Fabiola G. Arcos

Feasible predictive criteria for reproductive performance of white shrimp Litopenaeus vannamei: egg quality and female physiological condition

The present study analyzed the effects of consecutive spawnings on egg quality in a homogeneous domesticated population of Litopenaeus vannamei under optimal maturation conditions. A multidisciplinary approach was used to evaluate egg quality and female condition, using production, morphometric, biochemical, and histological criteria. For this purpose, 106 individually tagged females were stocked with males in maturation tanks, and productivity variables were recorded over 36 days. Biochemical composition of eggs, hemolymph, hepatopancreas, and ovaries was also analyzed. Results indicate that about half (48%) of females did not spawn, 18% spawned once, 15% spawned twice, 11% spawned three times, and 8% spawned four times or more. Variables associated with reproductive quality, such as number of eggs per spawn, fertilization rate, and egg diameter, were not affected by consecutive spawnings. Fourth-spawn eggs had significantly higher levels of total lipids, triacylglycerides, and total proteins than first-spawn eggs. First-spawn eggs from females that by the end of the production period had spawned four or more times had higher triacylglycerides and vitellin levels than first-spawn eggs from females that had three or less spawns. This indicates that triacylglycerides and vitellin could be used as predictors of female reproductive performance. Significantly higher condition index (weight to length ratio) was observed for females that spawned four or more times. No significant difference was observed in biochemical composition of hepatopancreas and ovaries as a function of the effect of number of spawns. This study indicates that egg quality and physiological condition of females were not affected by consecutive spawnings, and that females with multiple spawn capability are desirable for greater reproductive performance. Production variables and biochemical composition of first-spawn eggs and some morphometric characteristics of females may be used as indicators of multiple spawn capability.

Seasonal variations of biochemical, pigment, fatty acid, and sterol compositions in female Crassostrea corteziensis oysters in relation to the reproductive cycle.

Wild female Crassostrea corteziensis oyster (n=245) were analyzed over one year to understand the main ecophysiological events associated to gonad development. Different indicators (mainly biochemical) were analyzed to infer: i) utilization and accumulation of energy reserves (e.g. neutral lipids, carbohydrates, proteins; vitellogenin), ii) membrane components provided by the diet as essential nutrients and indicative of cell proliferation (e.g. highly unsaturated fatty acids linked to phospholipids, sterols), iii) indicators of food availability (chlorophyll a in water, pigments in tissues, specific fatty acids and sterols), iv) gonad development (e.g. gonad coverage area, vitellin). A PCA analysis was applied to 269 measured variables. The first PC (PC1) was composed of total carbohydrate and lipid concentration, percentage of esterified sterols, fatty acids specific of diatoms; 16:1n-7/16:0, 20:5n-3 in neutral lipids with positive loadings and non methylene-interrupted fatty acids (NMI) in neutral lipids with negative loadings. The second PC (PC2) was composed of 18:4n-3 in lipid reserves and the concentration of zeaxanthin, a pigment typical of cyanobacteria with positive loadings and the proportion of 20:4n-6 in polar lipids with negative loading. The third PC (PC3) was composed of gonad coverage area (GCA) and the concentration of vitellin. Variation in GCA confirms that gonad development began in April with an extended period of spawning and rematuration from April to November. The PCA further shows that a second period of minimal maturation from November to March corresponds to the accumulation of reserves (PC1) together with an initial high availability of food (PC2) at the beginning of this period. These two periods are in accordance with the classical periods of allocation of energy to reserves followed by gonad development reported for several mollusks.

Transcriptomic information from Pacific white shrimp (Litopenaeus vannamei) ovary and eyestalk, and expression patterns for genes putatively involved in the reproductive process

The increased use of massive sequencing technologies has enabled the identification of several genes known to be involved in different mechanisms associated with reproduction that so far have only been studied in vertebrates and other model invertebrate species. In order to further investigate the genes involved in Litopenaeus vannamei reproduction, cDNA and SSH libraries derived from female eyestalk and gonad were produced, allowing the identification of expressed sequences tags (ESTs) that potentially have a role in the regulation of gonadal maturation. In the present study, different transcripts involved in reproduction were identified and a number of them were characterized as full-length. These transcripts were evaluated in males and females in order to establish their tissue expression profiles during developmental stages (juvenile, subadult and adult), and in the case of females, their possible association with gonad maturation was assessed through expression analysis of vitellogenin. The results indicated that the expression of vitellogenin receptor (vtgr) and minichromosome maintenance (mcm) family members in the female gonad suggest an important role during previtellogenesis. Additionally, the expression profiles of genes such as famet, igfbp and gpcr in brain tissues suggest an interaction between the insulin/insulin-like growth factor signaling pathway (IIS) and methyl farnesoate (MF) biosynthesis for control of reproduction. Furthermore, the specific expression pattern of farnesoic acid O-methyltransferase suggests that final synthesis of MF is carried out in different target tissues, where it is regulated by esterase enzymes under a tissue-specific hormonal control. Finally, the presence of a vertebrate type steroid receptor in hepatopancreas and intestine besides being highly expressed in female gonads, suggest a role of that receptor during sexual maturation.