Yolk-sac Larvae Research Articles

Sagittal otolith microstructure, early growth and development of Coilia ectenes in the Yangtze Estuary, China

Larvae and juveniles of Coilia ectenes were collected in the Yangtze Estuary during June through September 2009 and in May 2011. Our objectives were to reveal the otolith microstructural pattern, and then to reveal the early growth and development process through otolith analysis for C. ectenes. A total of 368 individuals, ranging 4.4-81.2 mm body length (BL) and spanning a continuum from yolk-sac larvae to early juveniles, were analyzed. There is a single primordium in the core of the sagittal otolith, surrounded by a prominent dark band (PD-band) and a wide light area (WL-area). Regular bipartite increments deposit outside of the WL-area. Similar to other Engraulidae species, the PD-band forms corresponding to hatching, increments form daily, and the first increment forms on the 3rd day post hatching, corresponding to the first feeding. The relationship of otolith radius and BL was significantly fitted to a piecewise regression with the inflection point at 34.0 mm BL. Mid-age and mid-size of transition from yolk-sac to preflexion was calculated as 5 days and 6.1 mm BL, from preflexion to flexion was 18 days and 15.2 mm BL, and from flexion to postflexion 29 days and 21.5 mm BL. Mid-size from postflexion to juvenile was 26.6 mm BL. These results can provide an essential basis for future studies on early-life ecology of this species.

Microbial interference and potential control in culture of European eel (Anguilla anguilla) embryos and larvae

Abstract Recent experimental research applying hormonally induced maturation in European eel has resulted in production of viable eggs and yolk-sac larvae. However, present incubation and larval rearing conditions are suboptimal and few larvae survive until onset of first feeding. The aim of this work was to investigate if high mortality during egg incubation and larval culture resulted from microbial interference. By suppressing microbial coverage and activity on fertilised eel eggs using antibiotic and disinfection treatment, egg hatching success and larval longevity were significantly improved. A new approach based on scanning electron microscopy was developed to quantify microbial coverage of eggs. Measurements of microbial coverage in combination with growth curves of egg-associated bacteria indicated that microbial activity rather than physical coverage led to reduced hatch success. In addition, an inverse relationship between microbial coverage of eggs and larval survival indicated that attachment of micro-organisms on the egg surface during the last 24 h of incubation affected later larval survival. These results suggest that microbial control through application of egg surface disinfection in combination with microbial management will be fundamental for improved post-hatch larval survival.

Floating along buoyancy levels: Dispersal and survival of western Baltic fish eggs

Vertical distribution is an important feature of pelagic fish eggs and yolk sac larvae impacting their survival and dispersal, especially in heterogeneous and highly variable estuarine environments like the Baltic Sea. Egg densities determining the vertical distribution pattern were experimentally ascertained for cod (Gadus morhua), plaice (Pleuronectes platessa) and flounder (Platichthys flesus) from the western Baltic Sea. Plaice eggs floated at lower mean (±standard deviation) density range (1.0136±0.0007gcm−3) compared to cod (1.0146±0.0009gcm−3) and flounder eggs (1.0160±0.0015gcm−3), which floated on the highest density level. In flounder egg diameter was significantly related to egg density and in cod a weak correlation could be found between egg dry weight and density. All other relationships between female size, egg size, egg dry weight and egg density were not significant for any of the species. Available egg density data for Baltic Sea cod, plaice and flounder are summarized considering ICES subdivisions and stock management units. A hydrodynamic drift modeling approach was applied releasing drifters in the Belt Sea continuously from December to May, covering the species’ spawning seasons. The model implemented experimentally derived egg density ranges and included ontogenetic egg density modifications for cod eggs, increasing egg density from a late egg development stage to first hatch. A drifter was removed from the model, i.e. considered dead, when its initially prescribed density value exceeded the density range available at the temporally resolved geographical positions along the drift trajectories. Highest survival occurred during releases in April and May but no cohorts survived if they were drifted east into the central Arkona Basin or the central Baltic Sea, irrespective of whether a major Baltic Inflow (1992/1993) or a stagnation-year (1987/1988) was simulated. The dispersal characteristics of the surviving yolk sac larvae of all three species reflected retention within the Belt Sea or northwards transport through the Great Belt into the Kattegat and partly into the Skagerrak. There was no successful transport to more eastern Baltic areas past a hypothetical line from the island of Moen (Denmark) to Kap Arkona on Rügen Island (Germany).

