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Fish migrate for varied reasons, including to avoid predators and to access feeding, spawning, and nursery habitats, behaviors that enhance their survival and reproductive rates. However, the migratory ecology of many important fishes, especially those in river–floodplain ecosystems, remains poorly understood. One fish of the Amazon Basin whose migratory behavior is poorly understood is the catfish Pseudoplatystoma fasciatum. Here, we used otolith elemental microchemistry to characterize the migration ecology of P. fasciatum in the Amazon Basin. The main research questions of this study were: (1) does P. fasciatum move between waters with different Sr isotopic signatures (87Sr/86Sr) and chemical compositions? (2) What distance do they migrate? (3) Is the migration of P. fasciatum related to age? And (4) does P. fasciatum migrate mainly upstream, downstream, or in both directions? We assessed whether P. fasciatum migrates between waters with different 87Sr/86Sr values, comparing the Sr isotopic signature of otolith transects of each individual with the range of Sr isotopic signatures within the respective rivers. We found that 34% of the 71 fish analyzed migrated between rivers with different Sr isotopic signatures and 66% did not. The mean migration distance migrated was 126 km, with most specimens migrating between 72 and 237 km. Apparently, no fish of age one or age six or older migrated. All fish that migrated were between two and five years of age, with 20% of the specimens that migrated being two years old, 40% three years old, 30% four years old, and 20% five years old. Sixty-six percent of all individuals that migrated between rivers with different Sr signatures did so bidirectionally, while 33% moved unidirectionally. According to our definition of homing behavior in which fish migrated back to the same river where they were born, 41% of all fish that migrated displayed apparent homing behavior. Our findings provide insights into the migratory ecology of P. fasciatum, corroborating and refining knowledge reported in the literature. Our results on the migratory ecology of P. fasciatum have implications for sustainable fisheries conservation and management: conserving P. fasciatum requires habitat maintenance and suitable fishing practices in spawning and nursery habitats, and managers must consider large geographic areas for effective fishery management and conservation. [ABSTRACT FROM AUTHOR]

Upstream migration of the Atlantic blue crab Callinectes sapidus is well described in its native range, but it is little known in invaded areas.Here, we report several long‐distance migration events of the blue crab in the Iberian Peninsula and use a global database to calculate the probability of occurrence of the species in relation to distance to sea. We then exemplify the potential of blue crab impacts on freshwaters by overlapping its probability of occurrence with that of the critically endangered European eel Anguilla anguilla. Finally, we evaluate the extent to which dam barriers can halt the upstream migration of the blue crab.Invasive blue crab has been detected at 108 km from the sea in the Guadalquivir River (the farthest distance reported in the non‐native range), at 71 km in the Guadiana River and at 53 km in the Ebro River. The probability of occurrence decreased steeply in the first upstream kilometres, but it is still concerning at a dozen kilometres from the river mouth (50% at 19 km, 25% at 38 km, and 3% at 100 km). The blue crab invasive potential widely overlaps (63%) with the Iberian range of the European eel. The blocking effect of dams on the potential invasion of freshwater systems by the blue crab was limited (13%).Our study highlights the need to study the upstream migration of the blue crab within its non‐native range, since it could involve serious impacts in reachable river and stream habitats. [ABSTRACT FROM AUTHOR]

One of the most conspicuous impacts of dam construction on fish is the blocking of their migratory routes. However, the formation of the reservoir, a lentic environment with distinct hydrological and ecological characteristics, can also constitute an obstacle to migration. This impact, however, is poorly explored in the scientific literature. Therefore, this study aimed to assess the movements of Prochilodus argenteus tagged with radio telemetry transmitters and manually translocated across the Três Marias Dam in the São Francisco River. The Três Marias reservoir covers an area of 1090 km2 and ranks among the largest artificial reservoirs in Brazil. Individuals translocated to the Três Marias reservoir showed reduced movement rates and home ranges. They appeared disoriented in the new environment, with many of them settling near fish farms and remaining there throughout the study period. A comparative analysis with existing literature on Neotropical species' reproductive migration through artificial reservoirs revealed a trend: the ability of migratory fish to navigate reservoirs diminishes with their area, especially those exceeding 50 km2 or with a residence time surpassing 30 days. These results indicate that caution is needed when designing fish passage facilities for dams that form larger artificial reservoirs in the Neotropics. Even if these facilities are efficient in attracting and translocating migratory species, behavioral and physiological thresholds may prevent them from reaching suitable areas to complete their reproductive cycle in the new environment formed. [ABSTRACT FROM AUTHOR]

