Re: gephyra or agassizii?

[Marco Lacerda <marcolacerda@ax.apc.org>]

Randy or Deb Carey wrote:

> I feel obligated to respond in some way.
> 
> Identifying fish is hard enough from photo's, so all I can do is comment.
> 
> I'm assuming that in all other features the fish look like agasizzi and gephyra.
> So aside from feature 'b', it could qualify as agasizzi.  A rule I believe in is:
> 
>    "the presence of a feature carries more weight than does the absence of a
> feature."
> 
> In this case, 'a' and 'c' are features which are "present" and suggest
> agassizii.  Feature 'd' argues agaisnt gephyra due to an absence of gephyra's
> caudal markings.  The color of the caudal in feature 'd' sounds acceptable for
> agassizii.   Feature 'b' argues against agassizii due to the absence (or late
> development) of a feature.  I'd say the stated evidence leans strongly for
> agassizii, but with some doubt that perhaps it is a third species (or a deviant
> population).  Afterall, new species crop up fairly often.

Thanks for the opinion.
Yes, it is clear what you stated, but already Kullander told me that he 
himself was having problems to identify agassizii/gephyra from Rio 
Negro. For some populations within Rio Negro the difference is not 
really clear, as the characters used as diagnosis for A. gephyra may 
fail, like the example above. I think more scientific research is needed 
regarding this matter.

> Romer's new book (due next May?)  is supposed to have info indentification info.

I heard about the book, but I think it will not solve the problem.
I have seen in David Soares' home page a fish identified as A. pulchra, 
that is absolutely mistaken!!! (did this id came from Roemer?). The same 
mistake is found on Mayland's new dwarf cichlid book.

> I hope it is not the typical binary key which is standard in zoology.  That's
> where the key tells you to check a feature and go 'left' or 'right' depending on
> the answer.  The problem is, if you can't quite determine any one of the required
> features (maybe a young specimen or a difficult feature to read), then you have
> no hope of coming to the right conclusion.   That method was the best they could
> come up with a couple hundred years ago, but with computers we can do much
> better.  The user should be able to respond to as many features/questions as
> possible and ignore uncertain responses.  A computer can evaluate the responses
> against the features of all candidate species.  Well, that's much of how I view
> ID'ing a species from visible features.

Yes, I'm quite familiar with the binary keys, many ichthyological books 
/ revisions use it. Without a computer they are very useful.
With computer programs you can evaluate regression (I wonder if it is 
the English word for it) through graphics for characters that vary 
according to fish age. This is currently done within other fishes group, 
like Hypoptopomatinae (Otocinclus subfamily), for example.
 
> --Randy

Thanks for your reply.
All the best, Marco.