Late Juveniles Research Articles

Adamts9 is required for the development of primary ovarian follicles and maintenance of female sex in zebrafish.

Previous studies have suggested that adamts9 (a disintegrin and metalloprotease with thrombospondin type-1 motifs, member 9), an extracellular matrix (ECM) metalloprotease, participates in primordial germ cell (PGC) migration and is necessary for female fertility. In this study, we found that adamts9 knockout (KO) led to reduced body size, and female-to-male sex conversion in late juvenile or adult zebrafish; however, primary sex determination was not affected in early juveniles of adamts9 KO. Overfeeding and lowering the rearing density rescued growth defects in female adamts9 KO fish but did not rescue defects in ovarian development in adamts9 KO. Delayed PGC proliferation, significantly reduced number and size of Stage IB follicles (equivalent to primary follicles) in early juveniles of adamts9 KO, and arrested development at Stage IB follicles in mid- or late-juveniles of adamts9 KO are likely causes of female infertility and sex conversion. Via RNAseq, we found significant enrichment of differentially expressed genes involved in ECM organization during sexual maturation in ovaries of wildtype fish; and significant dysregulation of these genes in adamts9 KO ovaries. RNAseq analysis also showed enrichment of inflammatory transcriptomic signatures in adult ovaries of these adamts9 KO. Taken together, our results indicate that adamts9 is critical for development of primary ovarian follicles and maintenance of female sex, and loss of adamts9 leads to defects in ovarian follicle development, female infertility, and sex conversion in late juveniles and mature adults. These results show that the ECM and extracellular metalloproteases play major roles in maintaining ovarian follicle development in zebrafish.

The ontogenetic status of a small hadrosauroid dinosaur from the uppermost Cretaceous of Bulgaria, and implications for the paleobiogeography and assembly of European island faunas

During the latest Cretaceous hadrosauroids were the most numerous and taxonomically diverse herbivorous dinosaurs on the European island archipelago, including diminutive non-hadrosaurid hadrosauroids and lambeosaurine immigrants from Asia and, possibly, from North America. In recent years the existence of small-bodied adult hadrosauroids (or ‘island dwarfs’) in the Maastrichtian of Romania and Spain has been confirmed by histological study of their bones. The first fossils attributable to Hadrosauroidea discovered in Bulgaria (from the upper Maastrichtian Kaylaka Formation) are also of diminutive size, but it has been unclear whether the bones belonged to small adults or simply to juveniles. Here, we subjected a tibia, fibula, indeterminate long bone diaphyseal fragment, and six indeterminate bone fragments, which are associated with the hadrosauroid hind limb elements and assumed to had been broken off from one or more of them during excavation, to a histological analysis. The analysis shows that the specimens belong to a young, actively growing individual(s), as evidenced by the presence of highly vascularized primary tissues in the outer cortex, secondary remodelling mostly restricted to certain areas of the bone sections, and absence of annual growth lines or an external fundamental system that would signify skeletal maturity. The bone matrix of the periosteal tissues exhibits high amounts of parallel-fibered and lamellar bone, similar to the long bones of other European island-living non-avian dinosaurs, a feature probably linked to lower growth rates. In general, the histomorphology and size of the Bulgarian hadrosauroid correspond well with ‘late juveniles’ and young ‘subadults’ in the osteohistologically well-studied hadrosauroid Maiasaura peeblesorum. The presence of a medium-sized hadrosauroid in the south-eastern part of the Late Cretaceous European archipelago suggests a dispersal route that allowed large-bodied terrestrial fauna to populate emergent islands in the region.

Songbird mesostriatal dopamine pathways are spatially segregated before the onset of vocal learning.

