Elena Palacios

Shrimp larval quality in relation to broodstock condition

This review focuses on the different criteria currently used to assess offspring quality of penaeid shrimp and the factors that affect this characteristic. The term ‘larval quality’ generally refers to the physiological condition of the larvae and is related to survival and growth rates during several larval developmental stages. The criteria fit into five general categories, depending on the approach used: biochemical, morphological, behavioral, production and survival to stress tests. Several variables at the broodstock management level are known or suspected to affect larval quality. These include variables that can be more easily controlled by producers or researchers than others. Broodstock nutrition is probably the best reviewed aspect and is supported by many papers on the metabolism of several components during maturation, use of fresh vs. artificial food and specific requirements of particular components, such as lipids and vitamins. Endocrine control of reproduction has been widely studied in crustaceans. Eyestalk ablation still represents the most commonly used endocrine manipulation to induce maturation and spawning. Other alternatives are considered although few evaluate larval quality and none has been used in production. More recently, the use of captive broodstock and genetic improvement programs have gained importance. The effect of other biological characteristics of shrimp, such as age and size, season of the year when induced to intensive maturation conditions, time spent in maturation tanks and consecutive spawnings are also considered.

Tissue biochemical composition in relation to multiple spawning in wild and pond-reared Penaeus vannamei broodstock

The effect of the number of spawnings on several biochemical components of ovary, hepatopancreas, and haemolymph was investigated. Shrimps of two origins were compared; wild-caught and pond-reared spawners. Individually tagged females were sampled at the end of a production period in a commercial hatchery. Females with multiple spawnings had a higher gonadosomatic index (GSI), increased levels of protein in the ovary, and increased levels of acylglycerides (AG) and total protein in the hepatopancreas. Wild shrimps had a higher fecundity and higher levels of AG in hepatopancreas, and AG, cholesterol, protein, and glucose in haemolymph. Pond-reared shrimps had a higher hepatosomatic index than wild counterparts. The biochemical composition of the ovary reflected the typical nutrient accumulation associated with maturation. The capacity for multiple spawning could be related to metabolism of energetic lipids that are accumulated in the hepatopancreas, which in turn depends on size and origin of the broodstock. Females with multiple spawning capacity may be adequate for production purposes, although more research is needed to address the possibility of specific metabolic indicators of a multiple spawning capacity without a decline in spawn quality, and to define whether this is an inherited characteristic that can be selected in an improvement program.

Reproductive exhaustion in shrimp (Penaeus vannamei) reflected in larval biochemical composition, survival and growth

Penaeus vannamei larval quality in terms of biochemical composition and survival was studied throughout a spawning period. Spawns from broodstock at three different times during a commercial production period were sampled (15, 45, and 75 days after ablation). Biochemical composition of eggs, nauplii, 15-day old postlarvae (PL15), and growth and survival during culture were determined. As the days after ablation increased, a reproductive exhaustion of spawners was reflected in the energy reserves of the eggs produced. Overall larval performance during culture and survival was considerably higher in recently ablated spawners (15 days) and decreased in spawners 45 and 75 days after ablation. At PL15, a test for larval resistance to a salinity stress was applied that showed a decreased PL condition related to reproductive exhaustion of spawners: survival to stress decreased from 89% in recently ablated to 68% in larvae produced 45 days after ablation, and to 39% in larvae produced to the end of the spawning period. Nauplii condition index (NCI), calculated from nauplii triacylglycerol (TG) levels, percentage of viable nauplii, and nauplii length declined in nauplii produced with spawners sampled 45 and 75 days after ablation. This study demonstrated that reproductive exhaustion of shrimp spawners occurs and it becomes largely evident as time after ablation increases: spawner exhaustion is reflected in the quality of the larvae produced.

Growth and gametogenesis in the lion-paw scallop Nodipecten (Lyropecten) subnodosus

Abstract The lion-paw scallop ( Nodipecten subnodosus ) represents an important fishery resource along the Baja California Pacific coast in Mexico and has high potential for aquaculture. Although some previous studies have analyzed the growth rate of this species, knowledge of its reproduction is very limited, and no studies exist on the pattern of energy storage and utilization in relation to its reproductive cycle. Spat obtained in the laboratory from wild adults were cultured at Bahia Magdalena (Baja California Sur, Mexico). Growth and gametogenesis were analyzed over 18 months and biochemical composition of several tissues was analyzed during the last 6 months of culture. Growth rate, in terms of increase in shell height, averaged 0.22 mm/day. The weight of adductor muscle was 20 g after 12 months, and 55 g after 18 months of culture, respectively. Gonad maturity was observed mainly from July to September during the first year (1999) and started again in April in the second year (2000). Lipid and carbohydrate concentrations in female gonad increased with gonad development, but protein concentration remained unchanged. Adductor muscle index and carbohydrate concentration increased in parallel to gonad index during the second year (2000). However, a slight but significant decrease in adductor muscle proteins was observed as gonad developed. A continuous increase in digestive gland index concomitant to gonad development might indicate an increased availability of nutrients. From an aquaculture point of view, these results indicate that Bahia Magdalena is an adequate site for scallop growth and reproduction. From a physiological point of view, these results indicate that natural food availability could sustain the full cost of gametogenesis in this species in optimal environmental conditions, without or with minimal energy transfer from storage tissues.

Effects of Alexandrium minutum exposure upon physiological and hematological variables of diploid and triploid oysters, Crassostrea gigas.