Stage-Specific Ontogeny of Digestive Enzymes in the Cultured Common Dentex (Dentex dentex) Larvae

Stage-specific ontogeny of main digestive enzymes in common dentex, Dentex dentex, were assayed during early life development according to notochord flexion studied from hatching to 45 days after hatching (DAH). The notochord was straight in yolk-sac larvae of D. dentex and preflexion stage was observed between 0 and 18 DAH as 2.75 and 6.27 mm at total length (TL). Then, flexion of the notochord was estimated between 19 and 30 DAH as 6.27 and 10.9 mm at TL. Important alterations in specific activities of all digestive enzymes measured during period of this study were mostly related with metamorphosis and co-feeding. Trypsin and chymotrypsin specific activities were firstly detected on day 3 and were related with mouth opening, whereas they slightly increased until 25 DAH respectively. Pepsin was firstly detected on day 28 and related with stomach formation and a sharp increase was observed until 30 DAH. Both amylase and lipase were measured on day 2 and 4, respectively and they also sharply increased during the first week of life. Additionally, except pepsin, most of the digestive enzyme activities were firstly secreted in the preflexion stage and also gastric secretion started and functional development digestive system were occurred in in flexion and postflexion stages, respectively.

Effects of stocking density and water conditioners on yolk-sac larvae of two marine finfish during simulated air transport

As marine finfish aquaculture expands, there is an increasing interest in the ability to ship early life stages from breeding centres to hatcheries so that each hatchery does not have to maintain its own broodstock. Here, we conducted 24 h air-shipping simulations with yolk-sac larvae of California yellowtail (CYT; Seriola lalandi) and white seabass (WSB; Atractoscion nobilis) to help fill in the informational gaps for shipping marine fish larvae. We examined the effects of a pH buffer on water quality, post-shipping larval survival and subsequent survival to first feeding at larval densities of 1000, 3000, 6000 and 9000 larvae L−1. The pH buffer, 8.3 Trizma®, was tested at varying concentrations of zero (NT = 0.00 g L−1), low (LT = 0.75 g L−1), medium (MT = 1.5 g L−1) and high (HT = 3.0 g L−1). Trials were conducted using replicate 2 L aquarium bags filled with 500 mL of seawater and held in a water bath at 19–20°C. Results showed an interspecific difference in survival at the highest shipping densities under these experimental conditions. Shipping densities up to 6750 CYT larvae L−1 or 3000 WSB larvae L−1 consistently yielded >90% survival immediately after simulated shipment and >85% survival 48 h after the simulations. Furthermore, at these densities, pH was maintained at ~8.0 when buffered at 1.5 g L−1. The highest tested densities of 9580 CYT larvae L−1 and 9940 WSB larvae L−1, yielded lower survival 69–79% and 0.0–1.3% respectively after 24 h. Final pH in the high density CYT trials were unsatisfactory (below 7.0), regardless of the buffer concentration; however pH in the WSB high density trials improved with increasing buffer concentration. On the basis of the results from these air-shipping simulations, we recommend CYT and WSB larvae be shipped in seawater with 1.5 g L−1 Trizma® at densities not greater than 6750 larvae L−1 for CYT and 3000 larvae L−1 for WSB. We believe this represents an important step in improving long distance transport protocols for these species and provides useful guidance in air transport of other economically and ecologically important marine species. Additional research is warranted to compare these simulation results with those from actual air shipments, as we did not account for factors that may vary in flight like temperature and pressure variations, and physical agitation.