Diverse dopamine (DA) pathways send distinct reinforcement signals to different striatal regions. In adult songbirds, a DA pathway from the ventral tegmental area (VTA) to Area X, the striatal nucleus of the song system, carries singing-related performance error signals important for learning. Meanwhile, a parallel DA pathway to a medial striatal area (MST) arises from a distinct group of neighboring DA neurons that lack connectivity to song circuits and do not encode song error. To test if the structural and functional segregation of these two pathways depends on singing experience, we carried out anatomical studies early in development before the onset of song learning. We find that distinct VTA neurons project to either Area X or MST in juvenile birds before the onset of substantial vocal practice. Quantitative comparisons of early juveniles (30-35 days post hatch), late juveniles (60-65 dph), and adult (>90 dph) brains revealed an outsized expansion of Area X-projecting neurons relative to MST-projecting neurons in VTA over development. These results show that a mesostriatal DA system dedicated to social communication can exist and be spatially segregated before the onset of vocal practice and associated sensorimotor experience.

Loggerhead turtle oceanic-neritic habitat shift reveals key foraging areas in the Western Indian Ocean

Loggerhead sea turtles (Caretta caretta) use both oceanic and neritic habitats depending on their life stage, eventually undertaking an ontogenetic shift. Juveniles likely start foraging in a purely opportunistic manner and later seek resources more actively. In the Indian Ocean, it is still unclear where oceanic-stage individuals go, what they do, and importantly where they forage. Yet, such information is crucial to protect this endangered species from anthropogenic threats such as bycatch in fisheries. To address this, 67 individuals (66 late juveniles and one adult) bycaught in the open ocean were equipped with satellite tags and released in the Southwestern Indian Ocean between 2008 and 2021. Most individuals traveled to the Northwestern Indian Ocean where they used neritic habitats of the continental shelf (i.e., largely between 0 and 200-m depth). Using hidden Markov models, we identified three types of movements likely associated with traveling, wandering, and foraging behaviors. We found that the movement characteristics of these behaviors differ depending on turtles’ target destination and habitat (oceanic vs neritic), highlighting different strategies of habitat use among individuals of presumably the same life stage (late juveniles). The turtles that traveled to the Northwestern Indian Ocean encountered warmer waters (mean = 27.6°C, min. = 20.6°C, max. = 33.1°C) than their counterparts remaining in the Southern Hemisphere (mean = 22.5°C, min. = 14.6°C, max. = 29.7°C) but were found foraging at locations with comparable biomass of potential prey (mean = 2.5 g C m-2, min. = 0.5 g C m-2, max. = 10.4 g C m-2) once in the Northern Hemisphere. It remains obscure why these individuals undertook a trans-equatorial migration. Once in neritic habitats, the proportion of time spent traveling was considerably reduced (from 33% to 19%) and allocated to foraging instead. In light of this, it is very likely that the individuals migrated to the Northwestern Indian Ocean to undergo an oceanic-to-neritic ontogenetic shift. Our study sheds light on the behavioral ecology of loggerhead turtles and identifies important foraging areas in the Western Indian Ocean, with the top-three most densely used ones being the Gulf of Oman, the Central Somali Coast, and the Western Arabian Sea.

Mercury isotope clocks predict coastal residency and migration timing of hammerhead sharks

Abstract The management of migratory taxa relies on the knowledge of their movements. Among them, ontogenetic habitat shift, from nurseries to adult habitats, is a behavioural trait shared across marine taxa allowing resource partitioning between life stages and reducing predation risk. As this movement is consistent over time, characterizing its timing is critical to implement efficient management plans, notably in coastal areas to mitigate the impact of fisheries on juvenile stocks. In the Mexican Pacific, habitat use of the smooth hammerhead shark (Sphyrna zygaena) is poorly described, while the species is heavily harvested. Given the large uncertainties associated with the timing of out‐migration from coastal nursery grounds to offshore waters prior to reproductive maturity, a more precise assessment of smooth hammerhead shark movements is needed. Photochemical degradation of mercury imparts mass‐independent isotope fractionation (Δ199Hg) which can be used to discriminate between neonate coastal shallow habitats and the offshore deep foraging patterns of late juveniles. Here, we present the application of muscle Δ199Hg as molecular clocks to predict the timing of ontogenetic habitat shifts by smooth hammerhead sharks, based on their isotopic compositions at the initial and arrival habitats and on muscle isotopic turnover rate. We observed decreases in Δ199Hg values with shark body length, reflecting increasing reliance on offshore mesopelagic prey with age. Coastal residency estimates indicated that smooth hammerhead sharks utilize coastal resources for 2 years prior to offshore migration, suggesting a prolonged residency in these ecosystems. Policy implications. This study demonstrates how mercury stable isotopes and isotopic clocks can be implemented as a complementary tool for stock management by predicting the timing of animal migration—a key aspect in the conservation of marine taxa. In the Mexican Pacific, fishing pressure on shark species occurs in coastal habitats depleting juvenile stocks. Consequently, management decision support tools are imperative for effectively maintaining early life stage population levels over time. The finding that smooth hammerhead sharks extensively rely on highly fished habitats for 2 years after parturition supports the relevance of establishing a size limit in coastal fisheries and demonstrates how the current temporal shark fishing closure could lack efficiency for the species.

