14 pages, 7 figures, 4 tablesThe diel variation in feeding intensity and daily ration of the sardine Sardina pilchardus (Walbaum, 1792) was investigated based on 50 pelagic trawl hauls carried out during the period of thermal stratification (July 2007 and July 2008) and mixing (December 2007 and February 2009) in a coastal area of the North Aegean Sea (eastern Mediterranean). Concurrently collected hydrographic (temperature and salinity), plankton (chlorophyll a, microzooplankton and mesozooplankton) and fish parameters (somatic condition, sexual maturity and catch per unit effort of sardine, CPUE) were used to explain seasonal and inter-annual variability in feeding periodicity and daily ration. A piecewise regression fitted to the weight-length data indicated a significant inflexion point at a length of ~100 mm that was used to split the fish sample into adults and juveniles. The stomach fullness index (stomach content mass/fish mass) was strongly dependent on size, and a generalized linear model was used instead to standardize stomach content mass. During summer, sardine fed consistently during daytime with a prominent peak at around sunset. In winter, high feeding rates were recorded in the early night (first 6 h after sunset) but not in the second half of the night. Field estimates of gastric evacuation rate (R) ranged from 0.101 to 0.225 h−1 and were strongly related to temperature (T) (R = 0.075e0.038T, r2 = 0.785). Daily rations were estimated by applying the Elliott-Persson and the Eggers models and varied from 2.02 to 3.67% total weight (TW) in adults and 4.18 to 5.36% TW in juveniles. A significant positive relationship emerged when daily ration was regressed against the ratio of mesozooplankton biomass to sardine CPUE, implying a density-dependent rate of food consumption.The present study was part of the European Project SARDONE (‘Improving assessment and management of small pelagic species in the Mediterranean’, FP6-44294).Peer reviewe

In this study, we provide evidence, based on field-collected data and published articles, that the stage of caudal fin formation, initiated by notochord flexion (NF), might be a developmental milestone in the early life history of engraulids and other fishes, associated with changes in capabilities of the developing fish. An analysis of morphometric characters in anchovy (Engraulis encrasicolus) larvae collected from the Aegean Sea indicated a significant change in multivariate allometry at NF, with a marked increase in the growth of tail width and eye diameter. Initiation of swim-bladder inflation, which is considered to trigger the onset of vertical migrations and subsequent schooling behavior, was first observed at NF. This is further supported by a length-specific analysis of spatial patchiness (Bez's index of aggregation) based on data from three broad-scale ichthyoplankton surveys in the Aegean Sea; after the onset of NF (i.e. >7 mm preserved length), the aggregation of anchovy larvae started to increase rapidly implying that schooling might be well established in the early post-flexion stages. Published studies further support these field observations indicating that the NF in European anchovy is associated with the start of diel vertical migrations, the increase in otolith growth, a change in prey selectivity and an increased ability to evade plankton nets. The development of the caudal fin might be an important event in engraulids and other fishes but has generally been overlooked.