Larval development and salinity tolerance of Japanese flounder (Paralichthys olivaceus) from hatching to juvenile settlement

Salinity tolerance and growth of Japanese flounder Paralichthys olivaceus at different developmental stages were evaluated, including newly hatched larvae (nhl), yolk sac larvae (ysl), oil droplet larvae (odl), post oil droplet larvae (podl), premetamorphic larvae (preml) and prometamorphic larvae (proml), at 11 salinities from 5 to 55 g L−1 for 96 h. The ontogenesis during the early life of P. olivaceus was investigated under hatchery salinity 35 g L−1. The results showed that suitable salinities for nhl, ysl, odl, podl, preml and proml larvae were 10 to 25 g L−1, 10 to 30 g L−1, 20 to 30 g L−1, 30 g L−1, 10 to 30 g L−1, 15 g L−1, respectively, demonstrating an ontogenetic variation of salinity tolerance. The salinity tolerance of nhl, ysl, preml was higher than that of odl, podl and proml. The ysl and preml larvae displayed wide salinity tolerances. The present findings demonstrate that the suitable salinity for larviculture of P. olivaceus is 20–25 g L−1 before the depletion of oil droplet; after that, higher salinity (30 g L−1) should be ensured for the post-oil droplet larvae; the premetamorphic larvae can be cultured at a wide salinity range (10–30 g L−1), and the metamorphosed larvae should be reared at salinity about 15 g L−1.

Post-hatch dispersal of lake sturgeon (Acipenser fulvescens, Rafinesque, 1817) yolk-sac larvae in relation to substrate in an artificial stream

Summary Knowledge of the effects of environment and genotype on behavior during early ontogenetic stages of many fish species including lake sturgeon (Acipenser fulvescens) is generally lacking. Understanding these effects is particularly important at a time when human activities are fundamentally altering habitats and seasonal and diel physical and biotic stream features. Artificial stream channels were used in a controlled experiment to quantify lake sturgeon yolk-sac larvae dispersal distance and stream substrate preference from different females (N = 2) whose eggs were incubated at different temperatures (10 and 18°C) that simulated stream conditions during early and late spawning and incubation periods in the Black River, Michigan. Data revealed that yolk-sac larvae exhibited considerable variability in dispersal distance as a function of family (genotype), temperature experienced during previous (embryonic) ontogenetic stages, and environmental ‘grain’. Yolk-sac larvae dispersal distance varied as a function of the juxtaposition of substrate to location of egg hatch. Lake sturgeon yolk-sac larvae dispersed from mesh screens attached to bricks and settled exclusively in gravel substrate. Dispersal distance also varied as a function of family and egg incubation temperatures, reflecting differences in offspring body size and levels of endogenous yolk reserves (yolk sac area) at hatch. Expression of plasticity in dispersal behavior may be particularly important to individual survival and population levels of recruitment contingent upon the location, size, and degree of fragmentation of suitable (gravel) habitats between adult spawning and yolk-sac larvae rearing areas.

Spatio-temporal Variability in Larval-Stage Feeding and Nutritional Sources as Factors Influencing Striped Bass (Morone saxatilis) Recruitment Success

Prey availability and feeding success affect survival of larval striped bass (Morone saxatilis) in Chesapeake Bay and contribute to the >30-fold interannual recruitment variability. Gut contents and stable isotope analyses (δ15N and δ13C) were conducted on striped bass larvae to evaluate sources of nutrition in 2007 and 2008, years of high and poor recruitment, respectively. Ichthyoplankton and zooplankton were surveyed in the upper Chesapeake Bay, in proximity to the estuarine turbidity maximum and associated salt front. Feeding incidence and numbers of prey per gut were similar in both years and varied in relation to the salt front. The primary prey in each year was the estuarine copepod Eurytemora affinis. Substantial consumption of the freshwater cladoceran Bosmina spp. also occurred, especially up-estuary of the salt front in 2007, demonstrating that secondary prey are important to larval diets in some years. Stable isotope analysis of yolk sac and feeding-stage larvae of striped bass revealed an ontogenetic shift from maternal stable isotope signatures to those indicative of prey source. Feeding-stage larvae from up-estuary locations had the most negative δ13C values, indicating a relatively high terrestrial carbon source in prey. Spatio-temporal variability in δ15N signatures of larvae followed similar trends of δ15N variability in zooplankton prey with the highest δ15N values up-estuary of the salt front and estuarine turbidity maximum. A stable isotope analysis on archived striped bass larvae collected in 1998 and 2003, years of moderate and high recruitment, respectively, expanded the documented range of isotope signatures but did not clearly distinguish effects of nutritional sources on recruitment.

