Herring Larvae Research Articles

Mackerel predation on herring larvae during summer feeding in the Norwegian Sea

Abstract In the course of the past two decades, Atlantic mackerel, Scomber scombrus, have expanded their summer feeding distribution in the Norwegian Sea substantially, and now potentially overlap with pelagic larvae of Norwegian spring-spawning herring, Clupea harengus, as these drift northwards. Mackerel are known to be opportunistic predators, and the aim of this study was to evaluate mackerel predation in an area of overlap between mackerel and herring larvae, with particular focus on predation on herring larvae. In early June 2013, we followed a predefined transect in the expected core larvae distribution area on the Norwegian coastal shelf between about 66°N and 69°N. The transect was repeated twice, and samples of mackerel for stomach analyses and subsequent herring larvae samples were obtained at pre-defined stations. Mackerel were caught in all but one of the trawl hauls, but were hardly ever observed acoustically, suggesting that they were dispersed close to the surface throughout the study area. Herring larvae were caught in all samples. Calanoid copepods were the dominant prey of the mackerel, but 45% of the mackerel guts contained herring larvae, with a maximum of 225 larvae counted in a single gut. Both the frequency of guts containing herring larvae and the average amount of herring larvae increased in line with increasing abundance of larvae. On the other hand, no spatial correlation between mackerel abundance and herring larvae abundance was found at the station level. The results suggest that mackerel fed opportunistically on herring larvae, and that predation pressure therefore largely depends on the degree of overlap in time and space. Rough areal projections suggest that the mackerel would be capable of consuming the herring larvae present in the investigation area in 6–7 d, and that such predation therefore could have regulatory effects on stocks of Norwegian spring-spawning herring.

The proteome of Atlantic herring (Clupea harengus L.) larvae is resistant to elevated pCO2

Elevated anthropogenic pCO2 can delay growth and impair otolith structure and function in the larvae of some fishes. These effects may concurrently alter the larva’s proteome expression pattern. To test this hypothesis, Atlantic herring larvae were exposed to ambient (370μatm) and elevated (1800μatm) pCO2 for one-month. The proteome structure of the larvae was examined using a 2-DE and mass spectrometry. The length of herring larvae was marginally less in the elevated pCO2 treatment compared to the control. The proteome structure was also different between the control and treatment, but only slightly: the expression of a small number of proteins was altered by a factor of less than 2-fold at elevated pCO2. This comparative proteome analysis suggests that the proteome of herring larvae is resilient to elevated pCO2. These observations suggest that herring larvae can cope with levels of CO2 projected for near future without significant proteome-wide changes.

Impact of extreme climate and bioinvasion on temporal coupling of spring herring (Clupea harengus m.) larvae and their prey

We used weekly observational data from mid-May to end of July in 1958–2012 in Gulf of Riga to investigate temporal coupling between spring herring larvae and their first prey – copepod nauplii, under the extreme hydroclimatic conditions. We focused on a small shallow estuary that is important nursery ground for larvae of the Gulf of Riga (Baltic Sea) herring population. We quantified the effect of extreme values of the winter air temperatures, time of ice retreat and spring water temperatures on the timing of peak abundance of herring larvae and copepod nauplii. We also assessed whether the invasion of the non-native cladoceran Cercopagis pengoi had notable effect on timing and abundance of copepod nauplii during the peak occurrence of herring larvae. In the years of earliest ice retreat the peak abundance of herring larvae was five weeks earlier than in the years of latest ice retreat, while the timing of nauplii remained unchanged. Abundant presence of the C. pengoi affected neither timing nor maximum abundance of copepod nauplii during the herring larvae first feeding period. Thus, we conclude that processes induced by climate variability are superior to invasion of C. pengoi in determining the timing and coupling of larval herring and copepod nauplii.

