Scary Halfbeak Science

[nmonks]

Livebearers really are cool. Reading a scientific paper this evening on halfbeak reproduction, I learned that there are no fewer than 5 different modes. "Type 5", as it is cunningly called involves the embryos swimming about inside the ovaries, eating eggs and smaller siblings! I'd heard of this with sharks, but never bony fish. Anyway, I wrote it up for the halfbeak page at Wikipedia (one of the pages I look after), and if you want to find out more, click the link below:

http/en.wikipedia.org/wiki/Halfbeak#Reproduction

And people think livebearers are boring...

Cheers,

Neale

 

[willtang3000]

thanks for the info its amazing to see even fry at such a young age competing to be the top

 

[diburning]

Livebearers really are cool. Reading a scientific paper this evening on halfbeak reproduction, I learned that there are no fewer than 5 different modes. "Type 5", as it is cunningly called involves the embryos swimming about inside the ovaries, eating eggs and smaller siblings! I'd heard of this with sharks, but never bony fish. Anyway, I wrote it up for the halfbeak page at Wikipedia (one of the pages I look after), and if you want to find out more, click the link below:

http/en.wikipedia.org/wiki/Halfbeak#Reproduction

And people think livebearers are boring...

Cheers,

Neale

Peacock bass (cichla sp) do that.

 

[nmonks]

Peacock bass are livebearers? Never heard that before. I thought they laid eggs?

Neale

Peacock bass (cichla sp) do that.

 

[Annastasia]

You know that you know way too many random things, when you come upon a Halfbeak fact before Neale. I'd read about this a few years back, in some article I came across somewhere. It's quite interesting, yet scary for their siblings! Survival of the fittest (or the one with the biggest stomach...), I suppose.

 

[diburning]

Peacock bass are livebearers? Never heard that before. I thought they laid eggs?

Neale

Peacock bass (cichla sp) do that.

lmao no... peacock bass fry cannibalize each other.

 

[nmonks]

meepster -- I knew perfectly well peacock bass weren't livebearers. I was being polite. I understand _now_ that you mean the young fish eat one another, but what I was describing was that the embryos eat each other, which cichlids can't do, since they're in eggs, not their mom.

Annastasia -- yes indeed, you do know too much random stuff. Like that Paul Simon song, Kodachrome:

"When I think back on all the cr*p I learned in High School, it's a wonder I can think at all..."

Cheers,

Neale

 

[guppymonkey]

Have their been any studies into what effect this embryo cannibalism has on the fry compared to other related species? I would interested to see if they could discover a reason why some species would have this kind of development. Livebearing in fish is generally considered a primative trait, would this cannibalism be an advanced livebearing trait or a primative livebearing trait? Just wondering how this half beak phenomenon could be explained.

 

[nmonks]

guppymonkey --

Where did you hear livebearing was a primitive trait? Yes, (some) sharks and coelacanths are livebearers, but they evolved livebearing themselves, and it's evolved half a dozen times at least in bony fish, not to mention in rays and stingrays. Livebearing is an advanced trait relative to egg laying, but one that has evolved multiple times, as opposed to livebearing in mammals, which seems to have evolved one only.

Be that as it may, your question is a fascinating one. Certainly within livebearing, the most primitive state is ovoviviparity. But what comes next I don't know. At a guess, I'd say cannibalism is quite advanced because it results in a small number of very large offspring with a good chance of success, which is the opposite of most fishes (lots of small offspring, most of which die). Whether this is more or less advanced than umbilical cord nutrition like the goodeids do, I don't know. Goodeids are supposedly among the most advanced livebearers, I believe. Anyway, all good stuff!

What's interesting is the freshwater halfbeaks in Southeast Asia are "trying out" the different things done by all the livebearers in Central America. It's a nice example of parallel evolution.

Cheers,

Neale

Have their been any studies into what effect this embryo cannibalism has on the fry compared to other related species? I would interested to see if they could discover a reason why some species would have this kind of development. Livebearing in fish is generally considered a primative trait, would this cannibalism be an advanced livebearing trait or a primative livebearing trait? Just wondering how this half beak phenomenon could be explained.

 

[guppymonkey]

I have read it in several books but the only one i can reference right now (because its the only one I have at hand at the moment) is Livebearers by David Alterton (easy book but still good info). One of the main arguments for livebearing in fish being a primative trait is that almost all the species are brackish or can be adapted easily to a marine environment. Even those that are not brackish usually prefer hard alkaline water.

 

[nmonks]

May be an easy book to read but what it's saying is just wrong. All the most primitive bony fish are freshwater (bichirs, arowanas, gar, etc.). All the most advanced bony fish evolved in the sea (perches, puffers, flatfish). All primitive bony fish lay eggs (again, bichirs, but also salmon carps, catfish, eels) as do most advanced fish (puffers, flatfish, most perches). Livebearing has evolved independently in particular lineages: poecilids, goodeids, surf-perches (cichlid-like livebearers), eelpouts, halfbeaks, and a few others. It is very rare (something like 5% of fish species, if that). So yes, it's an advanced character.

Cheers,

Neale

I have read it in several books but the only one i can reference right now (because its the only one I have at hand at the moment) is Livebearers by David Alterton (easy book but still good info). One of the main arguments for livebearing in fish being a primative trait is that almost all the species are brackish or can be adapted easily to a marine environment. Even those that are not brackish usually prefer hard alkaline water.