Inhibition of alternative oxidase disrupts the development and oviposition of Biomphalaria glabrata snails

BackgroundBiomphalaria glabrata is one of the main intermediate hosts of Schistosoma mansoni, the most widespread species of Schistosoma. Our previous studies proved that alternative oxidase (AOX), the terminal oxidase in the mitochondrial respiratory chain, widely exists in several species of intermediate host snails of Schistosoma. Meanwhile, inhibition of AOX activity in Oncomelania hupensis snails could dramatically enhance the molluscicidal effect of niclosamide. As a hermaphroditic aquatic mollusc, the high fecundity and population density of B. glabrata increase the difficulty of snail control, which is one of the critical strategies for schistosomiasis elimination. The present study aimed to investigate the possible role of AOX in the development and fecundity of B. glabrata snail, which could be manipulated more manageable than other species of intermediate host snails of Schistosoma.MethodsThe dynamic expression of the AOX gene was investigated in different developmental stages and tissues of B. glabrata, with morphological change and oviposition behaviour observed from juvenile to adult snails. Furtherly, dsRNA-mediated knockdown of BgAOX mRNA and the AOX protein activity inhibiting was performed to investigate the effect of AOX on the development and oviposition of snails.ResultsThe BgAOX gene expression profile is highly related to the development from late juveniles to adults, especially to the reproductive system of snails, with a positive correlation of 0.975 between egg production and BgAOX relative expression in ovotestis of snails. The inhibition of BgAOX at the transcriptional level and AOX activity could efficiently inhibit snail growth. However, the interference at the BgAOX protein activity level led to more severe tissue damage and more significant inhibition of oviposition than at the transcriptional level. This inhibition of growth and oviposition decreased gradually with the increase in the snail size.ConclusionsThe inhibition of AOX could efficiently disrupt the development and oviposition of B. glabrata snails, and the intervention targeting AOX at the juvenile stage is more effective for snails. This investigation explored the role of AOX in the growth and development of snails. It would benefit snail control in the future by providing a potential target while using molluscicides more efficiently.Graphical abstract

Morphological variation of the maxilla in modern humans and African apes

Differences in morphology among modern humans and African apes are frequently used when assessing whether hominin fossils should be attributed to a single species or represent evidence for taxic diversity. A good understanding of the degree and structure of the intergeneric, interspecific, and intraspecific variation, including aspects such as sexual dimorphism and age, are key in this context. Here we explore the variation and differences shown by the maxilla of extant hominines, as maxillary morphology is central in the diagnosis of several hominin taxa. Our sample includes adults of all currently recognized hominine species and subspecies, with a balanced species sex ratio. In addition, we compared the adults with a small sample of late juveniles. The morphology of the maxillae was captured using three-dimensional landmarks, and the size and shape were analyzed using geometric morphometric methods. Key observations are that 1) the maxillae of all extant hominine species and subspecies show statistically significant differences, but complete separation in shape is only seen at the genus level; 2) the degree of variation is not consistent between genera, with subspecies of Gorilla being more different from each other than are species of Pan; 3) the pattern of sexual shape dimorphism is different in Pan, Gorilla, and Homo, often showing opposite trends; and 4) differentiation between maxillary shapes is increased after adjustment for static intraspecific allometry. These results provide a taxonomically up-to-date comparative morphological framework to help interpret the hominin fossil record, and we discuss the practical implications in that context.