Unravelling the Gordian knot! Key processes impacting overwintering larval survival and growth: A North Sea herring case study

Unraveling the key processes affecting marine fish recruitment will ultimately require a combination of field, laboratory and modelling studies. We combined analyzes of long-term (30-year) field data on larval fish abundance, distribution and length, and biophysical model simulations of different levels of complexity to identify processes impacting the survival and growth of autumn- and winter-spawned Atlantic herring (Clupea harengus) larvae. Field survey data revealed interannual changes in intensity of utilization of the five major spawning grounds (Orkney/Shetland, Buchan, Banks north, Banks south, and Downs) as well as spatio-temporal variability in the length and abundance of overwintered larvae. The mean length of larvae captured in post-winter surveys was negatively correlated to the proportion of larvae from the southern-most (Downs) winter-spawning component. Furthermore, the mean length of larvae originating from all spawning components has decreased since 1990 suggesting ecosystem-wide changes impacting larval growth potential, most likely due to changes in prey fields. A simple biophysical model assuming temperature-dependent growth and constant mortality underestimated larval growth rates suggesting that larval mortality rates steeply declined with increasing size and/or age during winter as no match with field data could be obtained. In contrast better agreement was found between observed and modelled post-winter abundance for larvae originating from four spawning components when a more complex, physiological-based foraging and growth model was employed using a suite of potential prey field and size-based mortality scenarios. Nonetheless, agreement between field and model-derived estimates was poor for larvae originating from the winter-spawned Downs component. In North Sea herring, the dominant processes impacting larval growth and survival appear to have shifted in time and space highlighting how environmental forcing, ecosystem state and other factors can form a Gordian knot of marine fish recruitment processes. We highlight gaps in process knowledge and recommend specific field, laboratory and modelling studies which, in our opinion, are most likely to unravel the dominant processes and advance predictive capacity of the environmental regulation of recruitment in autumn and winter-spawned fishes in temperate areas such as herring in the North Sea.

Shifts in the spring herring (Clupea harengus membras) larvae and related environment in the eastern Baltic Sea over the past 50 years.

Because of the high management relevance, commercial fish related aspects have often been central in marine ecosystem investigations. The iterative shiftogram method was applied to detect occurrence, type and timing of shifts in the single and multivariate time series linked to the spring spawning herring larvae in the Gulf of Riga (Baltic Sea). Altogether nineteen larval herring and related environmental variables were utilized during the period of 1957–2010. All the time series investigated, either single or multivariate, exhibited one or more shifts with variable type and timing. Multivariate shiftogram based on all time series identified two distinct states (1957–1983 and 1992–2010) in studied variables, separated by a smooth transition period lasting almost ten years. The observed shift was mainly related to hydroclimate and not to phenology or biota. Significantly increased variability was found in larval herring and recruitment abundances after the shift. While the shift in hydroclimate (1985–1991) was followed by the shift in phenology (1991–1997), the shift in biota occurred remarkably later (2003). It is likely that the dynamics in biota were affected by other drivers than those investigated in the current paper.

Vertical migration of Norwegian spring-spawning herring larvae in relation to predator and prey distribution

A diel vertical migration (DVM) pattern of Norwegian spring spawning herring (Clupea harengus) larvae was investigated during 19 and 20 April 2009. Factors influencing DVM included physical and biological properties of the water column. Data on larvae, prey and predators were collected with a depth-stratified multisampling device, inshore of Sklinna bank, close to the Norwegian coast, while light conditions were calculated using a Matlab® algorithm. A type I DVM pattern (i.e. deep during daytime, shallow at night) was observed for herring larvae, mainly occurring above the thermocline. No size-dependent differences were observed for larval vertical positioning. The highest overlap in depth distribution with their main prey was observed during daytime, when larvae were distributed deeper in the water column. From acoustics and macroplankton trawl data, a type I DVM was also observed for krill, although their concentrations were relatively low in the area. Cumulative predator–prey overlap plots suggest that krill most likely forage on copepods and smaller organisms. During the day, larvae concentrate near the thermocline to feed, while they move towards the surface at dusk, possibly to use the remaining light to continuing feeding. During the night, when light levels were too low to feed, larvae spread out in the water column above the thermocline. This migration pattern reduces the overlap between larvae and potential predators such as krill, which also move higher up during nighttime. It is suggested that the pattern of herring larvae DVM is a behavioural response to active pursuit of prey.