Egg quality criteria in Pacific red snapper (Lutjanus peru)

The aim of this study was to evaluate the biochemical parameters used as possible determinants of egg quality in Pacific red snapper (Lutjanus peru). Fertilized eggs of eight spawns were obtained by hormonal induction. Egg quality criteria, including abnormal cleavage (AC), hatching percentage (HR) and survival percentage at first feeding (SR) were recorded. Samples were taken during embryonic development and from yolk-sac larvae. Proteins, energetic metabolite concentrations and metabolic and digestive enzyme activities were determined using colorimetric methods. Pearson’s correlation, and simple and multiple regression models were performed using the biochemical parameters as the independent variables and AC, HR and SR as the dependant variables. Glucose-6-phosphatase activity (AC r = 0.87; HR r = ! 0.65; SR r = ! 0.67) and fructose concentration (AC r = ! 0.64; HR r = 0.54; SR r = 0.64) were the only biochemical parameters to be strongly correlated with the three egg quality criteria. The use of multiple regression models increased the regression coefficient of the three quality criteria. Fructose, glucose and glucose-6-phosphatase were involved in all multiple regression models. The models proposed in this study may be used to explain egg quality for Pacific red snapper and their use as predictors of egg quality is discussed.

Individual‐Based Modeling of Delta Smelt Population Dynamics in the Upper San Francisco Estuary: I. Model Description and Baseline Results

AbstractMany factors have been implicated in the decline of Delta Smelt Hypomesus transpacificus in the upper San Francisco Estuary, and the importance of each factor is difficult to determine using field data alone. We describe a spatially explicit, individual‐based population model of Delta Smelt configured for the upper estuary. The model followed the reproduction, growth, mortality, and movement of individuals over their entire life cycle on the same spatial grid of cells as the Delta Simulation Model (DSM2) hydrodynamics model. Daily values of water temperature, salinity, and densities of six zooplankton prey types were represented on the spatial grid. Reproduction was evaluated daily, and new individuals were introduced into the model as yolk sac larvae. Growth of feeding individuals was based on bioenergetics and zooplankton densities. Mortality sources included natural mortality, starvation, and entrainment in water diversion facilities. Movement of larvae was determined using a particle tracking model, while movement of juveniles and adults was based on salinity. Simulations were performed for 1995–2005. The baseline simulation was generally consistent with the available data. Predicted daily fractions of larvae entrained and annual fractions of adults entrained were similar in magnitude to data‐based estimates but showed less interannual variation. Interannual differences in mean length at age 1 had large effects on maturity and subsequent egg production. Predicted and observed spatial distributions in the fall showed moderately good agreement for extremely low‐ and high‐outflow years. As indicated by the population growth rate, 1998 was the best year and 2001 was the worst year. Water year 1998 (i.e., October 1997–September 1998) was characterized by fast growth in fall 1997, low entrainment, and high stage‐specific survival rates, whereas water year 2001 had opposite conditions. Our analysis further shows how multiple factors can operate simultaneously to result in the decline in abundance of Delta Smelt.

Early development and allometric growth patterns in burbot Lota lota L.

This study analyzed the morphological development and allometric growth patterns of Lota lota L. (burbot) larvae reared under controlled laboratory conditions. From hatching to day 50, twenty larvae were sampled each [between 1 and 14 days post-hatch (DPH)] or every second day (between 14 and 50 DPH) and measured under a stereoscopic microscope using analytic software. Based on the external morphology, the different stages during early development of burbot were identified: yolk sac larva 0–8 DPH [3.92–4.37 mm total length (TL)]; preflexion larva 9–26 DPH (4.57–12.06 mm TL); flexion larva (between notochord degradation and its replacement with rays) 28–34 DPH (14.00–16.34 mm TL) and postflexion larva/juvenile 36–50 DPH (18.20–29.27 mm TL). Allometric growth patterns of some parameters (e.g., total length, head length, body length, tail length, head depth, body depth, eye diameter) were modeled by a power function and described by the growth coefficient. Organogenesis and changes of body proportions in burbot larvae were more rapid and complex during the yolk sac and preflexion phase of development as larvae developed most of their sensorial, feeding, respiratory and swimming systems and after notochord flexion, when most morphological changes were related to the progressive transformation from pelagic larva to demersal larva/juvenile.

