>Forgive me for asking, but does this also apply to gizzard shad? I'm
>wondering about this because they don't have any saltwater populations that I
>know of, so it seems like they could be different in this respect. I guess I
>could still see them being really migratory (not travelling the same great
>distances that the other members of its family do though) but it seems like
>they would still have a better chance of being spawned in an artificial
>environment than other shads so I'm kind of curious as to whether or not the
>spawning cues are impossible to duplicate in aquaria with our current
>knowledge.
Gizzard and threadfin shad both move upstream into shallower waters to spawn,
but otherwise show no obvious spawning migration pattern. Gizzard shad spawn any
time of day, with large aggregations of adults rolling and tumbling near the
surface. Threadfin shad spawn only during the first few hours after sunrise.
Apparently darkness is the cue that prompts threadfin shad to ovulate; when
researchers squeezed the sides of females caught before and after the brief
spawning window, eggs were not in position to be released. These same
researchers believe that spawning in the early morning avoids the prime feeding
time of predators such as largemouth bass and sauger. In addition, this
reproductive strategy may help threadfin shad -- which are cold intolerant and
often die when temperatures abruptly drop, especially below 12C (54F) -- rapidly
rebuild populations where winter die-offs have taken a heavy toll.
Threadfin shad are cultured in nursery ponds and stocked into reservoirs and
lakes to provide forage for gamefish. (Threadfin shad are preferred over gizzard
shad because their smaller size makes them easier for predators to swallow.) The
ponds are seeded with a fertilizer, such as fresh cow manure, in order to
provide an adequate bloom of algae and plankton. Shallow portions of the ponds
are stacked with six-inch bales of hay to provide a place to spawn. Since
overfertilizing, overfeeding, or too much hay can deplete oxygen levels,
especially during the summer, an emergency water supply is recommended. As long
as the nursery ponds are free of other predators, a yield of 50,000-100,000
threadfin shad per acre is possible.
Spawning these fishes in aquaria without hormone injections is not practical.
They are large fishes (gizzard shad reach 20 in, threadfin 9 in), and will only
spawn in large schools.
Chris Scharpf
Baltimore
/-----------------------------------------------------------------------------
/"Unless stated otherwise, comments made on this list do not necessarily
/ reflect the beliefs or goals of the North American Native Fishes
/ Association"
/ This is the discussion list of the North American Native Fishes Association
/ nanfa_at_aquaria.net. To subscribe, unsubscribe, or get help, send the word
/ subscribe, unsubscribe, or help in the body (not subject) of an email to
/ nanfa-request_at_aquaria.net. For a digest version, send the command to
/ nanfa-digest-request_at_aquaria.net instead.
/ For more information about NANFA, visit our web page, http://www.nanfa.org