Optimum dietary seaweed (kelp) powder level in juvenile abalone, Haliotis discus hannai

Abstract

The present study was conducted to evaluate the optimum dietary seaweed (kelp) powder in juvenile abalone, Haliotis discus hannai. Juvenile abalone with average initial individual weight and shell length of 0.44 ± 0.01 g and 15.6 ± 0.7 mm, respectively were fed 7 formulated diets for 10 weeks at a temperature range of 20 ± 1 0C. The formulated diets contained 30% crude protein and 5.8 crude lipids. Dietary levels of seaweed powder were distributed in 7 diets from 25% (Con), 20% (SW20), 15% (SW15), 10% (SW10), 5% (SW5) to 0% (SW0) and 25% w/ 0.4% mushroom powder (SW25M), respectively. A formulated diet served as the control (Con). The diets were fed at 4% body weight once daily at 1700 h. Weight gain (WG), feed efficiency (FE), specific growth rate (SGR), protein efficiency ratio (PER), shell length increase (SLI) and survival rate (SR) were evaluated. Highest weight gain (WG) was obtained by abalone fed diet Con (25% seaweed powder). This value was, however, not significantly different (P <0.05) from those fed diets SW20, SW15, SW10, and SW5. Abalone fed SW0 (0% seaweed powder) showed significantly lower WG. The protein efficiency ratio (PER) and feed efficiency (FE) showed the same trend as the weight gain. The specific growth rate (SGR) was not significantly different from those fed diets Con, SW20, SW15, SW10, and SW5. Abalone fed diet SW0 showed significantly lower SGR. Survival rate was generally high ranging from 72 to 86% for all treatments. Diet SW25M, even though gained highest growth performances, was used just to find out the effect of mushroom powder in abalone growth compared with control diet as reference for further study in the future. Proximate body composition of abalone, Haliotis discus hannai was shown in Table 5. Moisture content has no significant differences among abalone fed diets Con and SW20, however, there were significant differences among diets SW15 ~ SW0 (P <0.05). It was observed that the decreasing concentration level of seaweed powder in the diet increased the moisture content in the whole body of abalone. Crude fat of abalone fed diets Con ~ SW5 has no significant differences except abalone fed diet SW0 which significantly lower than among other diets (P <0.05). Crude protein content of abalone meat fed diets Con ~ SW0 has no significant differences among all diets (P <0.05). Ash content of abalone meat fed diets SW10 was significantly higher than among abalone fed diets Con, SW20, SW15, SW5 and SW0 (P <0.05). Growth and feed utilization of abalone, Haliotis discus hannai fed diets containing 15% seaweed powder were significantly higher than those of animals fed the non-supplemented diet. Hence, faster growth could be achieved at 15% supplementation level. However, abalone, Haliotis discus hannai grows slowly. A lot would be saved at 5% supplementation compared to 15% over the long duration of culture, since no significant differences were recorded in WG among animals fed at 5% and 15%. Broken line regression analysis indicated that the optimum seaweed powder supplementation level could be 12.2% in juvenile abalone, H. discus hannai.