Reproductive Migration Research Articles

Reproductive health and Bolivian migration in restrictive contexts of access to the health system in Córdoba, Argentina

ABSTRACTAlthough issues of health have been thoroughly analysed in the field of migration studies, there are still very few studies that seek to understand the reproductive health of women in migratory processes. This article analyses the reproductive health of Bolivian migrant women living in the city of Córdoba, Argentina, through an analysis focused on the community assets that migrants deploy in the health-disease-care process within restrictive contexts of access to the health system. The research consisted of an exploratory study using in-depth interviews with Bolivian migrant women and health professionals through the implementation of semi-structured guidelines. The work shows that, in an environment characterised by a health system that acts to exclude, migrant women develop a series of rational strategies where they draw on community assets embodied in forms of self-care of the body and in community networks. Based on a process of reframing memories related to health practices in the Andean world, these women incorporate these assets and more easily confront the obstacles that they must overcome as migrants in different stages of their reproductive health.

Evaluating the usefulness of natural tags for host population structure in chondrichthyans: Parasite assemblages of Sympterygia bonapartii (Rajiformes: Arhynchobatidae) in the Southwestern Atlantic

The usefulness of parasite tags for population discrimination of elasmobranch hosts remains largely unexplored. In order to assess the existence of different populations of Sympterygia bonapartii in the Southwestern Atlantic using its parasites as biological tags and to evaluate their usefulness as indicators for chondrichthyan hosts, we analysed data on assemblages of both long-lived and short-lived parasites of 193 skates distributed in eight samples caught at different seasons, years, depths and latitudes. A total of 6527 metazoan parasites, belonging to 19 species, was recorded. Only three species were long-lived, being therefore suitable biological tags, and they were used to assess the population structure of S. bonapartii. As a result, three host populations were identified (one Bonaerensean and two Patagonian). Distance-based multiple linear regressions (DistLM) evidenced that latitude was the most important predictor of parasite distribution, confirming the value of long-lived species as biological tags. When short-lived parasites were analysed, most samples differed from each other. Furthermore, a bathymetric rather than a latitudinal pattern was observed across samples, which was associated with reproductive migrations displayed by S. bonapartii. DistLM analyses showed that depth and year were almost as important as latitude as predictors of parasite distribution. This proves the little value of this guild as indicators of host population structure. Transient parasites could be acceptable to study seasonal migrations of their hosts, but it is recommended to avoid their use as tags for population assessment, either alone or combined with long-lived species. This is especially relevant for elasmobranch hosts, for which the numerical dominance of short-lived species in their parasite assemblages is the rule. Based on these results, and upon a careful selection of suitable species, we recommend using parasites as reliable and robust sources of information that provide significant data for the implementation of management measures that ensure the conservation, recovery and sustainable use of elasmobranchs under exploitation.

Ecology of Exercise in Wild Fish: Integrating Concepts of Individual Physiological Capacity, Behavior, and Fitness Through Diverse Case Studies.

Wild animals maximize fitness through certain behaviors (e.g., foraging, mating, predator avoidance) that incur metabolic costs and often require high levels of locomotor activity. Consequently, the ability of animals to achieve high fitness often relies on their physiological capacity for exercise (aerobic scope) and/or their ability to acquire and utilize energy judiciously. Here, we explore how environmental factors and physiological limitations influence exercise and metabolism in fish while foraging, migrating to spawning grounds, and providing parental care. We do so with three case studies that use a number of approaches to studying exercise in wild fish using biologging and biotelemetry platforms. Bonefish (Albula vulpes) selectively use shallow water tropical marine environments to forage when temperatures are near optimal for aerobic scope and exercise capacity. Bonefish energy expenditure at upper thermal extremes is maximal while activity levels diminish, likely caused by reduced aerobic scope. Pacific salmon (Oncorhynchus spp.) reproductive migrations frequently involve passage through hydraulically challenging areas, and their ability to successfully pass these regions is constrained by their physiological capacity for exercise. Aerobic scope and swim performance are correlated with migration difficulty among sockeye salmon (O. nerka) populations; however, depletion of endogenous energy stores can also limit migration success. In another example, male smallmouth bass (Micropterus dolomieu) allocate a significant amount of energy to nest-guarding behaviors to protect their developing brood. Smallmouth bass body size, endogenous energy reserves, and physiological state influence nest-guarding behaviors and reproductive success. We suggest that in some scenarios (e.g., bonefish foraging, Pacific salmon dam passage) metabolic capacity for exercise may be the strongest determinant of biological fitness, while in others (e.g., long distance salmon migration, smallmouth bass parental care) energy stores may be more important. Interactions among environmental and ecological factors, fish behavior, and fish physiology offer important avenues of mechanistic inquiry to explain ecological dynamics and demonstrate how exercise is fundamental to the ecology of fish.

