Thanks, Chris. I didn't ask my question very well. I wonder if anyone
knows of the multiple spawning "rate". For example, Atlantic salmon and
steelhead are multiple spawners, too, but an individual fish isn't
statistically likely to spawn a second time. I was asking this question in
the context of natural spawning vs. hatchery spawning to try to throw out
thoughts on potential hatchery problems. Also, I assume the shad you are
referring to are American shad Alosa sapidissima, right?
> But shads are artificially spawned at hatcheries in one
> of two methods. Most "low-tech" hatcheries are located directly
> on the rivers
> where the young are to be released. Hatchery workers collect ripe
> males and
> females as they return to spawn, and squeeze their eggs into a
> bowl or pail.
> They fertilize the eggs by gently stirring in a drop or two of
Let's not lose sight of the goal of these hatcheries. It isn't to improve
the species population numbers, it's to produce more fish for harvest. But
that doesn't mean we can't insist that they do everything they can to
produce as natural of a generation of fish as possible under the
circumstances. The hand-mixing you describe may not duplicate natural
spawning and natural exchange of genetic material. Do the hatchery workers
mix sperm? Do they mix eggs? Sperm-mixing can be a bad thing depending on
the species, especially if the fish in the wild spawn with one female to one
male. Sperm of some fish has variable fertilization success rates. For
example, if sperm from 4 males are mixed prior to fertilization, say in a
small bucket, and poured into another bucket containing unfertilized eggs,
you won't get equal fertilization rates. Some sperm is just more likely to
fertilize, and "strong" sperm could fertilize 90% or more of the eggs in
this case situation. The result is the loss of genetic information
contained in the "weaker-sperm" fish; information that would have been
retained under natural spawning conditions.
> The eggs
> are then placed into hatching tanks that are continuously
> refreshed with water
> pumped from the river. As the newly hatched fry mature, they make
> their way
> through a pipeline that whisks them into their permanent home.
I guess by "their permanent home" they mean into the river below the dams,
where they can survive with reasonable success, etc. That sounds desirable.
If the fish don't receive extended hatchery rearing you reduce the selective
pressures for hatchery survival characteristics.
I'll bet there's a waiting committee of predators at the pipeline's outlet,
so any increase in hatching rates may be offset by initially high fry
mortality. Just rambling...
> A more "hi-tech" hatchery approach allows shad to spawn on their
> own with the
> help of hormone injections. Again, returning shad are collected
> from the wild.
The taking wild broodstock is critical. This high-tech spawning protocol
seems to be a much better method since the fish spawn themselves. Some
things I wonder: How many adults are included in these spawning
aggregations, and how are they selected? How are the eggs collected? Do
the fish receive any hatchery rearing and are they fed before release?
> As darkness fell, more and more shad seemingly lost their
> inhibitions and began
> falling out of their parallel swimming patterns and making random
> lane changes.
> The number and frequency of aggressive encounters, along with the
> U-turns and
> 360 degree loops, continued to increase as the evening wore on.
> Eventually, the
> aggressive pairings became mutually agreeable and spawning
Does this seem like any town in America or Canada, or what?! :-)
-- Jay DeLong Olympia, WA
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