The purpose of this study was to determine the effect of different feeds such as Porphyra, Laminaria japonica, Compound feed, and Gracilaria on the activities of alginate lyase, cellulase, and amylase in the digestive juice of H. diversicolor and to take their genes as candidate genes related to the growth traits of H. diversicolor. In order to provide data for selective breeding, SNPs that were significantly associated with growth traits were screened through gene cloning, high-throughput sequencing, and association analysis. It was found that there were no significant differences in the activities of alginate lyase and cellulase in H. diversicolor among different feeds, but there were significant differences between males and females in the group; beta-amylase activity is higher than alpha-amylase activity; the DNA, full-length cDNA, and upstream sequences of genes of alginate lyase, cellulase, and amylase were cloned, and we found that the expressions of three genes are similar; they have started expression in the early prostrate stage of larvae, have tissue specificity in adults, and are highly expressed in hepatopancreas; 84 SNPs were found in alginate lyase through high-throughput sequencing, and 2 which had significant differences were left after associating with growth traits, and they are ALG1016 and ALG1544.