Effects of salinity on gonadal development, osmoregulation and metabolism of adult male Chinese mitten crab, Eriocheir sinensis.

As a catadromous species, salinity is a key parameter that affects gonadal development of Chinese mitten crab Eriocheir sinensis during reproductive migration. It is however unclear the effects of salinity on the gonadal development of male E. sinensis as well as their physiological responses to salinity during reproductive migration. This study investigated the effects of four salinities (0 ‰, 6 ‰, 12 ‰ and 18 ‰) on gonadal development, osmoregulation and metabolism of adult male E. sinensis over a 40-day period. The results showed that elevating salinity promote gonadal development, increase hemolymph osmolality and K+ and Mg2+ concentrations (P < 0.05). The 12 ‰ salinity resulted in the highest contents of taurine and arginine in the hemolymph while the highest contents of threonine, phenylalanine, lysine, ß-alanine, tryptophan, ornithine and total free amino acids were found for 0 ‰ treatment (P < 0.05). A decreasing trend was detected for the Na+/K+-ATPase activity and its mRNA expression level in the posterior gills with salinity (P < 0.05). Total saturated fatty acids in the anterior gills decreased with increasing salinity (P < 0.05); the 0 ‰ treatment had the highest total polyunsaturated fatty acids in the posterior gills while total n-6 polyunsaturated fatty acids increased with salinity (P < 0.05). The hemolymph glucose and uric acid showed a decreasing trend as salinity while an increasing trend was found for the hemolymph triglyceride and high-density lipoprotein cholesterol (P < 0.05). The 12 ‰ treatment had the highest levels of hemolymph malonaldehyde and hepatopancreatic γ-glutamyltranspeptidase (P < 0.05). In conclusion, these results suggested that the brackish water promote gonadal development of male E. sinensis, and increase osmolality and ionic concentrations in hemolymph while reduced the activity of Na+ /K+- ATPase and its mRNA expression in the posterior gills as well as metabolism.

An approach to incorporate individual personality in modeling fish dispersal across in‐stream barriers

Animal personalities are an important factor that affects the dispersal of animals. In the context of aquatic species, dispersal modeling needs to consider that most freshwater ecosystems are highly fragmented by barriers reducing longitudinal connectivity. Previous research has incorporated such barriers into dispersal models under the neutral assumption that all migrating animals attempt to ascend at all times. Modeling dispersal of animals that do not perform trophic or reproductive migrations will be more realistic if it includes assumptions of which individuals attempt to overcome a barrier. We aimed to introduce personality into predictive modeling of whether a nonmigratory invasive freshwater fish (the round goby, Neogobius melanostomus) will disperse across an in‐stream barrier. To that end, we experimentally assayed the personalities of 259 individuals from invasion fronts and established round goby populations. Based on the population differences in boldness, asociability, and activity, we defined a priori thresholds with bolder, more asocial, and more active individuals having a higher likelihood of ascent. We then combined the personality thresholds with swimming speed data from the literature and in situ measurements of flow velocities in the barrier. The resulting binary logistic regression model revealed probabilities of crossing a barrier which depended not only on water flow and fish swimming speed but also on animal personalities. We conclude that risk assessment through predictive dispersal modeling across fragmented landscapes can be advanced by including personality traits as parameters. The inclusion of behavior into modeling the spread of invasive species can help to improve the accuracy of risk assessments.

