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Re: Pantanodon podoxys

Hi Folks,
	I suppose I started this thread, so here is my rationale.
Pseudomugil cyanodorsalis is a blue eye from nt Australia and inhabits a
very similar habitat to P. podoxys (mangrove esuarine, etc).  However, we
(the folks in Hawaii) have noticed that the conditions that the various
populations can withstand also vary from location to location.  This fish
seems to be able to tolerate 100% seawater to 100% freshwater (rainwater).
However the populations being kept in Honolulu in the mid to late 80's
would have problems surviving in less than 25%.  The most recent
population seems to be from an area that during the dry season are allmost
totaly (if not more) saline than seawater and inteh rainy season 100%
fresh.  Thus I suspect population variation important, may be true for the
P. podoxys, except that they are all probablly from one collection and a
single population.  I see these fish as analogs to many of the lampeyes
aand finding a species of lampeyes that may coexist with these blue eyes
would greatly improve my ability to develop a brackish tank of small fish,
marine/bracksih plants.

MTF

On Sun, 22 Aug 1999, Brian R. Watters wrote:

> 
> As I have recently described on KillieTalk, we collected Pantanodon podoxys
> from an estuarine environment at the edge of mangrove swamps and tidal
> flats. I was unable to measure the salinity but it was obviously quite high.
> When I brought the fish back to Canada I placed them in approximately 50
> percent seawater (=1.010-1.012) and they immediately did very well. When I
> distributed the fish I recommended that level of salinity.
> 
> In 1995 we inadvertantly changed the water in a couple of the podoxys bags
> with freshwater intended for Nothos and, within minutes, the podoxys started
> to die. We immediately realised what we had done and changed them back to
> brackish water. Obviously, any drastic changes in salinity should be done
> over a long period of time to allow the fish to adapt (assuming they can).
> 
> Clearly, this species can tolerate a wide range of salinity and that is not
> unexpected given the nature of its habitat. However, they also do not do
> well in freshwater or at very low salinities so why try to place them in
> those conditions ? In nature it is a brackish water fish and not a
> freshwater fish. I suppose if you want to try to keep them in a community
> setup with other freshwater species then one could try but, as Chris has
> pointed out, they don't do well under those conditions.
> 
> When we collected this species in 1995 the only other fish species in the
> pool was some form of Tilapia. This also is not unusual as Tilapia are often
> found in such coastal habitats.
> 
> When I returned to the habitat last year the only fish species I could find
> were Glassies of the genus Ambassis (there could have been other species but
> I did not spend too much time there because there was a big crocodile in the
> pool, as there had been in 1995 as well). I have not (yet) identified the
> species of Glassy. Glassies are also typically estuarine brackish water fish
> that can, under certain conditions, tolerate freshwater. This tolerance is,
> however, temperature dependant, the range and level of temperatures also
> varies with species. I mention this because one could speculate that Pant.
> podoxys might also be more tolerant of low salinities or even freshwater
> over a particular range of temperature.
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