Reproduction is a key process shaping the population dynamics and ecological impact of gelatinous zooplankton. In the ctenophore Mnemiopsis leidyi, temperature is widely considered a key driver of reproductive success, yet its relationship with reproductive output (RO) has rarely been evaluated experimentally across a broad thermal gradient. Here, laboratory experiments were conducted to examine how temperature influences whether individuals reproduce and their RO across a range of 7–27 °C. Adult individuals were collected in Mar del Plata Harbour (Argentina) during the spring-summer seasons (2023–2025). Reproduction was rare or absent at temperatures ≤ 10 °C, but occurred consistently between 15 and 27 °C, supporting the existence of a lower thermal threshold for reproduction in M. leidyi. Above this threshold, RO remained highly variable, and no consistent relationship between RO and temperature was observed under the short-term experimental conditions. These findings indicate that temperature influences whether reproduction occurs, while variation in short-term RO above the thermal threshold is likely driven by additional biological and ecological factors.

The Yellowtail Amberjack (Seriola lalandi) is a highly mobile Carangid species of significant recreational, commercial, and aquacultural value. In the Southwestern Atlantic (SWA), however, knowledge of its ecology remains scarce, limited to two previous studies. Here, we report a southward extension of its known range to 43 degrees S, approximately 5 degrees (560 km) beyond previously reported latitudes. Using a combination of fishers' interviews, baited remote underwater video stations (BRUVS), and gonadal histology, we assessed the local occurrence, population structure, and reproductive traits of the species at its southern distribution limit. Semi-structured interviews with recreational spearfishers and artisanal fishers revealed an increase in both local abundance and seasonal persistence of S. lalandi since 2019, shifting from summer-restricted occurrences to extended presence from October to May. BRUVS recorded the species in 1.36% of deployments over hard bottom habitats up to 43 degrees S, concurring with empirical knowledge gathered on interviews. Gonadal histology indicated developing and regressing phases from November to April, with peak gonadosomatic index (GSI) values in December, suggesting potential regional spawning activity. These findings confirm the recent establishment and seasonal persistence of S. lalandi populations in Patagonian waters, consistent with poleward range expansions documented elsewhere and likely influenced by regional ocean warming. Currently, S. lalandi occupies two distinct areas in the SWA during the same seasonal window: a northern zone (35-38 degrees S) and a southern zone (around 43 degrees S). Differences in size distribution and reproductive timing suggest the existence of two seasonally overlapping but potentially distinct stocks. These findings provide novel insights into the biogeography and reproductive ecology of S. lalandi in the SWA and raise key questions regarding stock structure, migratory connectivity, and overwintering habitats, offering a foundation for future ecological studies and management strategies in a changing ocean.

The emerald notothen, Trematomus bernacchii, is a key Antarctic fish species with a circumantarctic distribution; however its life history traits remain understudied in some areas such as the West Antarctic Peninsula (WAP). This study examines the reproductive biology, age structure and growth rate of T. bernacchii from Paradise Bay, based on specimens collected in the austral summer of 2019 and 2023. A total of 285 individuals were analyzed for size, sex composition, gonadal development, and age estimation through otolith readings. Females were significantly more abundant and attained larger body sizes and older ages than males. The von Bertalanffy growth model indicated sex-related differences in growth rates, with females achieving larger asymptotic sizes. As in many other notothenioids, histological analyses of females confirmed a group-synchronous ovarian organization, with a predominance of spent individuals, suggesting a spawning period occurring prior to the sampling period. Males also exhibited post-spawning gonadal conditions with empty spermatocysts. The estimated spawning dates, in combination with previous circumstantial findings in the area, suggest that Paradise Bay might serve as a spawning ground for this species. These findings provide new insights into the population dynamics and reproductive strategy of T. bernacchii in the WAP, filling a knowledge gap for this region.

