Humans possess self-awareness, enabling them to recognize that their reflection contingently moves with themselves, identify their face in a mirror by recalling their facial image, and use mirrors to check their appearance when necessary. These abilities correspond sequentially to public self-awareness (PuSA), private self-awareness (PrSA), and meta self-awareness (MSA), with the latter being considered more advanced. Animals capable of mirror self-recognition (MSR)—the ability to recognize one’s reflection as oneself—are thought to exhibit PuSA. However, it remains unclear whether they also possess more sophisticated forms of self-awareness. Cleaner fish (Labroides dimidiatus) are promising candidates for investigating PrSA and MSA, as previous studies suggest they exhibit PuSA and provide initial evidence of PrSA. Here, we demonstrate PrSA and MSA in cleaner fish. To evaluate PrSA, we tested whether they could recall their body size based on a mental image of their body. The mirror-naïve fish behaved aggressively when presented with photographs of two unfamiliar conspecifics that were either 10% larger or 10% smaller than themselves. However, after attaining MSR, they refrained from aggression toward a larger photograph while continuing to react aggressively toward a smaller one—without re-examining their reflections. These findings suggest that cleaner fish accurately recognize their body size based on mental images of their bodies formed through MSR. Additionally, mirror-experienced fish frequently revisited a mirror when presented with a larger photograph. This behavior suggests that they may intentionally use mirrors to reassess their body size, further supporting the presence of PrSA. Building upon these findings, we investigated MSA by examining whether cleaner fish can adjust their body size assessments based on memory confidence. Over time, the memory of their body size is expected to fade in the absence of a mirror. When presented with a larger photograph after a period without mirror access, they revisited the mirror more frequently, suggesting they reassessed their body size. In contrast, when presented with a smaller photograph, they did not revisit the mirror frequently, regardless of the mirror absence. These results suggest that cleaner fish adjust their behavior based on their confidence in their memory, suggesting MSA. Our findings suggest that cleaner fish are the first non-human animals to exhibit all types of self-awareness, including PrSA and MSA. These results may challenge the conventional view that animal behavior is primarily driven by instinct and simple learning mechanisms, instead supporting the idea that many vertebrates act with an awareness of their intentions.