Bycatch of the Southern King Crab (Lithodes santolla) in the Patagonian shrimp fishery in the Southwestern Atlantic Ocean. Can it contribute to the depletion of its population?

The Southern King Crab (SKC), Lithodes santolla, has supported a growing fishery in San Jorge Gulf (Patagonia, Argentina) since 2011. This fishery is developed by vessels called crabbers. SKC is also caught as bycatch in the Patagonian shrimp fishery, a major crustacean fishery in the Southwestern Atlantic Ocean. In this work, we characterized SKC bycatch in shrimp fishery and compared 1994–1996 data (which reflected little fishing impact) and 2011–2012 data (at the beginning of the current SKC fishery by crabbers in San Jorge Gulf), to determine the particular effects of bycatch on the SKC population. The frequency of occurrence of SKC in shrimp hauls was 84.08%. However, the relative abundance was low, in most of the hauls SCK represented less than 5% of the capture. Between 2006 and 2011, the estimated SKC bycatch was 2432 tn/year. Frequency of occurrence and abundance were higher in the same area where crabbers operate. SKC bycatch is commonly discarded, but, in 18% of the hauls, SKC are processed on board, although this is illegal. Mortality estimated at the beginning of handling was 19%, but this value may be greater due to the long time of onboard handling. SKC bycatch include critic stages of its life cycle such as juveniles, ovigerous females and molting individuals. Juveniles represented 26.9% of the total SKC bycatch, while ovigerous females represented 28.1%. Sex ratios and male size showed no differences between 1994–1996 and 2011–2012, whereas the proportion of ovigerous females decreased between both periods. This decrease can be related to the interference of trawlings in their reproductive migration to coastal waters or in their mating grounds. We consider that the main problem of SKC bycatch is the detrimental effects on its reproductive potential due to the increase in the proportion of non-ovigerous females and the mortality of ovigerous females along with extensive handling, which can also result in a significant egg loss.

Marriage migration, single men, and social reproduction in migrants’ communities of origin in Vietnam

ABSTRACTThis article analyzes the repercussions of marriage migration for Vietnamese communities of origin in two ways. Firstly, it argues that a life-course perspective and the concept of “care circulation” expand understandings of the implications of marriage migration for reproduction and care in countries of origin. Secondly, it documents how marriage migration unsettles reproduction and care patterns primarily because sending communities face difficulties in marrying their own sons to village women. The article is based on extensive ethnographic fieldwork conducted in 2012 in two regions of Vietnam particularly affected by international marriage migration and is informed by other projects conducted since the mid-2000s. Results suggest that migration among young women who migrate without the intention of return bears a different significance for gender and development than migration among women who have moved further along in their life course. Marriage migration in Vietnam takes place at a critical juncture of the life course when gender power relations may be reconfigured in the country of origin. A focus on men and their families in migrants’ communities of origin provides new insight. In sum, a life-course perspective broadens the scope of the relationship between migration, gender inequalities, reproduction, and care.

Tracking the southern Brazilian schools of Mugil liza during reproductive migration using VMS of purse seiners

Brazilian mullet Mugil liza is a schooling fish that migrates in fall and winter, leaving estuaries and coastal lagoons to spawn in ocean waters. In order to understand the reproductive migration pattern of southern stock along Brazil’s coast, we analyzed data collected through the Brazilian Satellite Vessel Tracking Program (Programa Nacional de Rastreamento das Embarcacoes Pesqueiras por Satelite-PREPS) from 2008 to 2012. The migration period overlaps with the fishing season (May-July) when the licensed purse seine fleet fishes along the southern and southeastern coast of Brazil, motivated to capture mullet by the high value of the roe. During the five fishing seasons the average effort was of 51 active vessels. The average time per season that each vessel navigated in the Speed Compatible with Fishing Operation (SCFO) was 349.3 h, which represented an average of 17% of the total time at sea. From May to July the highest frequency (54%) of SCFO transmissions occurred in June ( P 0.05).