Trophic Niche Dynamics and Diet Partitioning of King Crab Lithodes santolla in Chile’s Sub-Antarctic Water

The southern king crab Lithodes santolla is one of the most economically important fishery species in the southern waters of the Atlantic and Pacific Oceans. A combination of stomach content and stable isotope analyses was used to reveal the potential dietary characteristics, isotopic niche, overlap among maturity stages and sexes, and trophic relationships of an L. santolla population in the Nassau Bay, Cape Horn region. Stable isotope analyses indicated that L. santolla assimilated energy from a basal carbon source, the giant kelp Macrocystis pyrifera, forming the trophic baseline of the benthic food web. Moreover, the trophic position of L. santolla varied among late juveniles and adults, suggesting that the southern king crab does undergo an ontogenetic diet shift. L. santolla exhibited intraspecific isotopic niche variation, reflecting niche differentiation which allows the species to partition resources. The trophic relationships of L. santolla with the associated fauna suggested some potential interactions for food resources/habitat use when they are limited. This study is the first attempt to characterize the trophic dynamics of the southern king crab in the Cape Horn area and, by generating more data, contributes to the conservation of the king crab population and the long-term management of local fisheries that rely on this resource.

Taphonomy and taxonomy of a juvenile lambeosaurine (Ornithischia: Hadrosauridae) bonebed from the late Campanian Wapiti Formation of northwestern Alberta, Canada.

Hadrosaurid (duck-billed) dinosaur bonebeds are exceedingly prevalent in upper Cretaceous (Campanian–Maastrichtian) strata from the Midwest of North America (especially Alberta, Canada, and Montana, U.S.A) but are less frequently documented from more northern regions. The Wapiti Formation (Campanian–Maastrichtian) of northwestern Alberta is a largely untapped resource of terrestrial palaeontological information missing from southern Alberta due to the deposition of the marine Bearpaw Formation. In 2018, the Boreal Alberta Dinosaur Project rediscovered the Spring Creek Bonebed, which had been lost since 2002, along the northern bank of the Wapiti River, southwest of Grande Prairie. Earlier excavations and observations of the Spring Creek Bonebed suggested that the site yielded young hadrosaurines. Continued work in 2018 and 2019 recovered ~300 specimens that included a minimum of eight individuals, based on the number of right humeri. The morphology of several recovered cranial elements unequivocally supports lambeosaurine affinities, making the Spring Creek sample the first documented occurrence of lambeosaurines in the Wapiti Formation. The overall size range and histology of the bones found at the site indicate that these animals were uniformly late juveniles, suggesting that age segregation was a life history strategy among hadrosaurids. Given the considerable size attained by the Spring Creek lambeosaurines, they were probably segregated from the breeding population during nesting or caring for young, rather than due to different diet and locomotory requirements. Dynamic aspects of life history, such as age segregation, may well have contributed to the highly diverse and cosmopolitan nature of Late Cretaceous hadrosaurids.

Admission and Survival Trends in Hedgehogs Admitted to RSPCA Wildlife Rehabilitation Centres

