DESARROLLO MORFOLÓGICO DE LAS ESTRUCTURAS INVOLUCRADAS EN LA PRIMERA ALIMENTACIÓN EXÓGENA Y EVALUACIÓN DE LA EFICIENCIA ALIMENTICIA DE LAS LARVAS DEL HUACHINANGO DEL PACÍFICO LUTJANUS PERU (NICHOLS & MURPHY, 1922)

Abstract

Pacific red snapper Lutjanus peru is considered a species of great commercial importance, which in recent years has been tried to bring into cultivation. Despite its importance is a species which at present little is known about its development. This work to describe the morphological development of the necessary structures to initiate exogenous feeding larvae of the Pacific red snapper during the initial development and to evaluate feed efficiency during the first days of exogenous feeding under culture conditions. The larvae were obtained after the induction of spawning of wild broodstock. The eggs were incubated in a conical tank with 100L capacity at 25-26.5 ° C. In the first part of this work we describe the development of the sense organs, mouthparts and digestive system. To describe the development of these structures was collected larvae at hatching and at 6, 12, 18, 24, 36, 48, 70 (first feeding) and 93 hours after hatching (hah). We sampled about 50 larvae for conventional histology (hematoxylin-eosin), 50 for electron microscopy (SEM) and 50 for transmission electron microscopy (TEM). To describe the mouthparts development we employed, the method proposed by Potthoff (1984) modified for larvae. The larvae hatch with a size of 2.45 mm (total length) and few structural developments, it mouth still closed. There is no pigment in the eyes, showing sensory structures are free neuromasts and inner ear. A few hours after hatching were observed lamellae of the olfactory plates. At the time of first feeding they have a size of 3.72 ± 0.19 mm and a width of mouth 0.22 ± 0.02 mm. Structures such as Meckels cartilage, square, hyoid, interhial and hyomandibular are present. The eye is differentiated and functional. It features simple and unique cone photoreceptor cells. The gastrointestinal tract presents a regionalization: oro-pharyngeal cavity, esophagus, foregut and hindgut. Both intestines have a columnar epithelium and folds in the mucosa with apical microvilli. The ultrastructural characteristics of enterocytes were similar at differentiated cells. The accessory glands have been differentiated. The pancreas is connected to the foregut through the pancreatic duct. Islets of Langerhans are differentiated and surrounded by exocrine pancreatic cells that synthesize zymogen granules denoting functionality. In the liver sinusoids and there are some bile canaliculli. The hepatocytes presented in supranuclear position, inclusions appear as glycogen reserve and lipoproteins. In the second part of this work, we realized 5 experiments in which we evaluated the feeding incidence (percentage of larvae with food in the digestive tract) and feeding intensity (number of prey per larva) at first feeding. These experiments were conducted in aquaria (10-L capacity). Were tested, Exp 1) the incubation temperature (26, 28 and 30 º C), Exp 2) light intensity (2000, 2500 and 3000 lux), type of prey (nauplii of copepods and a mix of copepod nauplii and rotifer neonates 1:1) and tank color (white and black), Exp 3) size of prey (46 ± 8μm, stage I-III and 72 ± 12μm, stage IV-VI) and density (5, 10 and 15 nauplii ml-1), Exp 4) water temperature (25 and 28 º C) and salinity (25, 30 and 35 gL-1), Exp 5) the microalgae concentration (0, 3x105 and 1x106 cells ml-1) and prey density (10 and 15 nauplii ml-1). Generally in all the experiments, no significant differences were observed in the feeding intensity for any factor (p> 0.05). No significant differences were found for feeding incidence (p> 0.05), in Exp 1 and 5. In Exp 2 significant differences were observed (p <0.05) for prey type and light intensity. Also showed a significant interaction (p <0.05). At 3000 lux, there was no significant difference between the type of prey while 2000 and 2500 lux, was significantly higher (p <0.05) with copepod nauplii. However, it is important to mention that with 3000 lux, there was no consumption of rotifers in the treatment of mixed diet. In Exp 3, the feeding incidence was higher with nauplii stage I-III at densities of 10 and 15 nauplii ml-1. In Exp 4, the water temperature was the only factor that showed significant differences (p <0.05) reaching a higher incidence feed the larvae fed at 25 °C. Finally we conclude that the larvae of Lutjanus peru can receive live feed from the 70 hde (day 3), when the mouth is open and articulate. The digestive tract is differentiated in the esophagus, foregut and hindgut. The eye is pigmented. Since higher feeding incidence was presented with copepod nauplii stage I-III, at light intensity of 3000 lux and water temperature of 25 ºC, we recommend using these conditions in the larval rearing of the Pacific red snapper.