RESUMEN

The study of digestive physiology is an important issue in species that have been introduced in aquaculture like the spotted rose snapper (Lutjanus guttatus). The aims of this study were to describe the expression of digestive enzymes (trypsinogen, chymotrypsinogen, α-amylase, lipoprotein lipase, phospholipase A and pepsinogen) and their relation with orexigenic (neuropeptide Y, NPY) and anorexigenic (cholecystokinin, CCK) factors during the larval development and to evaluate the effect of weaning in their expression. The results showed that the transcripts of all the assayed digestive enzymes, with the exception of pepsinogen, and NPY and CCK were already present in L. guttatus from the hatching stage. The expression of all the enzymes was low during the yolk-sac stage (0-2 days after hatching, DAH), whereas after the onset of exogenous feeding at 2 DAH, their expression increased and fluctuated throughout larval development, which followed a similar pattern as in other marine fish species and reflected changes in different types of food items and the progressive maturation of the digestive system. On the other hand, weaning of L. guttatus larvae from live prey onto a microdiet between 25 and 35 DAH significantly affected the relative expression of most pancreatic digestive enzymes during the first weaning days, whereas chymotrypsinogen 2 and lipoprotein lipase remained stable during this period. At the end of co-feeding, larvae showed similar levels of gene expression regardless of the diet (live prey vs. microdiet), which indicated that larvae of L. guttatus were able to adapt their digestive capacities to the microdiet. In contrast, feeding L. guttatus larvae with live feed or microdiet did not affect the expression of CCK and NPY. The relevance of these findings with regard to current larval rearing procedures of L. guttatus is discussed.

Asunto(s)

Digestión/genética , Perciformes/genética , Animales , Colecistoquinina/genética , Quimotripsinógeno/genética , Femenino , Expresión Génica , Larva/genética , Larva/crecimiento & desarrollo , Lipoproteína Lipasa/genética , Masculino , Neuropéptido Y/genética , Pepsinógeno A/genética , Perciformes/crecimiento & desarrollo , Perciformes/metabolismo , Fosfolipasas A2/genética , ARN Mensajero/metabolismo , Tripsinógeno/genética , alfa-Amilasas/genética

RESUMEN

Most pennate diatoms are allogamous, and various types of mating systems have been described. In Pseudo-nitzschia, reproductive stages have been identified in some species, and it is generally accepted that the genus is mainly heterothallic. Here we report homothallic auxosporulation of Pseudo-nitzschia brasiliana Lundholm, Hasle et G. A. Fryxell. To our knowledge, this is the first verified description of homothallic sexual reproduction in the genus. Auxospore formation was observed in all 16 subclones derived from three initial clonal cultures of P. brasiliana. Pairing was followed by production of two gametes per gametangium, which fused to give two zygotes. Each zygote (early auxospore) was initially spherical and adhered to one girdle band of the parental frustule. The two auxospores tended to expand parallel to each other and perpendicular to the parental frustule. Elongation was synchronous, slightly asynchronous, or totally asynchronous. The entire process of sexual reproduction, from gamete formation to the appearance of the initial vegetative cells, took 2-4 d. The occurrence of sex in a homothallic species seems an advantageous life strategy for this species in that any encounter between cells of the right size class is potentially sexual.