The hedgehog (Erinaceus europaeus) population is in decline in the UK and they are the most frequently admitted mammal to British Wildlife Rehabilitation Centres (WRCs). Whilst successful, UK rehabilitation is time-consuming and expensive and few large-scale studies into UK WRC admission and survival rates have been published in the last decade. This paper examines admission and survival trends in 19,577 hedgehogs admitted to Royal Society for the Prevention of Cruelty to Animals centres over a 13 year period (2005–2017) to gauge the state of Britain’s hedgehogs in WRCs and to gain indirect insight into the wild population. During the studied period, admissions more than doubled. Admission weights were greater in later than early litter juveniles. The survival improved 26% overall, and 33% in juveniles. Twenty two percent of animals died or were euthanased within 48 h of admission. Kaplan–Meier analysis gave survivor functions of 0.78 at 2 days, 0.66 at 10 days, 0.62 at 20 days, and 0.53 at 80 days. Survival was independent of admission weight in each age category. In particular, survival was greater in early litter juveniles than in adults or late litter juveniles; and across the breeding season diminished in juveniles and increased in adults. These data suggest factors impacting hedgehog survival have remained stable despite population decrease; that care methods have improved; and that late litters are more vulnerable than early. For WRCs this reaffirms that current methods are successful, but that further resources could be directed towards late litters.

Seasonal changes in body size and mass of Red Knots Calidris canutus during autumn migration through southern Baltic

Body size and mass of 1,458 juvenile and 558 adult Knots were measured during autumn migration in Puck Bay, Poland, between 1983 and 1999. The measurements fit well with those gathered along the migration route of Siberian Knots Calidris c. canutus. All linear measurements of adults, except body mass adjusted for size, were significantly higher than those of juveniles. Shorter wing in juveniles than in adults seems to be a general rule regardless of geographical region. Adult females migrated ahead of males, confirmed by decreasing mean measurements. Juveniles carried larger relative energy stores than adults. Puck Bay may be an emergency feeding place for adult Knots, whereas juveniles may use it as one of many stop-over sites. Juveniles were significantly smaller, but had higher adjusted body mass, in late September than earlier, indicating a behavioural difference between late and early birds during preceding stages of migration. Late juveniles probably follow a time-minimising strategy with larger fuel stores and fewer stop-over sites, whereas birds passing in August migrate with very small energetic reserves, making only short flights and stops.

Effects of aging on the skin and gill microbiota of farmed seabass and seabream

BackgroundImportant changes in microbial composition related to sexual maturation have been already reported in the gut of several vertebrates including mammals, amphibians and fish. Such changes in fish are linked to reproduction and growth during developmental stages, diet transitions and critical life events. We used amplicon (16S rRNA) high-throughput sequencing to characterize the skin and gill bacterial microbiota of farmed seabass and seabream belonging to three different developmental age groups: early and late juveniles and mature adults. We also assessed the impact of the surrounding estuarine water microbiota in shaping the fish skin and gill microbiota.ResultsMicrobial diversity, composition and predicted metabolic functions varied across fish maturity stages. Alpha-diversity in the seabass microbiota varied significantly between age groups and was higher in older fish. Conversely, in the seabream, no significant differences were found in alpha-diversity between age groups. Microbial structure varied significantly across age groups; moreover, high structural variation was also observed within groups. Different bacterial metabolic pathways were predicted to be enriched in the microbiota of both species. Finally, we found that the water microbiota was significantly distinct from the fish microbiota across all the studied age groups, although a high percentage of ASVs was shared with the skin and gill microbiotas.ConclusionsWe report important microbial differences in composition and potential functionality across different ages of farmed seabass and seabream. These differences may be related to somatic growth and the onset of sexual maturation. Importantly, some of the inferred metabolic pathways could enhance the fish coping mechanisms during stressful conditions. Our results provide new evidence suggesting that growth and sexual maturation have an important role in shaping the microbiota of the fish external mucosae and highlight the importance of considering different life stages in microbiota studies.

Stage-dependent effects of river flow and temperature regimes on the growth dynamics of an apex predator.

