Estudos da ontogenia e da alimentação inicial de larvas de peixes, com ênfase em dourado Salminus brasiliensis (Characiformes, Characidae)

Abstract

Samples were carried out on embryos and larvae of dourado Salminus brasiliensis from 6 hours after fertilization (haf) until the 17th day after fertilization (daf) in order to study the development of sensory system, by scanning electron microscopy, and on the structural and functional development of digestive tract by histological and histochemical analysis. From the sensory system were studied: the development of the eyes, the olfactory organ, the cephalic mechanoreceptors and the lateral line mechanoreceptors and chemoreceptors (taste buds). It was observed that the eyes and the nostrils develop very early (from 18 haf), followed by the cephalic mechanoreceptors and by the mechanoreceptors of the principal and secondary lateral line (48 haf). These types of senses are probably the most used for feeding during this initial phase. The taste buds showed a later development compared to the other sensorial structures cited, and were first observed sparsely distributed along the bucopharynx at 8 daf. The morphological development of the digestive system was described based on histological slides and its functionality was analyzed by histochemical staining. At 18 haf, the gut was observed dorsally to the yolk-sac. At this phase were also observed a group of cells that would form the liver and the pancreas. At 24 haf were verified the formation of oesophagus and the future orobranchial, which were characterized as mouth and pharynx at 48 haf. The oesophagus and the oesophagic sphincter were also defined and the gut remains as a straight tube at 48 haf. The rectum, ileo-rectal valve and anus were already present, as well as the liver and pancreas were differentiated, characterized by the hepatic cells and pancreatic acini, respectively. Teeth were observed at 72 haf, and folds were seen in the rectum epithelium. Between 96 and 120 haf the liver and pancreas showed complete development. In the same time, folds appeared and increased in number on the mucosal wall of the entire intestine. From the 8º daf, the digestive system was completely developed, possibly able to absorb the nutrients of a formulated diet. Experiments were also conducted in order to evaluate different feeds for weaning the dourado larvae from live feed onto inert diet, aiming at to reduce the costs during the larviculture. The treatment using piau Leporinus obtusidens as prey promoted the higher survival rates compared to the others. Bovine s heart and frozen artemia biomass induced to the worst performances in both co-feeding regime and in abrupt regime. Artemia used as live feed in both XIII regimes, and even inert diet offered directly, produced very low survival results along 17 days of trial, but at in a short term, could allow some growth. Therefore, an ideal diet was not identified to dourado, specially concerning to inert diet amount offered that avoid high concentrations of ammonium as the same time that reaches the nutritional requirements, being also attracting to these fish during the larviculture phase. A last experiment of this thesis is related to techniques for radioactive labeling of food with C14, used for monitoring the effects of early introduction of inert diet in lipid digestibility and metabolism of sole Solea senegalensis. Larval feed intake, growth and survival were also monitored in larva reared on a standard live feed regime (ST) and co-feeding regime with inert diet (Art R). Trials using sole larvae fed with Artemia enriched with two different lipid emulsions, containing glycerol tri [1-14C] oleate (TAG) and L-3-phosphatidylcholine-1,2-di-[1-14C] oleoyl (PL), were performed at 9 and 17 days after hatching (DAH) to study lipid utilization. Co-feeding did not affect sole survival rates (ST 59.1±15.9%; Art R 69.56±9.3%), but was reflected in significantly smaller final weight at 16 DAH (ST 0.71±0.20; Art R 0.48± 0.14 mg). Higher feed intake was observed in sole larvae fed on Artemia enriched with labeled PL at 9 DAH but not at 17 DAH. At 17 DAH, the smaller larvae (Art R treatment) ingested proportionally more Artemia in weight percentage, independently of enrichment. At 9 DAH lipid digestibility was equal among treatments and higher than 90%, while at 17 DAH it was higher in ST treatment (around 73%) compared to the Art R group (around 66%). Lipid retention efficiency at 9 DAH was higher in the Art R treatment, reaching values of 50%, while these values almost duplicated at 17 DAH, ranging up to 80% in both treatments without significant differences. These results show that co-feeding of live feed and inert diet from first-feeding in Senegalese sole has a toll in terms of growth and lipid digestibility but does not seem to compromise lipid metabolic utilization.