Distribution Of Larvae Research Articles

Ecology and diversity of mosquito larvae in ponds and lagoons of Northwestern Spain.

Galicia, located in the northwestern part of Spain,has a great number and variety of aquatic ecosystems where mosquitoes can breed. Despite the sanitary relevance of these insects, studies on mosquito populations in the region are still scarce. The field research was carried out in 48 sampling points (27 continental lagoons, 12 coastal lagoons and 9 temporary ponds) throughout the entire Galician territory. The samples were collected intermittently and seasonally through different water quality monitoring projects between 2001 and 2017. More than 1500 mosquito larvae belonging to 10 species of five genera (Aedes, Anopheles, Coquillettidia, Culex and Culiseta) were identified. Anopheles (Anopheles) maculipennis s.l. Meigen was the most widely distributed species in the study, being especially dominant in rural areas. In contrast, Culex (Culex) pipiens Linnaeus and Culex (Culex) theileri Theobald showed a preference for breeding in urban areas. New contributions to the knowledge about the larval ecology and distribution of these mosquito species are made throughout this study, including information about the tolerance of each species to water parameters (temperature, pH, dissolved oxygen and conductivity). Likewise, the relationship between culicid diversity and the habitat characteristics of the breeding sites (water body type, climate and level of anthropization) is discussed.

Mesoscale-driven dispersion of early life stages of European eel

The larvae of the European eel travel an extensive distance of approximately 5,000 km from the spawning area in the Sargasso Sea to the European coasts. We here study the larval drift with focus on the effects of mesoscale processes, analyzing data from a targeted survey and modeling possible drift trajectories. The survey covered the initial distribution of larvae in the Subtropical Convergence Zone (STCZ), which is characterized by complex patterns of oceanic fronts and mesoscale eddies. During March–April 2014, sampling was carried out along north–south transects. Hydrography was described using vertical CTD casts and UCTD profiles, and larval distributions assessed from hauls of a large ring net. Patterns in water mass distribution and particle dispersion dynamics were analyzed by reconstruction and diagnosis of mesoscale dynamics, combining satellite observations and Argo profiles. Lagrangian drift trajectories of eel larvae were subsequently simulated starting from a data-driven high-resolution 3D reconstruction of the modeled flow. We found the area of larval distribution delimited by frontal zones, defined by the combined effects of marked longitudinal salinity gradients and large-scale zonal temperature variations. Modeled patterns of eel larvae dispersion were predominantly influenced by the current shear and eddy strain, and while the direction was mainly westward, a significant dispersal was also observed in northeastward directions. Such almost isotropic transport of European eels is supported by historical data on larval size distribution, and results challenge common interpretations of eel larval drift, which propose an initial westward advection of the entire population to the Gulf Stream along the offshore edge of the Antilles current.

Abundance and Distribution of the Larvae of Family Carangidae in the Philippine Waters

A spatio-temporal study on the abundance of the Carangidae larvae in Philippine waters was conducted to minimize the lack of information on their spawning grounds. The study analyzed fish larvae data from M/V DA-BFAR cruises between 2006 and 2018, covering various areas in the Philippines. A total of 589 sampling stations were examined and grouped into seven zones: Batanes-Polillo, Catanduanes-Eastern Samar, Inland waters (Bohol Sea, Davao Gulf, Lagonoy Gulf, Leyte Gulf, Ragay Gulf, Sibuyan Sea, Samar Sea, Tayabas Bay, and the Visayan Sea), Mindanao-Sulawesi Sea, Sulu Sea, West Philippine Sea, and Davao Oriental-Surigao. The results indicated a patchy distribution of carangid larvae, with the highest concentration found in northern Palawan (Sulu Sea and West Philippine Sea areas). The total density of composite samples ranged from 1 to 865 larvae/1000m³. The abundance showed fluctuation over the years, with higher densities in 2016 and 2017 compared to other sampling years. The highest mean density was observed in September 2017 in the West Philippine Sea, while the lowest was recorded in May 2015 in Batanes-Polillo waters. The variations in carangid larvae abundance in Philippine waters are likely related to the species' spawning habits, as the timing of reproduction may vary by region based on ecological factors. Other factors influencing the results include sampling incidence and the sampling period of M/V DA-BFAR.