In the world's rivers, alteration of flow is a major driver of biodiversity decline. Global warming is now affecting the thermal and hydrological regimes of rivers, compounding the threat and complicating conservation planning. To inform management under a non-stationary climate, we must improve our understanding of how flow and thermal regimes interact to affect the population dynamics of riverine biota. We used long-term growth biochronologies, spanning 34years and 400,000km2 , to model the growth dynamics of a long-lived, apex predator (Murray cod) as a function of factors extrinsic (river discharge; air temperature; sub-catchment) and intrinsic (age; individual) to the population. Annual growth of Murray cod showed significant, curvilinear, life-stage-specific responses to an interaction between annual discharge and temperature. Growth of early juveniles (age 1+ and 2+ years) exhibited a unimodal relationship with annual discharge, peaking near median annual discharge. Growth of late juveniles (3+ to 5+) and adults (>5+) increased with annual discharge, with the rate of increase being particularly high in adults, whose growth peaked during years with flooding. Years with very low annual discharge, as experienced during drought and under high abstraction, suppress growth rates of all Murray cod life-stages. Unimodal relationships between growth and annual temperature were evident across all life stages. Contrary to expectations of the Temperature Size Rule, the annual air temperature at which maximum growth occurred increased with age. The stage-specific response of Murray cod to annual discharge indicates that no single magnitude of annual discharge is optimal for cod populations, adding further weight to the case for maintaining and/or restoring flow variability in riverine ecosystems. With respect to climate change impacts, on balance our results indicate that the primary mechanism by which climate change threatens Murray cod growth is through alteration of river flows, not through warming annual mean temperatures per se.

Sex and Age-related Parasitism of <i>Clarias gariepinus</i> in earthen ponds in African Regional Aquaculture Centre, Aluu, Rivers State, Nigeria

This study aimed at investigating the sex and age-related parasitic burden of Clarias gariepinus cultured in earthen ponds. Eighty–five (85) fish samples were selected randomly for analyses from three earthen ponds. Sexing was done by the observation of the urinogenital papillae. For parasitological analysis, skin and gill scrapes were taken for external parasites while the stomach and intestines were slit open, rinsed and observed for helminthic worms. Parasites identified included; Chilodonella sp. (0.3%), Ichthyophthirius sp. (41.1%), Trichodina sp. (55%), Icthyobodo sp., (1.0%) and Gyrodactylus sp. (2.4%). From the study 31 out of 56 males and 20 out of 27 females were infected with parasites. Prevalence of infection in males and females were 55.36% and 74.07% respectively. Mean intensity of parasites was also higher for females (150.75) than for males (62.68) Chi square analysis however, revealed no significant effect (p<0.05) of parasitism on gender. It was further observed that juvenile males and early adult females respectively, had more parasites with 55.3 and 92.4 parasite mean intensities. Among age groups, the mid juveniles (25-99g) (19%), late juveniles (100-299g) (65%) and early adults (300-500g) (14%) were most infected, although there was no significant effect (p<0.05). Sex-related prevalence could be based on hormonal changes and reproduction in females, and competitive search for mates by males. Age-related infection was predicated upon active feeding habits reported among fish of these ages It is therefore recommended that routine health checks be carried out for pond cultured fish. Furthermore, that older fish be sorted and kept together, as they would have stronger immunity than younger fish.
 Keywords; Zoonoses, fish infection, late juveniles, earthen pond, Clarias gariepinus, sex, age

Use of an embedded fruit by Nicobar Long-tailed Macaque Macaca fascicularis umbrosus: II. Demographic influences on choices of coconuts Cocos nucifera and pattern of forays to palm plantations

Adaptive pressures of human-induced rapid environmental changes and insular ecological conditions have led to behavioral innovations among behaviorally flexible nonhuman primates. Documenting long-term responses of threatened populations is vital for our understanding of species and location-specific adaptive capacities under fluctuating equilibrium. The Nicobar Long-tailed Macaque Macaca fascicularis umbrosus, an insular sub-species uses coconuts Cocos nucifera, an embedded cultivar as a food resource and is speculated to have enhanced its dependence as a result of anthropogenic and environmental alterations. We explored demographic patterns of use and abandonment of different phenophases of fresh coconuts. To study crop foraging strategies, we recorded daily entry and duration of forays into coconut plantations. We divided age-classes into early juvenile (13–36 months), late juvenile (37–72 months), and adults (>72 months) and classified phenophase of coconuts into six types. Consistent with the theory of life history strategies, late juveniles were found to use a greater number of coconuts, which was considerably higher in an urban troop but marginally higher in a forest-plantation dwelling group. Except in late juveniles, males consumed a higher number of coconuts than females in the remaining age-classes. Owing to developmental constraints, juveniles of both types used higher proportion of immature coconuts though adults showed equitable distribution across phenophases. Pattern of entries to plantations and duration of forays were uniform through the day in the urban troop but modulatory in the forest-plantation group, perhaps due to frequent and hostile human interferences. Observations corroborating adaptations to anthropogenic disturbances are described.