Fish diversity in the Río de la Plata and adjacent waters: an overview of environmental influences on its spatial and temporal structure.

The fish diversity and the main environmental factors affecting the spatial distribution of species, life history stages and community structure in the Río de la Plata (RdP) and adjacent waters are reviewed and analysed, with emphasis on the functional guild classification. The functional guild classification indicated that most species in the RdP were marine stragglers, zoobenthivores and oviparous species, although the biomass was dominated by estuarine species. Salinity had a stronger influence than temperature on the spatial pattern for all life stages, shallower and fresher waters are the preferred habitats of neonates and juveniles. During the breeding season (spring-summer), adults showed an intrusion into the inner part of RdP or to its adjacent nearshore waters from the offshore waters for spawning or mating, respectively. Variations in river discharge and wind patterns greatly affected the spatial extent of estuarine water, which ultimately influenced the domain of the main life-history stages (juveniles or adults) for both marine and estuarine fishes, as well as species and fish assemblage composition. The strong environmental gradient restricts some species and life-history stages to a particular section and defines three main fish assemblage areas. The composition of the fish assemblage is indicative of the recruitment of freshwater and marine species to the estuary in opposite ways, determined by the vertical stratification. Seasonal changes in the species composition were related to migration as a result of salinity and temperature variations and reproductive migrations to spawning and mating areas. This overview reveals that the RdP is under environmental variations that are likely to produce modifications to fish distribution and abundance that affect its fisheries. This context plus fish stock declines and changes in exploitation patterns could amplify the magnitude of the variations in the fisheries resources availability and affect the sustainability of fishing communities.

Temperature modulates testis steroidogenesis in European eel

This study evaluates the effects of temperature on hCG-induced spermatogenesis in European eel (Anguilla anguilla), subjected to three thermal regimes: T10: 10°C (first 4weeks), 15°C (next 3weeks) and 20°C (last 6weeks); T15: 15°C (first 4weeks) and 20°C (last 9weeks); and T20: constant 20°C for the duration of the experiment. At 10°C, maturation stopped in the A spermatogonial stage (SPG1), and no further maturation was observed until the temperature was ≥15°C. With the aim of explaining these results, the influence of temperature on steroidogenic enzyme gene expression and steroid synthesis was tested. The initial synthesis of androgens (T and 11-KT) increased at SPG1, and was not influenced by temperature. Likewise, the gene expression of the steroidogenic enzymes linked to androgen synthesis (aacyp11a1, aacyp17-I and aa11βHSD) also increased at SPG1. In contrast, no correlation was seen between the increase in E2 and the aacyp19a1 gene expression peak in the testes, with E2 increasing as a consequence of the seawater acclimation carried out before hormonal treatment, and peaking the aacyp19a1 gene expression at B spermatogonial stage (SPG2). Aacyp21 gene expression was also higher at SPG2, and this stage was only reached when the rearing temperature was ≥15°C.In conclusion, androgen synthesis is not dependent on temperature, but further maturation requires higher temperatures in order to induce a change in the steroidogenic pathway towards estrogen and progestin synthesis. This study demonstrates that temperature plays a crucial role in European eel maturation, even perhaps controlling gonad development during the reproductive migration.

Restricted grouper reproductive migrations support community-based management.

Conservation commonly requires trade-offs between social and ecological goals. For tropical small-scale fisheries, spatial scales of socially appropriate management are generally small—the median no-take locally managed marine area (LMMA) area throughout the Pacific is less than 1 km2. This is of particular concern for large coral reef fishes, such as many species of grouper, which migrate to aggregations to spawn. Current data suggest that the catchment areas (i.e. total area from which individuals are drawn) of such aggregations are at spatial scales that preclude effective community-based management with no-take LMMAs. We used acoustic telemetry and tag-returns to examine reproductive migrations and catchment areas of the grouper Epinephelus fuscoguttatus at a spawning aggregation in Papua New Guinea. Protection of the resultant catchment area of approximately 16 km2 using a no-take LMMA is socially untenable here and throughout much of the Pacific region. However, we found that spawning migrations were skewed towards shorter distances. Consequently, expanding the current 0.2 km2 no-take LMMA to 1–2 km2 would protect approximately 30–50% of the spawning population throughout the non-spawning season. Contrasting with current knowledge, our results demonstrate that species with moderate reproductive migrations can be managed at scales congruous with spatially restricted management tools.

