Egg Transfer Research Articles

Sex ratios in mule duck embryos at various stages of incubation

Mule duck hatcheries have long reported varying degrees of unbalance in the sex ratio, with a preponderance of male mules at hatching. The aim of the present study was to assess the distributions of sex ratios at various stages of development in embryos originating from intra- and intergeneric crosses between parental lineages (Muscovy male×Muscovy female, Pekin male×Pekin female, Muscovy male×Pekin female or Mule, and Pekin male×Muscovy female or Hinny). In Experiment I, embryo sexing was performed on Days 1 and 5 of incubation (by multiplex PCR) and at hatching (by vent observation). The sex ratio was not significantly modified during the early stages of embryo development whatever the genetic origin ( P>0.05, Days 1 and Day 5) but our results in mule and hinny ducklings confirmed the preponderance of males among normally hatched ducklings originating from the intergeneric lineage (58.9 and 55.4% males in mules and hinnies, respectively; P<0.05 in both cases). Sex ratio (vent sexing) in second grade (cull) ducklings revealed that 68% of these ducklings were females ( P<0.05). In Experiment II, the distribution of sex ratio was also performed in mule duck eggs from 6 batches (400,000 eggs/batch) first examined for fertility (candling) on Day 18 of incubation. These results indicate that the percentage of males present in the population of normally hatched ducklings increases when fertility decreases. In addition, this experiment also revealed that 83.7–90.5% of viable male mule embryos develop up to hatching, compared to only 43.0–51.0% of female mule embryos. Given that a deviation in sex ratio during the first stages of incubation is unlikely (Experiment I), it is concluded that the skewed sex ratio of mule ducks at hatching is primarily due to increased late mortality in female mule embryos occurring between egg transfer and hatching. This mortality originated, at least in part, from the intergeneric origin of female mules, and was marked to a greater or lesser extent depending on the initial success of fertilization in a given batch, a possible indication that the initial quality of gametes may selectively exert its influence at the later stages of embryo development.

Effects of maternal and paternal alcohol consumption on the success rates of in vitro fertilization and gamete intrafallopian transfer

ObjectiveTo determine whether the amount and timing of female and male alcohol use during IVF and GIFT affect reproductive endpoints. DesignMulticenter prospective study. SettingClinics in southern California. Patient(s)Two hundred twenty-one couples with female infertility. Intervention(s)None. Main outcome measure(s)Egg retrieval, transfer, fertilization, pregnancy, miscarriage, live birth, and multiple gestations. Result(s)Female alcohol consumption was associated with: (1) a 13% decrease in the number of eggs aspirated (adjusted 95% confidence interval [CI]: −2% to −23%, for one additional drink per day, 1 year before the IVF or GIFT attempt); (2) an increase in risk of not achieving pregnancy by 2.86 times (0.99–8.24, 1 month prior); and (3) an increase in risk of miscarriage by 2.21 times (1.09–4.49, 1 week before the procedure).For men, one additional drink per day increased the risk of not achieving a live birth by 2.28 (1.08–4.80) to 8.32 (1.82–37.97) times, depending on the time period; beer also affected live births (ORs = 5.49–45.64). This outcome may be due partially to increased risk of miscarriage by 2.70 to 38.04 times for men who drank ≤1 month before and during IVF and GIFT. Conclusion(s)This is the first study to report an association between alcohol use and reproductive endpoints of IVF and GIFT. Because alcohol use is ubiquitous, modifying drinking habits may increase assisted reproductive technology success rates.

Effect of stocking density and gender segregation in the seahorse Hippocampus abdominalis

The aims of this investigation were to determine the effects of stocking density and gender segregation on growth and survival of the seahorse Hippocampus abdominalis. Growth and survival of juvenile seahorses (72 mm in standard length and 0.5 g in wet weight) was tested at 1, 2, and 5 juveniles/l and monitored for 60 days. Growth parameters (standard length, weight, and Condition Factor) generally increased as stocking density decreased. There was no difference in survival between 1 and 2/l (mean±1 SE survival=100% and 95.8±2.7%, respectively), but survival in the 5/l treatment was significantly reduced (mean survival=78.3±3.7%). With increasing stocking density, a greater incidence of physical interference between juveniles (i.e. tail-grasping and wrestling) was observed. The effect of gender segregation was tested with sexually mature seahorses in tanks where courtship displays were possible, but egg transfer prevented by limiting tank vertical height. There were no significant differences in growth (standard length, wet weight, Condition Factor, and mean Specific Growth Rate) in males and females either gender segregated or kept together for 90 days. Overall, comparison between males and females revealed no significant differences in growth, apart from the normal difference in wet weight, which begins at the onset of sexual maturity with male brood pouch development. Survival was 100% across all treatments. In addition to courtship displays occurring between males and females kept together, same-sex displays were also observed between males and females and females which were gender segregated, although to a lesser extent, and not always with the full range of courtship behaviours exhibited.