Seasonal abundance and diel behavior of roughneck shrimps (species of Rimapenaeus Pérez Farfante & Kensley, 1997) (Decapoda: Dendrobranchiata: Penaeidae) in northwestern Florida Bay, Florida, USA

Abstract A large number of roughneck shrimps, Rimapenaeus Pérez Farfante & Kensley, 1997, were collected in northwestern Florida Bay, southern Florida over four consecutive years (2000–2003) of monthly sampling during new-moon periods. Juveniles of Rimapenaeus spp. were more abundant than pink shrimp Farfantepenaeus duorarum (Burkenroad, 1939) juveniles, which are well-recognized and abundant inhabitants of Florida Bay. High Rimapenaeus spp. abundance was unexpected because the genus was previously reported only as occasional in Florida Bay. The populations of Rimapenaeus spp. were composed of late postlarvae and immature juveniles, suggesting that the northwestern border of Florida Bay serves as a nursery ground for this species. A clear seasonal recruitment pattern was observed with large peaks of postlarvae and small juveniles occurring in summer-fall and large juveniles in spring. The summer-fall peaks occurred during months with high mean water level and sea surface temperature; these two factors significantly predicted Rimapenaeus spp. abundance. Overnight hourly behavioral studies revealed that Rimapenaeus spp. juveniles were almost exclusively present in the water column during the dark hours of the ebb tide during current speed minimum. Juvenile abundance significantly differed between moon phases with shrimps being virtually absent during the illuminated full moon. These results indicate that Rimapenaeus spp. are phototactic negative, which may explain the low presence of this species in previous Florida Bay surveys conducted during daylight hours. This study highlights the previously unrecognized contribution of the abundance of juveniles of Rimapenaeus spp. to benthic-oriented crustacean communities of western Florida Bay and its border at the southwestern Florida Shelf.

Diet and prey preferences of larval and pelagic juvenile Faroe Plateau cod (Gadus morhua)

The availability of suitable prey during the early life of fish may determine recruitment to the adult population. Since larval and juvenile feeding can be highly selective, their preferences for certain prey species and sizes should be considered when estimating the availability of prey. In this study, diet composition (and prey preferences) of 4984 (1366) Faroe Plateau cod (Gadus morhua) larvae and juveniles between 3 and 63 mm sampled on the central Faroe shelf (62°N, 6.8°W) over an 8-year period was investigated. Cod preyed on successively larger food items as they grew. Yolk-sac larvae consumed phytoplankton, copepod eggs and nauplii before the yolk sac was exhausted. Copepod eggs followed by calanoid nauplii were the predominant and preferred food items in the early larval stage. In the late larval stage these were replaced by small to medium sized (0.6–1.2 mm) copepod species mainly Pseudocalanus sp., Acartia sp. and early stage Calanus finmarchicus, of which the two former species appeared most preferred. Temora longicornis was highly abundant in juvenile cod, but the preference for this species was neutral. Positive selection and high abundance of late stage (≥ 1.5 mm) C. finmarchicus was observed in early juveniles, but C. finmarchicus was replaced by decapod larvae in late juveniles. Other abundant prey species such as Oithona sp. and barnacle larvae occurred in varying numbers in the guts, but were generally not positively selected at any stage. Late larval and early juvenile cod appeared to suffer from unfavourable feeding conditions as they fed on smaller prey than what they prefer potentially indicating bottle necks in the feeding at these development stages.

