Fish Being Assassinated

H Town Reefer · Jul 18, 2021

Good morning reefers. I have something happening that I have never experienced before. I have added green chromis to my 40 gallon cube. These are the only fish in the tank. I have tested for ammonia(none) nitrite(none) and nitrate(very low to none). Each day I have been waking up to 1 being devoured by my hermits and nasarius snails. Tank has nothing else in it but corals. My question to all. Is it somehow possible for this cleanup crew to attack and kill these fish? I would be forever grateful for any thoughts.

lapin · Jul 18, 2021

Maybe one of the fish does not like the rest of them.
Is your rock live, from the ocean ?

H Town Reefer · Jul 18, 2021

No. It is all dry rock

davidcalgary29 · Jul 18, 2021

I'd guess that your chromis are fighting for dominance and killing each other off. Your CUC are just...cleaning up.

Lost in the Sauce · Jul 18, 2021

Your chromis are killing off the weaker fish

Cell · Jul 18, 2021

I dont believe your experience is atypical when dealing with groups of chromis. Few are able to keep groups of them successfully long term. Most of the time you end up with just one. I read once that there are different species of blue green chromis that look alike but arent really compatible, never verified the accuracy of the claim though.

H Town Reefer · Jul 18, 2021

Thank you for your responses. I just assumed that schooling fish would not be so aggressive towards each other. I have 2 left so I will see what happens with them. Fingers crossed they get along.

DeniseAndy · Jul 18, 2021

Most fish in our small systems with pick each other off until a dominant fish or pair emerge. Very common in chromis. I have also experienced this in anthias, cardinals, clowns (no brainer there), even neon goby.

Mr. Mojo Rising · Jul 18, 2021

how many did you add and did you add them all at once?

stewie · Jul 18, 2021

This always happen when I get chromis. Always a risk that they will die off and often left with only one remaining.

DeniseAndy · Jul 18, 2021

Lets see... (these are all in my 210g display)
With the blue streaked cardinals I added 10 all at once. Within the first month I was down to 7. They were all healthy and went through qt like champs. Then slowly they would disappear and by 1 year I had 3. These lived form many many years as a group of 3.
My dot-dash cardinals were 4 all at once that were 2 by a few months.
My anthias would just fight until the largest was my only one. Different species too. Man, off hand cannot remember the main big ones. Not lyrtail, bartlettes orsquarebacks though.
My clowns, well, lets just say that all can be fine for up to 2 years when they will decide, nope. Only one dominant pair for this tank.
My neons were in a 6g tank and one took offense to the other so killed it.
Survival of the fittest/smartest/best adaptable is life on the reef.

Jamesmost · Jul 18, 2021

Started with 11 blue reef chromis
2 monts later were 6, added 7 more...
Now 14 months and only 2 left

Karen00 · Jul 18, 2021

My saltwater tank is new so I can't speak to it but this very thing happened with my 15g freshwater. There is a species of goby I wanted to keep and all of the care guides said a group of six would work in my tank so I got a group of six. There are two left. No matter how many times I tried to keep six, two always emerged. I don't even try anymore because clearly two are fine and six are not plus it's cruel to keep trying. I've had the same two from about two years now. I'm still shocked at how quickly they picked each other off. It took about two weeks.

H Town Reefer · Jul 18, 2021

LordofCinder said:
how many did you add and did you add them all at once?

I put 4 in all at the same time.

davidcalgary29 · Jul 18, 2021

Karen00 said:
My saltwater tank is new so I can't speak to it but this very thing happened with my 15g freshwater. There is a species of goby I wanted to keep and all of the care guides said a group of six would work in my tank so I got a group of six. There are two left. No matter how many times I tried to keep six, two always emerged. I don't even try anymore because clearly two are fine and six are not plus it's cruel to keep trying. I've had the same two from about two years now. I'm still shocked at how quickly they picked each other off. It took about two weeks.

Nature is amazing, and it's incredible how things move toward a state of equilibrium even when we have other plans.

I'd love to see someone do a study of maximal groupings of fish based on tank size. I have a pair of orchid dottybacks in each of my 65g and 13.5 tanks, and they seem to have paired off in those settings. I certainly wouldn't add a third in the Evo, but I'd love to know how big a tank has to be to build a harem. And certainly people keep groups on anthias and chromis: I'd love to see tank size for suggested groupings.

It'd also be instructive to have different suggestions for different life stages, such as any noted differences between juveniles, breeding pairs, and mature adults.

Maybe there could be a subforum where people could list their tank sizes, inhabitants, and aggression levels. Here's mine: Evo, mixed reef, two (paired?) orchid dottybacks. No aggression aside from typical dottyback drama at feeding time. RSM 250 (with softies): keyhole angel (sub-adult?), multicolor (adult), female lubbock's wrasse, paired orchid dottyback couple. Some aggression by multicolor to keyhole in the first four days; all no current aggression, but competitive at feeding time. Plenty of rocks in which to hide/stake out territories.

DeniseAndy · Jul 18, 2021

My 3 indigo dotyybacks were all added as juveniles and lived a good 6 years all together. Breeding too.
My anthias were always paired off, my cardinals always eventually paired (except some I had for years with 3), my clowns, well, only two have ever worked for me long term (longer than1-2 years). I have 6 azures and 3 talbots and they all seem fine. My lemons I only have two and they mate and are fine too.

Maybe I should write all this down to keep track. (oops, showed my age there.)

davidcalgary29 · Jul 18, 2021

DeniseAndy said:
My 3 indigo dotyybacks were all added as juveniles and lived a good 6 years all together. Breeding too.
My anthias were always paired off, my cardinals always eventually paired (except some I had for years with 3), my clowns, well, only two have ever worked for me long term (longer than1-2 years). I have 6 azures and 3 talbots and they all seem fine. My lemons I only have two and they mate and are fine too.

Maybe I should write all this down to keep track. (oops, showed my age there.)

Tank size and aquascape?

Karen00 · Jul 18, 2021

davidcalgary29 said:
Nature is amazing, and it's incredible how things move toward a state of equilibrium even when we have other plans.

I'd love to see someone do a study of maximal groupings of fish based on tank size. I have a pair of orchid dottybacks in each of my 65g and 13.5 tanks, and they seem to have paired off in those settings. I certainly wouldn't add a third in the Evo, but I'd love to know how big a tank has to be to build a harem. And certainly people keep groups on anthias and chromis: I'd love to see tank size for suggested groupings.

It's also be instructive to have different suggestions for different life stages, such as any noted differences between juveniles, breeding pairs, and mature adults.

You're spot on about equilibrium and it would be awesome to have something to refer to, like you mentioned, to guide us!! If anything it would save us killing fish needlessly in an attempt to keep a grouping of fish that will never happen due to the tank's specific factors. What's funny is that the gobies I mentioned are small and don't seem to have readily identifiable male/female characteristics so I have no idea if they're an actual pair or just happened to be the last two standing in the battle for supremacy. They could be male/male or female/female and not necessarily a male/female pair. Haha.

DeniseAndy · Jul 18, 2021

My tank for all those were a 210g with lots of caves and hidey holes. Also plenty of room to swim. Some day I will track this stuff. I would have to look back at notes too.