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It seems that 2 of 12 baby arowana still only take bloodworms and haven't taken to floating arowana Hikari sticks and pellets yet. I missed this and was offering little bloodworms or some days none. These two are the smallest, IDK if this is because they haven't taken to pellets or because they couldn't take down pellets due to their smaller size at arrival... In any case, one of them goes behind the divider as it seems to have a damaged fin on the top.

The starry night had been feeding overzealously in the 1800 gal for a a good half a year, after which time it stopped feeding (fed only occasionally) and started to sit in the corner lethargic, maybe swollen, and show white fuzz here and there on the body, which I presume is the saprolegnia fungus eating away necrotizing skin and scale. Looks eerily similar to our other cichlids that overfed, had same external symptoms, then died.

It's a bad idea to shuffle fish in the beginning of the warm season, when many fish are preparing for courtship and spawning. I wanted to give our ~15" Taiwan mahseer a bigger and safer home. The bigger I did, the safer not so much. The predators taste scared new tank mate and even though they cannot prey on it because of comparable size, they still try, namely three 1.5ft lima shovelnose, 2ft dorado catfish, a little bit from black ear shark catfish and even Aral barbel:

The dorado grew to 4"-5" in 1 month with us. Started nipping the smaller deformed Chinese hifin shark. And I thought arowana too (but that was erroneous, that was aro on aro damage as future showed). Got their own 240 gal for now.

Turns out the damage on 2 small arowana (out of 12) was likely caused by other arowana, not by dorado or any other tank mate:

At first GGG thought it was a new food item in his tank but things quickly turned around and the gulper went into deep hiding, sporting several abrasions from midas teeth. Lando the midas won't leave GGG the gulper alone either:

Jello has been just tolerating her 240gal tank, it seemed to me - appetite on and off, moody, taking uncomfortable positions, because she is much longer by 6" or so than the tank's width and the tank's height, unable to assume a totally vertical position when begging under a lid. Plus we needed the tank space. So decided to give her a try in the less aggressive 4500 gal, where she had never been (she did spend a few years in the other 4500gal with the jumbos, some of whom were bothering Jello, hence the move year ago to the 240 gal to stop risking her life and health).

Also, she has had this fuzzy spot on her tail for like a year it seems. I had removed it physically but it comes back. This time I decided to dab it with concentrated potassium permanganate.

Do you have room to spread them out, maybe in groups of 2, 3 or 4? Might be better than watching them thin themselves out?

Thank you. Not conveniently but I can install dividers for one. I am wondering though why they are doing it. I didn't expect it because in my prior experience with baby and juvi silver arowana groups, up to 5, they fought initially for the alpha status but there have never been deaths - we raised them all to adulthood.

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Good question. I've never raised Arowana so can't help you there. It could be the way they were raised, genetics of the parents, balance of the number of males, or females, or males and females, personality of one fish, or the personalities of some, or the combination of fishes. One thing is clear though: they are not playing well together.

Thank you for thinking with me, appreciate it. Jumping ahead of the lagging videos, I can tell you that the remaining 8 arowana had stressed the smallest one, which died in isolation (kill #4), and then they stopped (short or long term, IDK), also I placed a large plastic plant to break up the lines of vision some.

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At 3:59 of your second Hemiodus sp. video (with the "kill first 3 of their kind" in the tag line), there is one specimen with a single dot on the side. I know Hemiodus gracilis can be variable, but it may be that you have another species in this one? According to Baensch & Riehl that fish might be Hemiodus orthonops, H. unimaculatus or Hemiodopsis argenteus.
That being the case, maybe that has something to do with the attacks?

I really like the shoal of these that you have, never seen that many together, they will be impressive when they get older.
Ive had Hemiodus a number of times, usually in groups of 5-6 and never seen any issues ever with aggression. They are very quiet and peaceful fish in my observations. The thing that I have seen is that they are very fragile and need plenty of food. Id suggest that any damage happened either before you got them, or them trying to fit through a small hole etc.
One other observation is that I usually keep them in tanks with slightly less current than you have.
Good luck with them, keep us posted on progress.

Thank you much guys! Yes, there seems to be mixed in at least two different species - black tail hemiodus and that fish (or two) with the dot in place of line. Maybe those are more aggressive, I dont know. My first try ever.

5th dies, 6th dies - this was a week ago. No deaths or obvious signs of attacks since then. No change in the tank at all. The killings just stopped.

Arowana kill 4th, no damage on this one that's obvious but obviously stressed out bad (this is from more than a week ago; videos are lagging behind)

visit to a good peer

Ideal and peaceful community fish turn out to bite tails of Phalacronotus sp Giant Siamese Glass Catfish:

Viktor, I don't mean to alarm you, but here on the west coast, Pets Mart fish are known for having "superbugs". If I ever just have to buy a fish from that store chain, I double quarantine them. I don't know the quality of the 'Pets Mart' fish on the east coast (could be better?), but I hope you quarantined them.

Thank you so much, Naturalart! I'll keep in mind. The superbugs are the ones resisting common medications used against them, right? No I didn't QT them. All the fish in the store looked good to my eye.

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