Transition from endogenous to exogenous nutritional sources in larval Black Sea turbot Psetta maxima

ABSTRACT: Early growth, yolk and oil globule absorption, early morphological development and initial feeding were studied in the Black Sea turbot Psetta maxima . Based on energy transition and morphological development, the nutritional transition process from endogenous to exogenous sources was divided into six phases: (i) primordial phase (from hatching to ≈ 30 h after hatching, HAH); (ii) organogenesis phase (to ≈ 90 HAH); (iii) onset of feeding (to ≈ 110 HAH); (iv) early feeding (to ≈ 190 HAH); (v) intensified feeding (to ≈ 230 HAH); and (vi) completion of oil globule absorption (to beyond 345 HAH). Based on comparisons with early life stage features of other marine species, the turbot larvae were shown to possess the following characteristics: (i) oil globule remaining for a long period, resulting in an extended mixed feeding period; and (ii) feeding rate extremely high in larvae immediately following final absorption of the oil globule. These features in early turbot larvae were regarded as advantageous for survival in a rearing condition, although the coincidence of initial feeding with completion of yolk absorption signaled a period of leveled-off growth rate.