15 replies to this topic

[Betta132]

Is there any environment in particular that's more likely to have melanistic gambusia, or are the chances of finding one about the same in any habitat? I'd like to find a few, they're really pretty.

[Kanus]

I've seen thousands of Gambusia but the only melanistic ones I've seen have been from springs in Florida. I believe they can be found for sale on aquabid.com from time to time.

[Dustin]

I catch them in fresh water with a salt influence down around Charleston, SC in the same habitat as bluefin killies and Heterandria.  Oddly, it seems like I only catch them during the summer months.  I'm really not sure why.

[gerald]

Are there any melanistic Gambusia in TX?  I was under the impression (maybe wrong) that only eastern moquitofish (from Mobile AL eastward) had the black-spotted mutation.

[Betta132]

I actually don't know if they're found in Texas at all. However, though I understand why one population might be more prone to mutations, I don't see how it's possible for a mutation to be completely absent everywhere else. It's a mutation, after all, basically a genetic accident. And melanistic variations are found in most species, it's not like they're some bizarre thing that leads to extra eyeballs.

[zooxanthellae]

Is there any environment in particular that's more likely to have melanistic gambusia, or are the chances of finding one about the same in any habitat? I'd like to find a few, they're really pretty.

I read a paper once that (if memory serves) stated the mutation was both genetic and temperature dependent. They were able to induce the effect when the water temperature was above a certain point. I'll see if I can locate that paper, but if I am remembering it correctly, then certain warmer habitats would have a higher prevalence of melanistic individuals. I know in NC, I've never seen one north of the New River (onslow county), and I have been on the lookout. 

[zooxanthellae]

I read a paper once that (if memory serves) stated the mutation was both genetic and temperature dependent. They were able to induce the effect when the water temperature was above a certain point. I'll see if I can locate that paper, but if I am remembering it correctly, then certain warmer habitats would have a higher prevalence of melanistic individuals. I know in NC, I've never seen one north of the New River (onslow county), and I have been on the lookout. 

It's behind a paywall, but here is the paper in question:

 

A sex-linked allele, autosomal modifiers and temperature-dependence appear to regulate melanism in male mosquitofish (Gambusia holbrooki)J. Exp. Biol. (2006) 209 (24): 4938-4945

 

http://jhered.oxford.../80/5/387.short

[Dustin]

I read a paper once that (if memory serves) stated the mutation was both genetic and temperature dependent. They were able to induce the effect when the water temperature was above a certain point. I'll see if I can locate that paper, but if I am remembering it correctly, then certain warmer habitats would have a higher prevalence of melanistic individuals. I know in NC, I've never seen one north of the New River (onslow county), and I have been on the lookout. 

 

Well, that explains why I have only seen them in the summer.  I suppose they are eaten by late fall/winter since they stick out so much.

[Betta132]

Does Texas in midsummer count as a warmer habitat? 

I may have to go seining before it cools off. I'm assuming that my best option is to just capture as many gambusia as possible and hope that I find a melanistic one. 

Should I search through areas with a whole lot of cover, since the dark ones would stick out over ordinary mud? 

[gerald]

Betta -- The western mosquitofish (G. affinis) is considered a different species from the eastern (G. holbrooki) and they may not share the same mutations. 

 

Zoox  -- A guy who used to work for New Hanover Co Mosquito Control raised melanistic holbrooki in his yard and spread them around in stormwater ponds in southeast NC during the 90's-00's.  I dont recall if he got them from local native stock or from another state farther south. 

[killier]

Several summers ago I had 3 melanistic holbrooki (all males) I separated all of them with mixed results.

 

first group was a melanistic male and 5 female G. affinis (Western Mosquito Fish, petco rescues) resulting in no melanistic offspring. maintained until f3 

 

second group was a melanistic male and 3 female holbrooki from an inland population (Golf course pond near Middle Saluda), no melanistic offspring. maintained up to f4

 

third group was a melanistic male and 2 female holbrooki from a site where one of the males had been captured. (should have kept better track but hadn't planned on the experiment) resulting in 3 male melanistic offspring and no additional in the subsequent generations. 

[swampfish]

I obtained some Gambusia holbrooki with melanistic males at the national American Livebearer Association conference in Indianapolis, IN a few years ago. The source was southern AL or GA. I kept them in my basement in unheated aquariums that range from 54 degrees in the winter to 72 degrees F. in the summer. All the old males stayed melanistic, but none of the new males (about 30) were melanistic. Based on widespread information in the aquarium world about male guppies being produced in warmer water, I installed heaters in the tanks and raised the temperature to about 78 degrees F.in the fall. In the spring, I could only find a couple of non-melanistic males, all of the others (about 30) were melanistic. I didn't watch the tanks close enough to know whether the males turned melanistic or if the older ones died and were replaced by young melanistic males. I had 60-70 fish spread across two 29 gallon tanks on the bottom shelf of my tank stand. My suspicion is that the males turned melanistic as I had very few young fish. There were so many fish in the tanks that most fry were eaten by the adults.

 

Phil Nixon

[Isaac Szabo]

I read a paper once that (if memory serves) stated the mutation was both genetic and temperature dependent. They were able to induce the effect when the water temperature was above a certain point. I'll see if I can locate that paper, but if I am remembering it correctly, then certain warmer habitats would have a higher prevalence of melanistic individuals. I know in NC, I've never seen one north of the New River (onslow county), and I have been on the lookout. 

If i'm reading the abstract correctly, it actually says that melanistic individuals were much more common at the lower temperature (22C/72F) than at the higher temperature (26-29C/79-84F). So that paper is actually kind of saying the opposite of most others here. Like Derek, I can attest that melanistic individuals are very common in many of the Florida springs, which are a very stable 72F year-round. I'm pretty sure we also dipnetted some in the much warmer waters of Tate's Hell.

[zooxanthellae]

If i'm reading the abstract correctly, it actually says that melanistic individuals were much more common at the lower temperature (22C/72F) than at the higher temperature (26-29C/79-84F). So that paper is actually kind of saying the opposite of most others here. Like Derek, I can attest that melanistic individuals are very common in many of the Florida springs, which are a very stable 72F year-round. I'm pretty sure we also dipnetted some in the much warmer waters of Tate's Hell.

D'oh! It looks like I linked to a different article than the one I cited! Also, After having read it, I'm a bit confused, and will have to give it my full attention after work.

 

http://jeb.biologist...09/24/4938.full

[Isaac Szabo]

A few interesting points from this second paper:

• melanism is absent in western mosquitofish
• in some melanistic populations of eastern mosquitofish, temperature has no effect on melanism
• in other melanistic populations of eastern mosquitofish, melanism is induced by temperature
• in the temperature induced populations, lowering the temperature is the trigger to induce the melanism

[zooxanthellae]

 

A few interesting points from this second paper:

• melanism is absent in western mosquitofish
• in some melanistic populations of eastern mosquitofish, temperature has no effect on melanism
• in other melanistic populations of eastern mosquitofish, melanism is induced by temperature
• in the temperature induced populations, lowering the temperature is the trigger to induce the melanism

 

 

Well it looks like I had it backwards after all, good catch!