The supply of macroalgal feed materials for abalone aquaculture is threatened by increasing costs, limited availability, and the allocation of seaweed resources for other purposes. The use of biofouling Sargassum horneri (SH) as additional macroalgal biomass for abalone has been studied, albeit full inclusion is discouraged due to low utilization. This study applied heat treatment and fermentation to increase the nutritive value of SH meals for the aquaculture feed industry. Untreated (UN) as control, heat treated (HT, 121°C for 20 min), and fermented (FE, 10⁷ CFU/mL each of Bacillus sp. SJ-10 and Bacillus sp. KRF-7) SH meal was fed to the abalone (11.60 ± 0.02 g body weight and 42.98 ± 0.53 mm shell length) for 8-wk growth trial. The results showed that there is no apparent difference in the growth performance (body weight and shell length morphometrics) and survival of abalone given experimental diets (P > 0.05). The crude protein, lipid, and ash composition of edible abalone flesh were similarly unaffected (P > 0.05). The gut microbiota profile of abalone was analyzed through next-generation sequencing. The α-diversity indicators (microbial richness and abundance) were statistically similar (P > 0.05), and the β-diversity of operational taxonomic units revealed short distances within samples and clustering among diet groups. The core phyla (Fusobacteria, Proteobacteria, Tenericutes) and genera (Psychrilyobacter, Vibrio, Mycoplasma) known to inhabit the gut of abalone predominantly were likewise identified irrespective of diets; however, there is a difference in their relative abundance. Genus Psychrilyobacter was relatively abundant in UN and FE compared with HT, whereas Vibrio and Mycoplasma had higher abundance in FE and HT-fed abalone, respectively. Taste sensory attributes were discriminated in the abalone meat using an electronic tongue. Principal component analysis of sensor scores revealed several overlapping points, resulting in a negative discrimination index (–184), which means no apparent difference in the general taste profile was detected. Furthermore, the taste screening matrix through radar mapping revealed slight intensity differences in the umami, saltiness, and sourness flavor. Overall, the methods used for heat treatment and fermentation procedures herein were ineffective in improving the nutritive value of seaweed meal for abalone.