Distribution and Abundance of Shrimp Larvae in The East Beach of Aceh, East Aceh Regency, Indonesia

Shrimp fisheries are one of the targets for local governments in designing and developing a marine protected area, especially in East Aceh Regency. In general, one of the efforts to preserve shrimp production requires information on larval distribution. The larval phase in the shrimp life cycle is essential for continuing stock production in nature. This study aims to analyse the distribution of shrimp larvae which become potential resources. This study was conducted at ten stations in the coastal area in April and September 2015. The data collected used a “bongo net” with a mesh size of 500 mm with a mouth opening of 60 cm and a length of 3 metres which was pulled flat at a speed of ± 2 knots for 10 minutes. Faund, the highest shrimp larvae abundance, was the family Palaemonidae. At the same time, the lowest was the family Sergestidae. In addition, found two families (Squillidae and Penaidae) were besides these, other shrimp species were grouped in the unidentified category. To conduct further research, such as analysis of habitat utilisation and degradation status that can affect shrimp stocks, risk assessment and evaluation, and support factors, as input in determining the conservation area of shrimp resources.

Genetic Variability of Pacific Rainbow Smelt Osmerus dentex (Osmeridae) from the Seas of Japan and Okhotsk according to the Data of Analysis of Microsatellite Loci and Mitochondrial DNA

The genetic diversity of Pacific rainbow smelt Osmerus dentex from the seas of Okhotsk and Japan has been studied based on nine microsatellite loci and the control region of mitochondrial DNA (940 base pairs). The lowest values of all parameters of genetic diversity of mitochondrial DNA were observed in the group of samples from the northern coast of the Sea of Okhotsk. The highest value of the haplotype diversity was found in the sample from the Sakhalin Island and in rainbow smelt from the Sea of Japan. The star-shaped topology of the genealogical structures indicates a rapid expansion of the abundance and the origin of all populations of the species from a single common ancestor from the main refugium. Based on the results of analysis of nuclear markers, we have revealed a statistically significant genetic structuring of rainbow smelt within its Pacific range (the coefficient of genetic differentiation (FST) is 0.033), which is adequately described by the model of isolation by distance. The greatest genetic differences in two types of markers from the other samples have been found in rainbow smelt from the Shkotovka and Botchi rivers of the basin of the Sea of Japan and from the Naiba River (Sakhalin). The observed patterns of genetic differentiation of Pacific rainbow smelt by the nuclear and mitochondrial markers complement each other well and are most likely associated with differences in the distribution of smelt larvae from the spawning grounds, which are determined by the differentiation of oceanographic conditions.

Surveillance spilled Chironomidae (Diptera) larvae from drinking water treatment plants in South Korea using morphogenetic species analysis and eDNA metabarcoding

Chironomid larvae (Diptera: Chironomidae) are tremendous indicator species that can tolerate a broad range of environmental conditions, from polluted to unimpaired water ecosystems. These species are ubiquitously observed in all bioregions and can even be found in drinking water treatment plants (DWTPs). Detection of chironomid larvae in DWTPs is a critical issue because their presence may be indicative of the water quality in the supply of tap water for human consumption. Therefore, the aim of the present study was to identify the chironomid communities that reflect the water quality of DWTPs and develop a biomonitoring tool to detect biological contamination of the chironomids in DWTPs. To do so, we investigated the identity and distribution of chironomid larvae in seven DWTP areas using morphological identification, DNA barcoding, and sediment environmental DNA (eDNA) analysis. A total of 7924 chironomid individuals encompassing three subfamilies and 25 species of 19 genera were identified in 33 sites within the DWTPs. The Gongchon and Bupyeong DWTPs were dominated by Chironomus spp. larvae, which were correlated with low levels of dissolved oxygen in the water. In the Samgye DWTP and Hwajeong DWTP, Chironomus spp. were almost absent, and instead, Tanytarsus spp. were abundant. Additionally, the Gangjeong DWTP was dominated by a Microtendipes sp., and two species of Orthocladiinae (a Parametriocnemus sp. and a Paratrichocladius sp.) were found only in the Jeju DWTP. We also identified the eight most abundant Chironomidae larvae found in the DWTPs. Furthermore, eDNA metabarcoding of DWTP sediment indicated the presence of different eukaryotic fauna and confirmed the presence of chironomids in DWTPs. These data provide useful morphological and genetic information regarding chironomid larvae that can be used for the water quality biomonitoring of DWTPs to support the supply of clean drinking water.

