Feeding behaviour and prey size selection of gilthead seabream,Sparus aurata,larvae fed on inert and live food

Prey selection shortly after the onset of feeding by laboratory-reared gilthead seabream, Sparus aurata L., larvae was studied using larvae fed on two types of microcapsule (hard- and soft-walled) having diameters ranging from 25 to 300 m. Preferences between inert food and live prey (rotifers and Artemia sp. nauplii) were also studied. Seabream larvae were able to ingest inert food from first feeding. Larvae of all size classes ingested hard microcapsules with diameters in the range 25 to 250 m. However, larvae with a total length (TL) below 4 mm preferentially selected particles 25 to 50 m in diameter, larvae of TL 4 and 5 mm preferred particles 51 to 100 m in diameter, while larvae above 5 mm TL preferred particles 101 to 150 m in diameter. With soft microcapsules, larvae always preferred particles larger than in the previous case, and above 4.5 mm TL they preferentially selected particles 201 to 250 m in diameter. In addition, the gradual increase of preferred diameters with increasing TL was more pronounced when larvae were increasing TL was more pronounced when larvae were fed on soft particles. Mean values for prey width/mouth width ratios were approximately 0.24 and 0.30 when larvae were fed on hard-walled and soft-walled microcapsules, respectively, irrespective of the absolute value of larval length. When a mixed diet of live and inert food items was offered, live prey were always preferentially selected, even if the prey width/mouth width ratio was apparently not favourable. Only a physical constraint such as excessive prey width could counter this preference for living prey vs inert microcapsules. These results contribute to our knowledge in larval feeding behaviour, especially in the presence of inert food, and represent a fundamental step in developing prepared food for marine fish larvae.