Van fish is an anadromic fish in the family Cyprinidae, endemic to the Lake Van basin. Fish feeding and care enters the streams flowing into the lake from Lake Van in April-July. In these aquatic environments, differences are observed in the feeding behavior of the fish. In this study, the digestive tract of 30 Van fish sampled from Lake Van and Karasu Stream between April and July were examined morphometrically and histologically. When the digestive tract of the Van fish was examined, it was observed that there was no obvious stomach structure. It was determined that the digestive tract consists of the esophagus, stomachlike structure that serves as the stomach, anterior intestine, posterior intestine and anus. When the digestive tract of Van fish is examined, it consists of the outermost serous layer, the muscularis layer, the submucosa layer and the innermost mucosa layer consisting of folds towards the lumen. It was determined that these layer thicknesses varied between fish sampled from lakes and streams. Diameter, mucosal width, mucosal length, mucosal folds, muscularis thickness, submucosa thickness and length were measured morphometrically. It was determined that these values were higher in the fish sampled from the lake compared to the fish sampled from the rivers. Measurements in the digestive tract of van fish were determined for the first time in this study. These measured values are thought to be related to the nutrition, stress and physicochemical structure of the water. [ABSTRACT FROM AUTHOR]

Fish migrate for varied reasons, including to avoid predators and to access feeding, spawning, and nursery habitats, behaviors that enhance their survival and reproductive rates. However, the migratory ecology of many important fishes, especially those in river–floodplain ecosystems, remains poorly understood. One fish of the Amazon Basin whose migratory behavior is poorly understood is the catfish Pseudoplatystoma fasciatum. Here, we used otolith elemental microchemistry to characterize the migration ecology of P. fasciatum in the Amazon Basin. The main research questions of this study were: (1) does P. fasciatum move between waters with different Sr isotopic signatures (87Sr/86Sr) and chemical compositions? (2) What distance do they migrate? (3) Is the migration of P. fasciatum related to age? And (4) does P. fasciatum migrate mainly upstream, downstream, or in both directions? We assessed whether P. fasciatum migrates between waters with different 87Sr/86Sr values, comparing the Sr isotopic signature of otolith transects of each individual with the range of Sr isotopic signatures within the respective rivers. We found that 34% of the 71 fish analyzed migrated between rivers with different Sr isotopic signatures and 66% did not. The mean migration distance migrated was 126 km, with most specimens migrating between 72 and 237 km. Apparently, no fish of age one or age six or older migrated. All fish that migrated were between two and five years of age, with 20% of the specimens that migrated being two years old, 40% three years old, 30% four years old, and 20% five years old. Sixty-six percent of all individuals that migrated between rivers with different Sr signatures did so bidirectionally, while 33% moved unidirectionally. According to our definition of homing behavior in which fish migrated back to the same river where they were born, 41% of all fish that migrated displayed apparent homing behavior. Our findings provide insights into the migratory ecology of P. fasciatum, corroborating and refining knowledge reported in the literature. Our results on the migratory ecology of P. fasciatum have implications for sustainable fisheries conservation and management: conserving P. fasciatum requires habitat maintenance and suitable fishing practices in spawning and nursery habitats, and managers must consider large geographic areas for effective fishery management and conservation.

Purpose – There is abundant research on surrogacy; however, migration scholars have not addressed surrogacy-driven migration. Policies related to surrogacy and surrogacy-led migration are under-researched. The paper argues that surrogacy-led migration or fertility/reproductive migration constitutes a significant part of mainstream migration. The purpose of this paper is to reflect on the policy dilemmas in various countries. Design/methodology/approach – A total of 9 surrogate mothers (4 from India; 2 from Thailand, 2 from Indonesia and 1 from Nepal) and 8 commissioning parents (2 from Japan; 4 from Europe; 1 from the USA; 1 from Australia) and 2 doctors (1 from India and 1 from Thailand) selected on snowball basis were interviewed between 2014 and 2016 by using a checklist. Findings – The deficiency and inconsistency of laws regarding surrogacy facilitated the growth of the surrogacy market. Therefore, a uniform policy would help to define and improve the surrogacy and surrogacy-led migration management. Originality/value – This paper demonstrates the interplay of surrogacy and mainstream migration. This is a fresh addition to the study of migration.

