Effect of dietary carbohydrate sources on growth performance and carbohydrate utilisation in abalone, Haliotis discus hannai Ino

Despite the importance of carbohydrates in the natural diet of abalone, there is little information about the specific effects of commonly available dietary sources. Therefore, this experiment was conducted to determine the effects of several carbohydrate sources, using a semi-purified base diet containing casein and gelatine, on the growth performance metrics and metabolic response of abalone, Haliotis discus hannai Ino. Six experimental diets were formulated containing 33.50 % of different carbohydrate sources including dextrin, pregelatinized wheat starch, wheat starch, tapioca starch, potato starch and corn starch. The diets were fed to the abalone with an initial weight of 3.42 f 0.02 g in triplicate tanks for 24 weeks, housed in a recirculation system, with seawater maintained at 18-20 degrees C. There were no significant differences detected in the average daily increment in shell length (DISL, mu m/day) or survival of abalone fed the six treatments containing different carbohydrate sources. However, there were significant differences detected in the average final weight and weight gain rate (WGR, %) parameters, with the lowest final weight (8.16 f 0.29 g) and WGR (140.38 f 6.57 %) observed in the potato starch fed abalone. While the potato starch group had the ssignificant highest valuein the moisture content (79.31 f 0.07 %), crude protein (75.37 f 0.37 %) and crude ash (10.52 f 0.20 %) present in the soft-tissue and similarly in the crude ash level (96.06 f 0.29 %) in the shell composition among the six dietary treatments. There was no significant difference found in the soft-tissue lipid content (5.84-6.87 %). The dextrin-based diet led to elevated plasma glucose (0.85 f 0.06 mmol/l) in abalone compared with the other treatment groups. The concentration of muscle glycogen in abalone fed with pregelatinized wheat starch showed the highest values with 78.45 f 1.53 mg/g tissue, which was significantly different to the other treatment groups, however, the digestive gland glycogen content (15.56-19.27 mg/g tissue) was maintained at a constant level regardless of the dietary carbohydrate sources. The digestive gland alpha-amylase activity in abalone was significantly higher in the pregelatinized wheat starch fed abalone (211.65 f 16.16 mg starch/ 30 min/g protein) compared to the dextrin (93.58 f 13.40 mg starch/30 min/g protein) and potato (99.37 f 11.15 mg starch/30 min/g protein) starch fed abalones. The results presented demonstrate that abalone efficiently utilized the carbohydrate sources evaluated in the present study, the dextrin and pregelatinized wheat starch were the most suitable sources based on the growth performance alone. There were discrete metabolic and enzymatic responses observed among the dietary groups, like the interrupting the normal glucose metabolic processes by the potato starch,which may lead to improved dietary formulations.