Jack Dempseys: Love them, hate them, why?

  • We are currently upgrading MFK. thanks! -neo
Judge Holden said:
It tells me there's genetic variation in the pool. In terms of evolutionary biology, define "defect" and "deformity" and "weakness." ALL traits of all living things arise as mutations. Preferring trait X to trait Y is a matter of aesthetics. Why is a fish that isn't shaped like a submarine (or rolling pin, or whichever standard we've all agreed on) "defective" or suffering from some "weakness"? Again, I haven't seen ANY pics of 10" wild JDs. Do we know there's no variation in that gene pool?
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I don't see how the spine curvature would give this fish any advantage in the wild. No other wild fish has a spine like that. We see this problem in all kinds of fish and in any other species its abnormal for the tail to be lower than the eyes as you see in many adult JDs. It's almost like the fish is too long and chunky to support itself properly. I've seen oscars with this same issue.

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If you trace the line of scales that runs along the lateral line, you'll almost always see it dive, snapped like a pencil, right about where the anal fin starts. Go back even on this very thread and every large dempsey you see is cracked in half. It's probably just the inbreeding - this has been a staple species in our hobby for almost 100 years! That's a lot of sister-brother matings going on!
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The possibility that it's how Jack Dempseys look when they're big is ruled out on what ... a priori grounds? Some Platonic or MFK standard of fish beauty & perfection? This is an empirical statement, requiring evidence that would take the form of actual pictures of 10"+ wild JDs. I often marvel at the variety this species displays. The coloration & markings are as diverse as human languages. Why would other aspects of their appearance be immune to this genetic range?
 
The variation is there, but I think fish like our lfs dempseys with the curved bodies would be lunch for other fish in the wild imo.

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Since they've been in the hobby for a hundred years and wild JD are difficult to find that would mean that most of the JD in todays fish trade would be related to the 'founding mothers of fathers' of captive bred dempseys, that's a small genetic pool if nothing new has been brought in since.

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but I think fish like our lfs dempseys with the curved bodies would be lunch for other fish in the wild imo.
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How so? If trait X does not prevent a fish from having offspring, what's to stop it from spreading? Not every genetic trait necessarily improves or kills an animal.

I don't see how the spine curvature would give this fish any advantage in the wild.
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How does it help angels, discus, severum? Not every genetic trait necessarily improves or kills an animal.
 
Hey I saw the pics of the "crack back" here are better pic to explain I guess here's pics of my 3year old male then 5 year old female I think its just genetics right?...things I like bout them they have great personalitys some and things I hate is this new pair I have are super skitish and always hide! I dolnt ever see them.. uploadfromtaptalk1340941742251.jpguploadfromtaptalk1340942025401.jpg

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Judge Holden said:
How does it help angels, discus, severum? Not every genetic trait necessarily improves or kills an animal.
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Those fish were built for it. I think its irrelevant to compare the two.
 
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