Lithodes santolla is a key benthic resource in the Patagonian region of South America, sustaining major fisheries in Chile and Argentina. Assessing population condition is essential, as it influences recruitment dynamics and informs sustainable management. This study evaluated energy allocation and physiological condition in adult females during the pre-reproductive period. Samples were collected during the austral spring of 2024 from the central Patagonian sector (43° 30′ S-48° 00′ S). Proximate composition (moisture, protein, and lipid contents) and energy density were determined in muscle, hepatopancreas, and ovary across three management zones: northern national waters (NN), southern national waters (SN) of 46° S, and San Jorge Gulf (GSJ). The ovary exhibited the highest energy density, followed by the hepatopancreas, while muscle showed lower values. Most females were in ovarian regression or post-ovigerous stages, indicating entry into a new molt-reproduction cycle. Consistent with this condition, the ovary exhibited high protein and lipid contents and showed no significant spatial variation. In contrast, females from SN sector tended to exhibit higher hepatopancreatic protein content, whereas females from NN sector showed higher muscle moisture and lower protein content. These findings provide new insights into tissue-level energy allocation patterns in female L. santolla and highlight the need for future studies encompassing additional stages of the reproductive cycle, which could contribute to a better understanding of temporal variation in energy allocation and reproductive physiology in the central Patagonian sector.

The existing literature has classified Engraulis anchoita larvae as exclusively zooplanktophagous, with copepod eggs and nauplii larvae as their main prey. However, there is evidence that other plankton components that have not been identified by intestinal content analysis may be a part of their diet. The objective of this work was to explore trophic positions and main food sources of E. anchoita larvae by analyzing stable nitrogen and carbon isotopes (δ15N and δ13C) with respect to other plankton components (particulate organic material, calanoid copepods, and chaetognaths) at a fixed sampling station close to the coast of the Province of Buenos Aires, Argentina, southwest Atlantic. Samples were collected at different times of the year between the end of 2016 and the beginning of 2018. By averaging δ15N and δ13C values of all surveys, it was found that the anchovy larvae in their three development stages coincided with the same trophic position as chaetognaths, suggesting that their diets overlap. When surveys carried out in autumn were analyzed separately, trophic levels of anchovy larvae differed in a staggered manner among their stages, being situated between the positions of copepods and chaetognaths. Compared to other stages of development, anchovy larvae in the preflexion stage consumed a higher proportion of particulate organic material rather than small copepods. These findings suggest that anchovy larvae may consume a variety of food items and shift their trophic position in response to environmental conditions.

Understanding the life history traits of Antarctic fish species is crucial for effective management and conservation purposes. This study provides a comprehensive evaluation of the reproductive dynamics, age and growth characteristics in Trematomus newnesi, a common nototheniid species in the High-Antarctic zone. Field observations conducted in Potter Cove, South Shetland Islands, revealed significant variations in photoperiod and water temperature from November to March, with water temperatures reaching a peak in mid-December. The gonadosomatic index, as a proxy of gonad development, increased exponentially in both sexes from November to March. Sex steroid plasma levels, particularly testosterone (T) and estradiol (E2), showed significant temporal variations, with a significant increase in the period when late vitellogenesis was evident, suggesting the proximity of final maturation and spawning. Age estimation through otolith readings provided a range of ages up to five years for both sexes. Comparison with previous studies on T. newnesi from other Antarctic areas highlighted similarities in reproductive patterns and differences in growth parameters. Photoperiod and an increase in temperature resulted to be trigger factors promoting vitellogenesis in T. newnesi, ending in an early austral autumn spawning event. The environmental cues and reproductive data recorded at Potter Cove suggest that this area serves as a spawning ground for T. newnesi. Likewise, larval hatching was estimated to occur from early to mid-August, after an egg incubation period of four months. Overall, this study provides insights into the life history traits of T. newnesi, as a valuable contribution for appropriate management and conservation of Antarctic fish populations.