Abstract Monitoring reproductive migration is essential for the conservation of anadromous species. Shishamo smelt (Spirinchus lanceolatus) is endemic to Hokkaido, the northernmost large island in Japan. S. lanceolatus is an anadromous species that is known to migrate into rivers for a very short period in early winter. While this species has a special value for local fisheries, the catch amount has drastically declined in the last few decades. Information about S. lanceolatus reproductive migration dynamics is limited, which prevents them from being efficiently managed as a resource. In this study, we used environmental DNA (eDNA) methods as a noninvasive molecular tool for estimating presence/absence and abundance/biomass of S. lanceolatus during their migration into rivers. We developed a species‐specific qPCR system for S. lanceolatus, examining (a) temporal variation in S. lanceolatus eDNA concentrations compared with catch data gathered by traditional methods and (b) variability of migratory patterns among river systems. In a core river for their spawning migration, we consistently detected S. lanceolatus eDNA throughout the spawning season, and the temporal distribution of eDNA concentration was consistent with that of the number of migrating S. lanceolatus estimated by catch survey data. In addition, we were able to detect S. lanceolatus eDNA even from rivers without any official record of their migration. Among rivers with eDNA detection, the relative eDNA concentrations varied, indicating that the population biomass differs largely among the river populations. Our study suggests that eDNA detection systems are useful for tracking reproductive migration of S. lanceolatus at fine spatio‐temporal scales.

Abstract Background The Tibetan highland fish, Gymnocypris przewalskii, migrates from Lake Qinghai to its spawning grounds every summer. This seasonal reproduction is critically regulated by intrinsic and extrinsic signals. However, the molecular mechanisms that process environmental oscillations to initiate the seasonal mating are largely unknown. Results A transcriptomic analysis was conducted on the brain and gonad of male and female G. przewalskii in reproductive and nonreproductive seasons. We obtained 2034, 760, 1158 and 17,856 differentially expressed genes between the reproductively active and dormant female brain, male brain, ovary and testis. Among these genes, DIO2 was upregulated in the reproductively active brain and gonad of both males and females. Neuroactive ligand-receptor genes were activated in male and female brain. Functional enrichment analysis suggested that retinol metabolism was uniquely stimulated in reproductively active males. Genes involved in GnRH signaling and sex hormone synthesis exhibited higher expression levels in brain and gonad during the reproductive season. A co-expression network classified all the genes into 9 modules. The network pinpointed CDC42 as the hub gene that connected the pathways in responsible for modulating reproduction in G. przewalskii. Meanwhile, the sex pheromone receptor gene prostaglandin receptor was identified to link to multiple endocrine receptors, such as GnRHR2 in the network. Conclusions The current study profiled transcriptomic variations between reproductively active and dormant fish, highlighting the potential regulatory mechanisms of seasonal reproduction in G. przewalskii. Our data suggested that the seasonal regulation of reproduction in G. przewalskii was controlled by the external stimulation of photoperiodic variations. The activated transcription of neuroendocrine and sex hormone synthesis genes contributed to seasonal reproduction regulation in G. przewalskii, which was presumably influenced by the increased day-length during the breeding season.

