Migration of grey mullet fry into the Arno river [Italy]: seasonal appearance, daily activity, and feeding rhythms
1982
Torricelli, P. (Prma Univ. (Italy). Ist. di Zoologia) | Tongiorgi, P. | Almansi, P.
Samples of mullet fry were taken hourly, for 24h, once a month, from September 1979 to October 1980. Five species were found to enter the estuary of the Arno river: Mugil cephalus, Liza ramada, Liza aurata, Liza saliens and Chelon labrosus. Seasonal occurrence and migrational peaks were determined for each species. Variations of standard length and of condition factor were studied during the migrational phase. Hourly samples gave further information on daily variations in the catches of juvenile mullets, on the influence of tidal movements and on feeding activity during the 24-h cycle. Our results showed that the greatest number of fry was caught at sunset, a second peak occurring in the morning hours. Furthermore, the catches seem to be affected by tidal movements, being higher during high tide. The variations of the vacuity coefficient (the percentage of empty stomachs in the total sample) related to dial rhythm, were considered to indicate the daily feeding activity of each species. The analysis showed that the trophic activity of L. saliens, L. ramada and L. aurata occurs mainly during daylight. On the contrary, M. cephalus seems scarcely to feed in this condition, but increases its activity slightly at dusk and in the first part of the night.
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