22 SEPTEMBER 2023 • WORLD AQUACULTURE • WWW.WAS.ORG The barred sand bass Paralabrax nebulifer (Figure 1), is a commercially important marine species in Baja California Sur, Mexico, with annual harvests reaching around 7000 tons (INAPESCA 2021). In 2016, however, the captures declined due to by-catch impacts on the yellow turtle. In the Interdisciplinary Center of Marine Sciences (CICIMARIPN) in the city of La Paz, we attempted to establish guidelines for the conditioning and larviculture of this species, but first it was necessary to know some basic aspects of the fish. One important aspect related to the need to identify the different steps in the development of the larval digestive system and the times in which each occurs. Larval development is one of many critical phases in the culture of most species in aquaculture because many different transformations occur from embryo to juvenile, and this is the period in which, by far, the most deaths are registered. There is a high priority during this process to make adequate changes in food quality and size for the many transformations that occur during larval development, in order to meet nutritional requirements. The first step for solving this situation was to describe the ontogenetic changes in the digestive tract to help decide the optimal moments to administer the correct foods. The objective of the present study was to describe the changes in morphology of the digestive system of the barred sand bass from the beginning of exogenous feeding at 3 days after hatching (DAH) until 30 DAH following transformation to the juvenile phase. Our group, the Department of Technologies Development within CIMAR-IPN, works in the establishment of adequate food protocols for larval fish, in this case for barred sea bass. We used a spawn from brood stock maintained in captivity (Figure 2) and stocked 30 larvae/L in 300-L tanks. Larval development was monitored daily throughout the experiment (Figure 3). Samples were collected daily for 30 days and sent to a laboratory for histological analysis to describe the changes in the structure of the digestive system. We administered a particulate food from 3 DAH to 8 DAH as co-feed with live food (rotifers and artemia), and changed the size of the particulate successively with respect to the mouth size. At 26 DAH live food was replaced in totality with particulate food. At 1 DAH, embryos displayed a neural tube, notochord, liver and an incipient tube formed by a simple epithelial layer. At this stage of development, the embryos were feeding with enzymes that Structural Changes of the Digestive Tract of Barred Sand Bass Paralabrax nebulifer During the Larval Period O. Rosales-Navarro, M.O. Rosales-Velázquez and J.L. Ortiz-Galindo FIGURE 1. Barred sand bass, in captivity. Photo Martin Rosales, CICIMAR FIGURE 2. Closed spawning induction system by phothotermal control. Photo Martin Rosales, CICIMAR FIGURE 3. Closed system larval culture, checking water quality parameters. Photo Martin Rosales, CICIMAR
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