Phototoxicity of TiO2 nanoparticles to zebrafish (Danio rerio) is dependent on life stage

Zebrafish embryos have been used increasingly to evaluate nanomaterial toxicity. The present study compared phototoxicity of TiO2 nanoparticles with zebrafish at 4 life stages (embryos, yolk-sac larvae, free-swimming larvae, and juvenile) under simulated sunlight using the 96-h standard toxicity assay. Yolk-sac larvae were found to be the most sensitive to TiO2 phototoxicity, suggesting that the widely used zebrafish embryo test may not fully or accurately predict hazard and risk of these nanoparticles to small fish.

Morphological and ultrastructural characterization of ionoregulatory cells in the teleost oreochromis niloticus following salinity challenge combining complementary confocal scanning laser microscopy and transmission electron microscopy using a novel prefixation immunogold labeling technique

Aspects of ionoregulatory or mitochondria-rich cell (MRC) differentiation and adaptation in Nile tilapia yolk-sac larvae following transfer from freshwater to elevated salinities, that is, 12.5 and 20 ppt are described. Investigations using immunohistochemistry on whole-mount Nile tilapia larvae using anti- Na⁺/K⁺-ATPase as a primary antibody and Fluoronanogold™ (Nanoprobes) as a secondary immunoprobe allowed fluorescent labeling with the high resolution of confocal scanning laser microscopy combined with the detection of immunolabeled target molecules at an ultrastructural level using transmission electron microscopy (TEM). It reports, for the first time, various developmental stages of MRCs within the epithelial layer of the tail of yolk-sac larvae, corresponding to immature, developing, and mature MRCs, identifiable by their own characteristic ultrastructure and form. Following transfer to hyperosmotic salinities the density of immunogold particles and well as the intricacy of the tubular system appeared to increase. In addition, complementary confocal scanning laser microscopy allowed identification of immunopositive ramifying extensions that appeared to emanate from the basolateral portion of the cell that appeared to be correlated with the localization of subsurface tubular areas displaying immunogold labeled Na⁺/K⁺-ATPase. This integrated approach describes a reliable and repeatable prefixation immunogold labeling technique allowing precise visualization of NaK within target cells combined with a 3D imaging that offers valuable insights into MRC dynamics at an ultrastructural level.

Ontogenesis from embryo to juvenile and salinity tolerance of Japanese devil stinger Inimicus japonicus during early life stage.

Embryonic development and morphological characteristics of Japanese devil stinger Inimicus japonicus during early life stage were investigated. Larvae were hatched out 50 h after fertilization at temperature 21°C. Total length of the newly hatched larva was 4.03 mm, the mouth of the larva opened at 3 days after hatching (DAH), and the yolk sac of the larva disappeared at 5 DAH. After hatching, the pectoral fin first developed, then the tail fin, dorsal fin, anal fin and pelvic fin continuously developed, and all fins formed completely at 15 DAH. The metamorphosis was complete at 25 DAH, and the body color and habit of the metamorphosed individuals were different from the larvae. At 30 DAH, the morphology and habit of the juveniles were the same to adults. In order to determine the suitable salinity for larviculture of I. japonicus, salinity tolerance at different early developmental stages was compared in terms of the survival activity index (SAI) and mean survival time (MST). The results indicated that salinity tolerance varied with development stages. The optimum salinity range for newly hatched larvae was 10–25‰. Larvae showed low tolerance to low salinity (5‰) before the mouth opened, and the suitable salinities for the larvae with open mouth, yolk-sac larvae, post yolk-sac larvae were 10–15‰. The flexion larvae showed a wider salinity tolerance with range of 5–20‰. After metamorphosis, the juveniles showed a preferable adaptability of salinities of 15–20‰. The SAI and MST of individuals at various stages under different salinity conditions were positively correlated.

