>From the upcoming NANFA Encyclopedia...
Few fishkeepers seek Hybognathus for their aquaria. Usually they're just
bycatch, that unidentified silvery minnow that makes it into the collecting
bucket simply because it turns up in nearly every seine haul. Maybe it'll
color up in the aquarium after the stress of capture has worn off. Except
that Hybognathus never color up. They remain plain, which is not to say that
a small school of them, under proper lighting that picks up the shimmering
glint in their scales, makes for a plain exhibit. As with other dull,
silvery, schooling fishes, Hybognathus are best maintained as a group in a
large community tank. They'll hang together, forming a moving, living,
aesthetically pleasing contrast to more charismatic solitary fishes. Brassy
minnows are easily alarmed in captivity, forming pods under vegetation after
swimming eratically or a minute or two (Copes, 1975). Despite some
skittishness, captive Hybognathus are hardy and accept just about any
aquarium fare that's small enough to be swallowed.
Plains minnow and Rio Grande silvery minnow have been spawned in laboratory
aquaria by researchers studying their reproductive biology (Platania and
Altenbach, 1998). Specimens were collected from the wild, injected with carp
pituitary extract to induce spawning, and maintained in greenhouse aquaria
with natural sunlight. (All attempts to spawn the minnows without the
hormone were unsuccessful.) The temperature was 27C (80.6F). A tubular
air-diffuser across the width of the aquaria provided oxygen and current.
Males pursued a single female, nudging her abdominal region. When the female
was ready, the male wrapped around it. Eggs and milt were expelled-in-the
same time. Some individuals spawned several times, with-in-least 10-minute
intervals between each event. Both males and females ate their own eggs.
Eastern silvery minnow are easily cultured in shallow earthen ponds. Raney
(1942) describes raising several thousands minnows in a 0.15-acre pond
ranging from four inches to four feet in depth. The pond was fertilized
three times during the summer with cottonseed meal, and fresh-cut timothy
was scattered along the pond's shallow borders several times. The bottom was
silt and lacked vegetation except for filamentous algae later in the summer.
The fish were not fed. Spawning occurred in late April and early May. A
stocked total of 68 males and 14 females produced 6,650 young 4-7 cm
(1.5-2.75 in) in length by the end of September.
Little information is available on the aquarium care of Macrhybopsis
minnows, probably because they are difficult to collect. Silver chub, for
example, inhabit depths of 10 feet or more and thus are out of the reach of
most minnow seines. Sturgeon and sicklefin chubs were once thought to be
rare and perhaps in need of federal protection, but that was partly due to a
"sampling bias." Biologists who were sampling for them using small seines in
shallow water didn't find many; when they switched to benthic trawls in
deepwater habitats the two species were found to more abundant and better
distributed throughout their range than previously believed (FWS, 2001). The
shoal chub (M. hyostoma) often evades capture by apparently diving into the
loose, shifting sand that is its preferred habitat; even in a seine it is
translucent and easily overlooked unless it wriggles (Eddy and Underhill,
1974). Perhaps the best time to catch them is-in-night. And, of course, the
sheer size of the Mississippi and Missouri rivers make sampling for sturgeon
and sicklefin chub impossible for one or two guys with a minnow seine.
The little that has been reported on the captive maintenance of these
interesting minnows indicates that they are hardy, but slow to recognize
food when housed in community aquaria with more visually oriented feeders.
Sicklefin chub are particularly timid feeders that should only be kept with
themselves in a long, well-aerated tank. Provide a sand substrate and
position a powerhead to create a current in the upper half of the water
column. David P. Herzog of the Missouri Department of Conservation
recommends collecting sicklefin chub early in the spring because they tend
to be more robust than specimens collected in the summer (pers. comm.). Dave
also warns that summer temperatures can be hard on this species when it's
being transported.
Spawning has not been observed in aquaria, but eggs from wild-caught
peppered chub have been hatched. According to Bottrell et al. (1964), newly
hatched larvae repeatedly swim upward in a spiral fashion then sink towards
the bottom of the tank. They begin feeding on powdered egg yolk 2-3 days
after hatching. Older juveniles aggressively fed on dried food and white
worms, but perhaps was not an adequate diet since some of fry developed
malformed vertebrae. After about 10 days the young chub were taking most of
their food from the bottom, or while it fell downward from the surface.
Should Macrhybopsis spawn in your aquarium, it's important to keep the eggs
suspended in the water; after all, they spend a day or so floating
downstream in the wild. Goldstein et al. (2000) recommends collecting the
eggs by swirling a net through the water, and transferring them to a gallon
jar with vigorous aeration.
Laboratory experiments show that speckled chubs never learn to respond
visually to food, even after three months in aquaria in water that's crystal
clear (Davis and Miller, 1967). Live daphnia remain unnoticed until they
touch or swim close to the chubs. Dry food is likewise ignored until it
sinks to the bottom and is later found as the chubs forage. Interestingly,
when live and dry food are given simultaneously, the chubs consume the dry
food first, probably because they sense its presence more readily. Bottrell
et al. (1964) noted that their chubs became increasingly secretive as they
grew, hiding in plants, behind objects, and in the corners of the tanks.
"They seem to cling with their pectoral fins," the researchers wrote, "and
are very nervous and easily startled by movement, noise, or light."
Chris Scharpf
NANFA HQ
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