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Ever since I moved my 8 diamond tetras from a 40g to a 90g they've been much more aggressive towards each other. They all look basically the same, but I think there are mainly 3 who are flaring, circling, and nipping at each other. These guys are acting like cichlids!

What do think is up with them?

Check the fins.

Are the really feisty ones the ones with elongated finnage?

If so, it's your males.

Quite a few Characins will display this macho 'jousting' behaviour among the males (my Lemons did this incessantly). Look closely though, and check to see whether or not the male Diamond Tetras actually make contact or whether they 'pull their punches'. In the case of my Lemons, it was all macho ritual - they pulled their punches, but performed enough parrying and thrusting to get their point across!

Usually, this behaviour reaches a peak just before spawning. My Lemons would launch into a veritable jousting frenzy, then 48 hours later it would be replaced by madcap chasing of the females around, followed by explosive spawnings. Lemons in tip top condition, in my experience, will spawn once a month in a community aquarium with little or no prodding on the aquarist's part other than good housekeeping and regular live foods.

Quite often, the species that are most e to this have tall dorsal and anal fins, and usually have high-contrast markings on their fins too - Lemons, Rosies, Black Phantoms are classic examples. Your Diamond Tetra males will have the extended finnage, but lack the contrasting markings, so this makes them somewhat unusual among the 'jousters' if that's what they're doing!

The worst ones I had were Beckford's Pencil Fishes. Mine may have been exceptions to the rule, but after 6 weeks of 'typical' shoaling behaviour, it was as if a switch had been flipped, and my two most dominant males embarked upon a campaign of systematic extermination of the rest, starting with the females. Those fish were evil - the switched from behaving like Characins to the point where they more closely resembled hardcore criminals among Malawi Cichlids such as Pseudotropheus elongatus!

Oh, one thing that will probably calm your Diamonds down if there isn't one present already, is the introduction of a larger and potentially predatory fish. If they think they have a predator to avoid, they may well calm down a bit! If they have a Blue Gourami cruising around, that should make them a bit more watchful and less inclined to be scrappy with each other. Put Characins in an aquarium without a faux predator to keep them on their toes, and once they realise they're the top dogs in the aquarium, it can go to their heads ...


Panda Catfish fan and keeper/breeder since Christmas 2002

i'd say they are just super happy in their new, bigger surrounds. they are jousting and it's actually beautiful to watch, as a) it is pre-breeding behaviour, and only happy, healthy fish want to breed and b) it is highly ritualised and you can actually see who your alpha males are. they will not hurt each other. my black phantoms are at it all the time.

I think it is the ones with longer fins so you're probably right. I guess it means they like their new home

However, there's a least one guy whose fins are a little tattered so I guess the bully isn't all bark and no bite.

It is very interesting to watch though. They're swimming around eachother on an angle and their fins seem to have a much "redder" hue.

Thanks

When your Diamonds are 'jousting', do they do so head up or head down?

Lemon Tetras joust head-up. Head down postures are coaxing gestures aimed at females immediately prior to a spawning coupling if the female is receptive, and is accompanied by different fin-flicking mannerisms.

Black Phantoms, as far as I'm aware, joust on an even keel, so to speak, relying more on holding their elongated finnage as erect as possible to make themselves look big and strong. Get an exceptional pair of well-matched males with really well-developed fins and the resulting match is utterly replete with piscine pomposity and bombast - so much so that you're tempted to play Tchaikovsky's 1812 Overture as an accompaniment!


Panda Catfish fan and keeper/breeder since Christmas 2002

Hmmm, I'll have to double check the next time I see them going at it. It seems to me they are even keel, but on a slant to one side. / \

While we're on the subject of fin-flicks, I can't resist recounting the most unusual fish romance I've ever seen. A friend of mine tried his hand at running a pet store about a decade ago (he ended up turning it into more of a personal zoo for himself), and in one shipment of saltwater fish he got a Blue Damsel who for some reason had fallen passionately in love with an orange and white Ocellaris Clownfish in the same tank. The Damsel followed it everywhere, continually darting in front of it and then fluttering his dorsal fin seductively, while ignoring all the other Damsels in the tank. The Clownfish, of course, totally ignored him. Scott was so enchanted by this piscine variation on "Of Human Bondage" that he refused to sell either fish until the unrequited affair finally broke up a week later.