Identification of Winter Flounder (Pseudopleuronectes americanus) Estuarine Spawning Habitat and Factors Influencing Egg and Larval Distributions

A long-term (2002–2011), spatially robust, ichthyoplankton sampling program conducted in the New York/New Jersey Harbor produced 3,033 epibenthic samples from which the relationships between winter flounder egg and larval distributions and environmental parameters were examined. Variations in water temperature, sediment characteristics, and tidal phase were all significantly associated with egg distributions. Inferences about spawning habitats were based on the presence of early-stage eggs (ES1 and ES2). In the Lower Bay (LB), these habitats were primarily non-channel and characterized by more sandy substrates, averaging 96.5 % sand, 2.3 % silt/clay, 0.2 % total organic carbon (TOC), and shallower water (average depths of 5.3 m) compared to LB non-channel stations without ES1 and ES2 eggs (50.2 % sand, 42.0 % silt/clay, 2.1 % TOC, and 7.9 m depths). Occurrences of all stages of eggs in channels were associated with strong tides and severe cold winter water temperatures. These conditions increase the probability of egg transport from shallow spawning sites through increased vertical mixing (strong tides) and delayed development that prolongs the risk of displacement (cold temperatures). Yolk-sac (YS) and Stage-2 larvae were smaller in 2010 when spring water temperatures were highest. Overall, YS larval size decreased with warmer winters (cumulative degree-days for the month preceding peak YS larval collections, r2 = 0.82, p < 0.05). In all years, YS larvae collected in LB were smaller and Stage-3 larvae collected in channels were larger and possibly older than those from non-channel habitat. Because estuarine winter flounder populations are highly localized, adverse effects experienced during egg and larval stages are likely to propagate resulting in detrimental consequences for the year class in the natal estuary.

Temperature stress induces notochord abnormalities and heat shock proteins expression in larval green sturgeon (Acipenser medirostrisAyres 1854)

The effects of thermal stress on survival, development and heat shock protein (hsp) expression of green sturgeon (GS) yolk-sac larvae, from hatching through yolk depletion were investigated to provide insight into effects of highly altered natural river hydrographs. Hatched GS larvae were reared at constant water temperatures 18°C (control) through 28°C at 2°C increments. Larval survival significantly decreased at 26–28°C, with 28°C being lethal. Significant proportions of deformed larvae were found at sub-lethal (20–26°C) and lethal 28°C rearing temperatures, with kyphosis (i.e. backward flexion of notochord) accounting for >99% of morphological deformities. Histological analysis of larvae preparations indicate that elevated water temperature affects notochord cell function and physiology. At rearing temperatures 20–28°C, thermal stress elicited a quick (24 h) and long lasting (yolk-sac absorption) significant over-expression of measured heat shock proteins (hsps), all of which are known components of intracellular protein repair and stabilization mechanism. Thermal sensitivity, as indicated by the incidence of abnormalities and expression of different hsps, varied significantly between crosses. Thermally tolerant progeny exhibited a short but rapid hsp72 (size in kDa) over-expression, and more pronounced hsp60 and hsp90 over-expression, than less tolerant progeny which exhibited a prolonged hsp72 and hsp78 over-expression. At environmentally relevant water temperatures bent larvae exhibited spiral swimming, which in the wild would compromise the ability of emerging larvae to forage, avoid predators, and migrate downstream, ultimately compromising survival and recruitment. Before larvae hsp content can be used as a thermal-stress biomarker for GS, field validation studies are needed.

Аналіз рибоводно-біологічних результатів роботи з плідниками російського осетра на базі ОРЗ «Лебяжий» (Астраханська обл., Російська Федерація)

Проведено аналіз рибоводно-біологічних результатів, отриманих під час роботи з плідниками російського осетра у 2011 р. на ОРЗ «Лебяжий». У результаті аналізу отримано інформацію про стан запасів осетрових видів у Волго-Каспійському басейні. Наведено порівняльні результати роботи з плідниками російського осетра в період нерестової кампанії, яка проводилась у два тури. Використання синтетичного препарату сурфагон для стимуляції статевої активності плідників забезпечує майже 100% відповідь самок. У результаті проведення нерестової кампанії отримано 170 кг ікри, при цьому середня робоча плодючість самок першого туру складала 198,2 тис. ікринок, а самок другого туру – 184, 6 тис. ікринок, що відповідає нормативам.

Changes in fatty acid composition, cholesterol and fat-soluble vitamins during development of eggs and larvae in shabbout (Barbus grypus, Heckel 1843)

Summary Changes in fatty acid composition, cholesterol and fat-soluble vitamins were studied during development (fertilized eggs, yolk-sac larvae, and after yolk resorption of shabbout, Barbus grypus). Significant differences were found in the monounsaturated fatty acids (MUFAs), polyunsaturated fatty acids (PUFA), PUFA/saturated fatty acids (SFA), ∑n-3 and eicosapentaenoic acid (EPA)/docosahexaenoic acid (DHA) ratios between eggs and larvae (P 0.05).