The effects of an artificial bloom of the toxin-producing dinoflagellate, Alexandrium minutum, upon physiological parameters of the Pacific oyster, Crassostrea gigas, were assessed. Diploid and triploid oysters were exposed to cultured A. minutum and compared to control diploid and triploid oysters fed T. Isochrysis. Experiments were repeated twice, in April and mid-May 2007, to investigate effects of maturation stage on oyster responses to A. minutum exposure. Oyster maturation stage, Paralytic Shellfish Toxin (PST) accumulation, as well as several digestive gland and hematological variables, were assessed at the ends of the exposures. In both experiments, triploid oysters accumulated more PSTs (approximately twice) than diploid oysters. Significant differences, in terms of phenoloxidase activity (PO) and reactive oxygen species (ROS) production of hemocytes, were observed between A. minutum-exposed and non-exposed oysters. PO in hemocytes was lower in oysters exposed to A. minutum than in control oysters in an early maturation stage (diploids and triploids in April experiment and triploids in May experiment), but this contrast was reversed in ripe oysters (diploids in May experiment). In the April experiment, granulocytes of oysters exposed to A. minutum produced more ROS than those of control oysters; however, in the May experiment, ROS production of granulocytes was lower in A. minutum-exposed oysters. Moreover, significant decreases in free fatty acid, monoacylglycerol, and diacylglycerol contents in digestive glands of oysters exposed to A. minutum were observed. Concurrently, the ratio of reserve lipids (triacylglycerol, ether glycerides and sterol esters) to structural lipids (sterols) decreased upon A. minutum exposure in both experiments. Also, several physiological responses to A. minutum exposure appeared to be modulated by maturation stage as well as ploidy of the oysters.

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.

Comparison of ovary histology between different-sized wild and pond-reared shrimp Litopenaeus vannamei (=Penaeus vannamei)

Summary Ovarian maturation of pond-reared and wild Litopenaeus vannamei (= Penaeus vannamei) broodstock was compared by analyzing morpho-histological characteristics. The number of spawns by each female was also considered to determine if successive rematurations can affect ovarian development. Individually tagged 42 wild and 47 pond-reared females were sampled at the end of a production period in a commercial hatchery. Morphological variables were recorded and ovaries were histologically evaluated for oocyte type and diameter. Although wild shrimp were bigger than pond-reared, no differences were seen in gonadosomatic indexes, either considered as a group or within stages of maturation. Differences between pond-reared and wild shrimp were observed in previtellogenic and early-vitellogenic oocyte distribution in vitellogenic and cortical stages. However, no differences were obtained in relation to the proportion of late vitellogenic oocytes and mature oocytes with cortical rods, or oocyte diameter in each...

Relation between lipid and fatty acid composition of eggs and larval survival in white pacific shrimp (Penaeus vannamei, Boone, 1931)

In this study, lipid classes and fatty acid composition were determinedin eggs of P. vannamei as a function of survival to zoeaIII stage. Spawns were reared individually to zoea III and grouped, accordingtotheir final survival to this larval stage, into spawns of high and lowsurvival.Eggs of individual spawns were analyzed for lipid and fatty acid composition ofneutral and polar lipids and the results were then grouped according tosurvivalto zoea III. The lipids within each group (high and low survival to zoea III)were pooled for the separation of phospholipids and the analysis of their fattyacid composition.Higher levels of triglycerides, carotenoids, and linoleic (18:2n-6) acid ineggs were associated with improved survival to zoea III. Linoleic acid washigher in spawns from the high survival group in both neutral and polarfractions and in most of the phospholipid classes analyzed. Docosahexanoic acid(DHA) was not related to survival to zoea, probably because its content washighenough (> 15% of total fatty acids) to satisfy embryo and early larvaldevelopment needs. A high content of eicosapentaenoic acid (EPA) was found inphosphatidylethanolamine, lysophosphatidylethanolamine, phosphatidylserine, andphosphatidylinositol compared to other phospholipid classes, suggesting aspecific role of EPA in these lipids. These results describe the specificphospholipid composition of penaeid eggs and could (potentially) be used aspredictive indicators of larval quality for research and production purposes.

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.

Heavy metals in the clam Megapitaria squalida collected from wild and phosphorite mine-impacted sites in Baja California, Mexico: considerations for human health effects.

The “chocolate clam” Megapitaria squalida, is widely consumed by the population of several localities along the Pacific coast. Clams collected from seven stations in Bahía de la Paz, a bay within the Gulf of California, before and after the summer rainy season were analyzed for Pb, Ni, Cd, Mn, Zn, Cu, and Fe. The location of the sampling sites significantly affected the concentration of metals in clam tissues, but not in relation to the proximity to alleged contaminated sites. Clams from a site close to a phosphate mine had the highest levels of Pb, but only in April, and the highest concentrations of Cd were recorded in clams collected in areas with no anthropogenic activities. Clams from sites considered clean had higher levels of Cd, Fe, Zn, and Mn. The mean concentrations (μg/g dry weight) ranged from 0.1 to 7.8 for Pb, from 1.9 to 8.8 for Ni, from 1.5 to 11.1 for Cd, from 2.5 to 14.1 for Mn, from 47.2 to 64.6 for Zn, from 5.4 to 18.7 for Cu, and from 154 to 558 for Fe. Collecting clams in sites apparently pristine is no guarantee that metals will be in low concentrations.