Ana M. Ibarra

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.

Realized heritabilities and genetic correlation after dual selection for total weight and shell width in catarina scallop (Argopecten ventricosus)

Abstract A one-generation selection for total weight and shell width at age 1 year in catarina scallop, Argopecten ventricosus , was done on two lines to estimate direct and correlated responses to selection, realized heritabilities, and the realized genetic correlation between these two traits. For both lines, two experiments were done to estimate response, one after inducing spawning of field-conditioned scallops, and the second after conditioning the same individuals from the first experiment for spawning in the laboratory. Responses to selection were significant for both direct traits. A significantly higher correlated response of shell width when selection was on total weight was seen, whereas the correlated response for total weight when selection was on shell width was small or zero. Realized heritability of total weight was higher (0.33±0.08 to 0.59±0.13) than that of shell width (0.10±0.07 to 0.18±0.08) regardless of the experiment. Estimates of the genetic correlation between the two traits varied widely between experiments (1.25±−0.22 in experiment 1 and 0.33±0.31 in experiment 2). Regardless of this, we concluded there must be a high genetic correlation between these two traits, evidenced by the high correlated response of shell width when selecting on total weight. Correlated responses larger than direct responses as those seen for shell width result because the accuracy of selection for total weight to indirectly improve shell width ( r a h TW ) is larger than the accuracy of direct selection for shell width ( h SW ).

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.

Triploid catarina scallop ( Argopecten ventricosus Sowerby II, 1842) : growth, gametogenesis, and suppression of functional hermaphroditism

Abstract Triploidy was induced in catarina scallop, Argopecten ventricosus, using two concentrations of cytochalasin-B (CB). Growth of triploid scallops exceeded that of diploids in all evaluated traits. The largest percent difference between the diploid control group and the treated groups was seen after diploid scallops reached the peak of sexual maturation and began spawning. The gonad of triploid scallops was easily recognizable by visual inspection because of a brownish discoloration and lack or few egg masses present. That characteristic allowed for the separation of ‘putative triploids’ (PTs), which when compared with diploid scallops from within the same treatment (treated diploids), had a significantly larger muscle weight than the differences seen between treated and control groups. Gametogenesis and the condition of hermaphroditism in this normally functional hermaphrodite were greatly affected by the triploid condition. In the female portion of the gonad, few oocytes developed. The male portion of the gonad was arrested early during development, and the male acini were replaced by female acini, producing all female gonads in increasing percentages during the culture period, suppressing the normal condition of hermaphroditism. Oocytes of diploids were larger than those of triploids early in the culture, probably because of delayed maturation in triploids. Later during the culture, oocytes of triploids were larger than those of diploids only when compared with treated diploids.

Effects of inbreeding on growth and survival of self-fertilized catarina scallop larvae, Argopecten circularis

Abstract Artificial production of the catarina scallop in controlled conditions is a recent event. Contrary to most other mollusks artificially produced, this scallop is a functional hermaphrodite. This reproductive strategy and the mass spawning methodology commonly used for mollusks results in some selffertilized larvae that can have an effect on the production systems due to deleterious effects of inbreeding. To determine the magnitude of these effects, three experimental groups were produced: self-fertilized, pair-mated, and mass-spawned. Larvae produced from exclusive self-fertilization and grown over a period of 18 days are smaller (112.03 μm) and have lower survival (31.27%) than larvae produced from either pair-matings (120.76 μm; 53.52%) or mass-spawning (118.31 μm; 55.76%), which were not different from each other. At the end of the rearing period, 18-day-old larvae with an inbreeding coefficient of F = 0.5 showed a depression for length of 12.4% and 11.2%, and a depression for survival of 43.9% and 41.6%, in relation to mass-spawned and pair-mated groups, respectively. Lack of significant differences among the mass-spawned and pair-mated groups, as well as the cumulative distributions, indicated that self-fertilized larvae did occur among the pair-mated group probably as a consequence of the intermixed release of gametes even after the exchange of individuals between the two tanks used for each of the pair-matings. Additionally to the increase in average inbreeding coefficient due to the presence of some amount of self-fertilized larvae during mass spawning, a high variability of family size seen within the pair-mated and selfed groups is expected to contribute significantly to the total accumulated inbreeding on the medium and long run of a production system. Further loss of genetic variability is expected as a consequence of early culling of small larvae, presumably because they are self-fertilized, although we have found that self-fertilized larvae were not differentiated in mean length from pair-mated larvae until they were 11 days of age.

Biochemical composition of gonad and muscle in the catarina scallop, Argopecten ventricosus, after reproductive conditioning under two feeding systems

Abstract Favorable nutrition of scallops during reproductive conditioning in hatcheries can be related not only to qualitative and quantitative aspects of diets, but also to the way in which food is supplied. The aim of the present study was to investigate whether continuous rather than discontinuous feeding could improve reproductive performance of Argopecten ventricosus . For this purpose, the influence of two feeding systems (continuous and discontinuous) on gonadosomatic and condition index, and biochemical composition were analyzed in two experiments. In Experiment 1, scallops were induced to spawn and a sample sacrificed after seven days of conditioning. Continuously fed ( C 1 ) spawned scallops showed lower gonadosomatic index (GSI) and a higher dry weight of spawned eggs, compared to discontinuously fed ( D 1 ) scallops. The remaining scallops derived from both feeding systems ( C 1 and D 1 ) during Experiment 1 were conditioned for rematuration under both continuous ( C 2 ) or discontinuous ( D 2 ) feeding during Experiment 2, obtaining in this way a total of four groups: C 1 C 2 , D 1 C 2 , C 1 D 2 , D 1 D 2 . Continuous feeding during this experiment yielded higher GSI, accompanied by increased concentrations of acylglycerol (AG) and cholesterol (CHL) in the groups C 1 C 2 and D 1 C 2 . This result indicated that feeding condition during the first experiment did not detract from the positive response to continuous feeding during the second experiment. The C 1 D 2 group had intermediate values of GSI and AG, and CHL levels equal to those of C 1 C 2 and D 1 C 2 groups, suggesting that better nutrition during the first experiment partially compensated for inadequate nutrition during the second experiment. No significant differences were obtained for other variables such as gonad proteins, muscle condition index, and adductor muscle levels of AG, CHL, proteins, and glycogen. Continuous feeding during conditioning of A. ventricosus thus resulted in a better spawning capacity and increased rematuration ability than discontinuous feeding.

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.

Genetic Variability Assessed by Microsatellites in a Breeding Program of Pacific White Shrimp (Litopenaeus vannamei)

Genetic diversity in a shrimp-breeding program was monitored for 2 generations by microsatellite DNA markers (Pvan1578 and Pvan1815) to establish levels of variation and proceed with a selection program. An increase in the number and frequencies of some alleles in both microsatellite loci from G0 to G2 was induced by foreign sire contributions. Most common alleles and high heterozygosities (around 70% in both loci) were maintained through the generations, indicating that there had not been a significant loss of genetic variability in the breeding program. However, when compared with variability in other wild and cultured stocks, the presence of 4 main alleles at both loci may be an indication that a certain reduction in variability already was present in the line used as founder stock (G0). Therefore, it is recommended that additional genetic variability be introduced to the breeding stock by crossing it with a different line.