Vertical distributions of the early life stages of walleye pollock (Theragra chalcogramma) in the Southeastern Bering Sea

The present study examines vertical distributions of the early life stages of walleye pollock (Theragra chalcogramma) in the Southeastern Bering Sea to assess ontogenetic and diel vertical migration in relation to development and habitat. Walleye pollock demonstrated a decrease in the depth of occurrence following hatching, indicating an ontogenetic change in vertical distribution. Eggs occurred deepest in the water column and early juveniles occurred shallowest. Vertical distributions were related to the date of collection, water column depth, and thermocline depth. Non-feeding stages (eggs and yolksac larvae, <4.5mm standard length [SL]) did not exhibit diel vertical migration. Feeding larvae exhibited diel vertical migration, although patterns varied between two feeding stages. Preflexion stage larvae (4.5–9.9mm SL) were concentrated between 10 and 20m during the day and deeper at night. Postflexion stage larvae (flexion and postflexion, 10.0–24.5mm SL) underwent regular diel migrations (0–20m, night; 10–40m, day). Low sample sizes limited our ability to assess diel vertical migration in early juveniles, but this stage tends to occur in the upper 20m of the water column, regardless of time of day. These results suggest that vertical distributions and diel migration potentially are driven by prey availability at sufficient light levels for preflexion larvae to feed and a trade-off between prey access and predation risk for postflexion larvae. Vertical distributions of eggs and preflexion larvae varied with habitat examined (on the continental shelf versus over the continental slope). Vertical distributions of walleye pollock eggs, yolksac larvae, and preflexion larvae in the Bering Sea are different from distributions in other ecosystems, which can impact transport and modeling efforts.

Temperature effects on early development and biochemical dynamics of a marine fish, Inimicus japonicus

A study was undertaken to evaluate the development and metabolic substrates (carbohydrate, protein, lipid and fatty acids) dynamics during the embryonic and yolk-sac larval stages of the devil stinger, Inimicus japonicus, at different water temperatures (18, 21, 24, 27 and 30°C). The hatching time was significantly shortened when the temperature increased (P<0.05). Only 14.5% of embryos hatched at 30°C, while the hatching rate was 92.5% at 24°C. Larvae incubated at 21°C displayed the greatest survival at mouth-opened larva stage (96.5%), but the rate dropped sharply when the temperature surpassed 24°C (P<0.05). The full length and yolk-sac volume of newly hatched larva at 18°C and 30°C were significantly smaller than those at 21, 24 and 27°C. Larva at 21°C always had the largest full length during early development. The advent of mouth-opened larvae was closely related to temperature, so were the full length and yolk volume of the mouth-opened larva. As the incubation temperature declined, the mouth-opened larva obtained longer full length and less yolk remain. Lipid was, to a large extent (47.0% of the initial amount), a fuel for development when the embryo was incubated at 18°C. The depletion of protein in the embryo was significantly higher at 30°C (67.6%) than that at 21°C (31.3%). Consumption of carbohydrate was observed only in embryo at 18°C. During the development of yolk-sac larva, a lower incubation temperature induced more protein anabolism and less lipid consumption. In I. japonicus, polar lipids (PL) constituted the principal class of lipid in eggs (74.0% of the total lipid); and it was the most consumed portion during embryogenesis in all treatments. The lipid composition in mouth-opened larva was affected by the incubation temperature. The storage triglycerides (TG) tended to comprise a higher proportion in larva incubated at 30°C than in those at lower temperatures. The PL proportions in larva at 18°C and 30°C were lower than those in larvae at 21°C, 24°C and 27°C. Low concentrations of polyunsaturated fatty acid (PUFA) in embryos and larvae were correlated with increased temperatures; this indicated that the rapid development at higher temperatures was at the cost of more PUFA loss. It is concluded that 21–24°C is an appropriate range for incubation of I. japonicus eggs and larvae and that 24°C is optimal in terms of shortening the endogenous nutritional stage and improving metabolic efficiency.