Comparison of biochemical, histological and morphological response of muscle-based condition indices to varying food levels in pre-flexion Dicentrarchus labrax (L.) larvae

Abstract

The time-response, dynamics, classification power and relationship with survival of three muscle-based condition indices were analysed in pre-flexion sea bass (Dicentrarchus labrax L.) larvae in response to three feeding treatments: fed, non-fed and late-feeding. Larvae were reared at 19 {+/-} 0.8{degrees}C and analysed from the second day of feeding (6 days after hatching (DAH)) to just prior the flexion stage (21 DAH). The indices were analysed in trunk muscle at biochemical (RNA/DNA, R/D), histological (percentage of muscle fibre separation, MFS) and morphometric (size-standardised body depth at the anus level, DAZ) level. No index was correlated with muscle length in the fed treatment regardless the period analysed (before or after full external feeding). The R/D was the only index that could detect past feeding differences in larvae [≤] 13 DAH. For larvae > 13 DAH, MFS, R/D and DAZ in that order, yielded the best discrimination among treatments. For late-feeding larvae, latency was two days (R/D) and two-four days (MFS). Dynamics of recovery after food addition was also similar for R/D and MFS. Significant relationships between muscle growth and R/D or MFS were only found in larvae > 13 DAH. Both R/D and MFS encompassed the mass mortality event observed in non-fed larvae at 17 DAH. The DAZ largely failed to give information on the feeding status.