The term ‘condition’ is used to describe the overall health status of an animal and to describe its energy reserves. The storage and use of energy reserves are fundamental components of a species’ life strategy, and these processes directly influence the balance between current and future reproductive success. Understanding the energy allocation strategy adopted by a species is an important aspect in assessing possible variations in reproductive potential. The aim of this work was to analyse the seasonal variations of condition indices, biochemical composition, and energy density of different tissues in order to determine the strategy of energy allocation during the reproductive cycle of females Acanthistius patachonicus. Mature females were collected between April 2016 and March 2017 from commercial landings. Biochemical components such as lipids, proteins, and water content were measured in liver, gonad and muscle. The gonadosomatic index was highest during winter, at the beginning of the reproductive period, while the hepatosomatic index and condition factor did not differ among seasons. The study of the proximal composition of tissues revealed that the liver was the primary source of energy reserves. Highest values of these reserves in the liver were found before the onset of gonadal maturation (autumn). As the reproductive period progresses (winter and spring), these energy reserves decreased significantly, suggesting they were mobilized to support reproductive processes. This suggests that A. patachonicus primarily adopts a capital breeding strategy, but females possibly incorporate energy by feeding during the spawning period.

Fish larvae feeding success is crucial for adult recruitment, which affects both fisheries and ecosystem regulation processes. Engraulis anchoita is a species of great ecological and fishing relevance in the South-West Atlantic Ocean, with a wide latitudinal distribution and active spawning throughout the year and strongly associated with frontal areas. E. anchoita larvae have been described as exclusively feeding on small copepods and their early developmental stages. In this study, the diet, nutritional condition, and daily growth of E. anchoita larvae were estimated in different environmental scenarios in the South-West Atlantic Ocean. Carbon and Nitrogen stable isotopes analysis, otolith microstructure analysis, and RNA/DNA index determination were performed. The larval diet, which was evaluated based on the availability of potential prey, varied with respect to the water column stability. It was observed that the larvae tend to feed on microphytoplankton in stratified waters and on calanoid copepods in waters with a homogeneous vertical structure. The growth and nutritional condition indexes responded to ontogeny, presenting higher values at larger larval sizes. Growth indexes also responded positively to the stratified water column structure in comparison to the homogeneous one. The nutritional condition index was only explained by the size of the individuals. This study found that E. anchoita larvae had greater trophic flexibility than previously suspected, as they included microphytoplankton as the main food item under certain oceanographic conditions without negative impacts on their growth or nutritional condition.

ABSTRACT The early life stages of fish represent a period of high energy requirements due to profound changes that characterize the passage to adulthood, crucial for fisheries recruitment. This study focuses on the North Patagonian Frontal System (NPFS) that guarantees successful larval development and fulfills the three postulates of Bakun's “fundamental triad” in regards to nutrients, concentration of food, and retention of eggs and larvae inside the favorable area. The objective was to evaluate the nutritional condition of Merluccius hubbsi larvae and juveniles, from the Patagonian stock in January during austral summer (2010–2021). The standardized RNA/DNA index (RDs) was used. Interannual variation in the larval condition was observed in relation to NPFS features. RDs were positively linked to the stratification of the water column in the stratified zone. An opposite trend was observed between larval condition and potential egg production that might indicate the existence of density‐dependent mechanisms. On the other hand, the positive relation between larval condition and egg production of older females (≥7 years) supports the idea of a maternal effect on larval survival. There was also a positive relationship between juveniles condition, body size, and recruitment, but no relationship was observed with the stratification of the water column. The high sensitivity of the RDs index links physiological state with survival probability, informing on factors affecting eggs, larvae, and juveniles until their posterior recruitment. This study identified the stratified area of the NPFS as a favorable nursery zone, providing crucial information for managing populations under high fishing pressure.

