Evaluation of the Cathepsin-L gene expression changes and growth factors in Litopenaeus vannamei under different biofloc systems

Cathepsins represent a major component of the lysosomal proteolytic system and, as such, are responsible for intracellular protein degradation. The aim of this study was to evaluate the cathepsin-L (CTSL) gene expression changes and growth factors in Litopenaeus vannamei  under various biofloc systems (BFT) and different protein levels. Four bioflocs were used: BFT fed diets of 25% CP and spoilage palm date extract (P25), diets of 25% CP and molasses (M25), diets of 15% CP and spoilage palm date extract (P15), diets of 15% CP and molasses (M15) and clear water without biofloc fed with 38% CP (Control) that were performed in triplicate. A 35-day study was conducted with 35 juvenile (average 5.37±0.33 g) shrimp randomly stocked in fifteen 300 L tanks at a stocking density of 175 shrimp m−3.  Real time PCR technique was used to estimate the effect of biofloc on the CTSL gene expression in shrimp hepatopancreas and Beta actin gene was used as an internal control gene. In all the biofloc treatments, a significant increase in the expression of CTSL gene was observed (P <0.05), although P25 had the highest expression (P> 0.05). Moreover the highest growth parameters (weight gain, better feed conversion ratio (FCR), growth rate and survival) was showed in P25 and the lowest in the control (P <0.05). The results showed that there were no significant differences in the expression of CTSL gene in change of carbon sources or dietary protein in the biofloc treatments (P> 0.05). It seems the biofloc technology with its positive effects on digestion and immunity provides the basis of increasing the CTSL gene expression in this species.