Dietary chromium polynicotinate enhanced growth performance, feed utilization, and resistance to Cryptocaryon irritans in juvenile large yellow croaker (Larmichthys crocea)

• Dietary chromium polynicotinate (Cr-Nic) supplementation enhanced growth and feed utilization efficiency of large yellow croaker.
• Dietary protein can be lowered at least 3% without negative impacts on growth of large yellow croaker by Cr supplementation.
• Cr-Nic supplementation enhanced resistance of large yellow croaker to Cryptocaryon irritans.

A feeding trial was conducted to determine the effects of dietary chromium polynicotinate (Cr-Nic) on growth, feed utilization, and resistance to Cryptocaryon irritans in juvenile large yellow croaker (Larimichthys crocea). Six diets containing 42% crude protein and graded levels of Cr-Nic (0, 5, 10, 20, 40 and 80 mg kg− 1 diet) were fed to croaker juveniles initially averaging 8.74 ± 0.48 g for 10 weeks. Another diet containing 45% crude protein without Cr-Nic supplementation was also fed and served as a control. Wheat starch was used as the carbohydrate source for all of the experimental diets. Fish fed the diet supplemented with 5 mg kg− 1 Cr-Nic had significantly higher rates of survival, specific growth rate (SGR), feed efficiency (FE), and protein efficiency ratio (PER), but lower feed intake than fish fed diets with 0 and 80 mg kg− 1 Cr-Nic. Fish fed the diet containing 5 mg kg− 1 Cr-Nic had significantly higher SGR and PER than fish fed the 45% crude protein control diet. Analysis of SGR, FE, and PER by second-order regression indicated that the optimal dietary level of Cr-Nic for juvenile large yellow croaker was estimated to be 6.70–7.10 mg kg− 1 of diet. The 3-week cumulative mortality rate following natural infection of the parasite C. irritans was lowest in fish fed the diet containing 5 mg kg− 1 Cr-Nic, which was significantly lower than in fish fed the diet without Cr-Nic addition. It is suggested that Cr-Nic supplementation protects against C. irritans infection prior to parasitic outbreak to alleviate mortality.