Citrus byproduct as a vitamin C source for Korean rockfish Sebastes schlegelii diet

The present study was conducted to evaluate the availability of citrus byproduct (CBP) as a vitamin C additive compared with the L-ascorbyl-polyphosphate (LAPP) for juvenile Korean rockfish Sebastes schlegelii. Four experimental diets, based on the basal diet (Con; semi-purified, crude protein 48%), were prepared by supplementing LAPP or CBP to achieve a dietary vitamin C concentration of 90 or 360 mg/kg (designated as LAPP90, LAPP360, CBP90, and CBP360, respectively). Three replicate groups of S. schlegelii (mean body weight ± standard deviation = 4.5 ± 0.0 g) were fed the experimental diets for 13 weeks. After the feeding trial, growth performance, feed utilization efficiency, and survival were significantly lower in the Con group. Liver vitamin C concentration was significantly increased (36.7–117 mg/kg) with increasing dietary LAPP levels; however, there was no significant difference in the CBP groups (14.2–14.3 mg/kg) compared with the Con group. Bone collagen concentration was significantly affected by LAPP and CBP supplementation. The LAPP and CBP groups showed significantly higher lysozyme activity and total immunoglobulin levels than the Con group. Disease resistance against Streptococcus iniaewas significantly improved in the LAPP and CBP groups (60–92% survival) than in the Con group (39% survival). These results indicate that dietary vitamin C is essential for S. schlegelii and CBP could be a LAPP substitute as a vitamin C additive.