ON THE ISSUE OF CHANGING THE MORPHOLOGY OF THE SPLEEN IN NEMATODOSES IN MICE DURING IMMUNOSTIMULATION

Background. The study of the reaction of the immune system organs to the introduction of immunomodulators in nematodes is relevant for the development of treatment regimens. The purpose of the study was to examine the spleen (the organ of immunogenesis that plays an important role in the formation of immunity). In addition, the aim of the study was also to find the morphological changes of nematodes (capsules of trichinella larvae) and the features of siphatiа.
 Materials and methods. In the experiment, 35 white mice were used, which were divided into 5 groups of 7 animals in each group. The first and second groups were injected with 0.004 mg saline solution subcutaneously, the 3rd and 4th groups were injected with polyoxidonium at a dose of 0.004 mg/mouse, the 1st and 3rd groups were infected with trichinella larvae, the 2nd and 4th were spontaneously affected by syphilis, the 5th group served as control. Evaluation of the protective properties of polyoxidonium in laboratory models with trichinosis was carried out by determining the intensity of invasion during postmortem studies of all muscle groups of the animal and siphations by the number of eggs in perianal scrapings.
 Results. The study showed protective efficacy with the introduction of polyoxidonium was 99.43%, 57 ± 20 trichinella larvae / per animal were detected in the entire muscle mass, while only 72% with syphaciosis. The parenchyma of the organ of the spleen is a red-white pulp, in healthy animals the area of the red pulp was 70+5% of the area of the organ, and the white pulp was 26.5+ 5% of the mass of the organ. In animals infected with nematodes, the area of the white pulp increased dramatically to 50% of the organ area or more.
 Conclusion. Significant protective activity of polyoxidonium (99.43%) was established in parasitological studies, which was accompanied by an increase in the area of lymphoid tissue associated with the intestine. When studying histological preparations of the spleen, it was noted that the restructuring of the structure under the action of trichinella and siphacia antigens is of the same type: the ratio of red and white pulp, their cellular composition changes. It was found that in all infected animals, the area of the white pulp increased dramatically by more than 60% with trichinosis and up to 50% with syphacosis of the organ area or more. The final result of this thesis was using polyoxidonium, there was also a decrease in the number of eggs in the control group and changes in the number and actual distribution of trichinella larvae in various muscle groups.

CONTAMINATION OF LANDS AND HABITATS OF WILD UNGULATES BY EGGS AND LARVIES OF HELMINTHS OF THE STRONGYLATA SUBORDER

Different types of forest land are not the same, as are the places of circulation of eggs and larvae of helminths of the Strongylata suborder. Plant formations with a low risk of infection are young pine forests, middle-aged and old pine forests, old mixed forests, spruce forests. Potentially dangerous in terms of infection are bushes of river floodplains and forest meadows. Plant formations with a high risk of infection are young mixed forests, middle-aged mixed forests with undergrowth. The most dangerous for infection are swampy forests and forest swamps. The degree of contamination and accumulation of invasive larvae of helminths of the Strongylata suborder in different lands and habitats is different and differs depending on the season of the year. The most favorable for mass infection is the end of summer, the beginning of autumn, namely August-September. The distribution of eggs and larvae of helminths of the Strongylata suborder in forest lands has a mosaic character. The number of plots depends on the areas preferred by wild ungulates. The movement of wild ungulates across the land occurs also under the influence of the anthropogenic factor, which affects the distribution of infection. If we know the habitats of wild ungulates, we can assess the degree of contamination by eggs and larvae of species and characterize the risk of infecting wild ungulates with them. The number of eggs and larvae of helminths of the Strongylata suborder in excrement may vary over time depending on weather conditions. Infection with helminths of the suborder Strongylata occurs through the trophic links of wild ungulates. The addition of young grass vegetation to the diet of wild ungulates in spring leads to an increase in eggs and larvae of helminths of the Strongylata suborder in excrement. In the autumn season, when wild ungulates switch to rough forages, the number of eggs and larvae of helminths of the Strongylata suborder in excrement decreases.