Effects of different concentrations of crude oil on first feeding larvae of Atlantic herring ( Clupea harengus)

Studies have shown that exposure to Polycyclic Aromatic Hydrocarbons (PAHs) and other oil related components alter normal fish larvae development and can cause increased mortality in early life stages. Modelling of results from controlled laboratory exposure experiments will help relate typical oil exposure parameters (biomarkers) to field observations and are valuable tools for oil exposure monitoring and risk assessment. Post yolk sack larval stages of Atlantic herring were exposed to different concentrations of dispersed Arctic crude oil. The selected nominal concentrations were 0.015, 0.040, 0.060, 0.250 and 0.750 mg l − 1 raw dispersed oil (0.129, 0.373, 0.496, 2.486 and 6.019 μg l − 1 Total Polycyclic Aromatic Hydrocarbons (TPAH) respectively), and control seawater in flow through systems. The larvae were exposed for 12 days and daily mortality recorded in all treatments. Thereafter, the larvae were transported to two large (300 l) rearing tanks, one for control/trace oil and one for oil exposed larvae. The larvae were allowed to recover for 8 weeks after exposure, and mortality and morphological factors then assessed, giving preliminary information on recovery of Atlantic herring larvae after oil exposure. Throughout the testing period, there was a general trend for higher mortality of herring larvae in the oil exposure concentrations than in control, and significantly higher mortality was found in all oil concentrations than in the control after 12 days. We did not detect a clear dose related mortality for our test concentrations, except for the highest concentration. There was no difference found in mortality rates of the herring larvae from either the oil or control/trace oil batch during the recovery phase during the following 60 days. Morphological observations of the herring larvae after 2 months recovery in clean seawater showed that the oil exposed larvae had morphological features that could be described as deformities, and growth was found to be significantly impaired for the oil exposed group when compared to the control/trace oil group.

Can IBMs tell us why most larvae die in the sea? Model sensitivities and scenarios reveal research needs

Biophysical individual-based models (IBMs) are the only tools that can provide estimates of spatial and temporal changes in mortality rates of marine fish early life stages as well as the various processes that contribute to those changes. Given the increasing use of these models, one must ask the question: How much faith can we have in their estimates? We briefly review mortality processes acting on marine fish early life stages and how IBMs have been used to estimate those processes. Next, we provide a summary of the sensitivity analyses and scenario results conducted in 50 studies that provided estimates of: 1) advection-based losses from drift modeling, 2) mortality due to starvation from foraging and growth modeling, and/or 3) modeled mortality due to predators. We illustrate how IBM estimates of larval distribution and survival can be sensitive to assumptions regarding the magnitude and timing of mortality by performing drift model simulations for Atlantic herring ( Clupea harengus) larvae in the North Sea. Despite the growing number of studies applying IBMs, less than 25% reviewed here included formal sensitivity analyses of parameters. Our literature review indicated a need for biological research on 1) larval swimming behavior including cues for movements, 2) foraging parameters such as larval visual field estimates, and 3) parameters associated with growth physiology including assimilation efficiency and energy losses due to active metabolism. Ontogenetic changes in those factors are particularly relevant to examine for modeling activities. Methods also need to be developed for depicting predator encounter in a dynamic way (e.g., based upon predator–prey overlap). High priority should be given to developing (and funding) research programs that not only construct and apply IBMs but also that measure the aspects of larval behavior and physiology as well as aspects of the larval environment needed to parameterize them. Coupling these research activities will strengthen our confidence in IBM-derived estimates of mortality and the processes responsible for death of larvae in the sea.

Physiological individual-based modelling of larval Atlantic herring (Clupea harengus) foraging and growth: insights on climate-driven life-history scheduling

AbstractHufnagl, M., and Peck, M. A. 2011. Physiological individual-based modelling of larval Atlantic herring (Clupea harengus) foraging and growth: insights on climate-driven life-history scheduling. – ICES Journal of Marine Science, 68: 1170–1188. A physiological individual-based model for the foraging and growth of Atlantic herring (Clupea harengus) larvae was constructed, validated using laboratory and field data, tested for parameter sensitivity, and used to examine climate-driven constraints on life-history scheduling. Model scenarios examined how natural (phenological and magnitude) changes in key environmental factors (temperature, prey, and photoperiod/daylength) affected the estimates of survival and growth of spring- and autumn-spawned larvae. The most suitable hatching seasons agreed well with the periods of larval abundance in Northeast Atlantic waters. Modelled survival is unlikely in June, July, and November. Mean annual temperature, prey concentration, and composition significantly influenced larval growth of both autumn and spring spawners. The model suggested that climate-driven changes in bottom-up factors will affect spring- and autumn-spawned larvae in different ways. It is unlikely that autumn-spawning herring will be able to avoid unfavourable conditions by delaying their spawning time or by utilizing more northern spawning grounds because of limitations in daylength to larval growth and survival. Conversely, earlier spawning in spring, or later, midsummer spawning will be tightly constrained by match–mismatch dynamics between larvae and zooplankton production.

