what factors affect head shape

[edwliang]

apisto's head shape is very important to many hobbiests as a good head shape is a priority when hobbiests select their apistos. head shape is expecially important to some species. for example, bitaeniata, agassizi, elizabethae etc. many of them we seem to prefer bigger head size, and round, full head shape.

even among the offspring born at the same birth, there are some big, full head shape, and some small and narrow headshape.

what factors may cause apistos to have different head shapes and head sizes?

 

[Mike Wise]

For me it is similar to judging different breeds of dogs, cats, horses, cattle, etc. Each species has a specific shape. This is what I look for. Deviations from the wild type form isn't acceptable for me. Deviations from the type shape can be caused by many different factors: physical damage, genetics/inbreeding, nutrition, water quality.

 

[Chrisd123]

I know this is way off topic ( kind of) but a few years ago I did some research/monitoring of a European eel population as part of my job, a really interesting project that threw up more questions than answers. Anyway, I noticed that the Yellow eels had different head shapes, when born first born elvers are pretty much identical, however once they have migrated into a river system and into a loch or lake, it seems that head shapes change as they grow depending on what food is available. The waters I was studying up here in the highlands are very low in productivity, with very few invertebrates for food, however there are plenty of Salmonids and minnows. It was noticed that the bulk of eels had very broad heads, large jaws and prominent teeth. Narrow pointed heads were present but these were generally small and low in number. In addition, there was what I called dolphin heads, they had massive bulbous heads and very prominent sensory pits. The jaw width exceeded the jaw length. One eel of 760mm regurgitated a smaller narrow head of over 300mm. To conclude I think the Dolphin heads were primarily pisciverous predators, the normal broadhead more opportunistic whilst the narrow hed were suited to grubbing arounf amongst bottom debris looking for inverts....this also coincided with the baits they wer caught on

NH - all worm baits
BH - Fish and worm
DH Fish only.

This is common in eels, a particular water will have a dominant head shape depending on the prey that's available. As eels are panmictic breeders ( one mass spawning event, if that's the case nobody as seen them spawn) it throws the genetics out of the window, so these must adapt once they reach the water they live in.


I know its off the scale of Apisto's but I thought I would share it with you.

 

[Mike Wise]

Crisd, that's interesting. Food type dictates morphology instead of primarily genetics? I wonder if, instead, specimens genetically predisposed to each specific head shape were equally available, but those better able to feed on the primary type of food in the biotope were able to grow faster and out-compete the other head forms. If that were the case, I'd believe that the broad-headed form, being a more generalist feeder, would be the most adaptable and successful - and most common form.

 

[Chrisd123]

With eels, nothing is certain as there is a huge lack of information, probably due to their lifecycle and very long lifespan.
For example, it is assumed that they spawn in the Sargasso yet nobody has ever seen this happen.

But back to head shapes...it is also assumed that spawning takes place as a mass event, where males and females release eggs and sperm at the same time so it, in theory rules out any genetic studies if you get my meaning. bearing in mind that all the eels spawning would come from all over Europe. So unlike Salmon it would be hard to trace the rivers they grew in. During my studies It did cross my mind that perhaps it wasn't a mass event and as you say Broadhead mate with broadheads etc etc or perhaps eels from particular waters mate with each other and then the offspring make for the waters their parents grew in....

Friends of mine who also fish for and study them have found the same things regarding head shapes, waters in the South of England which are rich in invertebrate life usually hold eels of the narrow head variety although the more predatory broad heads still exist but in lower numbers, this often results in the BH eels found there being larger as they have less competition.

In the highlands of Scotland, waters are generally oligotrophic, and largely unproductive hence the numbers of Salmonids being the dominant species. Temperatures are much colder than down south, this results in slower growth rates. An adult spawner eel in the south maybe ten to twenty years old, yet up here they can be as much as sixty or seventy years old. In fact one was caught a good few years ago in a net on a highland loch, it weight over 7lbs and otolith readings gave it an age of 84 years old.

As I said more questions than answers.......sorry to go off topic as I don't yet know enough about apisto's. But this is one area I want to know more about from a biological/ecological and scientific view point....so if you can point me in the right direction I would be most grateful.

 

[gerald]

Genes can "turn on" or "turn off" in response to food and environmental factors, so they might all have "genetic plasticity" for a variety of head shapes. Where they end up, and what they eat, can then affect which genes become active and control their growth.

In the USA, female eels migrate hundreds of miles upriver, while most males stay near brackish estuaries or travel just a few miles upstream into freshwater. Is that the usual trend for European eels too?

 

[Chrisd123]

Yes, it is the same also, males tend be found in higher numbers at the bottom end of river systems whilst females migrate further upstream, although fewer in number they tend to grow much larger, less competition I assume along with the need to bulk up for egg production.

I think American and European eels spawn in roughly the same area ( I am led to believe) and I don't think there is much difference between the two....number of vertebrates I think. Makes you wonder how much hybridisation goes on...that is if all European eels spawn in the Sargasso as there is no definitive proof.