Spatial and seasonal distribution of fish eggs and larvae in one free-flowing river in the Neotropical savanna.

Reproduction is one of the most important biological aspects for the maintenance of viable populations and understanding the spatial and seasonal patterns in the reproduction of Neotropical fish is a point that still needs considerable investigation. In this study, the main aim was to reduce knowledge gaps concerning fish eggs and larvae distribution patterns. For this, we used the River Araguaia basin, one of the main hydrographic basins of the neotropical savanna, as focal point of study. Samplings of fish eggs and larvae were carried across the hydrological regime during flooding and drought events between December 2018 and July 2020 at 15 sites distributed along a 350 km stretch of the River Araguaia basin. Fish eggs and larvae were found in all sampling sites with the highest number of catches in the flood season. The fish larvae were represented by five orders, 22 families, and 22 at the genus or species level. Both environments, tributary and main channel of the River Araguaia, are important for fish reproduction, and no difference was found in the use between the main channel and the tributaries. The results showed that spatial factors are important to explain the change in larval composition, which may have a wide or restricted distribution related to specific habitats. The main factors related to the reproductive activity of fish in this region are the physical and chemical changes in the water that occur in the flood season. These results indicate that the River Araguaia basin has environmental integrity and provides favorable conditions for the reproductive activity of fish, including long-distance migratory species. Considering this, mitigate measures that guarantee the preservation of the natural flow are crucial for the maintenance of fish biodiversity. This article is protected by copyright. All rights reserved.

Diel variability in the vertical distribution of coastal barnacle larvae in the Bay of Cartagena, Chile

BackgroundVertical distribution of zooplankton is an important biological factor that can modulate zooplankton transport, dispersal, and survival in the ocean. Seawater temperature and the associated formation of a thermocline can affect the spatial distribution of organisms in the water column and possibly modulate larval vertical distribution in coastal waters. In this study, we examined larval vertical distribution over small spatial scales where environmental conditions could exhibit strong and fairly predictable variability.MethodsDiel variation in vertical distributions of barnacle larvae across the thermocline was characterized within the Bay of Cartagena of central Chile. Two intensive 21- and 24-h surveys were conducted in the northern (ECIM) and southern (CTGN) extremes of the bay in summer 2016 and spring 2017. In each survey, vertical tows were conducted at both sites every 3 h above and below the thermocline.ResultsDuring summer 2016, larval vertical distribution differed between taxa (balanids and verrucids), barnacle stages (nauplii, cyprids), and sites within the bay. Of all taxa analyzed Balanid nauplii at ECIM were more abundant in the bottom layer during the day and at the surface during the night, suggesting they can control their vertical distribution and follow a diel pattern.Acording to the results all barnacle larvae were found in diferent positions in the water column between day and night during periods of high stratification in this survey.. In spring 2017 all barnacle larvae were confined to the upper layer, despite the strength of stratification, potentially as a result of the intrusion of hypoxic water (< 2 mL L−1) at the bottom, which reached up to around 5 m deep.ConclusionsWe conclude that diel vertical distribution is not uniform across different barnacle larvae taxa and stages within the Bay of Cartagena and is not affected by stratification. Of all the taxa analyzed, only balanid nauplii showed a pattern of diel vertical migration across the thermocline under certain hydrographic conditions.

Shifts in the composition and distribution of Pacific Arctic larval fish assemblages in response to rapid ecosystem change.

