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Hello everyone,
I would like to drop my 2 cents in the pan, and see if there is any merit to these definitions:
With my fish ecology and fish repro students I have used "immature" to describe any fish prior to its recruitment to the sexually mature stock.
I have emphasized to the students that quite often we see a change in the ecology of many fish species as their change diet or habitat. I have used "juvenile" to describe the post-larval fishes exhibiting a nursery ecology (typically YOYs), and I use "sub-adult" to describe those fishes which have moved to the adult congregation habitats and/or feeding niches but may have one or more years to recruitment.
Too much hair-splitting?
Bill Snyder
Aquaculture & Aquatic Science
State University of New York - Morrisville
-----Original Message-----
From: Scientific forum on fish and fisheries [mailto:[log in to unmask]] On Behalf Of Chris McDonough
Sent: Tuesday, March 01, 2005 2:41 PM
To: [log in to unmask]
Subject: Re: definition of juvenile
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Fernando,
In terms of strict definitions, a juvenile or immature fish is one that has
not reached sexual maturity, regardless of size or age. One usually thinks
of a Y-O-Y when you hear the term "juvenile" and immature certainly falls
within this stage as well. But many fish species (billfish for example)
don't reach sexual maturity until they reach a fairly large size. While you
are correct that taking the terms by themselves "juvenile" (usually used to
refer to a life stage) and "immature" (used to refer to reproductive state)
may mean something slightly different, in terms of the life history of a
fish, any fish that has not reached sexual maturity is both a juvenile and
immature. Ergo, an adult fish is one that is sexually mature (in it's most
basic definition). Due to the large variety of reproductive strategies used
by fish, there are probably some valid arguments that could bend the edges
(somewhat) of the both the terms "juvenile" and "immature". What about
protandry or protogyny? Is a small male Grouper a juvenile female that's
still immature?
I think the basic definition still holds that a juvenile or immature fish is
one that has not reached sexual maturity. Even when you separate the terms
relative to either life stage or reproductive state this basic definition
should still hold true.
Well, that's my 2-cents.
Cheers,
Chris McDonough
Fisheries Biologist
Marine Resources Research Institute
South Carolina Dept. of Natural Resources
217 Fort Johnson Rd.
Charleston, S.C. 29412
(843)953-9231
(843)953-9820 fax
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-----Original Message-----
From: Scientific forum on fish and fisheries
[mailto:[log in to unmask]]On Behalf Of FZB - MCN - Fritz
Sent: Tuesday, March 01, 2005 1:12 PM
To: [log in to unmask]
Subject: definition of juvenile
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Dear colleagues,
I was recently confronted with the problem of determining what is a
"juvenile" fish and whether "immature" would have the same meaning. As it is
probably a tricky question, I would like to hear your comments.
I did a quick research on definitions, and juvenile is often defined as
being an immature fish or YOY.
However, it seems to me that "juvenile" refers to a development stage in
the life-cycle of the individual, while "immature" refers specifically to a
stage of gonadal development. A juvenile fish would necessarily be an
immature one, however there are situations in which an "adult" fish can be
immature (i.e., it has the length of an adult fish, but its gonads are still
immature). I would say that these terms refer to different contexts: the
gonadal development stages (e.g., immature-maturing-mature-spent) and the
individual ontogenetic development phases (egg, larvae, post-larvae,
juvenile, and so on - I´m not particularly familiar with these).
I realized that a biological, technical definition of "adult" is not
easy find too.
Is there a precise definition for "juvenile"? Or is it just a term with
a losely defined meaning?
Any comments are welcome.
Thanks
Fernando.
Fernando Gertum Becker
Ichthylogy Lab
Museu de Ciências Naturais
Fundação Zoobotânica do RS
av. Salvador França, 1427, Jardim Botânico
Porto Alegre, RS 90690-000
Brazil
tel. 51 - 3320-2053
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