Copella arnoldi (previously
Copeina arnoldi; order: Characiformes, family: Lebiasinidae, for those who are actually interested in such things) is a small freshwater fish found in the Amazon River basin. I recently learnt about it and frankly, I think it's the coolest thing swimming around in the Amazon (cooler than red-bellied piranhas, you ask? Hmmm. We'll get back to that :) ).
What's truly remarkable about this fish is not it's defences (none that I know of), or appearance (cute little gray/reddish thing), but rather its unique method of breeding. I've seen a stunning video of it, but unfortunately I could not find any adequate visual representation on the net. The only decent picture I found was from Animal Diversity Web, (view
here), but it's copyrighted so I didn't post it up. Since I did not think explanations alone would give this feat it's due credit, I finally made some quick
schematic sketches myself. Meet Mr and Mrs
Copella arnoldi - the dashing male in white and the sleek female in black (aww, aren't they cute? Ahem.):
When it's time for
Copella arnoldi to mate, the male first ushers the female to a suitable location. He then darts back and forth apprehensively, as though communicating the plan to the female. The female reciprocates. Then suddenly, they make their move.
The male literally
jumps inches into the air, followed in synch by the female. For
Copella arnoldi have the rare distinction of being the only freshwater fish to breed out of water. Somehow, the male has determined a suitable target: an overhanging leaf where they will mate, and where the female will deposit her eggs. The timing and positioning is absolutely critical. They have to aim exactly and land perfectly. The target surface must also be appropriate - rough enough to adhere on, but not too much that it injures the little pair.
Once the male has hurled himself at the breeding surface, suckers on his underside help him attach to it. And this illustrates another remarkable fact (termed in pathopoet jargon as, "super-cool"): although it's the male who has determined where they are going, the female must jump at exactly the right time, because she in fact has no way to attach to the leaf [edit: I'm quite sure this is correct, but nosing around, I've found that early journal articles say that
both male and female use their ventral fins to attach. Since I'm hardly qualified, I'll put in a disclaimer of caution: I'm writing this solely from memory - a dangerous thing - so I appologise for any errors and encourage you to do your own research]. They must arrive together, in order for the male to grab and hold her long enough for her to lay her eggs; to aid this, they lock fins partially before the jump. After seconds, the pair fall off, leaving some eggs behind. They repeat their stunt a few more times, after which the male chases away the female. He has more important things to do now :)
As if this aerodynamic courtship wasn't enough, the male now exhibits behaviour even stranger among fathering fish: he proceeds to care for his young. In order to prevent the eggs from dehydration, he splashes the eggs with his fin, aiming water at his developing progeny with remarkable accuracy.
The fry develop quickly, and when they are mature enough, the weight of the water drops actually
pulls them down. A fry-containing drop splashes into the river below, and the little fish darts away immediately and instinctively to safety within water plants that hopefully will obscure him from hungry eyes, assuming of course he hasn't already been intercepted by a hungry mouth!
For their unique characteristics,
Copella arnoldi are known by several appropriate names, like "jumping characin," "splashing characin," or "splash tetra." Well after all that, I hope you can understand some of my enthusiasm! (if not, I still think they're super-cool) :)
After finding out about these little darlings, I mean vertebrates, I - being a ponderous person -, began to ponder how one could explain the complex traits of
Copella arnoldi. Sure, the scientific answer I'm programmed to give is, "some unknown selective pressure must have lead to the divergence of the characin fish, such that the species
Copella arnoldi lay their eggs above water, increasing the chance of survival of their brood." But how exactly would you outline these intricacies of development? Thus, I decided to make an evolutionary map of
Copella arnoldi. I tapped into my dusty brain archives of ecology/genetics/phylogeny/etc. and came up with the following "plausible" explanation, likely to be found in some journal a few years down the road. Or, maybe even someone's dissertation. Hey, feel free :) :
- 1- Unknown selective pressure (e.g. predatory) selected for Copella arnoldi that had the ability to jump into the air (i.e., some mutation in Copella gives them ability to jump, jumping Copella have advantage since they die less, frequency of jumping Copella increases etc. -- viola, natural selection).
- 2- Some mutation(s) arise(s) that gives rise to Copella with suckers; these Copella are selected for (again, they survive/die less because they can attach to surfaces and avoid the unknown (here, let's assume predatory) selective pressure.)
- 3- Some jumping-attaching-Copella have mutation(s)/polymorphisms (i.e. genetic differences) that compell them to mate above water (e.g., some female Copella has propensity to mimic behaviour and jump alongside male. Some male Copella have propensity to hang on to female. And etc.) Brood from jumping-attaching-mating Copella survive more/die less and inherit mutations/polymorphisms from parents.
- 4- Jumping-attaching-mating Copella progeny: some mutation(s) arise(s) that compells one of them to "splash" eggs. Brood from this fish survives more/dies less, carrying the trait to a later generation.
All this happens in thousands/millions years, i.e. whatever you can slot into "evolutionary time".
Sounds plausible? It is. But I myself would call it a tad preposterous :). So let me, like any good cartographer/phylogenist, be the first to dissect my little blueprint(note: no animal was harmed during the making of this post):
- 1- It's a bit difficult to accumulate the mutations one would need to make a Copella "jump." Unless one fish was born with an unnatural tick that made him sporadically jump into the air every so often, you would assume it would take an accumulation of mutations, that would lead to a "jumping" characteristic. Thus, each "mutation-step" must be heritable, plus a benefit to the Copella, to be passed on to the next generation. But, all in all, this is still plausible. Let us move on.