The Patagonian redfish (Sebastes oculatus Valenciennes 1833) is a viviparous species inhabiting the mid and outer shelf waters, as well as the rocky reefs along the Patagonian coast of Argentina. At present, the energy allocation strategy of this species during reproduction remains unknown. Thus, in this study, we analyzed the variations in biochemical and bioenergetic condition indices of adult females over a seasonal cycle. A total of 157 specimens were collected by onboard observers in commercial vessels between November 2016 and September 2017. The gonadosomatic index (GSI), morphophysiological condition (hepatosomatic index HSI and relative condition factor Kn), and the proximate composition (lipids, proteins, and moisture) along with energy density in muscle, liver, and gonads, were evaluated. Results showed an increase in lipid and protein reserves in the muscle and gonads during winter, coinciding with the onset of maturation. It was also observed that the energy density (kJ g-1) in the liver and muscle decreases in spring, coinciding with the greatest gonadal development (GSI). The highest energy density values in muscle were recorded during winter, which coincides with increased feeding activity of the species, suggesting a reproductive strategy closer to a ‘capital breeder’, with energy storage prior to the beginning of spawning.

Environmental conditions have a significant influence on the physiological processes that regulate the reproduction of fish. However, there is less information on this subject for chondrichthyans, and particularly for males. This study describes the spermatogenic cycle of the narrownose smooth hound shark Mustelus schmitti related to sex steroid plasma levels and the potential influences of photoperiod and temperature as reproductive cues. A total of 70 males were caught bi-monthly for over a year in the coastal waters of Argentina. Testicular samples were taken for histological characterization and blood samples were taken for the measurement of testosterone (T) and progesterone (P4) plasma levels from each male. Bottom temperature was recorded at each sampling point and the daily photoperiod was estimated from Julian Day Calendar. Histological assessment revealed that the complete cycle of spermatogenesis in M. schmitti lasts just over a year, with the onset of the new spermatogenic cycle (spermatocyte formation) overlapping with the end (spermiation and filling of the seminiferous ducts) of the previous cycle. This particular phase was associated with the peak in T plasma levels, which was found to be significantly explained by the increase in photoperiod in spring. The rise in temperature above 15–16 °C at the end of spring was significantly associated with a reduction in T plasma levels. Additionally, an elevation in P4 plasma levels was observed after the photoperiod increase phase. Males would be ready to mate from mid-spring, following female parturition and just before ovulation/pregnancy.

Understanding the reproductive biology of Antarctic notothenioid fish species is crucial for effective management and conservation efforts. This study investigates the reproductive biology of Notothenia coriiceps, focusing on the location of spawning grounds and the influence of environmental factors on this process. Sampling included 120 specimens caught at Potter Cove, South Shetland Islands, from November to late March of years 2016-2018 (austral spring -summer season). Gonadal macroscopic, histologic and physiologic features are reported. Histological analysis revealed two distinct groups of oocytes in the ovaries: a leading clutch of vitellogenic oocytes for the upcoming reproductive event and a second remnant clutch of smaller oocytes in cortical alveoli and primary growth stages. Photoperiod phases significantly associate with variations in the gonadosomatic index throughout ovarian development, indicating the influence of this parameter on fish reproduction at high latitudes. Elevated plasma levels of estradiol during vitellogenesis support its role in stimulating yolk precursor synthesis and incorporation into oocytes. In March, an increase in testosterone levels during late vitellogenesis suggests the proximity of final maturation, ovulation, and spawning. A sharp increase in both sex steroids and accelerated gonadal development of N. coriiceps was particularly evident after water temperature reached maximum values (similar to 2 degrees C), suggesting that high temperature acts as a driver of the physiological mechanisms that allow to complete vitellogenesis and reach the ovulation. Our results show that (1) N. coriiceps females captured in mid-March at Potter Cove were in late developing, suggesting that spawning likely start on April; (2) Potter Cove is likely a spawning ground for N. coriiceps in part due to its thermal regime, emphasizing the importance of inshore areas as spawning grounds for Antarctic notothenioids. Thus, this study underscores the necessity of investigating the impact of water temperature changes on notothenioids reproductive patterns in the context of global warming at West Antarctic Peninsula region.