The Pacific Arctic marine ecosystem has undergone rapid changes in recent years due to ocean warming, sea ice loss, and increased northward transport of Pacific-origin waters into the Arctic. These climate-mediated changes have been linked to range shifts of juvenile and adult subarctic (boreal) and Arctic fish populations, though it is unclear whether distributional changes are also occurring during the early life stages. We analyzed larval fish abundance and distribution data sampled in late summer from 2010 to 2019 in two interconnected Pacific Arctic ecosystems: the northern Bering Sea and Chukchi Sea, to determine whether recent warming and loss of sea ice has restricted habitat for Arctic species and altered larval fish assemblage composition from Arctic- to boreal-associated taxa. Multivariate analyses revealed the presence of three distinct multi-species assemblages across all years: (1) a boreal assemblage dominated by yellowfin sole (Limanda aspera), capelin (Mallotus catervarius), and walleye pollock (Gadus chalcogrammus); (2) an Arctic assemblage composed of Arctic cod (Boreogadus saida) and other common Arctic species; and (3) a mixed assemblage composed of the dominant species from the other two assemblages. We found that the wind- and current-driven northward advection of warmer, subarctic waters and the unprecedented low-ice conditions observed in the northern Bering and Chukchi seas beginning in 2017 and persisting into 2018 and 2019 have precipitated community-wide shifts, with the boreal larval fish assemblage expanding northward and offshore and the Arctic assemblage retreating poleward. We conclude that Arctic warming is most significantly driving changes in abundance at the leading and trailing edges of the Chukchi Sea larval fish community as boreal species increase in abundance and Arctic species decline. Our analyses document how quickly larval fish assemblages respond to environmental change and reveal that the impacts of Arctic borealization on fish community composition spans multiple life stages over large spatial scales.

Anopheles Larval Rearing.

Mosquito larvae are aquatic and go through four development stages (larval instars L1-L4) before pupation. Species vary in the duration of larval development, and a variety of external factors affect the development rate (e.g., water temperature, food type, and larval density), which are discussed more thoroughly elsewhere. Here, we detail how to rear Anopheles larvae. This protocol describes appropriate distribution of larvae into rearing pans, feeding of larvae, cleaning of pans, and care until pupation.

Simulation of the distribution, growth, and survival rate of chub mackerel larvae and juveniles in the East China Sea

Simulation of the distribution, growth, and survival rate of chub mackerel larvae and juveniles in the East China Sea

Spatial-Temporal Distribution of Fish Larvae in the Pearl River Estuary Based on Habitat Suitability Index Model.

The spawning grounds are important areas for the survival and reproduction of aquatic organisms and play an important role in the replenishment of fishery resources. The density of fish larvae in the Pearl River Estuary (PRE) was analyzed to establish Habitat Suitability Index (HSI) based on marine environmental factors. Survey data and satellite remote sensing data, including sea surface temperature, sea surface salinity and chlorophyll a concentration, from 2014 to 2017 during April-September were analyzed. Results showed that the accuracy of the HSI model based on the larval density and environmental factors was more than 60%, and the distribution trend of HSI was consistent with the distribution trend of larval density. The HSI models constructed based on Arithmetic Mean Model (AMM), Geometric Mean Model (GMM) and Minimum Model (MINM) methods can better predict the spatial-temporal distribution of larvae in the PRE. Among them, the accuracy of the HSI model constructed by the AMM and GMM methods was the highest in April (71%) and September (93%); the accuracy of the HSI model constructed by the MINM method was the highest in June (70%), July (84%) and August (64%). In general, the areas with high HSI values are mainly distributed in the offshore waters of the PRE. The spatial-temporal distribution of larvae in the PRE was influenced by monsoon, Pearl River runoff, Guangdong coastal currents and the invasion of high-salinity seawater from the outer sea.

Toxocara tanuki larval distribution in mice and the infectivity of tissue larvae.

