RE: NANFA-- Bluenose Shiners & Pond Update
Tue, 23 Sep 2003 15:00:09 +0000

> Does anyone know if Pt.hypselopterus and Pt.welaka will cross.
> I believe they are found in some of the same locations, at least in
> the FL panhandle. If I were to put both species in my pond and the
> sailfins would spawn maybe it would stimulate the bluenose to also.
> Anyone got other ideas?

It's conceivable that they may, since many intergeneric hybrids occur in the
wild among nest associates. I would keep them separate. (FYI, hubbsi &
welaka will likely be placed in a separate genus from the rest of
Pteronotropis; they form their own monophyletic group.)

Also, it's not the nest per se that help induce facultate & obligate nest
associates to spawn, but likely pheromones from the spawning hosts.
(CFI has induced Phoxinus cumberlandensis to spawn in captivity by
adding stoneroller milt to the tank.) Therefore, keeping associates and
host in separate parts of the pond *may* be okay, depending on the size
of the pond and water circulation.

Regarding the benefits of nest association to host and associate --

At least 35 minnow species borrow the nests, and sometimes also the
parental duties, of larger fishes. Most of these associates are
broadcasters that spawn over the nests of nest builders like
Campostoma, Semotilus, Exoglossum, and Nocomis, while others have
the gumption to spawn in the nests of fishes that would otherwise eat
them, including bowfins, sunfishes, and basses. The benefits to the
associates are clear. Why expend the energy to move all those rocks and
dig those pits when you can get a bigger fish to do it for you instead? And
why worry about protecting your young when a bigger, meaner fish will
happily, if not unknowingly, "adopt" your eggs and babies?

But the benefits of nest associations are not one-sided. Both hosts and
associates benefit by the fact that the more eggs or fry there are in the
nest, the risk of losing them to other predators is spread out between the
two species.

Heres a simplified example:

Lets say an eel enters a chub nest and eats half of the chubs 1000 eggs
before it gets full or is chased away. Only 500 chub eggs survive. If that
nest contained an equal number of shiner eggs, then, statistically
speaking, only one in two of the chubs eggs will be eaten. By letting a
shiner spawn in its nest, the chub has increased its egg survivability from
500 to 750 eggs.

Chris Scharpf
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