Analysis of the rates of development and growth of Brachymystax lenok Savinovi during artificial reproduction by the industrial method

The article presents the results of the first research on artificial reproduction in industrial conditions of the endemic, narrow-areal subspecies of Brachymystax lenok Savinovi, which lives in lake Markakol, East Kazakhstan region. The indicators of the heat sum characteristic for each stage of development, the rate of development and growth of the Markakolsky lenok from the moment of pre-breeding to late juveniles are described. To develop technological approaches for artificial fish reproduction, one of the most important points is to determine the optimal conditions for each stage and assess the risks (loss of fish products). At the stage of insemination and transportation of eggs to the place of incubation, the loss was 50 %. The largest losses of fish products were registered during the incubation stage. The most painlessly passed the period of holding and lifting on the float, where the loss was only 3 %. When growing pre-larvae and larvae in the pool, the daily waste did not exceed 1 %. Small-sized animals that were unable to adapt to artificial feeds fell into the waste. Losses during this period amounted to 15 % of the previous stage. In General, the yield of juveniles from the moment of fertilization to the end of the experiment was 16 %. The crucial factor in the development and growth of Lenok Markakolosky is the temperature regime. For the period of embryonic development, the most favorable water temperature is 7–8 °C. From the moment of hatching, the water temperature must be increased to 10–12 °C, and the optimal temperature for the cage growing of fingerlings varies from 12 to 14 °C.

First study of sea turtle strandings in Algeria (western Mediterranean) and associated threats: 2016–2017

Between December 2015 and December 2017 a total of 63 sea turtles were recorded as being stranded along the Algerian coast. The loggerhead sea turtle Caretta caretta was the most commonly stranded species (n = 44) (69.8%), followed by the leatherback Dermochelys coriacea (n = 18) (28.6%) and the green turtle Chelonia mydas (n = 1). There was a slight dominance of the adult size class for stranded loggerhead turtles, while, for the leatherback, late juveniles and adults prevailed. Most loggerhead turtles stranded during the summer months (July and August), whereas most leatherbacks stranded during winter. The breakdown of the strandings by region shows a slight dominance along the western and central shores for C. caretta and a clear dominance in the west for D. coriacea. The primary cause of death was determined in 50.8% of the stranded turtles. Regarding the evidence of interactions with humans the major cause of stranding in loggerhead turtles was incidental catch by artisanal fisheries, followed by boats’ collisions. The main causes of leatherback strandings were boats’ collisions. Algerian data show that human activities affect loggerhead turtles and also prove a significant presence of the leatherback turtle on this coast.

Spatio-temporal distribution of polar cod (Boreogadus saida) and saffron cod (Eleginus gracilis) early life stages in the Pacific Arctic

Polar cod (Boreogadus saida) and saffron cod (Eleginus gracilis) are key fishes in the Arctic marine ecosystem, serving as important trophic links between plankton and apex predators, yet our understanding of their life histories in Alaska’s Arctic is extremely limited. To improve our knowledge about their early life stages (ELS), we described the spatial and temporal distributions of preflexion larvae to late juveniles (to 65 mm in length) in the Chukchi and western Beaufort seas based on surveys conducted between 2004 and 2013, and examined how their abundances varied in response to environmental factors. Species-specific differences in habitat use were found, with polar cod having a more offshore and northern distribution than saffron cod, which were found closer inshore and farther south. Polar cod preflexion and flexion larvae were encountered throughout the sampling season across much of the shelf, which suggests that spawning occurs over several months and at multiple locations, with Barrow Canyon potentially serving as an important spawning and/or retention area. Polar cod ELS were abundant at intermediate temperatures (5.0–6.0 °C), while saffron cod were most abundant at the highest temperatures, which suggests that saffron cod may benefit from a warming Arctic, while polar cod may be adversely affected. This research provides new insights into how environmental variability influences the distribution and abundance of gadids in the Pacific Arctic and advances our understanding of the habitats occupied by these key forage species during their first few months of life.