In Vitro Development of Parthenogenetic Eggs: A Fast Ecotoxicity Test with Daphnia magna?

In the present study, the authors investigated and defined development stages of Daphnia magna eggs that could be potential endpoints for sublethal toxicity tests with in vitro parthenogenetic egg cultures. Such an “egg test” could be a cost-effective alternative to the classic 21-day test with D. magna. Three main stages of embryonic development were considered: release of the egg external membrane, release of the internal membrane, and separation of the caudal spine. The first embryonic stage was attained approximately 30 h after transfer of eggs from ovaries to the brood chamber (considered as time zero), the second stage at 48 h, and the third stage at 68 h. Embryonic development was considered completed with the caudal spine separation. Thereafter, juveniles were able to swim in the water column. Egg mortality, duration of each egg stage, egg diameter, and egg abnormalities were investigated as potential endpoints. In vitro tests were carried out with several toxicants (DBS, 3,4-DCA, cadmium, and copper) and with acid mine drainage, sensitivity generally being higher than with the accepted chronic 21-day test with D. magna.

SPATIOTEMPORAL VARIATION IN LEAFMINER POPULATION STRUCTURE AND ADAPTATION TO INDIVIDUAL OAK TREES

Stilbosis quadricustatella leafminers are microlepidopteran specialists of sand-live oak (Quercus geminata). These tiny moths produce one generation per year and have a parasitic life-cycle and long larval stage that develops entirely within a single oak leaf. Differences in host-plant age, phenotype, and phenology generate a coarse-grained, spatially heterogeneous environment for the leafminer population. Previous reciprocal transfers of leafminer eggs among mature oaks revealed that S. quadricustatella are locally adapted to individual oak trees. In this paper we use genetic markers and an extinction–recolonization experiment to explore further variation in leafminer population structure. Allozyme loci indicate significant interdemic genetic structure among recent colonists of new host trees, which weakens in the 10th generation and disappears by the 40th generation. In contrast, adaptive demic structure is evident by the 10th generation and is strong in the 40th generation, despite the potential for substantial intertree dispersal. We propose that host heterogeneity combined with leafminer fidelity to natal trees promotes divergent selection and rapid demic evolution on individual oaks, despite potentially high gene flow between the leafminers inhabiting them.

An automated system for egg collection, hatching, and transfer of larvae in a freshwater finfish hatchery

An automated system for egg collection, hatching, and transfer of larvae of several cultured freshwater finfish has been developed. The system consists of a spawning tank, a filter, an incubation tank, hatching nets, and larviculture ponds. Using this system, grass carp ( Ctenopharyngodon idellus), bighead carp ( Aristichtys nobilis), silver perch ( Bidyanus bidyanus), palmetto bass ( Morone saxatilis× M. chrysops) and black carp ( Mylopharyngodon piceus) were successfully induced to spawn with a single hormone injection (LHRH-a at 15 μg/kg for grass carp and bighead carp; HCG at 200, 400 and 600 IU/kg for silver perch, palmetto bass and black carp, respectively). Using this system, fertilized eggs flowed freely into nets for normal hatching, and the hatched larvae were conveyed automatically into larviculture ponds. The new automated system reduces labor. It achieved relatively high rates of spawning, fertilization and hatching. The filtration and reuse of culture water conserves water. This system offers an improvement to the existing finfish hatchery technology.

