Sunday, December 18, 2005

Minnow Dance



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A while back, I mentioned that our fall is very dry and that it takes the stalled cold fronts of winter to break the fall drought. Yesterday, a cold rain fell steadily and heavily the entire day and night. It is still raining now on Sunday morning.

Weatherbug showed dense masses of clouds, much of it coded yellow and red parked above us. This map hardly changed all day as the clouds ground to a halt over Pure Florida. This morning, it's less intense, but they are still over us.

This was great news for my pond which had shrunk to it's thalweg. I haven't been down to check the water level yet, but by mid-day we had 3 inches and it poured for hours after that. My pond sits at the bottom of a slope (my house sits atop the slope) and typically it takes a day or so for ground water to seep downhill and show up in the pond.

The fish in the picture enjoying a bit of bread are Mosquito Fish, (Gambusia holbrooki). These fish are very active predators of small invertebrates and mosquito larvae are a favorite. Their reputation for mosquito control is legendary, but they are no magic bullet. I toss them into standing aquariums, tanks, etc that I use for my home aquaculture endeavours. While that tank is dormant, the gambusia will keep it clear of mosquito larvae. In a closed environment, with no plants, they are 100% effective in my experience.

In the wild, there are more places for mosquito larvae to hide, and the gambusia effectiveness is lessened somewhat, but they still do a good job. They look for all the world like a dull guppy and breed in the same enthusiastic manner. The males have a special pelvic fin which allows them to internally fertilize the larger females. The girls then carry the eggs inside them until they hatch. Live baby gambusia are then expelled.

So, gambusia are ovoviviparous, not to be confused with oviparous (the birds at the bird feeder), or viviparous (you).

They are basically tan in color, but out of every 100,000 or so, there will be males with pretty black and white speckles. I have never seen this trait on a female. Perhaps I just missed it.

I love these gambusia and they belong here in Pure Florida, but around the world they are seen as exotic invaders. Especially in New Zealand and Australia where they were introduced to control mosquitoes. They are aggressive and prolific and are seen as a threat to native fishes of those countries. I can relate to my "down under" friends as Florida is overrun with exotics like walking catfish, snakeheads, ball pythons, and retirees from New Jersey.

Still, my Gambusia are where they belong in the natural Florida ecosystem, so here they are the good guys. The catfish, bluegills, and shellcrackers in the pond also appreciate them as a food source.

The rain is really coming down now.

My fish would be really happy about this if their brains weren't so smooth and they could ponder things like rain and the world above.

I am happy for them and that will have to do.



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7 comments:

Rexroth's Daughter said...

Very cool fish, FC. It must be nice having some rain. We've been cold and dry here. Another 20 degree morning, and not a cloud in the sky.

Did I ever mention that I'm originally from New Jersey? We flee in all four directions!

swamp4me said...

Around here the common name for gambusia is "pus gut." Isn't that just lovely?
(I had to learn a whole new fish vocabulary when I moved to the eastern part of NC after having grown up in the piedmont.)

Floridacracker said...

RD,
I love all New Jerseyites who do not move to FL.

Swampy,
Yuch! Too good a fish for such a name. I assume it comes from the ever pregnant, ever bulging females appearance.

The Fat Man said...

You forgot the Ohio & Michigan migration :-)...

Floridacracker said...

Fatman,
I know, there's too many to list 'em all :)

vicki said...

Hey, youse guys! If you were stuck up here you would migrate, at least part time, too. I'll be there next week, FC, and I can hardly wait.

Great post- I knew that guppies were ovoviviparous but I did not know about these fish and thalweg was a good word to look up. Thanks!

Floridacracker said...

Vicki,
How can you leave that beautiful snowy yard at OutsideIn? Thalweg has stuck with me since a geomorphology course back in Pensacola.