In the wild, juvenile European seabass (SL <30 mm) have been found to feed mainly on copepods and nauplii of Cirripedia, while bigger juveniles (SL about 60 mm) feed on larger prey, particularly larvae of Decapoda and Mysidacea (Ferrari and Chieregato, 1981). Adult seabass are known to have piscivorous habits, including cannibalistic feeding behaviour (Henderson and Corps, 1997). European seabass is considered as having a trophic level of 3.8 (www.fishbase.org). Seasonal fluctuations in prey items are known to occur (Table 1). They generally have a diurnal feeding habit, with a high trophic activity during the dawn and dusk periods, but under farming conditions, are known to exhibit some plasticity. Feeding is known to correlate positively with both day length and water temperature (Begout-Anras, 1995).
They are eurythermic, but grow well only at temperatures above 18 °C. Juveniles and adults are highly euryhaline, capable of adapting even to freshwater. The osmoregulatory capacity increases as development proceeds; under natural conditions in coastal zones, the early development of European seabass occurs in seawater and only after they reach a size of about 2 cm do they exhibit greater osmoregulatory capacity and migratory movements towards estuaries.
Digestive system (Figure 3)
They have a terminal mouth that is moderately protractile. They have vomerine teeth in a crescentic band, without a backward extension on midline of roof of mouth. The digestive tract is relatively long, with an oesophagus, stomach, five pyloric caeca and a long intestine, generally separated as anterior and posterior parts.
Immediately after hatching and up to two to three days, the mouth is still closed, the gills are not developed, and the digestive tract is more or less a straight tubular structure open only at the posterior end. At this stage, nutrient supply is only from the endogenous reserves of the yolk vesicle. Even after mouth opening, which occurs about three days after hatching (or to be more precise, at about 50 degree days), endotrophy continues until about day 7 after hatching. The functional development of the digestive tract occurs slowly and is considered to resemble that of a juvenile only by about 30 days after hatching (Tue, 1983; Garcia Hernández et al., 2001; Zambonino Infante and Cahu, 2001). All the full complement of digestive enzymes are found in the intestine of European seabass juveniles; absorption essentially occurring in the anterior intestine.