Water Quality within Baitfish Spawning Mats during Egg Incubation in Commercial Ponds

A collection system was devped to measure dissolved oxygen (DO) concentrations and other water quality variables from within baitfish spawning mats during egg incubation in commercial ponds. A hand-operated vacuum pump was used to draw water from three pierced plastic pipes inserted lengthwise through each spawning mat. Dissolved oxygen concentrations in mats were routinely found to be below ambient pond levels. In three of five trials, DO concentrations within the mats were deemed potentially damaging to embryos. Mat DO measured twice a day did not differ significantly from concurrent DO levels within mats sampled only once a day. Mats that were suspended 15 cm above the pond bottom generally had higher DO than mats on the pond bottom. Levels at 15 cm above the pond bottom were similar to those in mats suspended 2–6 cm below the pond water surface. With one exception, total ammonia nitrogen was 0.3 mg/L or below in all trials. Abrupt drops of 4–7°C were recorded during egg transfer. Subsequent diel fluctuations of 10–12°C were common in incubation ponds. Improved incubation techniques, such as modified mats or tank hatching, could reduce risks inherent in the current methods used by the industry and improve hatching rates.

Reproduction in Anthelia glauca (Octocorallia: Xeniidae). I. Gametogenesis and larval brooding

Anthelia glauca Lamarck, 1816 is a gonochoric, external-brooding soft coral found in KwaZulu-Natal. It is reproductively active in the summer months. The development of gametes produced in late summer is arrested in winter. Several stages of gametes are found at the base of the polyps, and female polyps produce several cycles of larvae over an extended breeding period of 4 to 5 months. Larvae are brooded in a unique pharyngeal brooding pouch not yet described in other coral species. The brood pouch consists of an expansion of the pharynx with constrictions proximal and distal to the embryos and larvae. Our data suggest that egg transfer and fertilization occur at full moon and the mature larvae are released after new moon. Zooxanthellae are absent in A. glauca oocytes, but zooxanthella infestation commences at the immature larval stage.

Genetic variation of prenatal survival in relation to ovulation rate in sheep: A review

Varying rates of partial fertilization (2–40%) were found in literature. These data gave evidence that the `all-or-none' hypothesis on fertilization is not correct, at least in a number of sheep breeds and experimental conditions. Furthermore, there are indications for variability in prenatal mortality at different stages of pregnancy, as a function of ovulation rate (OR). Consequently, higher partial fertilization and foetal mortality rates interfere with the determination of prenatal survival (PS), based on the difference between OR and the number of living embryos at varying times before or at lambing, as was done in many studies on that subject. Indications for variability in PS within breeds were mainly an effect of differentiation between lines, depending on the selection criteria followed, e.g., growth rate vs. multiple ovulations. In some cases, this effect was associated with dam–embryo interactions or line–age interactions. Data on differences in PS between breeds and crosses were based, in most cases, on differences between twin and multiple ovulating ewes, or in ewes carrying multiple foetuses after egg transfer. Among twin ovulating ewes, all born to Romney dams, uterine efficiency (UE) was highest in Finnish Landrace (FL) sired ewes. The contribution of FL breeding to superiority in UE was supported in other FL crossbreeds and in crossbred genotypes with FL genes from their ancestry. Crossbreeding effects of the Booroola Merino on uterine capacity (UC) or on UE were variable, depending on the breeds used, on the presence of the Booroola Fecundity gene and on OR. A clear distinction should be made between UE (the marginal increase in LS as OR increases) and UC (the maximum number of foetuses a dam is able to support at birth) when comparing Finnish Landrace and Booroola Merino with other prolific breeds. There were indications of a higher genetic variability in PS, independent from the genetic variability in OR, in the Romanov breed than in other breeds and crosses. In conclusion, while genetic variation in litter size (LS) within some breeds can be statistically predicted on the basis of OR, between-breed variation in LS has consider the genetic variation in PS.

Early prenatal survival in relation to the parental environment in sheep: A review

