Fish with milk (Sheesh spinoff)

["A.P. Hazen" <a.hazen@philosophy.unimelb.edu.au>]

Tom  Holtz responded to my post:
        And as for fish milk: a gland that leaks liquid into
        another liquid might not be the best method of
        delivering nourishment. However,in a non-aqueous
        environment, glands already leaking liquid into air
        (e.g., sweat glands) might evolve, allowing for
        exaptation as a source of nourishment.

        A.P. Hazen: the skin-feeding animal you are likely
        referring to (the one announced earlier this year)
        was a caecillian (a member of Lissamphibia, the modern
        amphibians), not a fish. However, there might well
        be skin-feeding fish for all I know.

------------->> I'd missed the caecilian.  The example I was 
referring to was something I had read about a good many (?? 30 ??) 
years ago,  and definitely a fish.*  It  could well have been the 
discus fish that Tony Canning (with the assistance of Mickey Rowe) 
posted about.
   A priori, one WOULD think that "a gland that leaks liquid into 
another liquid might not be the best method of delivering 
nourishment."  The existence of the discus fish shows  the dangers 
of apriori thinking in biology.  If whatever discus fish exude has a 
fairly high fat content and is moderately viscous, it  might not 
disperse into the surrounding water too fast to be a useful source of 
nourishment.  Apparently it doesn't!

(*) Tom, didn't you  a few posts back applaud the insistence on not 
writing "dinosaur" for "non-avian dinosaur," because such a usage 
would be incorrect?  And haven't you, in responding to me, just  used 
"fish" to mean  "non-tetrapod fish"?  (Grin!)
---
Allen Hazen
Philosophy Department
University of Melbourne