Substitution effect of the combined fouling macroalgae Ulva australis and Sargassum horneri for Undaria pinnatifida in formulated diets on growth and body composition of juvenile abalone (Haliotis discus, Reeve 1846) subjected to air exposure stressor

The effect of substituting the combined macroalgae Ulva australis and Sargassum horneri for Undaria pinnatifida in formulated diets on growth and body composition of abalone subjected to air exposure stressor was investigated. A total of 1260 juvenile abalone were distributed into 21 cages. Six formulated diets were prepared. The control (CUS0) diet contained 20% U. pinnatifida. Twenty, 40, 60, 80, and 100% of U. pinnatifida were substituted with an equal amount of the combined U. australis and S. horneri, referred to as the CUS20, CUS40, CUS60, CUS80, and CUS100 diets, respectively. Finally, dry U. pinnatifida was prepared to compare the growth performance of abalone. Abalone were fed with one of the experimental diets once a day for 16 weeks and then subjected to air stressor for 24 h. The cumulative mortality of abalone was monitored for the following 4 days after 24 h of air exposure. Abalone fed all formulated diets attained higher survival, weight gain, and specific growth rate (SGR) than U. pinnatifida. Abalone fed the CUS100 diet achieved greatest weight gain and SGR, followed by the CUS80 and CUS60 diets. The greatest shell growth and heaviest soft-body weight were obtained in abalone fed the CUS100 diet. Proximate composition of the soft body of abalone, except for moisture content, was not affected by the experimental diets. The cumulative mortality of abalone fed the U. pinnatifida was higher than that of abalone fed all formulated diets at 84 h until the end of the 4-day post observation. The lowest cumulative mortality was obtained in abalone fed the CUS80 diet at the end of the 4-day post observation. Therefore, U. pinnatifida could be completely replaced with the combined U. australis and S. horneri in abalone (H. discus) feed.