After multiple egg transfer litter size (LS) in recipient ewes from some breeds was greater than their potential natural size; Finnish Landrace, not Booroola Merino recipients, tended to be superior to recipient ewes from other breeds with a lower natural ovulation rate (OR). In Finnish Landrace and Merino ewes the difference in prenatal survival (PS) between purebred and crossbred litters was small. In Berrichone and Romanov breeds PS was higher in crossbred than in purebred ewes. A significant variation in PS was found between eggs from Finnish Landrace donors. A dam–embryo interaction on PS was present in high and low twinning Merino ewes. Embryos from Romney ewes selected against lamb faecal egg count (LFEC) were more likely to survive than embryos from Romney ewes selected for LFEC. Various translocation types in heterozygous and homozygous combinations in rams and ewes did not influence their overall fertility, probably because of prezygotic selection of gametes. Scrotal heating in Merino rams caused an increased loss of fetuses. Fetal survival in Merino ewes increased as both the number of spermatozoa and feeding level were higher. Lower service activity was linked to lower pregnancy rates (PR) and PS in 1.5-year-old Merino ewes, interacting with the mean duration of oestrus as compared to that in adult Merino ewes. Service activity per ewe, PR and PS in Merino flocks were lower as ram: ewe ratio decreased from 1.0 to 0.5 and 0.25%. In Merino flocks selected for skin folds the percentage of twin births per ewe lambing was lower in hot weather than in Merino flocks selected against skin folds. PR and PS tended to be higher in ewes exposed to Rambouillet rams selected for high prolificacy, compared to Rambouillet rams selected for low prolificacy. PR and PS were lower in Clun Forest ewe lambs than in Clun Forest ewes. Survival of ova from Galway and Romney ewes was greater than that of ewe lamb ova. Conditions in the uteri of both ages were equally favourable. In Galway ewe lambs plasma estrogen concentration 12–36 h after sponge removal was more than 100% greater than in adults. Progesterone levels were similar, also on day 12 of pregnancy. After day 13 progesterone concentration increased at a slower rate and remained lower on day 28 in Clun Forest ewe lambs than in Clun Forest adults. The smaller and more variable preovulatory LH surge in Clun Forest ewe lambs was considered to be evidence of inadequate progesterone priming. These and other data support the suggestion that conditions in the developing follicle and in the reproductive tract between ovulation and the 8–16 cell stage are related to the reduced fertility and PS in very young ewes. It is concluded that endogenous, paragenous and exogenous factors can have similar and interacting effects on PS in sheep.

Egg culture: the foundation.

Ralph Brinster began his classic work on egg culture more than 35 years ago. His interest in mammalian egg culture had developed, in part, as a consequence of his experiences with animal breeding and reproduction that he gained while growing up on a farm. Ralph decided early in his career that an in vitro approach to culturing eggs would provide a powerful tool with which to study the development of these cells. Beginning at the close of the 19th century, a number of investigators had performed in vitro studies on egg culture and the related area of egg transfer; however, the ability to recover and transplant eggs had reached a much higher level of perfection than had culture. Eggs of many species could be successfully transferred, but there was no reliable technique for egg culture. In 1963, Ralph reported a method for culturing eggs in microdrops of medium under oil (Brinster, 1963), which has become universally used. Two years later, he identified pyruvate as the central and essential energy source for early stages of mouse eggs (Brinster, 1965b). These two developments revolutionized in vitro studies of mammalian eggs and issued in an era of intense research activity concerning egg culture and egg manipulation. Effective formulations of culture media could now be developed to allow routine in vitro maintenance of eggs, and important parameters for these recipes were soon determined. It was quickly established that the requirement for pyruvate as an energy source exists at ovulation in many species and is already present in germ cells of the mouse fetus. The metabolic activity of the fertilized mouse egg was shown to be low and comparable to bone; however, four days later, at the blastocyst stage of development, the metabolic activity was comparable to brain. Thus, a foundation of understanding about the biology of early mammalian eggs was established between 1960 and 1970, and subsequent studies have broadened this understanding. However, the greatest impact of a simple, reliable egg culture method has been to provide the ability to perform complicated manipulative procedures on preimplantation stages of mammalian embryos. In no area has this been more important than in development of transgenic animals. All methods for generating germ line genetic modifications rely on the ability to maintain and manipulate eggs and early developmental stages in vitro without loss of developmental competence. The importance of efficient egg culture to manipulation and transgenesis is fundamental and enabling.

Experimental Schistosoma bovis Infection in Goats: The Inflammatory Response in the Small Intestine and Liver in Various Phases of Infection and Reinfection

In a histopathological study of goats experimentally infected with Schistosoma bovis, the characteristics of the inflammatory response in the small intestine and liver related to tissue egg counts and fecal egg excretion were compared between goats at different time periods of primary infection and of primary infection followed by challenge. At early patency, coinciding with increasing egg excretion, the intestinal lamina propria showed numerous intact schistosome eggs devoid of any inflammatory reaction, whereas egg-associated inflammatory foci in the intestine were significantly few. Later in primary infection and after challenge, intestinal changes were marked by a granulomatous anti-egg response, with only a minor component of eggs lacking inflammatory change, and were consistent with a reduction of egg transfer into the gut wall. Hepatocellular necrosis with eosinophil infiltration was pronounced only during the early patent stage. The results indicate that the early cascade of fecal egg excretion in caprine schistosomosis bovis is aided by a low degree of tissue reactivity to eggs in the intestine. They also lend support to previous findings indicating that an anti-fecundity effect is operative after exposure to challenge in this parasitic infection in goats.

