THE FEEDING STRATEGIES OF LIZA-RAMADA (RISSO, 1826) IN FRESH AND BRACKISH WATER IN THE RIVER TAGUS, PORTUGAL

The stomach contents of samples of the mugilid Liza ramada (Risso, 1826), captured at Alcochete (brackish water zone of the Tagus Estuary) differed from those from Vala Nova (freshwater zone of the same estuary). In the freshwater zone of the estuary the mullet ingested preferentially planktonic micro-algae, while in the brackish water they ate benthic micro-algae. The stomach contents from Vala Nova showed a higher diversity of food items, compared with those from Alcochete. At Alcochete the Naviculales (numerical frequency, 82%) was the most representative order, while at Vala Nova it was the Coscinodiscales (61%) and the Chlorococcales (16%). In fresh water, the stomach contents contained about 25·4% organic matter, while at Alcochete only 8·7% was found. In the brackish water zone the ingestion rhythm was related to the tidal cycle, attaining a maximum during the high tide and a minimum at low tide. At Vala Nova the mullet ate regularly throughout the day, showing a slight increase at dawn and dusk. Apparently, the fish remained inactive by night, at both locations. © 1993 The Fisheries Society of the British Isles.