, with several varieties, is one of numerous species of unicellular free-swimming marine green algae that are widely used for intensive rearing of a variety of marine animal larvae. is a dinoflagellate capable of producing powerful biotoxins and it is commonly found in shrimp ponds. Chief physical and chemical concerns of the commercial growing environment of microalgae are pH and the nitrogen-phosphorus (N/P) ratio. To identify the optimum growth conditions of Prorocentrum minimum in shrimp ponds, we tested for interspecies competition at various nutrient concentrations after determining the optimum pH for each species. Prior to the start of each test, cultures were maintained for an adaption period of approximately 5 generations. Thereafter, the experiments were conducted in batch cultures and continued up to 10 days, and the microorganisms were grown until either late exponential phase or early stationary phase. The pH levels and N/P ratios chosen took into account the common environmental conditions found in shrimp ponds. With this in mind, a culture experiment was first carried out using four different pH levels (7.5, 8.0, 8.5 and 9.0) and a constant N/P ratio of 24, so as to determine the optimum growth rate for . After deciding the best pH conditions, the N/P ratio was selected considering the concentrations of DIN and DIP found in shrimp ponds. The next test thus used four different N/P ratios: 3:2, 6:1, 24:1 and 96:1. The results showed that the maximum carrying capacity ( was lower than that in the environments of individual cultivation. This finding indicated that the inhibition parameter of interspecies competition between these two algae could be significantly influenced by pH conditions. The maximum rate of competition inhibition of occurred at pH 8.5, with an inhibition parameter value of 5.7447, and the value of inhibition of was 3.4886, also at pH 8.5. Therefore, the nutrient limitation study was set at a constant pH of 8.5 against the four N/P ratios. The results of that experiment showed that the inhibition parameter of interspecies competition could also be significantly influenced by N/P ratio. Maximum inhibition of occurred at the N/P ratio 96:1, with an inhibition value of 9.2063, whereas the inhibition value for was 3.4886; hence, the inhibition effect of was stronger than that of . Thus, we propose that the optimum growth conditions of can be achieved at pH 8.5 and N/P ratio 96:1. In shrimp culture, the pH level and N/P ratio of the culture water can be accordingly adjusted to control algal growth; this approach can be applied for the purposes of controlling the production process, to assist with accurate water technology research, or to control eutrophication the culture water.