DEVELOPMENT OF THE DIGESTIVE TRACT OF PACIFIC RED SNAPPER Lutjanus peru LARVAE UNDER CULTURE CONDITIONS

Understanding the development of the digestive tract is important in terms of evaluating the nutritional physiology of fish larvae. This knowledge, combined with enzymological and molecular studies, can provide a better understanding of the larval digestive process, feeding efficiency, and functional capabilities; this information will be essential in implementing new feeding schedules or introducing new prey types during larval rearing. Such data may also be used to propose indicators of larval nutritional condition under different feeding protocols and rearing conditions.

The Pacific red snapper (Lutjanus peru) (Nichols & Murphy, 1922) is an important species to the fisheries along the Pacific coast of Mexico. In recent years there has been an increasing interest from both the private and public sectors in developing a sustainable culture program for this species as a viable economic alternative in the region. Larviculture trials of Pacific red snapper have been characterized by very low survival at first feeding. Therefore, several aspects related to feeding and early development have been studied in our laboratory. The objective of this study was to describe the development of the digestive tract and accessory glands of Pacific red snapper larvae in order to better understand their development and provide valuable information for future studies on larval rearing and feeding practices.

Histological sections of larvae sampled at hatching and at 1, 2, 3, 4, 6, 8, 10, 15, 17, 20, 23, 25, and 30 days post hatch (DPH) were cut and dyed using the hematoxylin-eosin technique. The development of the digestive tract of Pacific red snapper larvae follows a general pattern of differentiation that can be divided into three stages, each with distinct implications for the early life stages; this information will be useful for the larviculture of this species, particularly for developing feeding practices and selecting prey. Stage I lasted from 1-3 days post hatching (DPH) and included the endogenous nutrition period; it was characterized by the initial differentiation of the digestive tract in preparation for the onset of exogenous feeding (3 DPH). At this time, the digestive tract was differentiated into buccopharynx, esophagus, stomach anlage, anterior intestine, posterior intestine, and a short rectum. The liver, pancreas, and kidney were also present. The mouth and anus were open. Stage II occurred after first feeding, lasted for 16 days (4-23 DPH), and included both preflexion and flexion larvae. The main changes that occurred during this stage reflected the adaptation to exogenous feeding and the concomitant growth. Stage III (24-30 DPH) included postflexion larvae and the final changes in the larval digestive tract were the appearance of the gastric glands and pyloric caeca. The presence of the gastric glands at 23 DPH suggests that early weaning during culture trials may be possible at this early age.