Tracking bluefin tuna reproductive migration into the Mediterranean Sea with electronic pop‐up satellite archival tags using two tagging procedures

AbstractThirteen adult bluefin tuna were tracked with electronic pop‐up satellite tags during their reproductive migration towards Mediterranean spawning grounds as they entered the Strait of Gibraltar. Fish were caught in tuna traps and tagged either underwater, with the aid of a modified spear gun, or on the deck of the boat. Fish tagged on board initially showed a shallower behavior than those tagged in the water. The pattern of horizontal movements was also different between both groups. Shortly after tagging, the eight fish tagged in the water entered the Mediterranean Sea. Six of these fish reached the spawning ground located southwest of the Balearic archipelago before heading back for the Atlantic, whereas the other two traveled farther east, reaching its easternmost longitudes between Formentera and Sardinia and the South Tyrrhenian Sea, respectively. In contrast, two out of the five fish tagged on board never entered the Mediterranean Sea, and another one did enter the Mediterranean when the reproductive season was already over. These results suggest an impact of the tagging procedure on the post‐release behavior of bluefin tuna. Excluding the tags that popped‐off east of the Strait of Gibraltar, bluefin tuna stayed in the Mediterranean Sea for 22–28 days. Analysis of the median depth indicated a shallow behavior during both day and nighttime throughout the return phase of the fish from the Mediterranean Sea to the Atlantic Ocean with the exception of the area around the Strait of Gibraltar, where they showed a deeper behavior that coincided with a marked vertical gradient in the currents.

Simulated migration under mimicked photothermal conditions enhances sexual maturation of farmed European eel (Anguilla anguilla)

Sexual maturation from puberty to adulthood in European eels (Anguilla anguilla) occurs during and/or after the ~6000km 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 (2weeks; 689km) and subsequent seawater migration (9weeks; 3,103km) under mimicked photothermal conditions, using farmed silver eels. Silver eels swam under an 8hour light:16hour 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.

Repeated vertical movements of mature anguillid eels in a lake

Reproductive migration is a critical phase in the life history of anguillid eels. Nevertheless, fine-scale behaviours of migrating eels remain unknown, primarily due to the difficulty in attaching high-resolution recording devices to, and recovering them from, these small-sized teleosts. We attached a small accelerometer with time-scheduled release system to mature Anguilla celebesensis and A. marmorata in Lake Poso, Indonesia, during the pre-migration period. The eels repeated up-and-down movements in the water column (maximum depth, 77m), with slower, less active descents at shallower pitch angles, followed by faster, more active ascents at steeper pitch angles. The asymmetric diving pattern indicates negative buoyancy of the eels, which was confirmed by the measurements of body densities. The repeated diving is unlikely to represent foraging or thermoregulation because mature eels are thought to fast and water temperature changed little with depth. We suggest that the repeated diving is a result of the eels’ internal motivation for continuous swimming in preparation for oceanic migration, and is possibly energetically more efficient than if they keep swimming at a certain depth. The swimming energetics of eels in nature might be more complicated than previously thought because of the effect of vertical movements and non-neutral buoyancy.

Gonadal transcriptome analysis of wild contaminated female European eels during artificial gonad maturation

