Dartfish Aggression

[PotatoPig]

So I had two zebra barred dartfish. One male and one female, they spawn every few months.

A few weeks ago I added a third - much smaller than the other two. My understanding, which seems to be at least partially wrong, was these fish do well in groups.

Nope.

For a while the two established ones picked on the newcomer, but suddenly the dynamic has changed and the newcomer has paired with one of the existing two and the “rejected” one is now hiding out and gets picked on when it goes near the others and doesn’t seem to be doing well.

So…

Is the issue I have three and aggression is focused - ie if I add another they’ll start to do better? Or have I been misled on these fish and they’re strictly a One Pair Only species
- like clowns, species and I’ll need to wait for the situation to “resolve”

 

[Slocke]

You were misled. A mated pair or singly is the only way to keep them.

 

[PotatoPig]

Well dang.

Does this extend to adding other dartfish - eg will they also go hostile if I add blue gudgeons?

 

[Slocke]

Well dang.

Does this extend to adding other dartfish - eg will they also go hostile if I add blue gudgeons?

It’s certainly more doable. If you have deep sand you may want to consider a pair of yellow headed jawfish.

 

[ISpeakForTheSeas]

This is interesting, as they are schooling fish in the wild, and I've heard from a number of reefers with personal, hands-on experience with these that these will school peacefully in aquaria. So, either people keeping them had issues after discussing it on the forum here and didn't report that, or I would guess you need more than three, but I don't know for sure.

The below may help with schooling/shoaling behavior though:

My understanding is that keeping a large school can theoretically work, but - as mentioned above - there are a number of things to keep in mind with schooling:

- The number of schooling fish in the tank (I've heard odd numbers are preferred, and the preferred number of fish that I've seen seems to be 9 to 11 at a minimum; the more fish, the more diluted the aggression is between them)

- The size of the tank (for quality of life purposes for your fish, bigger is better - yes, some animals will be calm when shoved into tiny spaces with large numbers of conspecifics where if there was just one or two conspecifics, it would be a deathmatch, but they obviously wouldn't be happy in that situation long-term)

- The amount fed, the quality of the feed, and the frequency of feedings (basically more food = less aggression; and better food = better health = happier, less aggressive fish [theoretically])

- Tankmates (big, scary tankmates that the schooling fish could view as a threat may act as an outside force that keeps the schooling fish focused on not getting killed rather than on fighting amongst themselves)

- The scape of the tank (lots of fish need lots of places to hide/sleep - the more hiding places, the safer the fish feel; line-of-sight-breaks can also help with feeling safe)

That's all I've got for the moment (and pretty much all of it has been mentioned above), but basically - to my understanding - it's a balance of making the fish feel threatened enough by external sources to prevent infighting while also making them feel safe enough (largely through their numbers, the tank's scape, and food security) to not be too stressed. If you're able to strike that balance, you should be able to see schooling behavior (to the best of my current understanding).

 

[Slocke]

Went through some care guides that agree they are only aggressive to members of their own species. It is also my experience from this forum. Large groups tend to die off fast and only singles and pairs live long term.

Is a Firefish Goby Right for Your Saltwater Aquarium?

Information for hobbyists on characteristics, origin, feeding, and breeding of firefish gobies, a small fish with a sparky personality.

www.thesprucepets.com

Firefish: Saltwater Aquarium Fish for Marine Aquariums

m.liveaquaria.com

Scissortail Dartfish: Saltwater Aquarium Fish for Marine Aquariums | Ships from LiveAquaria® Wisconsin Facility

www.liveaquaria.com

 

[ISpeakForTheSeas]

Went through some care guides that agree they are only aggressive to members of their own species. It is also my experience from this forum. Large groups tend to die off fast and only singles and pairs live long term.

Is a Firefish Goby Right for Your Saltwater Aquarium?

Information for hobbyists on characteristics, origin, feeding, and breeding of firefish gobies, a small fish with a sparky personality.

www.thesprucepets.com

Firefish: Saltwater Aquarium Fish for Marine Aquariums

m.liveaquaria.com

Scissortail Dartfish: Saltwater Aquarium Fish for Marine Aquariums | Ships from LiveAquaria® Wisconsin Facility

www.liveaquaria.com

Doing a deeper dive, it's looking like this may be similar to Green Chromis schooling, where some keepers have them school fine and some slowly drop to 2 (interestingly, though, looking through some of the threads, I haven't seen any reports of visible aggression yet - just fish slowly disappearing).

Let me see if we can get a follow-up on some of the folks I know have personally kept these - @littlefoxx @Mr_Knightley @Jeffcb

 

[littlefoxx]

I had one, he always hid. I then got 4 and added them at the same time and they were good, but picked themselves off to a group of 3 and they were perfectly fine. None of mine were spawning though, that could be the issue. Right now Im back to one cause my other two jumped out of my container they were in temporarily and died. Only my big one was alive on the floor when I found them! He is back to hiding all the time, I need to get him some friends

Yours might be mad cause they are a bonded spawning pair and see the other one as a threat to that? Thats my theory at least

 

[i cant think]

So I had two zebra barred dartfish. One male and one female, they spawn every few months.

A few weeks ago I added a third - much smaller than the other two. My understanding, which seems to be at least partially wrong, was these fish do well in groups.

Nope.

For a while the two established ones picked on the newcomer, but suddenly the dynamic has changed and the newcomer has paired with one of the existing two and the “rejected” one is now hiding out and gets picked on when it goes near the others and doesn’t seem to be doing well.

So…

Is the issue I have three and aggression is focused - ie if I add another they’ll start to do better? Or have I been misled on these fish and they’re strictly a One Pair Only species
- like clowns, species and I’ll need to wait for the situation to “resolve”

Seeing as it’s the Ptereoletris genus you’re dealing with, they can be kept in groups but when introducing species to established pairs, you always want to have 4-5 total not just 3.

I’ve seen aggression between these guys, it’s never obvious but it’s there. Another thing I’ve noticed with these in LFSs, when they settle and have no reason to stay grouped they will split off and start the “killing spree”. So much like Chromis and Anthias, give them a reason to be scared (Damsels or other fish that will go for them) and they group. Give them a reason to feel safe, they split off.

Also, when grouping, the bigger the group then the more success you’ll have. Just bear in mind some species (like @Slocke found above) don’t always group naturally, specifically the “Firefish Dartgobies” of Nemateleotris aren’t always grouping species, although the only communal species in that genus is N. magnifica.

 

[PotatoPig]

Seeing as it’s the Ptereoletris genus you’re dealing with, they can be kept in groups but when introducing species to established pairs, you always want to have 4-5 total not just 3.

Yep - those are the ones.

This is the picked on one - either it’s belly is pinched or it’s egg bound/something is causing swelling around its front.

The weird thing is all the visible aggression is from its former mate. It keeps trying to approach, and then gets chased or fin-nipped.

Right now the tank is otherwise very peaceful - the only vaguely “caution, can be aggressive” fish are a pair of ocellaris clowns and a Tomini tang, and those three are buds who share a corner of the tank.

Intrigued by the Chromis idea - but do these go after other fish? I have clowns, tomini tang, the dartfish, one royal gramma, one court jester goby, and an engineer goby in a 75g tank. I doesn’t look particularly crowded as they’re all small fish.