Chromis in very large groups?

Phycodurus · Nov 21, 2019

hi all,

like many hobbyists here, i can attest to blue reef chromis & green chromis having the unfortunate reputation of picking each other off when kept in groups. i myself tried with a group of 10 (in a 180G tank), and eventually, they picked each other off. they seemed to hold steady at 3 individuals from what i keep reading.

i’m curious to ask if anyone (with tanks in the 100G to 300G range especially), had fared better success with groups in the 20-30 count range. i’m thinking of a kind of a “protection in numbers” approach where the weaker chromis can hide among the crowd.

realistically, i still think such a large group would inevitably still dwindle down to a very select few.

i also tried mixing different chromis (blue reef chromis, green chromis, black & white chromis) at a count of 3-5 each, but the same result.

i have a similar idea i’d like to try but with combined groups of chromis: 3-10 of each of the following species - - blue reef chromis, green chromis, black & white chromis, barrier reef chromis, vanderbilt chromis, etc. maybe mix is up with talbot damsels and rolland damsels (the more species, the lesser the count per species).

@JPergamo: you alluded to this in a post back in september; this may also be of interest to @Nobbygas, @Bob2bob, @Feet4Fish based on past threads that I checked. thanks for reading.

respectfully,
rick

MyTankSux · Nov 21, 2019

Im about to put 20 in my tank. The main ways ive found to circumvent "survival of the fittest" is to keep flow high, feed them a ton, and have lots of other fish in the tank to distract them.

Murica · Nov 21, 2019

My group picked each other off until there were three left. Two of the three literally stayed swimming face up at the surface opposite ends of the tank because they were scared of the larger dominant one.

tthomas · Nov 21, 2019

Started out our 150 gallon with 8, we're down to 4 presently. We are adding a larger shipment of fish tomorrow and I plan to add an additional 4 with the others in hopes that the increased numbers of fish will keep them content/occupied from picking on each other. We'll see! The new group includes 9 anthias and some larger fish. At least adding a few chromis every now and then won't break the bank!

C. Eymann · Nov 21, 2019

QT for Uronema specifically, 45min formalin bath before entering a sterile QT setup.

Also feed them as you would a delicate species of anthias, small amounts 3x a day minimum IMO.
Keep in odd numbers.

Phycodurus · Nov 21, 2019

C. Eymann said:
QT for Uronema specifically, 45min formalin bath before entering a sterile QT setup.

yes, i do plan to quarantine (specifically for uronema in mind). i have three 10-gal isolation/QT tanks. i figure i’d be able to get three batches going thru the quarantine process and then introduce them all at the same time.

ca1ore · Nov 21, 2019

I gave up on green chromis years ago. If you want a group that won’t break the bank, how about yellow tail damsels. Much better looking than the green chromis and easier to get a stable group. I’ve close to 50 in my tank, along with a few azures, Talbots and Rolands.

mort · Nov 22, 2019

I've never understood the often touted "keep in odd numbers" advice but agree with everything else C. Eymann says above with feeding being the key advice once your sure they are healthy. A fish behaviourist professor Ellen Thaler noted through observation that chromis need to be feed nearly constantly to maintain order. It only needs to be a few micropellets every 15 minutes or so but they spend their time picking plankton all day naturally, so they aren't battering each other. It was also noted that when predators came by the first fish out afterwards were the small weaker individuals that one needed more food but two more importantly were lower in the hierarchy.
So its important to get the feeding right, if only to occupy them more although being confined means this might not be enough.

The other thing I'd add is that there are several species that go under the name green chromis and they behave very differently in a tank. Most seem murderous but there is at least one species that plays relatively nice. I can't remember which it is off the top of my head but @Haydn has wrote about it before and he knows his chromis (worth looking on ultimate reef if I'm allowed to say that). He's also kept fusilier damselfish which would be a good option for a group as they seem to mix fine and are very underrated.

The final thing I say is mixing species only works if they are robust as each other. I see vanderbilts on the list and ime they are not the best when it comes to mixing with the average community.

ScottR · Nov 22, 2019

I started with 3 blue-green chromis. They schooled in my 40g. Then I added 3 more. 2 were bullied and died. The fourth joined the party. The 4 have been happily schooling for 6-7 months.

Phycodurus · Nov 22, 2019

thanks for the replies, all.

i do use an automatic feeder (flake food/pellet food) that i programmed for a noon feeding and then a 16:00 feeding ... just a small amount. the good stuff (thawed brine shrimp, live brine shrimp, thawed mysis, live black worms, spirulina blends, etc, etc, etc + the occasional in-n-out burger [kidding]) hits the tank at the 19:00-20:00 hour mark. if i do this chromis stocking experiment, i might go for a dash of food every hour during the tank's photo-period. that'd be awesome if feeding turns out to be a key component to maintaining civil order in the tank.

@mort, thank you for mentioning 'green chromis' as something of a generic catch-all for some C. species. i am indeed aware of this. re: the vanderbilts, maybe i'll start off with a large group of these only, and see if they buck the trend of picking each other off.