Methods for Conducting Bioassays Using Embryos and Larvae of Pacific Herring, Clupea pallasi

The rapid decrease of several stocks of Pacific herring, Clupea pallasi, in Puget Sound, Washington, has led to concerns about the effects of industrial and nonpoint source contamination on the embryo and larval stages of this and related forage fish species. To address these concerns, the state of Washington and several industries have funded efforts to develop embryo and larval bioassay protocols that can be used by commercial laboratories for routine effluent testing. This article presents the results of research to develop herring embryo and larval bioassay protocols. Factors evaluated during protocol development included temperature, salinity, dissolved oxygen (DO), light intensity, photoperiod, larval feeding regimes, use of brine and artificial sea salts, gonad sources, collection methods, and egg quality.

Effect of hatching date, vertical distribution, and interannual variation in physical forcing on northward displacement and temperature conditions of Norwegian spring-spawning herring larvae

Abstract Vikebø, F. B., Husebø, Å., Slotte, A., Stenevik, E. K., and Lien, V. S. 2010. Effect of hatching date, vertical distribution, and interannual variation in physical forcing on northward displacement and temperature conditions of Norwegian spring-spawning herring larvae. – ICES Journal of Marine Science, 67: 1948–1956. Early hatching has been shown to be associated with increased survival of Norwegian spring-spawning herring (Clupea harengus) larvae. We investigated whether the process behind this association is related to larval drift and ambient temperature. A three-dimensional hydrodynamic model was used to simulate the effect of hatching date on northward displacement and temperature conditions of larvae from spawning grounds off western Norway for 1989–2008. The simulations revealed that the displacement during a period of 60 d was greatest if the larvae hatched early in the season and if they were located near the surface. The relationship between drift speed and ambient temperature was significantly negative, but less so later in the season, because the coastal current became progressively warmer. Results from the simulated interannual variations in larval drift compared with the observed survival suggest that a rapid northward displacement to the main nursery area in the Barents Sea is more important for larval survival than ambient temperature. The significant effect of northward displacement on survival could be explained by reduced overlap with predators and/or higher prey densities, but the causal processes involved remain to be investigated.

Temporal trends in stock origin and abundance of juvenile herring (Clupea harengus) in the Irish Sea

Abstract Burke, N., Brophy, D., Schön, P-J., and King, P. A. 2009. Temporal trends in stock origin and abundance of juvenile herring (Clupea harengus) in the Irish Sea. – ICES Journal of Marine Science, 66: 1749–1753. Celtic Sea herring (Clupea harengus) larvae partly disperse into the Irish Sea, where they mix with the resident stock during their first year of life. This affects the reliability of the use of acoustic estimates of juvenile abundance on the Irish Sea nursery grounds as a recruitment index for use in stock predictions. Otolith microstructure analysis can be used to distinguish between autumn-spawned and winter-spawned individuals. Because winter spawners do not occur in the Irish Sea, this component can be assigned to Celtic Sea immigrants. We used this method to estimate the proportion of winter-spawned individuals in samples of age-1 herring from the western Irish Sea over a 10-year period (1993–2003), and subtracted a corresponding proportion from the acoustic age-1 abundance estimates. The adjusted index for autumn-spawned (supposedly Irish Sea) juveniles was significantly correlated with the abundance of age-3 fish from the same year class in commercial catches and in the acoustic surveys (p < 0.05 and <0.01, respectively), whereas the correlations for unadjusted indices were not significant. These findings are discussed in relation to the monitoring and assessment of herring in the two areas.