Toxocara tanuki is a common large roundworm in raccoon dogs. Experimental infection studies of T. tanuki in mice were conducted to clarify the distribution and infectivity of larvae in tissue. Groups of BALB/c and C57BL/6 mice (n = 5 mice/group) were each inoculated with 1000 embryonated T. tanuki eggs and necropsied at 7, 31, 91, and 182days post inoculation (dpi). The number of larvae in the central nervous system, heart, lungs, kidneys, spleen, gastrointestinal tract, liver, and carcass was examined. Larvae obtained from the aforementioned mice on different days of the necropsy were orally inoculated into four groups of ICR mice (n = 6 mice/group) that were then necropsied at 21 dpi. Larvae were recovered from all mice. In the BALB/c and C57BL/6 mice, most of the larvae (> 88.7%) were recovered from the liver and the remainder from other tissues. The total number of larvae recovered from C57BL/6 mice was significantly higher than that from BALB/c mice, but no difference in the relative larval distribution within the viscera between the two mouse strains was observed. The mean recovery percentage of larvae from ICR mice infected with 182-day-old tissue larvae was 3.3%. Our findings showed that T. tanuki larvae migrated predominantly to the liver of mice and that the larvae maintained their infectivity for at least half a year.

Macrozoobenthos Structure and Dynamics in a Mediterranean Hypersaline Ecosystem with Implications for Wetland Conservation

Within the framework of hypersaline environments, the Saline di Tarquinia salterns (Latium, Italy) represent an interesting case study from ecological, naturalistic, and conservationist perspectives. We studied macrozoobenthic community zonation related to the main environmental parameters, with particular emphasis on the beetle species Nebrioporus ceresyi (Aubé, 1836), one of the few Dytiscidae among Italian fauna particularly adapted to brackish and hypersaline waters. In this study, we report the structure and seasonal dynamics of the macrozoobenthic community, the spatial and temporal distribution of both larvae and adults of N. ceresyi, and the size–frequency distribution of the larvae. The results add new information on the macrozoobenthic assemblage of the Saline di Tarquinia salterns and the life cycle of this water beetle in the hypersaline habitat. A possible hypothesis about the discontinuous geographical distribution of the species of Dytiscidae investigated is also provided. Finally, N. ceresyi is proposed as an indicator species useful in characterizing the environmental zonation of hypersaline habitats.

Hydropower Dam Development and Fish Biodiversity in the Mekong River Basin: A Review

Over the last few decades, considerable concern has been expressed about the threat of Mekong River Basin hydropower dams to a range of important freshwater riverine fisheries, particularly for fish that seasonally migrate long distances. However, much less attention has been given to the threat of hydropower dams to fish biodiversity in the high-diversity Mekong River Basin, the focus of this paper. Through reviewing the existing state of knowledge regarding Mekong River Basin fish biodiversity, and threats to it, we argue that even though no species are definitively known to have been extirpated from the Mekong River Basin to date, hydropower dam development and various other developments nevertheless pose a serious threat to fish biodiversity. Indeed, dams typically significantly block fish migrations and fish larvae distribution, cause river fragmentation, fundamentally alter river hydrology, and change water quality, all factors that have the potential to intersect with each other and lead to significant species extirpation and extinction, or in some cases, functional extinction, when a small population remains but the important larger population is lost permanently. The circumstances are further exacerbated by the lag time between impact and when that impact becomes evident, cumulative impacts, a lack of consistent data collection, including the collection of base-line data, and insufficient post-project research related to biodiversity. We contend that much more could and should be done to ensure that the Mekong River basin’s exceptional fish biodiversity is not variously diminished and destroyed during the coming years.

Современное состояние биологии, запасов и промысла атерины (Atherina boyeri caspia (Eichwald)) в западной части Среднего и Северного Каспия