Haydn · Nov 23, 2019

I wrote this a while ago and TBH I'm being lazy just cutting and pasting here. Some of the info I have updated in red. I stress these are my personal opinions.
Firstly none of the species I have kept have been able to count so it doesn't matter if you have an odd or even number

' I have found with the 'green chromis' you need to make sure you have all C. Viridis, that is important, if you are not sure don't buy the group. The other fish sold as green chromis, C. Atripectoralis is the aggressive one (There are now at least 2 other species being sold as 'green chromis). A group will pick on and kill the sub dominant individuals and if you have a mixed group C. Atripectoralis will kill C. Viridis.

Even with C. Viridis they do not like to be cramped for space and in my experience cramming a large number in a small tank doesn't work, they tend to harass the sub dominant ones and if they have nowhere to hide and feed quietly they will fade away. I am lucky I have 2 cubic metres of water and 300kilos of LR so 15-18 green chromis in the tank is viable.

The other species of Chromis in my tank are:

C. Vandavelt, a very peaceful small fish, they do not show any within species aggression. Mid-water swimmers that interact rather than 'shoal' easy to keep and feed. One of my favourites. They need a quiet species tank. If the tank has boisterous fish even if they are not a thread the Vandavelt's will hid and not feed properly.

C.Retrofaciatus, the males defend a territory based on a small cave, the females 'visit' the males. Other than the males defending their space I haven't seen any aggression. This species tends to stay near the rocks but isn't shy. Easy to keep and feed. Still one of my favorites and very underrated.

C.Nitida, Mine are small at the moment (1"-1 1/2") and shoal. I don't know what their behaviour will be when they get bigger. They seem to be hardy and easy to feed. Don't live in groups once they get to 2.5" and you get WW3 until there is one left!! Absolute terrors.

C. Iomelas, these tend to be loners, I have 5 in the tank and they keep to themselves, i haven't seen any aggression but there could be if they were crowded. Easy to keep and feed, mid water swimmers.

C. Margaritifer a bit bigger than the C. Iomelas although they have a similar colour (black/white), C. Iomelas has more white (hence the common name half and half chromis). This is a grumpy one and will chase any fish smaller than it is out of its territory. Fortunately I only have 3 of these. Easy to keep and feed.

I don't have any real secret to keeping these fish other than lots of research before buying them and understanding their needs. I have been lucky enough to watch them in the wild on the reef, so I can see their eventual size and their behaviour. I did feed heavily with frozen, flake and pelleted food

Phycodurus · Nov 23, 2019

haydn, i tip my hat to you! thanks much for yr insights.

C. retrofasciata also caught my eye, but i didn’t want to appear too overzealous with my proposed list. i may well ditch the C. viridis to make room for these lesser known chromis.

do you find that all these chromis species intermingle somewhat [in the confines of a tank]? if and when you seen aggression, is it directed at like members of the same species??

i would think that there’s two types of aggression: (i) general hierarchy aggression (within the same species) and (ii) territorial aggression (i.e. “this is my rock and no one gets near it”).

thank you again.

Haydn · Nov 24, 2019

Phycodurus said:
haydn, i tip my hat to you! thanks much for yr insights.

C. retrofasciata also caught my eye, but i didn’t want to appear too overzealous with my proposed list. i may well ditch the C. viridis to make room for these lesser known chromis.

do you find that all these chromis species intermingle somewhat [in the confines of a tank]? if and when you seen aggression, is it directed at like members of the same species??

i would think that there’s two types of aggression: (i) general hierarchy aggression (within the same species) and (ii) territorial aggression (i.e. “this is my rock and no one gets near it”).

thank you again.

Retros won't 'replace' C. viridis they inhabit a different niche on the reef, much more secretive and solitary. I added 10 and as they grew I had 4 males, each male occupied a territory based on a cave in the LR. There were always border disputes between them, never actual fights just fin flaring and threat charges. The females wandered the whole tank as individuals checking out the males display and if impressed going into the males cave

The Chromis like any fish group in a tank intermingle, again because of their different niches they tended to congregate in different areas, Viridis on the top of the 'reef', Retros closer to the rocks, Vandervelts around their 'home' rock so they could dive for cover. Some, like the male Retros and the C. Margaritifer had a higher territory drive than the others and tended to try to keep other fish away from it. C. Margaritifer were the most driven I kept and would threaten pretty much all the other fish, Chromis or not, that came into their area.

Once the hierarchy was sorted there was very little of this type of agression just the odd short chase and fin flaring.

Fishfreak2009 · Nov 24, 2019

When my 380 gallon was running I had a school of 15 greens, a few black axil, a group of 5 Vanderbilt's, 5 bicolor and 3 blue reef chromis all together. Also had a school of dispar anthias and a lot of other assorted smaller fish. Fed the tank at least 3x daily, normally 5. Everyone got along. Also had a large 1' niger trigger that everyone tended to run from even though he never hurt anything. Kept them all schooling tight together. My current tank is a 110 tall and I have a group of 5 staghorn damsels (Amblyglyphidodon curacao) that have the same color and do not fight. Highly recommend them.