Comparative studies on growth, and stressor resistance of abalone (Haliotis discus) fed extruded pellets substituting tunic meal of sea squirt (Halocynthia roretzi) for fish meal and macroalgae in long term trial

Abstract

Fish meal (FM) and macroalgae (MA) are the expensive components in abalone feeds, searching for their alternatives is of great interest to abalone aquaculture. Tunic meal of sea squirt (TSS) is one of the marine fishery by-products that contains a variety of nutrients. In this study, we evaluated TSS as a substitute for FM and MA in abalone (Haliotis discus) diet. A total of 27,600 abalones was distributed into 36 net cages (2300 abalones in 3 cages/diet). Two-way [substitution source (FM and MA), and substitution ratio (50% and 100%)] ANOVA with the repeated design was used. Extruded pellets (EPs) were made up of the control diet (Con), which contained 14% FM, and 25% MA. Fifty, and 100% of both FM and MA were substituted with an equal amount of TSS, referred to as the FM50, FM100, MA50, and MA100 diets, respectively. Undaria pinnatifida was prepared to compare the effect of EPs on abalone. All experimental diets were fed to duplicate groups of abalone for 33 weeks. After the 16-week feeding trial, abalone were subjected to air, high temperature, and low salinity exposures for 24-h, and then monitored for survival. Weight gain and specific growth rate (SGR) of abalone fed with the MA50 and MA100 diets were greater than those of abalone fed with all other diets, except for SGR of abalone fed with the Con diet. Chemical composition of the soft body of abalone was reflected from the dietary nutrient composition. Abalone fed the MA50 diet achieved the highest survival after the 24-h air and high-temperature exposures. Conclusively, the desirable level of substituting tunic meal of sea squirt for FM is up to 50% and 100% for MA, respectively, in extruded pellet.