Effects of antimicrobial peptides (AMP) added to diets on aquatic animal health and body function are influenced by multiple factors such as animal species, initial body weight, the dosage of AMP and feeding duration. However, there is limited knowledge on the relationship between these factors and the body function of aquatic animals. Here, we aimed to perform multiple meta-analyses to investigate the effects of dietary AMP on growth performance (feed conversion ratio [FCR], specific growth rate [SGR]), enzyme activity (superoxide dismutase activity [SOD], lysozyme activity [LSA]), disease resistance (cumulative survival rate [CSR], the expression of immune-related genes [GENE]) and the abundance of gut microbiota (MICRO) from a pool of empirical studies. Additionally, the dose-effect model was applied to determine the optimal AMP dose, initial body weight and feeding duration to maximize body function. To conduct the meta-analyses, we included 34 publications that estimated 705 effect sizes across 21 fish, 2 shrimp and 2 shellfish species. The results confirmed that the inclusion of AMP in the diet can significantly improve SGR, SOD, LSA, CSR and GENE and decrease FCR for aquatic animals. Interestingly, our findings implied a slight positive effect of AMP on MICRO albeit with a limited number of studies available on fish gut microbial communities. Although no significant linear or quadratic relationship was predicted by meta-regression, the dose-effect indicated that the optimal AMP doses for FCR, SGR, SOD and LSA were 707.5, 750.0, 1,050.0 and 937.5mg/kg, respectively. Taken together, fish with an initial body weight of 30g could be fed with a dose of 600 to 800mg/kg for 2 mo when AMP-supplemented diets were applied in aquaculture, which can effectively improve body function and health while lowering aquafeed costs. In addition, more studies should address fish gut microbiota to delimitate the influence of dietary AMP on MICRO in the future.