Comparison between primary and secondary sex ratios in parasitoid wasps using a method for observing chromosomes

Hymenopteran insects, including parasitoid wasps, usually have a haplo-diploid sex-determination system. This enables an ovipositing female to choose the sex of her egg by controlling sperm access to the egg (Flanders, 1956). The potential for sex ratio control makes hymenopteran insects ideal experimental organisms for testing sex ratio theory (Charnov, 1982; Godfray, 1994). Although there are many sex ratio studies in parasitoid wasps, the data are based on sex ratio at wasp emergence. However, if differential mortality between immature sexes occurs, the sex ratio at wasp emergence will differ from that at oviposition, i.e., the sex ratio determined by the female wasps. In fact, in several parasitoid wasps, unsuitability of hosts and shortage of food are suggested to result in higher mortality of female larva than male larva (King, 1987). Because most sex ratio theories deal with sex ratio at oviposition, any studies using sex ratio at wasp emergence can be incorrect to test sex ratio theories, if different sex mortality occurs. Therefore, effects of differential sex mortality need to be clarified in sex ratio studies. To date, the effects of differential mortality on secondary sex ratio have been estimated by: 1) comparing mortality of offspring from mated females with that from unmated females (Sandlan, 1979); 2) egg transfer experiments between small and large hosts (Heinz & Parrella, 1990); 3) using a predictive model of primary sex ratio (Wellings et al., 1986); and 4) using differences in female behaviour as an index for predicting primary sex ratio (Suzuki et al., 1984; van Dijken & Waage, 1987; Ueno, 1995). These methods, however, are not suitable for determining exact sex ratio and are not always applicable. Since most Hymenoptera are haplo-diploid, cytological methods for observing chromosomes at the egg stage are available to determine exact primary sex ratio and are applicable to most parasitoid wasps. However, little research using cytological methods to determine primary sex ratio has been done (van Dijken et al., 1989, 1993). In this paper, we apply a cytological method to determine primary sex ratios in two idiobiont parasitoid wasps Pimpla nipponica Uchida and Itoplectis naranyae Ashmead (Hymenoptera: Ichneumonidae). These polyphagous parasitoids attack a variety of host species which differ in size (Ueno & Tanaka, 1994). In such a case, sex ratio control in response to host size could evolve (Charnov, 1982). Here we test whether these parasitoids change the sex ratio in response to host size and whether host size is responsible for differential mortality between immature sexes.

EFFECTIVENESS OF ULTRAVIOLET IRRADIATION IN REDUCING THE NUMBERS OF SALMONELLA ON EGGS AND EGG BELT CONVEYOR MATERIALS

The effectiveness of ultraviolet (UV) irradiation in potentially reducing Salmonella on eggs and in egghandling facilities was evaluated using four primary parameters: test materials, UV intensity, time of UV exposure, andinitial Salmonella contamination levels. Decontamination of fiber and plastic egg transfer belts, egg shells, and metal wasattempted. The results showed that each of these elements varied in its capacity for sterilization by UV whencontaminated with Salmonella. Regression models for system design were developed to define the relationship among UVintensity, Salmonella contamination level and time of UV exposure for each material.

