Growth improvement by probiotic in European sea bass juveniles (Dicentrarchus labrax, L.), with particular attention to IGF-1, myostatin and cortisol gene expression

In the present study a Lactic Acid Bacteria (LAB) strain Lactobacillus delbrueckii delbrueckii, acting as probiotic, was administered to Dicentrarchus labrax (European sea bass) juveniles for a short (25 days) and a long (59 days) time and the effects of the bacteria on gut colonization in sea bass juveniles cortisol level and growth were evaluated with respect to fish fed on live preys solely (control group). Measures of body weight and standard length (S.L.) were performed to assess juveniles growth, while cortisol, a hormone directly involved in stress responses, was chosen as a stress marker. In addition, the expression of two antagonistic genes involved in muscular growth (IGF-I and myostatin (MSTN) was analyzed through real-time PCR. Fish fed on live preys added with L. delbrueckii delbrueckii showed a high gut colonization by this Lactic Acid Bacteria strain. In the same fish a significantly (p < 0.05) lower cortisol level was observed with respect to those fed on live preys solely (control 5.1 ± 0.47 ng/g; group A: 3.6 ± 0.36 ng/g; group B: 4.5 ± 0.48 ng/g). In addition, an increase of IGF-I transcription was observed in fish treated with LAB, being IGF-I mRNA levels six times higher in both treated groups with respect to the control (control: 1 ± 0.01 a.u.; group A: 6.63 ± 0.18 a.u.; group B: 6.16 ± 0.15 a.u.). On the contrary, MSTN mRNA transcription was significantly inhibited in treated groups (control 1 ± 0.02 a.u.; group A: 0.71 ± 0.01 a.u.; group B: 0.26 ± 0.003 a.u.). These results are in agreement with the increase of body weight recorded in this study. Fish fed on LAB showed 81% higher body weight in long treated group and 28% in short treated one with respect to control.