An individual‐based model for the direct conversion of otolith into somatic growth rates

ABSTRACTOtolith increment width and larval fish data (length and weight) were used to develop an individual‐based model (IBM) to describe daily resolved growth rates of North Sea herring (Clupea harengus) larvae (Autumn Spawners) caught during International Herring Larvae Surveys in the ICES area IVa from 1990 to 1998. The model combines sagittal otolith readings (core and individual increment measurements), larval standard length and weight data, and solves an over‐determined set of linear system equations for all parameters using the method of least square residuals. The model consists of a matrix, which describes the increment width formation of 119 larvae, a vector containing their length/weight measurements, and a vector describing residuals. The solution vector yields age‐dependent maximum somatic growth rates of herring larvae up to an age of 41 days with sizes ranging from 10 to 25 mm. The observed environmental temperature in which larvae dwelled was relatively uniform. Therefore, measured increment width was individually used to determine daily growth from any single larva in relation to their potential maximum growth under optimal feeding conditions. The results are discussed with respect to the spatial and temporal variability of larval occurrence. Finally, an analysis of error estimation of the larval growth characteristics is presented.

Parental effects on early life history traits of Atlantic herring ( Clupea harengus L.) larvae

A significant part of the variation in the early life history traits of fish can be ascribed to the parental origin of the individual larvae. The primary source of this parental contribution has been attributed to maternal effects and evidence for paternal effects is equivocal. Maternal effects are a non-genetic contribution of a female to its offspring but most reported maternal effects are products of both genetic and non-genetic contributions, i.e. female effects. In this study, parental effects on traits of larvae of Atlantic herring ( Clupea harengus L.) at hatch were investigated at one temperature using a 5 × 3 factorial mating design (North Carolina Design II). This allowed estimation of the true maternal effect and the additive genetic variation (heritability). Furthermore, relationships between individual traits were examined and for the first time nucleic acid content and otolith size at hatch were examined together. A significant correlation between the two was found and it is argued to support the notion that otolith growth is more related to metabolic rate than to somatic growth. Maternal effects were detected in larval weight and yolk-sac volume, while paternal and, hence, genetic effects appeared in larval length, yolk-sac volume, RNA : DNA ratio, and lapillar area. The findings suggest that an increased emphasis should be placed upon the importance of male influence on success of early larval fishes.

The relationship between ultraviolet and polarized light and growth rate in the early larval stages of turbot ( Scophtalmus maximus), Atlantic cod ( Gadus morhua) and Atlantic herring ( Clupea harengus) reared in intensive culture conditions

Even small changes in light intensity and spectral composition can have significant effects on the feeding rate, survivorship and growth of marine organisms. For fishes that can perceive them, ultraviolet-A radiation (320–400 nm, UVA) and polarized (POL) light purportedly increase the visibility of prey by enhancing target contrast. Consequently, the efficiency of prey location and ingestion (and, therefore, growth) should be higher in environments rich in UVA and/or POL light. We tested this hypothesis in growth rate experiments with larvae of Atlantic cod ( Gadus morhua), turbot ( Scophthalmus maximus) and Atlantic herring ( Clupea harengus). Turbot larvae possess an UVA-sensitive retinal photoreceptor, while cod and herring larvae apparently do not. Cod, turbot and herring larvae were reared in intensive culture – for at least 18 to 35 d from first-feeding – in 45 l optically isolated matt-black tanks under four light conditions: UVA + POL; UVA + DIFFUSE; NOUVA + POL; NOUVA + DIFFUSE. All light environments were matched for photon flux. There were five replicates per light exposure treatment and larvae were sampled every 3 to 5 d for dry weight. There was no significant difference in growth for any of the larvae under any of the light treatment conditions. These results indicate that, for these species, neither UVA nor POL light significantly improves growth rate in typical intensive culture systems.

Temperature-dependent otolith growth in Norwegian spring-spawning herring (Clupea harengus L.) larvae

Norwegian spring-spawning herring larvae ( Clupea harengus L.) were reared at different temperature combinations in the laboratory, and marked twice with a fluorescent dye, alizarin complexone, to estimate otolith growth and increment deposition rate. A daily increment deposition rate was confirmed in the sagittae of larvae reared at 12 °C from day 16 (first marking age), while the apparent rate of increment formation of larvae reared at 4 °C was clearly less than one per day. A reduction in rearing temperature from 12 to 8 °C between days 16 and 30 (second marking age), significantly affected sagitta growth during the inter-mark period compared with those reared at 12 °C throughout. Similar somatic growth rates were observed in both groups temporarily reared at 8 °C between markings (about 6% day −1 ), but the otolith growth rate was more than four times higher in the group originating from 12 °C compared with the one originating from 4 °C. The body size versus otolith size relationship was temperature d...

