What is the fine-grained topic of the following text: One hundred sixty eight Convict Cichlids (mean weight: 2.1 ± 0.12 g and mean length: 2.2 ± 0.05 cm) were fed by commercial diets with different concentrations of S. cerevisiae (0, 0.5%, 1%, 2%). Only return the topic.
Effects of different concentrations of S. cerevisiae on the diet of Convict Cichlids.