Background: The Tibetan highland fish, Gymnocypris przewalskii, migrates from Lake Qinghai to its spawning grounds every summer. This seasonal reproduction is critically regulated by intrinsic and extrinsic signals. However, the molecular mechanisms that process environmental oscillations to initiate the seasonal mating are largely unknown. Results: A transcriptomic analysis was conducted on the brain and gonad of male and female G. przewalskii in reproductive and nonreproductive seasons. We obtained 2034, 760, 1158 and 17,856 differentially expressed genes between the reproductively active and dormant female brain, male brain, ovary and testis. Among these genes, DIO2 was upregulated in the reproductively active brain and gonad of both males and females. Neuroactive ligand-receptor genes were activated in male and female brain. Functional enrichment analysis suggested that retinol metabolism was uniquely stimulated in reproductively active males. Genes involved in GnRH signaling and sex hormone synthesis exhibited higher expression levels in brain and gonad during the reproductive season. A co-expression network classified all the genes into 9 modules. The network pinpointed CDC42 as the hub gene that connected the pathways in responsible for modulating reproduction in G. przewalskii. Meanwhile, the sex pheromone receptor gene prostaglandin receptor was identified to link to multiple endocrine receptors, such as GnRHR2 in the network. Conclusions: The current study profiled transcriptomic variations between reproductively active and dormant fish, highlighting the potential regulatory mechanisms of seasonal reproduction in G. przewalskii. Our data suggested that the seasonal regulation of reproduction in G. przewalskii was controlled by the external stimulation of photoperiodic variations. The activated transcription of neuroendocrine and sex hormone synthesis genes contributed to seasonal reproduction regulation in G. przewalskii, which was presumably influenced by the increased day-length during the breeding season. [ABSTRACT FROM AUTHOR]

Astyanax altiparanae is a Brazilian species of substantial commercial, environmental and scientific importance; however, existing studies on its reproduction do not seem to provide enough details. In light of the increasing use of this species in fish farming and the need for basic studies for the development of new production technologies, we describe the structural and ultrastructural characteristics of the ovaries of A. altiparanae , and characterize the species' reproductive cycle. Females were collected monthly from March 2013 to February 2014, and reproductive management began in October 2013. The ovaries were removed, fixed in Karnovsky's fixative, and prepared for light microscopy, transmission electron microscopy and immunohistochemistry anti-PCNA. These techniques enabled us to characterize the ovaries, the germ cells, and the somatic cells in detail, as well as their changes over time. The reproductive cycle was characterized based on the monthly variation in the gonadosomatic ratio, the proportion of germ cells, and the rate of oogonium proliferation. The macroscopic analysis of the ovaries suggests that the vascularization pattern and color of the ovaries vary according to development. There are new types of analyses that can be applied even in the fish farming industry, such as a comparison between ovaries staining and weight or the frequency distribution of these colors throughout the year. This study also provides details on microscopic characteristics that have never before been reported for species of Astyanax , such as the presence of annulate lamellae in oogonia, the development of the zona pellucida from oocytes in the one-nucleolus step, and the development of the micropylar apparatus in oocytes in the cortical alveolar step. When the reproductive cycle was analyzed, this species was found to have a long period of spawning, with a reproductive peak from October to February and multiple spawning events, confirming the period already described in the literature. Variations in reproductive periods and the ability to reproduce in lentic environments suggest that A. altiparanae has the ability to respond quickly to environmental changes and exhibits high reproductive flexibility. All of these characteristics confirm the great potential of this species in the fish farming industry. [ABSTRACT FROM AUTHOR]

Isolation-by-distance is recognized as a useful model for describing the spatial distribution of gene frequencies depending on dispersal characteristics of the species under study. However, some species may have populations that occupy the same geographic distribution during the breeding season yet reproduce at different time periods resulting in isolation-by-time (IBT). IBT may complicate investigations of spatial population structure if samples are obtained from multiple discrete time periods or may remain undiscovered if surveys are conducted with limited temporal scope. IBT has been observed in several studies of anadromous fishes (primarily salmon) as well as a few examples in taxa such as frogs, plants, birds and insects, but has not been rigorously tested in freshwater fishes. In this study, we assessed spatial and temporal genetic variation and tested for IBT in Dourado ( Salminus brasiliensis), a large and commercially-important potamodromous fish species found in multiple river basins of South America. Using 11 polymorphic microsatellite loci, we estimated genetic differentiation of 317 adult Dourado collected monthly during the breeding season at three locations along the Uruguay River in southern Brazil. Analyses identified three populations that were clustered in time (i.e. early, middle and late), suggesting an IBT pattern of population structure with no significant spatial structure. Our results contribute to the mounting evidence across a wide range of taxa that suggests IBT may be more common that currently considered, even for species with very high dispersal capabilities such as potamodromous fishes. [ABSTRACT FROM AUTHOR]

