Supplementation of commercial probiotic Lactobacillus casei in rearing early-stage silver therapon (Leiopotherapon plumbeus) larvae: Effects on growth, body composition and stress tolerance

Abstract

Supplementation of probiotics in live feeds and rearing water may improve the growth, survival, and resistance of fish larvae. This study examined the beneficial effect of a commercial probiotic bacteria Lactobacillus casei on the growth, body composition, and stress resistance in early-stage silver therapon (<i>Leiopotherapon plumbeus</i>) larvae. Larvae at 12 d post-hatch (DPH) (9.76 ± 1.32 mm total length [TL] and 13.48 ± 4.80 mg body weight [BW]) were reared in triplicate groups of 15 larvae per tank from 12 – 40 DPH (Phase 1) and 41 – 96 DPH (Phase 2). From 12 – 40 DPH, larvae were fed (I) unenriched <i>Artemia</i> nauplii (no-PB or control group); (II) probiotic-enriched <i>Artemia</i> nauplii (PB); and on (III) probiotic-enriched <i>Artemia</i> nauplii and rearing water (PB + W). The same feeding regime was used from 41 – 96 DPH except that the larvae were co-fed <i>Artemia</i> nauplii and microparticulate diet (MPD). Mean survival rates at 40 (97.78% – 100%) and 96 DPH (86.67% – 91.11%) did not show significant differences among treatments. However, except for body depth (BD) and Fulton’s condition factor (<i>K</i>), mean TL, BW, length increment (LI), and length- (SGRL) and weight-specific growth rates (SGRW) of PB + W-fed larvae were significantly higher than PB-fed and no-PB-fed larvae at 40 DPH. While these parameters were similar among treatment groups at 96 DPH, slightly higher values for BW and SGRW were noted for the PB + W group, as supported by the higher proportion of <i>L. casei</i> to total microbiota in the intestines of early-stage larvae. Whole body protein and lipid contents were highest in the PB + W and PB groups, respectively, but did not differ from the no-PB group. Survival rates (93.33% – 100%) after 18 h exposure to 30 ppt did not show significant differences. However, recovery rates after 15 min of air exposure of early juveniles in the PB and PB + W groups (93.33%) were significantly higher than those fed unenriched <i>Artemia</i> (66.67%). These results indicate that supplementation of probiotic bacteria <i>L. casei</i> in live feed and rearing water may support growth of early-stage larvae of silver therapon and its resistance to stress conditions during culture.