Since the early 1980s, the population of European eels (Anguilla anguilla) has dramatically declined. Nowadays, the European eel is listed on the red list of threatened species (IUCN Red List) and is considered as critically endangered of extinction. Pollution is one of the putative causes for the collapse of this species. Among their possible effects, contaminants gradually accumulated in eels during their somatic growth phase (yellow eel stage) would be remobilized during their reproductive migration leading to potential toxic events in gonads. The aim of this study was to investigate the effects of organic and inorganic contaminants on the gonad development of wild female silver eels. Female silver eels from two sites with differing contamination levels were artificially matured. Transcriptomic analyses by means of a 1000 candidate gene cDNA microarray were performed on gonads after 11weeks of maturation to get insight into the mechanisms of toxicity of contaminants. The transcription levels of several genes, that were associated to the gonadosomatic index (GSI), were involved in mitotic cell division but also in gametogenesis. Genes associated to contaminants were mainly involved in the mechanisms of protection against oxidative stress, in DNA repair, in the purinergic signaling pathway and in steroidogenesis, suggesting an impairment of gonad development in eels from the polluted site. This was in agreement with the fact that eels from the reference site showed a higher gonad growth in comparison to contaminated fish.

Environmental conditions and physiological state influence estuarine movements of homing sockeye salmon

The reproductive migration of anadromous salmonids through estuarine waters is one of the most challenging stages of their life cycle, yet little is known about the environmental and physiological conditions that influence migratory behaviour. We captured, sampled tissues, tagged and released 365 sockeye salmon (Oncorhynchus nerka) homing through inner coastal waters towards the Fraser River, British Columbia, Canada. Biotelemetry was used to assess the behaviour of individual sockeye salmon approaching estuarine waters and at river entry, which were related to both fish physiological condition at release and to prevailing environmental conditions. Sockeye salmon tended to stay close to the shore, migrated during the day, and movements were related to tide. Sockeye salmon migration rate was linked to wind-induced currents, salinity and an individual's physiological state, but these factors were specific to location and stock. We propose that wind-induced currents exposed sockeye salmon entering the estuary to stronger olfactory cues associated with Fraser River water, which in turn resulted in faster migration rates presumably due to either an increased ability for olfactory navigation and/or advanced reproductive schedule through a neuroendocrine response to olfactory cues. However, once the migration had progressed further into more concentrated freshwater of the river plume, sockeye salmon presumably used wind-induced currents to aid in movements towards the river, which may be associated with energy conservation. Results from this study improve our biological understanding of the movements of Fraser River sockeye salmon and are also broadly relevant to other anadromous salmonids homing in marine environments.

First evidence of potadromy and partial migration in black basses: shoal bass Micropterus cataractae (Actinopterygii, Centrarchidae) in the Upper Flint River, USA

Potamodromy, migration for reproduction within freshwater systems, is widely practiced among fishes, but has rarely been reported for Micropterus spp. Recent evidence has shown that shoal bass (M. cataractae; Williams & Burgess, 1999) in the upper Flint River, USA, undergo migrations during the spawning season to large shoal complexes; however, the magnitude and prevalence of these migrations are unknown. To test the hypothesis that these fish exhibit potadromy, 376 shoal bass were tagged with anchor tags over a four-year period. Each spring, shoal bass migrated up to 200 km to reach spawning areas in the piedmont, and these migrations appeared to be more common in fish living in the coastal plain area of the river. Fish from the piedmont area moved less, likely due to proximity of spawning habitat. Results of this study have suggested that shoal bass are highly migratory in connected systems, traveling long distances to spawn in specific areas. Thus, the scope of shoal bass management and conservation has broadened considerably. Other Micropterus species dwelling in lotic habitats may exhibit similar migratory patterns in their native and/or introduced ranges, and this possibility could be examined using mark-recapture techniques similar to those used in this study.

Trophic links of Atlantic Bluefin tuna (Thunnus thynnus L.) inferred by fatty acid signatures