- Assuming we now have a bunch o' jumpin fish, we get down to the business of attachment. I'm pretty sure that no single point-mutation will give rise to suckers. So we're again assuming a series of mutations, each selected for because it somehow benefits the fish, that finally leads up to a sucker. Hmm, a bit tougher than the last. You've now added a chunk to evolutionary time. And I can't think of how intermediary sucker-appendages would give a jumping Copella selective advantage. Plus there's the business of actually hurling oneself to a leaf to realise you have a sucker. Unless you assume the Copella has aquired a sucker before getting to the jumping part. Note that the male only has this trait. So now I'm sure you'll say, aha! Mutation in the Y chromosome. Hmm, getting complicated, but we'll leave it at that. Let's move on.
- Jumping-attaching Copella. One could see how they'd have a selective advantage. But grabbing a female in mid air? Now that's tough. And why, pray tell, would she want to hurl herself at a leaf? Unless we assume Copella have stunning cognitive abilities and can communicate a radical and novel plan for mating to females, here the ice gets thin. Although of course, you could attribute it to random chance that some Copella managed to mate above water. Again, plausible, as chance always is. Then perhaps later Copella aquired the ability to usher their mates to a suitable "jumping-spot" and communicate the need to synchronize jumps. Throw in a couple of mutations and a dollop of evolutionary time; plausible, as always. So, finally:
- We've been through the realms of superfluous probability, and agree that these changes can't be due to a directed development by the superior cognitive abilities of our dear Copella arnoldi (though we still love you!) But, the fish splashes its eggs - certainly not because it "knows" they will get dehydrated. Un-splashed eggs would be done for, minimizing the chance of those Copella mating above water to have a selective advantage (the fry have a hard time already after they come out of their eggs). It's difficult for me to imagine a series of evolutionary changes sustained by selective advantage that would lead to Copella aiming and splashing eggs which they don't particularly realise need such care (outline the development of instinct). So even with 'bronzed' scientific hypotheses (compared to my quick musings), I find there's mostly well-presented plausibility, which (when pondered by the most basic part of the logical mind) is oddly low in probabilty. :D
The above may be the ramblings of a pathopoet (as usual!), but I hope you found them amusing nonetheless. If you want to taste a more 'scientific' argument and a denser discourse in plausibility, I've referenced a journal article at the bottom of the page (it doesn't talk about Copella arnoldi though, but goes through similar spawners). But for me, I just like to be fascinated with Allah's (God's) super-cool creatures : )
And that I guess, my well-appreciated readers, is just the way the cogs of the mind grind :) Congrats to those who made it thus far!! I admire you for your patience and thank you sincerely for the contribution of your time and the straining of your eyes. Hope you enjoyed the weird (and wonderful?) turns of a pathopoet's brain as much as the leaps of a jumping characin. If you like my images/stuff contact me and I'll let you use them, just credit me please : )
----------------------------------------------
Read more:
Martin K, Swiderski D. 2001. Beach Spawning in Fishes: Phylogenetic Tests of Hypotheses. American Zoologist 41(3):526-537 [
Access it at Oxford Journals online]
(for an easier read: good essay by an undergrad student): Wesolowski, J. 2002 Copella arnoldi: the Spraying Characin. [access here:
University of Texas Online]
EDIT: View the footage that I watched in the first place! A snippet from a documentary entitled, Equator: Rivers of the Sun. Watch here uploaded by some person on YouTube.
When it's time for Copella arnoldi to mate, the male first ushers the female to a suitable location. He then darts back and forth apprehensively, as though communicating the plan to the female. The female reciprocates. Then suddenly, they make their move.
The male literally jumps inches into the air, followed in synch by the female. For Copella arnoldi have the rare distinction of being the only freshwater fish to breed out of water. Somehow, the male has determined a suitable target: an overhanging leaf where they will mate, and where the female will deposit her eggs. The timing and positioning is absolutely critical. They have to aim exactly and land perfectly. The target surface must also be appropriate - rough enough to adhere on, but not too much that it injures the little pair.
Once the male has hurled himself at the breeding surface, suckers on his underside help him attach to it. And this illustrates another remarkable fact (termed in pathopoet jargon as, "super-cool"): although it's the male who has determined where they are going, the female must jump at exactly the right time, because she in fact has no way to attach to the leaf [edit: I'm quite sure this is correct, but nosing around, I've found that early journal articles say that both male and female use their ventral fins to attach. Since I'm hardly qualified, I'll put in a disclaimer of caution: I'm writing this solely from memory - a dangerous thing - so I appologise for any errors and encourage you to do your own research]. They must arrive together, in order for the male to grab and hold her long enough for her to lay her eggs; to aid this, they lock fins partially before the jump. After seconds, the pair fall off, leaving some eggs behind. They repeat their stunt a few more times, after which the male chases away the female. He has more important things to do now :)
As if this aerodynamic courtship wasn't enough, the male now exhibits behaviour even stranger among fathering fish: he proceeds to care for his young. In order to prevent the eggs from dehydration, he splashes the eggs with his fin, aiming water at his developing progeny with remarkable accuracy. 
The fry develop quickly, and when they are mature enough, the weight of the water drops actually pulls them down. A fry-containing drop splashes into the river below, and the little fish darts away immediately and instinctively to safety within water plants that hopefully will obscure him from hungry eyes, assuming of course he hasn't already been intercepted by a hungry mouth!