Proliferation of cyanobacteria is a global problem in eutrophic freshwater ecosystems, and the associated cyanotoxins are of growing concern with respect to human health and environmental problem. Most of the studies on microcystins (MCs) have only focused on terrestrial mammals, few have been conducted on the effects of MCs on fishes. Actually, many fishes are at the top of the trophic pyramids in aquatic ecosystems. MCs, which are the secondary metabolites of cyanobacteria, may accumulate in fish via feeding or bioaccumulation, and finally harm human health through the food chain. On the other hand, the harmful effects of MCs on fishes were mainly limited to acute toxic experiments based on oral gavaging,intraperitoneal injection, or administration via the dorsal aorta of the toxins, which can't reflect the uptake route under natural environments. In fish, cyanobacterial toxins may ingestion via different routes: direct feeding on toxic cyanobacterial cells, uptake of dissolved toxins via the gill epithelium, or exposure via the foodweb. More importantly, cyanobacteria are an important dietary component for many fishes. Therefore, cyanobacteria is a kind of nutrient. On the other hand, it also has potential poisonousness on fish. Fortunately, the nutri-toxicological effects of microcystins on fish have been recently drawn to scientists's much attention. In rencent years, mass cyanobacterial blooms occurred frequently in many freshwater lakes in China,e.g., Lake Dianechi, Lake Taihu, Lake Caohu. In the project of the control of cyanobacteria in Chinese lakes, gathering the cyanobacteria using machine has been used in a large scale. Thus, it's a big amount of biomass for the gathered cyanobacteria, and it's an important issue on the comprehensive utilization of the gathered cyanobacteria using machines. Protein is the most expensive component in fish feeds. Due to the scarcity and cost of fish meal in the world market, it is imperative to reduce feed cost by exploring cheaper alternative protein in aquaculture feeds. In addition, cyanobacteria have been reported to contain more than 50% crude protein. Based on cost effectiveness, availability, and crude protein content, cyanobacteria seem to have considerable potential in fish feeds. Considering their contributions to both the basic research and the practice, it is necessary to explore the nutri-toxicological effects of cyanobacteria on fish. In the context of researching alternative protein sources for aquatic animals, growth (weight gain or specific growth rate), feed utilization (feeding rate, feed conversion efficiency, apparent digestibility coefficients of dry, protein and energy), and nutrient retention (protein retention efficiency and energy retention efficiency) are the main parameters for evaluation. More importantly, dietary cyanobacteria may severely influence fish's health and food safety, which would emerge from toxicological indices, such as mortality, antioxidant responses, histological and cytopathology alterations, and accumulation of toxin in tissues. In the present paper, the nutri-toxicological effects of cyanobacterial meal or cyanobacterial cells on fish were summaried, and it focused on both nutrtional and toxicological effects of cyanobacteria via oral administration on fish. The present review will help to gain a new insight in the toxic effects of cyanobacteria on fish and provide new solutions for comprehensive utilization of the cyanobacteria.