| dc.description.abstract | Daily rings were formed on saccular otoliths of known-age,
laboratory raised pumpkinseed (Lepomis gibbosus), green sunfish (Lepomis-cyanellus), bluegill (Lepomis macrochirus), and Tilapia mossambica for at least 176, 170, 125, and 60 days,
respectively. Subdaily rings were found in young laboratory
and wild fish, but were easily distinguished from daily rings.
Width of daily rings of green sunfish was linearly related to
daily increase in length of fish, and the number of rings was
a product of age of fish only, not length of fish or otolith
radius. Otolith growth and daily ring formation in wild bluegill
and largemouth bass (Micropterus salmoides) appeared to be
similar to those in laboratory-raised fish. Saccular otoliths
of green sunfish under simulated winter conditions ceased to
produce daily rings, but did form an annulus. Two kinds of
saccular otolith tissue were present in most of the larger
laboratory fish and wild bluegill, but were not observed in
wild largemouth bass: the first, which was present in all areas
of the otolith except the extreme posterior end, was translucent,
and daily rings were well defined in it; the second was present
only in the posterior end, was opaque, and daily rings in this
area etched poorly and were difficult to discern. Both tissues
were calcium carbonate in the aragonite form.
To determine if light, cyclic feeding or an internal clock
influenced daily ring formation, juvenile 1· mossambica, which
had been exposed to continuous light (LL) and constant temperature
since egg fertilization, were held under six experimental
conditions: 1) LL, 27°C, and fed at three hour intervals,
2) LL, 27°C, fed at three hour intervals with a nine hour break
in feeding every 24 hours, 3) L24:D12, 27°C, fed at 6 hour
intervals, 4) Ll5:D9, 27°C, fed at 6 hour intervals (the first
four conditions were maintained in environmental chambers,
the remaining 2 in the laboratory), 5) 15:D9, 27°C, fed at 6
hour intervals, 6) Ll5:D9, 25 to 26°C, fed at various times
every day. Daily rings were formed only in groups 4, 5, and 6,
indicating that a 24-hour light-dark cycle reinforcing an
internal, diurnal clock, were required for daily ring production. | en_US |