This study analyzed the inter-annual variability in the reproductive dynamics of the Argentine hake from Patagonian waters during the last 20 years concerning the environmental conditions and the nutritional status of females. Macroscopic and histological information on gonadal maturity, female condition factor (K), and oceanographic data at different sampling sites throughout the studied region were obtained from research surveys carried out during the main spawning season of this species. Four stages, according to the maturity ovarian phases composition, were assigned annually at each sampling site to assess reproductive dynamics: vitellogenesis, ovulation, regression, and resting. The spatial pattern of inter-annual variability in reproductive dynamics was described, and the influence of temperature and female condition on the probability of ovulation and regression was assessed using generalized linear models. The area with the lowest inter-annual variability in the hake reproductive dynamics was observed between 43 and 45 degrees S (50 to 80 m depth) in relation to ovulation events. The vitellogenesis stage was more frequently found adjacent to the reproductive area, whereas the regression was mainly observed in deeper waters. Both bottom and surface temperatures explained the ovulation and regression stages, showing a positive and negative relationship, respectively. Lower values of the K factor, associated with low food availability, were further linked to the occurrence of regression. Finally, it is worth noting that the relationship observed between the ovulation/spawning dynamics of Argentine hake and water temperature suggests that the reproductive success of this species could be affected in the future scenario of climate change.

The Patagonian Redfish (Sebastes oculatus) is a viviparous species that inhabits the mid and outer shelf waters and rocky reefs off the Patagonian coast of Argentina where two morphotypes have been identified: the "dark" or "shallow" (mostly <30 m depth) and the "light" or "deep" (>80 m depth). Information on the reproductive biology of the "light" morphotype is scarce, so the main objectives are to describe the gonadal maturation phases and to determine the oocyte growth pattern of the species in deeper waters. In addition, we analyze the annual cycle of gonadal and liver condition indices in relation to sexual maturity and provide a preliminary estimate of potential fecundity. Samples were collected on commercial vessels by on-board observers between November 2016 and October 2017. The pattern of oocyte development showed that S. oculatus is a group-synchronous species, with gonad development beginning in the late austral winter and continuing into the spring, while larval emergence occurs in spring and early summer. Males mature before females, so copulation may occur in the fall, and females would retain sperm in the ovary until oocyte fertilization. The evidence suggests that viviparity of this species is lecithotrophic, and positive relationships have been found between relative fecundity with maternal size, which indicate that larger and older females have greater reproductive potential (producing more eggs than younger individuals).

This is the first description of diurnal pelagic aggregations of the bottom-dwelling Argentine red shrimp (Pleoticus muelleri) registered with a broadband scientific echosounder. A pelagic trawl net and an underwater video camera were used to validate all the information presented in this paper. Shrimp aggregations were characterized by increasing frequency response, more evident at frequencies greater than 120 kHz. Identification of the acoustic signature of this resource is of particular interest for the development of new methodologies to complement the traditional swept area method of estimation.

Assessing the ecological role of ctenophores is crucial to understanding ecosystem functioning, including the recruitment of fish stocks. During austral summer in the North Patagonia Ecosystem (NPE) (41-48°S), the ctenophores Mnemiopsis leidyi and Pleurobrachia pileus co-occur with the peak of ichthyoplankton abundance of 2 important fishing resources: the Argentine anchovy Engraulis anchoita and the Argentine hake Merluccius hubbsi , in association with a highly productive tidal front system. We analyzed 367 plankton samples collected in the NPE over 13 yr (2005-2018) to determine the abundance and spatial distribution of M. leidyi and P. pileus , their spatial overlap with ichthyoplankton (eggs and larvae of hake and anchovy), and their relationship with environmental features. Both ctenophore species displayed contrasting distributional patterns, associated with different physical environments, particularly temperature. M. leidyi showed a higher spatial overlap with ichthyoplankton compared to P. pileus. In addition, we found a significant negative correlation between the biomass of M. leidyi and the abundance of both fish larvae, suggesting a potential negative impact (via predation and competition) on the survival and recruitment of these 2 fisheries resources.

