[RML] P. cyanodorsalis revisited
Mach T. Fukada (fukada at aloha.net)
Mon, 25 Jan 1999 08:19:47
Hi All,
just did some fooling around with some of my P. cyanodorsalis. A friend
of mine said that the fish I had given him had adapted to freshwater. He
had a tank that got overflowed many times over by rainfall, it has no
crushed coral, and we suspect that TDS is about 0. Fish are breeding and
doing OK just no color. TO test tings I brought my fish down in salinity.
Found similar things, they seemed OK in all aspects save color. The
brilliant blue and brassy yellow were abscent. Figured Ok myabe
temperature related as it is a bit cool now (<75 F/23 C). I added a heater
of all things. got the temp up to a constant 80 F/ 26 C and nothing
happened. Still same colorless fish. I added salt back up to 23-25 ppt
and boom all the fish are coloring up really nicely spawning increased
dramatically.
This leads me to wonder if the raising salinity is the cue that they would
use in nature to indicate that the dry season is arriving andit is necesary
to lay eggs and reproduce like mad. As it seems that the eggs hatch in
repsonse to a decerese in salinity and agitation, one might suggest that
eggs may remain dormant under highly saline conditions awaiting the rainy
season to hatch. I suspect that this is why it is necessary to force hatch
the eggs when they are kept at the optimal water salinity for the adults to
breed and show their best color. However, another thing that I have found
is that this population of cyanodorsalis is perfectly happy to spawn in the
gravel. The previous one, I am told, would not spawn in the gravel, and
would only spawn near the water surface. This population also wouldn't
tolerate less than 25% seawater (about 8 ppt). I suspect that the previous
surface spawing population did not need it's eggs forced. I suppose that
the conditions in the gravel would be cooler, anarobic, and promotes a
normal reduction in embryo development. Perhaps, envirnmental differences
as one population has more seasonal salinity fulctuation (and water level),
thus requiring a period of dormancy, and the other (surface spawning) is
from a more static salinity, thus not needing a dormant period. Any ideas?
Dave, would you by chance have seasonal salinity data for the streams in
the Darwin area? How about the Crab Creek population? hmmm. Maybe there
are population differences in this species also, might be more subtle.
Peter you think there could be gene flow between populations, preventing
the development of population specific morphological characteristics?
Aloha,
MTF
Mach T. Fukada, Editor
fukada at hawaii.edu
Honolulu Aquarium Society
http://www.geocities.com/Heartland/Meadows/2948/HASF.html