To molly or not to molly

[TamiW]

I'm in the process of setting up a 38 gallon biotope tank based on the lagoon areas of the florida keys I saw when I was visiting recently. I brought home with me a few different algaes, and a few fish. One was the boring, common sailfin molly found there. Right now, they're in a different tank, but I'm CONSIDERING putting them in the tank.

My fear at the moment, though, is that the mollies will eat the algae and any marine plants I might put in there. ANyone have any experience with this? Any thoughts?

[ClamIAm]

I've seen pictures of people doing it, but I don't remember who. If I remember right, I've heard they pick at epiphytic algae but will not harm any macroalgae or seagrass you have significantly. I've never done it myself though so don't quote me.

[Samala]

They will certainly pick at some of the algaes but seem restricted to more epiphytic forms. I have some in one of my tanks right now, delightful creatures, very friendly and we have some gorgeous color morphs all along the FL lagoon systems from Keys on up. The males are briliant red/orange and green hues.. beautiful fish. I have really got to get a good picture someday soon. :)

I havent found them to be a bad interaction just yet. One thing to note, wild mollies seem to come in often with gill parasites. Did you quarantine? Treat for those?

>Sarah

[TamiW]

They are in quarantine, but I only treated for intestinal parasites. It sounds like I might need another few weeks of quarantine. Or would a freshwater dip be enough?

[jmanrow]

I would leave the mollies in freshwater with same pH for a couple of days. That should rid them of any marine parasites. While most fish tolerate a rapid drop in salinity, it is recommended to acclimate them gradually back to a higher density saltwater. I usually do this over at least a two day period.
They did a fair job of keeping Derbesia under control, and did not disturb the macroalgae.
I have not kept mollies with seagrasses yet, so I really don't know how they will do with them.

[Samala]

I have killed a whole batch of molly juveniles by raising the salinity too fast, it seems to trigger "shimmy" disease in them. They sway back and forth very fast in the water, like S curves, and overdevelop their slime coats, then expire. Very sad.

You could do a freshwater dip with them for a few days as suggested. Did you treat with Praziquantel or Metronidazole? Those two are usually very effective with the gill/body parasites. :)

>Sarah

[TamiW]

Neither, I used Fenbendazole. In the same group of drugs as Metronidazole. But I only used it in feed. I may just go ahead with a 24 hour bath in praziquantel.

[piercho]

About 20 years ago, when I was even more ignorant of fish husbandry than I am now, I stumbled across a pair of true (likely wild) velifera (http://www.fishbase.org/Summary/speciesSummary.php?ID=4773&genusname=Poecilia&speciesname=velifera) at Something Fishy on Kingston Pike in Knoxville, TN. I purchased - at what then seemed and astronomical price - and quickly failed with them, possibly from parasitic flagelates in a high-nitrate tank. I've kept an eye out for another pair and never stumbled across them. I've forgotten some fish I've had, but not that pair. They were larger than tank-bred mollies that I've seen with a more subtle, silvery, irridescent coloration. A search through Fishbase shows a number of attractive tropical Poecilia that for some reason aren't in demand in the hobby.

IME with generic tank-bred latipinna/velifera/hybrids, they acclimate well to full strength saltwater. However, they seemed ignorant of the risks of large, potent cnidarians like Cerianthus anemones, and the ones I've put in my tank after quarantine eventually become food. As grazers, I don't remember them putting much of a hurt on any kind of macro, including relatively tender algae like Derbesia that I would have liked them to graze. To be honest, I find pet-store mollies kind of blah in coloration and behavior, and they seemed inferior to combtooth blennies and combtooth tangs as grazers of epiphytes.

[Samala]

Interesting.. I thought all sailfin's were P. latipinna. Looks like I need to read up to discover how to distinguish the two.

>Sarah

[jmanrow]

If I remember right, velifera comes from the Yucatan region of Mexico, and has a much larger dorsal.

There are quite a few non-native fish released, and are thriving in many of the US/Mexico Border States. I remember seeing 6" mollies in roadside ditches in Texas. These were possibly descendants of some released P. velifera.