Hatching rhythms in the capsalid monogeneans Benedenia lutjani from the skin and B. rohdei from the gills of Lutjanus carponotatus at Heron Island, Queensland, Australia

Spontaneous hatching of eggs of Benedenia lutjani and B. rohdei occurred after incubation for 4–6 days and 6–10 days, respectively, at a constant temperature in the range 22–28°C when exposed to natural illumination or to alternating 12-h periods of light and darkness (LD12:12; light on, 06.00 h; light off, 18.00 h). Under these conditions, hatching of the eggs of both species was rhythmical, all larvae emerging only during periods of illumination. Hatching was not confined to particular times within the illuminated period. Evidence for an endogenous component to the rhythm was revealed by transfer of eggs from LD12:12 to continuous darkness (DD) near the end of the incubation period. Hatching also occurred only during periods of illumination when eggs of each species were incubated under a DL12:12 regime (i.e. period of illumination 18.00 h to 06.00 h; period of darkness 06.00 h to 18.00 h). When the eggs of B. lutjani and B. rohdei were laid and incubated in DD or continuous illumination (LL), some degree of rhythmicity persisted, raising the possibility that the eggs inherit circadian rhythmicity from their parent. The hatching patterns of these 2 species of monogeneans are discussed in relation to host finding, host behaviour and limited observations on the behaviour of the oncomiracidia after hatching.

The significance of an early (premature) rise of plasma progesterone in in vitro fertilization cycles induced by a "long protocol" of gonadotropin releasing hormone analogue and human menopausal gonadotropins.

Our purpose was to assess and clarify the mechanism of whether an early progesterone rise in cycles with gonadotropin-releasing hormone agonist (GnRH-a) is associated with an impairment of IVF outcome. Seven hundred eighty-six cycles were induced with GnRH-a and human menopausal gonodotropin (hMG) ("long protocol"). Plasma progesterone (PP) levels on the day of human chorionic gonadotropin (hCG) administration were divided into three groups: < 0.9 ng/ml (Group A), 1-2 ng/ml (Group B), and > 2 ng/ml (Group C). We also analyzed the pregnancies achieved in our egg donation protocol in relation to the PP levels of each donor on the day of hCG administration. Group A involved 525 cycles, Group B had 223, and Group C had 38. The overall pregnancy rate per egg transfer was 19.2%, with the highest for Group A (22.3%), declining for Groups B (14.3%) and C (7.9%) (A = B = C; P < 0.005). The embryo implantation rate was found to be negatively correlated with the PP levels on the day of hCG administration. In contrast, there was an opposite trend between PP levels and the chance of conception in 30 pregnancies achieved by egg donation. Since premature luteinization is very unlikely to occur under the conditions of this study, our findings suggest that an early PP rise has a negative impact on endometrial receptivity but not on egg and embryo quality.

Maternal behavior and clutch manipulation in the ring-legged earwig (Dermaptera: Carcinophoridae)

The expression and maintenance of maternal behavior in the earwig,Euborellia annulipes, was examined through manipulation of clutch size, age, and species and through observations of interactions between brooding females. Females underwent discrete gonadotrophic cycles culminating in oviposition of first clutches that were highly variable in size. Neither the head capsule width nor the age of the mother was correlated with clutch size. Maternal care extended through embryogenesis and for the week following hatching. Clutch removal significantly shortened the interclutch interval, indicating that the presence of brood inhibited the onset of the second gonadotrophic cycle. Brooding females readily accepted replacement clutches of the same age. Thus, mothers did not appear to distinguish their own eggs from those of other females. Experimental doubling of clutch size did not significantly reduce the proportion hatching or fledging. In contrast, reducing clutch size diminished the percentage successfully fledging. Manipulation of clutch age resulted in reduced hatching/fledging success. Placing two females, each with newly laid clutches, in the same cage usually resulted in egg transfer from the nest of one female to that of the other within 12 h. Nests of females with larger forceps were significantly more likely to contain both clutches. When mothers with first clutches were paired with mothers with third clutches, eggs were more likely to be transferred to the nest of the older female.E. annulipes females with newly laid clutches appeared to accept as replacement clutches eggs of the earwigDoru taeniatum. Alien clutches were maintained for the typical duration of embryogenesis; however, noD. taeniatum hatchlings were observed.

Structural Changes of the Female Genital System during and after Feeding in Haemaphysalis longicornis (Acari: Ixodidae)

