Re: [Killietalk] Rivulus question - gender

[Scott Davis <unclescott at prodigy_net>]

The Rivulus spot as a distinguishing mark of females works, but not all of the time. We make need to study each species to sort that out.

Perhaps we can "candle" well fed adults (raised in the "correct water" for their species) by putting them in (covered) jars of water and shining a flashlight at them from behind. With a little luck and dilgence we may be able to see who is carrying eggs.

I'm also reminded of the story where a guy was given some Rivulus eggs (probably so long ago they were either cylindraceus, magdelenae or hartii). He came back to complain to his source. "About half of them are diseased! They have this black spot by their tails!"

Huber's Review of Rivulus, Ecobiogeography - Relationships wrestled with about 70 known species and maybe 30 doubtful species. Aside from that set of difficulties, that work was published in 1992 and there have been an amazing number of Rivulus descriptions since then. But he gave me real pause for thought with his lists, in the appendices, of Rivulus where the females had a supracaudal occelatus (62%), where both sexes had such a spot (8%), where neither gender has such a spot (22% and where the existence of such a spot depends upon where the Rivulus is collected (8%). Furthermore there were cases where juveniles (male and maybe female) had a spot but not as adults.

Allen, you can find images of both Kryptolebias caudomarinatus and brasiliensis in Huber, Plates 38 and 39. There are a couple of shots at
http://www.itrainsfishes.net/content/

Perhaps the best I caught in a quick look were at:
http://killifishbrasil.blogspot.com/search?q=Kryptolebias

There are always the usual image searches too. :)

All the best!
Scott
--- On Mon, 8/10/09, Gary Hoover <gmh52389 at yahoo_com> wrote:

From: Gary Hoover <gmh52389 at yahoo_com>
Subject: Re: [Killietalk] Rivulus question
To: "killifish discussion list" <killietalk at aka_org>
Date: Monday, August 10, 2009, 12:05 PM

All the Rivulus I can think of have the spot on the female--the catch is there are a couple with the spot on the male.  R. rectocaudatus, for instance.  As a general rule of thumb, though, the spot is the female.
Hope that helps.
-Gary

--- On Mon, 8/10/09, Tony Kline <afkline at ptd_net> wrote:

From: Tony Kline <afkline at ptd_net>
Subject: [Killietalk] Rivulus question
To: "Killietalk" <killietalk at aka_org>
Date: Monday, August 10, 2009, 9:22 AM

Do all female Rivulus species have the black spot near or at the caudal fin or are there some Riv species that do not have this spot?

Tony Kline
Northumberland, Pa.
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