Fatty acid profiles were obtained from perigonadal fat of 98 adult Atlantic Bluefin tuna sampled from 2008 to 2010 at their confluence near the Gibraltar Strait as a consequence of their reproductive migration to the Mediterranean. Ten additional individuals caught, at the same season, off the Canary Islands, a place where no sexual migratory confluence occurred, were also sampled for their fatty acid signatures. Gender was not significant in explaining differences in fatty acids, and other biological traits such as weight, gonad index and fat/gonad ratio all together only accounted for 13.4% of total variation. Body weight was the more relevant factor and showed maximum positive correlation with 18:1n-9 and the 22:6n-3/20:5n-3 ratio (as carnivoy and higher trophic position markers), and maximum negative correlation with the flagellate marker fatty acid, 18:4n-3. Multivariate analysis of fatty acid trophic markers revealed a main source of data variation (66.9%) due to segregation of individuals in which part of the tuna population showed signatures characteristic of trophic resources from high latitude Atlantic ecosystems as revealed by elevated contents of the marker fatty acids, 20:1n-9 and 22:1n-11. The vast majority of tuna individuals were characterized by fatty acid profiles enriched in n-3 polyunsaturated fatty acids and more associated to temperate and subtropical Atlantic ecosystems in which haptophyte/dinophyte markers prevailed over those for diatoms at the base of their corresponding food webs. Fatty acid profiles of tuna from the Canary Islands were less dispersed than those caught at the Gibraltar Strait, reinforcing the assumption of the possible tuna confluence from different trophic grounds in this zone.

Neuroendocrine gene expression reveals a decrease in dopamine D2B receptor with no changes in GnRH system during prepubertal metamorphosis of silvering in wild Japanese eel

Silvering is a prepubertal metamorphosis preparing the eel to the oceanic reproductive migration. A moderate gonad development occurs during this metamorphosis from the sedentary yellow stage to the migratory silver stage. The aim of this study was to elucidate the molecular aspects of various endocrine parameters of BPG axis at different ovarian developmental stages in wild yellow and silver female Japanese eels. The GSI of the sampled female eels ranged between 0.18 and 2.3%, corresponding to yellow, pre-silver and silver stages. Gonad histology showed changes from previtellogenic oocytes in yellow eels to early vitellogenic oocytes in silver eels. Both serum E2 and T concentrations significantly increased with ovarian development indicating a significant activation of steroidogenesis during silvering. In agreement with previous studies, significant increases in pituitary gonadotropin beta subunits FSH-β and LH-β transcripts were also measured by qPCR, supporting that the activation of pituitary gonadotropin expression is likely responsible for the significant ovarian development observed during silvering. We investigated for the first time the possible brain neuroendocrine mechanisms involved in the activation of the pituitary gonadotropic function during silvering. By analyzing the expression of genes representative of the stimulatory GnRH control and the inhibitory dopaminergic control. The transcript levels of mGnRH and the three GnRH receptors did not change in the brain and pituitary between yellow and silver stages, suggesting that gene expression of the GnRH system is not significantly activated during silvering. The brain transcript levels of tyrosine hydroxylase, limiting enzyme of DA synthesis did not change during silvering, indicating that the DA synthesis activity was maintained. In contrast, a significant decrease in DA-D2B receptor expression in the forebrain and pituitary was observed, with no changes in DA-D2A receptor. The decrease in the pituitary expression of DA-D2BR during silvering would allow a reduced inhibitory effect of DA. We may raise the hypothesis that this regulation of D2BR gene expression is one of the neuroendocrine mechanisms involved in the slight activation of the pituitary gonadotropin and gonadal activity that occur at silvering.

Migration and reproductive biology of Mugil liza (Teleostei: Mugilidae) in south Brazil.

The mullet Mugil liza occurs along the Atlantic coast of South America from Venezuela to Argentina, but 95% of the commercial catch is collected from south Brazil between São Paulo and Argentina. Mugil liza is a single spawner with oocyte development occurring synchronously in two groups. Spawning happens in marine areas and occurs after migration. The reproductive migration occurs from Argentina (38° S) to the southern Brazilian states (24-26° S) from April to July, with peak spawning in June between northern Santa Catarina and Paraná. The presence of hyaline oocytes was associated with high salinity and sea surface temperatures of 19-21° C, and followed the seasonal northward displacement of these oceanographic conditions. The average size at first maturity (Lm ) for both sexes was 408·3 mm total length, LT . Males (Lm = 400·1) matured earlier than females (Lm = 421·9 mm). Fecundity ranged from 818,992 to 2,869,767 oocytes (mean = 1,624,551) in fish that were between 426 and 660 mm LT .