The article considers the original results of observations and analysis of the catches of atherina (Atherina boyeri caspia (Eichwald)) by months by stationary nets in the Terek-Caspian fishery subarea (Republic of Dagestan). The size-weight and age indicators of the spawning stocks of atherina have been characterized. For the first time in recent years the conditions for atherina spawning in the western part of the Middle and Northern Caspian are described. All biostatistical indicators of atherina obtained in the recent years (2016–2021) are listed: average linear weight parameters, average fatness coefficient according to Fulton (0.944) indicate a high fattening of fish. Size and weight composition of females and males, age-related fluctuations in length and weight, comparative analysis of atherina concentrations, characteristics of atherina reproduction in the conditions of the Northern and Middle Caspian, fecundity of different age groups, quantitative distribution of roe, larvae and fry of atherina, as well as dynamics of the age composition from catches prove a satisfactory state of stocks of this fish species. Comparative analyses of autumn concentrations of atherina in the Middle Caspian in 1958–1963 and in 2018–2021 are presented, as well as spp/h of trawling, age-related fluctuations in the length and weight in the autumn period (2016–2021). It has been found that atherina in the Caspian Sea is the main object of by-catch when fishing for kilka with stationary seines (in average 56.3 tons per year); it plays an important role as a food component for many fish species (sea herring, sturgeon) and mammals (Caspian seal) living in the waters of the Caspian Sea. Prospective volumes of processing atherina for fishmeal are also considered for the first time. On the scale of the Caspian Sea, with intensive kilka fishing by stationary seines as by-catch, it is possible to catch atherina in the amount of 150–200 tons. Despite the small volumes, they would significantly cover the deficit in the fish feed. Due to the increasing population of atherina in the natural conditions it is required to actively involve atherina in the fishing processes of the organizations in order to maximize the development of the commercial stock.

Age and growth of Aplodinotus grunniens (Perciform: Sciaenidae) in the mid-Usumacinta River

Aplodinotus grunniens represent a crucial artisanal fishery in the Usumacinta River’s middle basin that generates food and a subsistence economy. This study aimed to create a model that best describes growth for A. grunniens and provides information on the growth of this poorly known pecies from the Usumacinta River. Data collection was carried out over one year through monthly sampling. A total of 447 specimens were collected from January to December 2017. Von Bertalanffy’s growth constants were calculated by separate sexes using linear fit and the non-linear Levenberg-Marquardt method. Hotelling’s T-squared test showed that growth was significantly faster in females than males. The estimated age at first maturity was two years in males and three in females. Considering the age reported for A. grunniens in other studies, the age determined in this study indicates that the population could be overexploited. Larger fish are more vulnerable to fishing pressure, mainly during their highest reproductive activity when they aggregate for spawning. More research is needed to evaluate the population status, catch per unit effort, distribution, and abundance of adults, juveniles, and larvae.

Spatial distribution and seasonal variation of fish larvae in the upper 200 m of the Philippine Sea

The Philippine Sea, owing to its complicated circulation pattern and the presence of numerous seamounts, is considered to be a hotspot for biodiversity and an important fishing ground. However, to date, few studies on ichthyoplankton in the Philippine Sea have been conducted. During the summer, autumn, and winter of 2020–2021, a series of investigations were conducted to study the spatial and temporal structure of fish larvae in the Philippine Sea. A total of 65 samples were collected by vertical hauling from a depth of 200 m to the surface. A total of 882 fish larvae representing 81 distinct taxa, 49 genera, and 23 families were identified. A seasonal pattern was also observed based on the differences in abundance and dominant taxa. The abundance of fish larvae was 11.35 ± 12.46 ind./100 m3 (mean ± sd.) in summer, 5.83 ± 7.03 ind./100 m3 in autumn, and 2.57 ± 2.73 ind./100 m3 in winter. The dominant species were Vinciguerria nimbaria, Encrasicholina punctifer, and Cyclothone sp. in summer, V. nimbaria, and Ceratoscopelus warmingii in autumn, and Diaphus spp., D. garmani, and Sigmops sp. in winter. A significant latitudinal variation in fish larvae assemblages was found via cluster analysis, and two geographic groups were separated by the northern boundary of the North Equatorial Current. In addition, the fish larvae species diversity also showed a significant latitudinal gradient in autumn, which disappeared in summer. Canonical correspondence analysis indicated that the structure of fish larvae assemblages was affected by average temperature, salinity, and net primary productivity in the upper ocean and sea level anomaly. All dominant species were associated with specific niche environments. This study suggests that latitudinal zonation of fish larvae also occurs in the oligotrophic low latitude Pacific Ocean and is enhanced in autumn. These results provide multi-seasonal baseline data of fish larvae assemblage in the upper Philippine Sea, being an important reference for the planning of marine protected areas in the high seas.