The feeding strategies of Liza ramada (Risso, 1826) in fresh and brackish water in the River Tagus, Portugal

Abstract

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.

Can Thin-lipped Mullet Directly Exploit the Primary and Detritic Production of European Macrotidal Salt Marshes?

“…This confirms that mullet was feeding in the salt marsh creek. Thus we assume that large Liza ramada forage in the superficial sediment layer of European macrotidal salt marsh creek, as is the case in other environments (Hickling, 1970;Bruslé, 1981;Almeida et al, 1993;Shapiro, 1998) and for many other mullet species (Odum, 1970;Fagade & Olaniyan, 1973;Masson & Marais, 1975). This interpretation is confirmed by many foraging marks, which are observed on the sediments in the creeks after the ebb.…”

“…This high feeding rate must be related to the site. Indeed, in brackish tidal areas, L. ramada feeds mainly at high tide (Almeida et al, 1993) in areas which are only accessible at spring tides (e.g. in salt marsh creek of Mont Saint Michel's bay during 43% of the tides) and for very brief moments (1 to 2 h in these creeks).…”

“…The percentage of particulate organic matter (%POM) was assessed each month in five stomach contents of mullets caught during ebb according to Almeida et al (1993): %POM=[1 (SWC/ SWD)]*100, where SWC is the stomach content weight after ignition (at 480 C during 48 h) and SWD is the stomach content weight after desiccation (at 50 C during 48 h).…”

“…Adapted from Almeida et al (1993), a 200 mg sample was removed monthly from three mullets' stomachs caught during ebb, and suspended in 5 ml of distilled water. The samples were shaken thoroughly and a known volume was pipetted onto a slide with an etched grid.…”

“…Although, an abundant literature focuses on various aspects of mullets' feeding habits (Odum, 1968;Albertini-Berhault, 1974;De Silva & Wijeyaratne, 1977;De Silva & Silva, 1979;De Silva, 1980), the available literature concerning feeding ecology of Liza ramada focuses on young stages (Albertini-Berhault, 1973, 1974, 1979Zismann et al, 1975;Ferrari & Chieregato, 1981) or in fish farming systems (Yashouv & Ben-Sachar, 1967;Cardona & Castello, 1994;Cardona, 1996). Only Hickling (1970), Almeida et al (1993), and Shapiro (1998) have studied the feeding habits of juveniles and adults in natural environments.…”