The species Prochilodus lineatus, with great commercial relevance in the rivers Grande, Pardo and Mogi-Guaçu, is characterized by the formation of great shoals which are capable of developing wide migratory displacements. Current assay evaluates, by means of the morphometric characteristics and age, whether the curimbatás (P. lineatus) of different migratory and resident stocks form a single population, with interactivities among the sub-populations during the ‘piracema’ period (reproduction migration). A completely randomized plot with a 4 x 2 factorial scheme, with four stocks (one resident and three migratory) as factors and two genders (male and female), with thirty replicates, was employed, with each fish taken as an experimental unit. An 80.19% variation for the first principal component and an 8.09% variation for the second principal component were reported as provided by the ten morphometric variables of resident and migratory stocks. The resident stock had the highest rate for the whole morphometric variables. There was superposition of individual scores of the same characteristics among the migratory stocks. Significant predominance of males was observed among resident stocks and migratory stocks I and II. Morphometric similarity verified among the migratory stocks showed a single population, with small inter-population variations.A espécie Prochilodus lineatus é de grande importância comercial na região dos rios Grande, Pardo e Mogi-Guaçu e tem como característica a formação de grandes cardumes, apta a desenvolver amplos deslocamentos migratórios. O presente trabalho objetivou avaliar, por meio das características morfométricas e etária, se os curimbatás (P. lineatus) dos diferentes estoques migradores e residentes constituem uma única população, havendo interação entre as sub-populações no período de piracema (migração reprodutiva). Utilizou-se um delineamento inteiramente casualizado em esquema fatorial 4 x 2, com quatro tipos de estoques (um residente e três migradores) e dois sexos (macho e fêmea) com trinta repetições, considerando cada peixe como unidade experimental. Foi observada variação de 80,19% para o primeiro componente principal e 8,09% do segundo componente principal fornecida pelas dez variáveis morfométricas dos estoques residentes e migradores. O estoque residente correspondeu aos maiores valores para todas as variáveis morfométricas. Houve sobreposição dos escores individuais das mesmas características entre os estoques migradores. Observou-se predominância de machos entre os estoques residentes e migrador I e II. As semelhanças morfométricas verificadas entre os estoques migradores indicam tratar-se de uma única população, com pequenas variações interpopulacional.

Sexual maturation from puberty to adulthood in European eels ( Anguilla anguilla ) occurs during and/or after the ~ 6000 km reproductive migration from their freshwater habitats to the spawning grounds in the Sargasso sea. This is the first study to simulate an anorexic, mixed-sex, group-wise freshwater migration (2 weeks; 689 km) and subsequent seawater migration (9 weeks; 3,103 km) under mimicked photothermal conditions, using farmed silver eels. Silver eels swam under an 8 hour light:16 hour dark regime in freshwater at 11.5 °C, and subsequently in complete darkness in seawater at daily fluctuating temperatures between 11.7 °C and 10.1 °C mimicking the vertical migrations in the Atlantic Ocean. The aim of these two consecutive experiments was to determine the effects of a simulated reproductive migration on the progression of sexual maturation. The freshwater migration significantly increased plasma testosterone levels in both migrating males and females, but did not enhance sexual maturation further as no significant increases in gonad weight, gonadosomatic index (GSI) nor eye index (EI) were observed. The subsequent seawater migration significantly increased gonad weight and GSI of the migrant males and, particularly, of the females (1.40 ± 0.06 vs. 1.00 ± 0.10%) vs. control groups, suggesting advancement of maturation. Also EI was significantly higher in migrant males (14.0 ± 0.6) as compared to their controls (12.3 ± 0.4). Plasma levels of the gonadotropins FSH and LH remained near the detection limits of the assays and levels were not elevated in migrating eels. These results show that simulation of migration under mimicked photothermal conditions has significant stimulating effects on early maturation which are presumably under steroid control. This brings farmed silver eels to a similar state of maturity as their wild conspecifics that are ready to embark on their oceanic migration. Simulated migration may therefore be used to condition farmed eels for the use as broodstock eels for further hormonal stimulation with gonadotropins in maturation protocols. [ABSTRACT FROM AUTHOR]