St,ructural changes in the female genital system of ZIuc~rnr~~~/~~~su.lis loi/gico?-rris during feeding, copulation and oviposition were observed in the light microscope. The genital system consists of the vestibular and cervical vagina, tubular accessory glands, connecting tube, receptaculum seminis, oviduct and ovary. As in H@otn?r~, epithelial cells lining the vestibular cuticle become the lobular accessory glands during feeding, secretions from which coat the surface of passing eggs and may function as a waterproofing agent. However, it is clear from these observations that dramatic feeding-related changes occur also in the other organs constituting the system. The cervical vagina and connecting tube both have a similar structure, their developed muscles being involved in transfer of male germ cells and/or eggs. Secretions from the feeding-stimulated tubular accessory glands may be a coating agent applied to the egg surface or act as a lubricant for egg passage. Epithelial cells of the receptaculum seminis are probably involved in destruction of the inserted endospermat,ophore. In t,he fed females, just, after copulation the oviducal epithelium produces a secretion, which also may exert some influence upon the passing spermatozoa and eggs. Muscles surrounding the oviduct,s cause peristalt,ic contract.ions during the passage of spermatozoa and eggs. In the developed ovary, the oocyte prot,rudes into the haemocoel, and is attached to special funicle cells which arise from ovarian epithelium. Numerous spermatozoa present in the ovarian lumen during oviposition imply that fertilization occurs in the ovary.

A method for the early assessment of the quality of turbot larvae

The bacterial environment should be taken into account for assessing the quality of fish larvae, besides biochemical and developmental criteria. Detrimental effects of associated flora have been observed on the survival rates of larvae (e.g. Nicolas et al., 1989), and experimental infections were performed on fish larvae by introducing the pathogen either directly into the rearing medium or into live food organisms (e.g. Kusuda et ai, 1986). A challenge test was used for assessing the effect of a food additive on the ability of turbot (Scophthalmus maximus) larvae to resist infection, but that required rearing the larvae separately (Gatesoupe, 1993). Bergh et al. (1992) have proposed an infection test with transfer of eggs into polystyrene dishes, but it was not convenient for larvae with exogenous food source. The present paper was an attempt to develop a new test with transfer of larvae after feeding. Then this test was inserted into a simple survey of the quality of turbot larvae, with a view to drawing up relations between rearing success, associated bacteria and resistance against pathogens. For this purpose, seven batches of larvae were successively reared in 150 1 cylindrical tanks with conical bottoms from day 1 after hatching until day 10. Three tanks were used for batches 1, 3, 5 and 6, while five tanks were used for batches 4 and 7. The larvae of batch 2 were reared in one tank. The rearing temperature was gradually increased from 14 °C to 18 °C by day 5. The salinity was 35%. For feeding the larvae, rotifers (Brachionus plicatilis) were cultured in seawater according to the method already described (Gatesoupe, 1990). The rotifer diet was made up of baker's years, menhaden (Breuoortia tyrannus) oi l (Sigma F8020), soybean lecithin, DL-a-tocopherol (USB), and vitamin premix (Spyridakis et ai, 1988), at the daily rates of 60.8, 7.7, 0.7, 0.015, and 0.7 mg r1, respectively, on a dry matter basis. The larvae were fed with the rotifers from day 3 to day 9, at the daily rates of 20, 50, 75, 100, 150, 200, and 250 rotifers per initial larva, corresponding to the seven consecutive days of feeding. Each day, the rotifers were transferred from their culture medium into clean seawater tanks (200 rotifers m l 1 ) , where they were enriched with spray-dried fish autolysate, menhaden oi l , soybean lecithin, and DL-a-tocopherol, at the rates of 15, 7.7, 0.7, and 0.015 mg T 1 , respectively, on a dry matter basis. The rotifers were continuously distributed to turbot with a peristaltic pump, the flow rate of which was adjusted so that the whole volume was carried through in 24 h. At day 10, the survivors were counted and 30 fish were sampled in each tank,

Smolting of Hatchery-Reared Steelhead Transferred as Eyed Eggs from the Northern to the Southern Hemisphere

Abstract The effects of a Northern-to-Southern Hemisphere shift on the growth and smolting of steelhead (Oncorhynchus mykiss) were monitored by reference to physiological criteria. Eyed eggs were imported from the Alsea River Trout Hatchery, Oregon, USA (latitude 44°N), to the Lake Rupanco Experimental Hatchery in Chile (latitude 41°S). This transfer of eggs resulted in a notable variation in the age and size at which fish smolted. A minimum smolting size of about 10 cm was observed in the first southern spring of life, when fish were 7–8 months old. Fish that did not reach this size smolted in the second spring of life at age 20 months. Based on our current understanding of the effects of environmental variations on smolt physiology, we offer guidelines for increasing the efficiency of smolt production for this anadromous salmonid in the Southern Hemisphere.