeing with you-by far you have the most experience but I wonder as to if that would cause stress and thus illness. It seems to me they would be on top of each other.
Right now I have 4 tanks of endlers. All started with 4 males and 4 females. I pull fry and feed to my cichlids regularly. It seems so crowded when the babies are in the tanks and I just wonder if you have had issues with those numbers ever?
  • Thread Starter


I have not been able to find a hard and fast rule for the maximum number of Endler's in a tank. I do agree with claireputput that social stress is a major factor that impacts the individual immune system and ultimately the overall health of a fish tank. Definitely, the lab tank that had the Endler's when I got them was overcrowded. It was a 20 gallon tank with some 200 fish. It was easier to catch the fry and juveniles, so out of the hundred fish I took home, only about 10 were adults.

(You cannot imagine what it is like to walk into a lab where there are shelves upon shelves full of tanks each with hundreds of pairs of eyes watching you when you enter a room. And they are all hungry :0 )

In comparison to the lab, my tanks are rather empty. Things have gotten better as far as the rate of illness. I prefer to pull fry as soon as possible and put them in a fry tank. I'm doing this to try to decrease the chance of disease with each generation. My first generation has had a survival rate of only about 7% between the ages of 10 and 13 months. My second and third generations survival rate is currently about 90% at 6 to 11 months in age. As each generation dies out, I put the survivors into smaller tanks until they finish aging out. Then I do a complete teardown.

I prefer to have a fry tank, a sexing tank, and separate male and female tanks for each generation. I also now prefer to put males and females in separate rooms in my house since they have shown me that they will leap into other tanks

The overall psychological situation of a tank does not depend on a number but rather on the group of individuals in that tank. As I wrote before, the 29 gallon tank with 65 girls was very violent. Only a handful of fry survived in that tank, and they were terrified. It was very hard to catch them. Every week I would have to pull all the plants and decorations out of that tank creeping across the substrate with two nets till I caught them.

My fry tank went down for a few months, and I had to keep them in the other 29 gallon tank that had over 100 fish at that time. When I put the fry in there, they would dive down into the substrate and hide for 2 to 3 days until they figured out they would be okay. That second 29 gallon tank had grown females, juvenile females, and babies. Even though it was much more crowded. not a single fry was eaten.

When I was able to get my fry tank running again and a separate sexing tank, only 80 girls were left in it. For some reason, this second tank of girls has always been much mellower. I believe it is simply a question of having enough peaceful individuals living together; they never became extremely competitive hunters. They are more aggressive at feeding time than the boys, but they do not injure each other. Instead, they have self-inflicted wounds from diving too hard into the eco-complete to get at the Repashy community plus gel.

At any rate, I can only say that the idea of too many depends on the personalities that you have in your tank. Overcrowding is more about how the fish can or cannot deal with each other and not about an actual number. Definitely, as you add more and more fish, you increase the odds of them not getting along.

I have found that there are certain numbers that generally work, and that's why I tell people roughly 14 male Endler's in 10 gallons even though my usual number over the years has been closer to 22. Of course, sometimes people find that with just five or six boys, there is one who is too aggressive. It is possible that I have not seen that because in my minimum of 14, there are enough aggressive boys to balance each other out.
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