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Abstract: Since the approval of Law N° 40/2004, Italian specialists have been applying assisted reproductive techniques in compliance with a number of restrictions. Several attempts were made to find a solution to the practical and ethical issues brought about by this restrictive legislation. Finally, in May 2009, the Italian Constitutional Court banned most of the limitations. In the last year the authors worked together to study the impact of the Italian Constitutional Court modifications on assisted reproduction from both a gynecological and medico-legal point of view. Despite the clinically positive impact of the ruling, a lot of technical and legal unsolved issues still exist. Analyzing these problems, the authors stress the importance of a multidisciplinary approach to achieve adequate legislation in order to improve patients’ outcome and avoid “reproductive migration” from Italy to other European Countries. New regulation could also be important for practitioners by keeping the risk of legal troubles to the minimum. [Copyright &y& Elsevier]

During the last 30 years, interpretation of the population structuring of Illex argentinus evolved from a single to a six-stock model, in which stocks are characterized by having distinct spawning seasons, areas and migration patterns. It is assumed that major spawning activity occurs in discrete pulses along the outer-shelf/slope off Argentina/southern Brazil during late-fall/winter and that early life stages develop near the Brazil-Malvinas Confluence (BMC). Nevertheless, there are inconsistencies in the delimitation of stocks and the interpretation of their life histories. Here, we developed a model based on records of seawater temperature and chlorophyll- a concentration to establish the quality of different areas of the species' geographic distribution as spawning and nursery grounds. Whereas the outer-shelf/slope domain south of 37°S presents marked seasonal restrictions for embryonic development and breeding, coastal areas within 44°-28°S are highly suitable most of the year. Squid in pre-spawning aggregations at the outer-shelf/slope south of 41°S would invest less energy to reach equally suitable spawning areas at the coast than at the BMC. Findings of paralarvae, stranded juveniles and mature squid in coastal areas off northern Patagonia support the predictions of the model. Based on these results, the population structuring and reproductive-migration patterns are reviewed and a new interpretation is proposed: Illex argentinus spawns not only in discrete seasons and areas on the slope and mid/outer shelf, but also conducts quasi-permanent spawning migrations to coastal areas, resulting in a more continuous pattern of recruitment than previously considered and in weak stock differentiation. [ABSTRACT FROM AUTHOR]

The onset of downstream migration of European eels is accompanied by a cessation of feeding and the start of sexual maturation which stresses the link between metabolism and sexual maturation, also suggesting an important role for exercise. Exercise has been tested with eels in swim tunnels and was found to stimulate the onset of sexual maturation. In this study, we have investigated the interplay between migration and maturation in the field during the downstream migration of female silver eels. Temporal changes in migratory status and sexual maturation among silver eels of the upstream Rhine River system over 3 months of the migration season (August, September and October) were determined in biometrical parameters, plasma 17β-estradiol and calcium levels, oocyte histology and gonadal fat levels. Furthermore, the ecological relevant parameters age as determined by otolithometry and health aspects indicated by haematocrit, haemoglobin and swim-bladder parasite load were measured. Silver eels were estimated to be 14 years old. A strong temporal progression in migratory stage was shown over the months of downstream migration. Catches probably represented a mix of reproductive migrants and feeding migrants of which the ratio increased over time. Furthermore, this study confirmed our hypothesis linking the migratory stage to early maturation as indicated by enlargement of the eyes, oocyte growth and fat deposition in the oocytes, exactly the same changes as found induced by exercise but not ruling out environmental influences. Migrants show extensive fat uptake by the oocytes, probably stimulated by the swimming exercise. In addition, at least 83% of the silver eels in this spawning run may have suffered from negative effects of swim-bladder parasites on their swimming performance. [ABSTRACT FROM AUTHOR]

The article focuses on the findings of a study concerning the use of acoustic tagging in determining adult spiny lobster or Panulirus argus movement patterns in the Western Sambo Ecological Reserve in Florida. Researchers used acoustic telemetry in studying the movements of spiny lobster during the spring and summer of 2003 and 2004 in Hawk Channel. They found that lobsters showed greatest movement after sunset and before sunrise with less movement between midnight and 2:00 a.m. Moreover, the study noted that female lobsters exhibit movement patterns consistent with reproductive migrations to the forereef.

