The x-ray tetra (Pristella maxillaris) is a n ornamental characid native to the Amazon River Basin. This species is highly desirable due to its unique transparent body and peaceful temperament in an aquarium setting. Although P. maxillaris has been successfully bred in captivity , peer-reviewed information on larval development, digestive physiology, and nutrition is scarce . This information would help improve the larval culture protocols of P. maxillaris by allowing for the transition of larvae from expensive live feeds to a cost-effective microdiet (MD) as early as possible while maintaining high growth and survival. To gain insight into the larval development of P. maxillaris , the digestive enzyme ontogeny and digestive tract morphology was examined at 20 timepoints throughout a 35-day trial . Pepsin, trypsin, and lipase activities were quantified using standard microplate assays and the morphology of the digestive tract was visualized using histology. The presence of a functional stomach was found at 22 DPH (days post hatch) indicated by the presence of gastric glands and pepsin activity. A 45-day dietetics trial was conducted to determine which of three commercially available MDs best promotes growth and survival in larval P. maxillaris compared to an Artemia reference diet . Survival was greatest for larvae fed Artemia compared to those fed MDs and standard length (SL) did not significantly differ among treatments (Fig. 1A) . Lastly, a 35-day trial was conducted to identify the appropriate timing for weaning P. maxillaris larvae from Artemia to a MD. Larvae were subjected to one of five treatments: Artemia reference diet, exclusively MD , or MD introduction at 12 (W1), 18 (W2), or 24 (W3) DPH. Survival was greatest for larvae fed Artemia compared to groups weaned onto MDs and SL did not differ significantly between the Artemia treatment and the W2 and W3 treatments (Fig. 1B). The long-term effects of MD feeding will be examined to determine the economic benefits resulting from replacing Artemia in the larval production process to market size .