Daily Rings in Saccular Otoliths of Lepomis sp. and Talipia mossambica
Taubert, Bruce D.
University of Wisconsin-Stevens Point, College of Natural Resources
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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.