Objective: To investigate the consequences of a law introduced in Italy in 2004 that forbids the fertilization or injection of more than three oocytes for assisted reproduction and does not allow any embryo selection or cryopreservation. Design: Retrospective observational analysis. Setting: Subfertile patients enrolled in an assisted reproduction program. Patient(s): Before the introduction of the law there were 1,179 cycles and after its enactment there were 1,860 cycles in 1,619 subfertile couples. Intervention(s): Ovarian stimulation for IVF/intracytoplasmic sperm injection (ICSI) attempts. Main Outcome Measure(s): Pregnancy and implantation rate. Result(s): Pregnancy rates (PR) per cycle (24.34% vs. 23.11%), per retrieval (28.64% vs. 25.65%), per transfer (31.37% vs. 27.74%), and the take-home babies per started cycle (19.1% vs. 18%) was not significantly different between the two periods. After introduction of the law, the PR significantly decreased in patients whose total motile sperm count was <1 × 106 (40.85% vs. 23.62%) and in patients receiving two embryos (35.71% vs. 23.53%). This difference was mostly the result of a reduced PR in patients <36 years old receiving two unselected embryos (41.16% vs. 30.90%). This result was, however, obscured by the higher proportion of patients <36 years (3.9% vs. 45.12%) receiving three embryos after the enactment of the law, which lead to a significantly higher PR (28.73% vs. 37.56%) and a consequent significantly higher triplet rate (0.58% vs. 4.71%). Conclusion(s): Women in whom elective transfer of two embryos was allowed before passing the law and couples with a severe male infertility factor had significantly reduced success rates. Although the overall PR did not change after the new law, if the transfer of frozen embryos is not considered, this was mainly the result of a higher number of embryos transferred into women <36 years old. This study shows how the negative effects of the new law are obscured by the transfer of a higher number of embryos in younger patients, resulting in a higher PR at the cost of a significantly higher triplet rate. [Copyright &y& Elsevier]

Abstract: Infection with the swim-bladder parasite Anguillicola crassus is suggested as one of the principal causes of the collapse of the European eel population. This nematode has been introduced in Europe from Asia in the 80s and parasitized in a short time Anguilla eel species in different geographical regions across the globe. The parasites drain energy due to their sanguivorous feeding and they cause mechanical damage on the swim-bladder wall. These two effects are hypothesized to impair the spawning migration of the European eel. In this study, we have investigated both effects on swimming performance. We hypothesized that parasitic sanguivorous activities – related to parasite weight – reduce swimming endurance, while mechanical damage of the swim-bladder impairs buoyancy control. Eighty eels suffering various degrees of infection were introduced in swim-tunnels and subjected to a swimming fitness test. The relation between A. crassus infection and swimming efficiency was measured for large female silver eels swimming at various speeds. Infected eels had lower cruising speeds and a higher cost of transport. Eels without parasites, but with a damaged swim-bladder showed similar effects. Almost half of the eels that contained damaged swim-bladders (43%) stopped swimming at low aerobic swimming speeds (<0.7 m/s). Simulated migration trials in a recent related study have confirmed that eels with a high parasite level or with damaged swim-bladder show early migration failure (<1000-km). Reduced swimming performance appears to be associated with swim-bladder dysfunction. As we found that especially silver eels have much higher infection levels than yellow eels, it is concluded that migrating silver eels with severely infected or damaged swim-bladders are unable to reach the spawning grounds. [Copyright &y& Elsevier]

Abstract: In this study, we subjected eels from Lake Balaton (Hungary) to a swimming period of 1 week and 2 or 6 weeks. Most eels were silver and were 13–21 years old. Time dependent changes in morphometrical parameters and developmental characteristics of the oocytes were determined. Already after 1 week of swimming, the gonadal mass increased and oocytes became larger, filled with large numbers of lipid droplets. After 2 and 6 weeks of swimming we found in addition a significant enlargement of the eyes, which is a sign of sexual maturation. In contrast to the resting eels, that had oocytes in the primary growth phase (stage 1–2); the swimming eels had oocytes in stage 3; the cortical alveolus or lipid droplet stage. The results indicate that lipid mobilisation induced by swimming is a requirement for the natural incorporation of lipid droplets in the oocytes, a crucial step in oocyte maturation. As the Balaton eels responded stronger to swimming than young farmed eels, it is suggested that older eels are more sensitive for maturation triggers. [Copyright &y& Elsevier]