Japanese anchovy Engraulis japonicus and ayu Plecoglossus altivelis altivelis larvae have transparent and elongated body, called shirasu type larvae, and often live in turbid estuarine waters. Our previous study revealed that turbidity improves their avoidance from visual predators. Schooling is an important anti-predator behavior for fishes; therefore we evaluated the effects of turbidity on school formation in shirasu larvae and compared them to that in yellowtail Seriola quinqueradiata juveniles. Fish were introduced into 30-L tanks at one of five turbidity levels obtained by dissolving 0, 5, 20, 50, or 300 ppm of kaolin into the seawater. After fish were acclimated to each turbidity level, their behavior was video recorded from above, and nearest neighbor distance (NND) and separation angle (SA) were compared among turbidity levels. Mean SA of anchovy larvae was significantly smaller at 50 ppm. Mean NND of ayu larvae was significantly smaller at 20 and 50 ppm, as was mean SA at 20 ppm. Mean NND of yellowtail juvenile was significantly larger at 300 ppm. These results suggest that moderate turbidities induce schooling behavior in shirasu type larvae, whereas turbidity has an inhibitive effect on the school of non-shirasu fish such as yellowtail juveniles. Anti-predator strategy utilizing turbidity would thus be particularly effective in shirasu larvae.