Zinc methionine and zinc sulfate as sources of dietary zinc for juvenile abalone, Haliotis discus hannai Ino

Abstract

A feeding experiment was conducted to determine the minimum dietary zinc requirement of juvenile abalone, Haliotis discus hannai, with zinc methionine (ZnMet) and zinc sulfate (ZnSO 4·7H 2O) as the zinc sources and to compare the bioavailability of the two zinc sources using a premium quality diet based on casein–gelatin as the protein sources. Semipurified experimental diets containing graded levels of dietary zinc (5.6–84.6 mg zinc/kg) provided as either ZnMet or ZnSO 4 were fed to juvenile abalone in triplicate groups for 16 weeks. The results showed that the average weight gain rate (WGR, %), daily increment in shell length (DISL, μm/day), soft-body alkaline phosphatase activity (SBAKP, U/g protein) and soft-body zinc concentration (SB zinc, μg/g) of the abalone were significantly (ANOVA, P<0.01) affected by dietary treatment, and responded in broken-line models to increases in dietary zinc levels from the two zinc sources. The requirements for dietary zinc using ZnMet and ZnSO 4 as the supplemental zinc sources, determined by broken-line regression analysis, on the basis of maximum WGR were 15.49 and 34.10 mg/kg, respectively, on maximum DISL were 15.16 and 33.99 mg/kg, respectively, on maximum SBAKP were 15.54 and 31.91 mg/kg, and on maximum SB zinc deposition were 17.75 and 34.29 mg/kg, respectively. The shell zinc concentration, as well as iron concentration in soft-body and shell of the abalone, however, was maintained relatively constant (ANOVA, P>0.05) regardless of dietary treatment. Based on these results, a minimum requirement for dietary zinc was recommended to be 16–18 mg/kg from ZnMet, and 35 mg/kg from ZnSO 4. This experiment also showed that the bioavailability of dietary zinc with ZnMet was approximately three times as high as that of ZnSO 4 to H. discus hannai Ino.