Replacement of Dietary Undaria pinnatifida Meal with Ulva australis or Saccharina japonica by-Product on the Growth Performance and Body Composition of Pacific Abalone Haliotis discus hannai

The continuous expansion and increased production of abalone warrant an alternative macroalgal biomass to sustain unhampered feed production. The sea lettuce Ulva australis (UA) and kelp Saccharina japonica by-product (SJBP) have been identified as potential candidates for use as an aquafeed ingredient. In this study, the conventionally used seaweed feed ingredient Undaria pinnatifida was replaced by UA or SJBP at different levels of replacement. Specifically, a diet containing 30% U. pinnatifida meal (control diet, CON) was replaced with 25%, 50%, 75%, and 100% UA meal or SJBP meal, designated as UA25, UA50, UA75, UA100, SJBP25, SJBP50, SJBP75, and SJBP100, respectively. These diets were fed to the abalone for 6 wk under laboratory conditions. Weight growth rate and specific growth rate were affected by algal source and replacement levels, with values similar in CON, all UA-based diets, and SJBP-diets up to 75% replacement levels (P < 0.05). Likewise, shell morphometry (shell length, shell height, and shell width), and soft-tissue weight mirrored body growth parameters (P < 0.05). Feed efficiency ratio, protein efficiency ratio, and condition index were statistically similar in all dietary treatments, except SJBP100-fed abalone. Generally, moisture content was high in UA-based (except UA25) and CON diets, crude protein in SJBP-based diets (except SJBP25), UA75, UA25, and CON dietary groups (P < 0.05). Crude lipid was similar and statistically higher in SJBP25 and CON than other dietary treatments (P < 0.05). Ash content was high in SJBP-based diets, followed by UA-based diets and CON groups (P < 0.05). Overall, these findings illustrate that up to 100% replacement of U. pinnatifida by UA and 75% of SJBP are feasible in formulated feed without detrimental effect on the growth. Nevertheless, in-depth long-term investigation on the actual commercial nursery complex and grow-out culture is necessary to realize full-scale application in abalone aquaculture.