Comprender las causas que generan la variabilidad del reclutamiento en las poblaciones marinas constituye uno de los mayores desafíos de la ciencia pesquera. Nuestra capacidad predictiva para explicar estas variaciones es relativamente baja, debido a la interacción de factores exógenos y endógenos, que varían en el tiempo y el espacio dentro de las poblaciones. Con el fin de obtener información sobre las fluctuaciones en el reclutamiento de la merluza argentina (Merluccius hubbsi) del stock patagónico, revisamos los resultados obtenidos analizando la ecología reproductiva, la dinámica trófica y energética durante las diferentes etapas de desarrollo de esta especie y su relación con variables ambientales. Observamos que el potencial reproductivo está fuertemente influenciado por las características parentales, particularmente de las hembras, en cuanto a su tamaño, edad y condición. Esta característica, denominada “efecto materno”, sugiere que la biomasa de la población reproductora, comúnmente utilizada como índice de productividad en la evaluación de pesquerías, es un predictor deficiente del reclutamiento. También observamos que la supervivencia durante los primeros años de vida de la merluza se ve afectada por la coincidencia espacial con el Sistema Frontal Norpatagónico, caracterizado por una alta concentración de nutrientes, alta productividad y disponibilidad de alimento. Las condiciones físicas y la densidad larvaria en la zona de crianza afectaron el estado nutricional y la mortalidad de la merluza, principalmente por competencia por alimento o depredación. Se observó que la transición del hábitat pelágico al demersal en los juveniles se produce durante un período más extenso que el reconocido anteriormente para esta especie, lo que destaca la importancia de utilizar los registros acústicos para complementar la información de las redes de arrastre de fondo. Este es uno de los principales temas a desarrollar para estimar nuevos índices de reclutamiento de merluza argentina, junto con otras líneas de investigación propuestas para mejorar la evaluación del stock.

The reproductive success of aquatic animals depends on a complex web of relationships between the environment, the attributes of the reproductive individuals and human-induced selection. All of them are manifested directly or indirectly through parental effects, which can also compensate for certain external impacts. Parental effects refer to the influence that the phenotype and environmental conditions in which individuals develop exert on the phenotype of their offspring, and they can even have transgenerational impact. This paper describes the different types of parental effects and reviews the published literature to analyze the causes of their variation and their impact on reproductive resilience and population dynamics.

The nutritional condition of anchovy and Argentine hake larvae in the Northern Patagonian Frontal System (NPFS) area was studied in the austral spring of 2018. We hypothesized that this area provides adequate features for larval growth and survival. The RNA/DNA index (RD) and its derived index of growth performance were employed. A critical RD value for starvation was calculated. The percentage of individuals under starvation and in optimal growth conditions was calculated. Because the period of study was the beginning of the hake spawning period, a limited number of larvae of this species were collected. The RD index showed a significant increase throughout larval ontogeny for anchovy larvae, being 1.84±1.39 (N=739) and 2.77±1.50 (N=220) in the pre-flexion and flexion stages respectively. These values were significantly higher at stations close to the NPFS and at the upper level of the water column. No differences were observed throughout the day. The area inside the NPFS showed a lower proportion of starved anchovy and a higher proportion of individuals in optimal growth, standing as a favourable nursing area. For hake larvae, the average RD was 1.64±0.55 (N=15). The great sensitivity of the RD index makes it a powerful tool for assessing the probability of larval survival and posterior recruitment into fisheries and allowing the identification of favourable rearing areas for these important species for fisheries.