Leticia Arena

Effect of a size-based selection program on blood metabolites and immune response of Litopenaeus vannamei juveniles fed different dietary carbohydrate levels

Blood metabolites in wild and seventh-generation cultivated shrimp were measured to determine how size-based selection could alter the nutritional and immunological conditions of Litopenaeus vannamei. Wild L. vannamei juveniles and a sample of seventh-generation cultured shrimp were acclimated under identical conditions. During 55 days, shrimp were fed a high (HCHO: 44%) or a low (LCHO: 3%) carbohydrate diet for 55 days. Wild shrimp showed a direct relation between dietary CHO and lactate, protein and hemocyte levels indicating that dietary CHO was used for protein synthesis via transamination pathways. In seventh-generation cultured shrimp these parameters were inversely proportional to dietary CHO level, indicating the capacity to synthesize protein from dietary CHO was repressed in cultured shrimp. Farmed shrimp showed a limited capacity to respond to LCHO diets demonstrating high protein dependence in their metabolism and immune response. These results demonstrate that during size-based breeding programs other metabolic process than CHO catabolism can be selected. The incapacity of shrimp to use dietary CHO could limit protein reduction of diets and limit the efforts of the shrimp industry to be ecologically and environmentally profitable.

Characterization and Tissue-Specific Expression of the Two Glutamate Dehydrogenase Cdnas in Pacific White Shrimp, Litopenaeus vannamei

Abstract Two glutamate dehydrogenase (GDH) cDNA sequences encoding 474 (GDH A, a truncated gene) and 552 amino acids (GDH B) were discovered in the Pacific white shrimp, Litopenaeus vannamei. Both GDH A and GDH B were fairly conserved as shown by the amino acid alignment. The two cDNAs differed only at the C-terminal sequences. The quantitative real time polymerase chain reaction (qPCR) assay was developed to estimate the specific expression on different tissues. Both GDH A and B were mainly expressed in shrimp muscle, followed by in the gill and epithelium, while the expression in shrimp hepatopancreas was the lowest when compared with other tissues. Though no significant difference was observed among all the test tissues, the ratio of GDH B to GDH A transcription was kept at a very high level ranging from 32.04 in the eyestalk to 64.52 in the muscle, indicating that GDH B was largely expressed in L.vannamei. The GDH activity in the muscle of L.vannamei was also the highest followed by in the epithelium, eyestalk and gill. The GDH activity in hepatopancreas was significantly lower than that in other tissues. As a control, the tissue expression of Na+-K+ ATPase was also determined. This enzyme was mainly expressed in the gill, followed by in the muscle and epithelium. Our results provide baseline data in physiological expressions of GDH and Na+-K+ ATPase for osmoregulation in L.vannamei. The research protocol offers a practical guideline for the analysis of gene expression in shrimp. The sequences and techniques developed in this study will also contribute to the GDH gene research in other crustacean species.

Seasonal Variability in Trypsin and α-Amylase Activities Caused by the Molting Cycle and Feeding Habits of Juvenile Pink Shrimp Farfantepenaeus duorarum (Burkenroad, 1939)

ABSTRACT In view of the relationship between shifts in diet composition and the activity of digestive enzymes in penaeid shrimp, the present study focused on the analysis of digestive trypsin and &agr;-amylase activities of wild Farfantepenaeus duorarum (Burkenroad, 1939) juveniles and their changes in phenotypic expression, during the molt cycle as endogenous factor and their changes due to different feeding regimes (exogenous factor) in relation with &dgr;13C and &dgr;15N isotopic signature as an index of food assimilation induced by the seasonal availability of food items in the nursery area. Wild juveniles of F. duorarum were captured from April 2007 to February 2008, in the Celestun coastal lagoon, Yucatan, Mexico. Samplings were carried out considering all quarters of the lunar cycle and in each of the recognized seasons for this region: dry, rainy, and the Nortes (North Wind). Copepods and amphipods were the main source of food for juveniles of F. duorarum. Values of &dgr;13C in the muscular tissue were near -20‰ hence the feeding regime of F. duorarum in the lagoon was composed by material of marine origin. Isotopic signature differences were found between the three annual seasons. It is an opportunist generalist organism that is located in the 4th trophic level. The digestive enzymatic activities of both trypsin and &agr;-amylase in fresh hepatopancreas tissue showed an interaction between season and molt stages (p < 0.05). Activity of the trypsin was highest during the Nortes at molt stage C (140 mU mg-1 HP) and activity of &agr;-amylase was higher in the Nortes at stage B2 (674 mU mg-1 HP). The amylase/trypsin ratio also showed significant interaction between season and molt stages (p < 0.05), with higher values in premolt stages during the rainy and Nortes seasons. Isoforms of these digestive enzymes differed in expression according to the molt stage and also to the season with expression generally being greater at stage C.

Characterization of microsatellite loci developed for the Mexican four-eyed octopus Octopus maya

Ten polymorphic microsatellite DNA loci were isolated from Mexican four-eyed octopus Octopus maya, by construction of an enriched genomic library. Genotyping of 35 individuals from Sabancuy Campeche, México, revealed variable levels of locus polymorphism with an average of 9.2 alleles. The observed and expected heterozygosity per locus ranged from 0.53 to 0.93 and from 0.48 to 0.87, respectively. No evidence of linkage disequilibrium was detected between pairs of loci and genotype proportions at all loci conformed to Hardy–Weinberg equilibrium expectations. The microsatellite loci developed constitute a suite of genetic markers applicable to sustainable fishery management for O. maya.