Sublethal effects of Orimulsion-400 on eggs and larvae of Atlantic herring (Clupea harengus L.).

Orimulsion-400 is a novel bitumen-emulsion power plant fuel. We exposed Atlantic herring (Clupea harengus L.) eggs to 0, 0.1, 1.0, 10, 100, and 1,000 mg/L concentrations of an oil-in-water dispersion of Orimulsion-400 for a 24-h period. No significant differences were found in daily mortality or percent hatch. The 1,000 mg/L exposure resulted in a significantly higher incidence of premature hatch, indicated by significantly shorter incubation time, significantly smaller total length and notochord length, and significantly greater yolk sac depth. The larvae exposed to the 1,000 mg/L treatment also had a significantly higher incidence of abnormalities than all other treatments.

A method for radiolabeling Artemia with applications in studies of food intake, digestibility, protein and amino acid metabolism in larval fish

The present paper describes a method for radiolabeling Artemia that has potential applicability in the study of food intake, Artemia digestibility, protein and amino acid (AA) metabolism in early stages of marine fish larvae. Artemia nauplii were labeled by adding a uniformly labeled 14C protein hydrolysate to its hatching or enrichment media. Both newly hatched and enriched nauplii assimilated rapidly the radiolabel and a very high proportion of the uptaken label was incorporated into the TCA precipitate (mostly protein) fraction after a short period of time—84–91%, at the end of the hatching period and 81–87%, after 12 h of enrichment. In addition, it was observed that the amount of radiolabel per Artemia, as well as its distribution between the TCA precipitate and soluble (free AA) fractions, was relatively stable (up to 8 h) in conditions simulating transfer to larval feeding tanks. During the radiolabeling trials a substantial amount of the total initial radioactivity in the media was not recovered at the end of the hatching or enrichment period (38% and 29%, respectively). An experiment was designed to study the release of the radiotracer into the atmosphere, as 14CO 2. It was concluded that although the Artemia catabolism may be responsible for some release of the radiolabel into the atmosphere, bacterial activity in the enrichment media has a major impact, being responsible for the loss of 19.2% of the total initial radiolabel from the system. The digestibility and transfer rates of the labeled nutrients from Artemia to fish larvae was analysed “in vivo” by feeding radiolabeled newly hatched nauplii to herring ( Clupea harengus) larvae and following the metabolic fate of the label. The results revealed a high digestibility (around 60%) of the Artemia, with 20% being retained in the body and 39% catabolised by the larvae, 24 h after feeding. The digestion process and subsequent absorption of the digested radiolabeled nutrients were quite rapid, given that 40% was recovered in the body only 2 h after feeding and 6% was found in the CO 2 trap at this time.

Amino acid requirements of fish larvae and post-larvae: new tools and recent findings

This paper reviews methodologies and recent findings in the study of the amino acid (AA) metabolism of fish larvae and post-larvae, in order to better understand the AA requirements. The larval indispensable AA (IAA) profile can be used as index of the IAA requirements. When turbot larvae and live food IAA profiles are compared, the profile of the latter seems to be deficient in some IAA. However, the larval IAA profile is only a rough indicator of AA requirements. A more precise estimate of the ideal dietary IAA profile implies the knowledge of the relative bioavailabilities of the individual AA, in particular, eventual differential rates of absorption and catabolism. Metabolic budgets (including unabsorbed AA, AA oxidation and AA retention) can be estimated using an in vivo method based on controlled tube-feeding of AA mixes containing a 14C-labelled AA. Results with fasted post-larval Senegal sole ( Solea senegalensis) and fasted herring ( Clupea harengus) larvae show a high retention of labelled doses of IAA (>60%) in the body, compared to catabolism as measured by liberated 14CO 2 (<25%). In contrast, dispensable AA (DAA) show a higher catabolism (>40%) and a lower retention (<57%). So, from the onset of exogenous feeding, fish larvae have high catabolic losses of AA, but use DAA preferentially to IAA as energy substrates. A new method combining the use of 13C-labelled live food and 13C-NMR spectroscopy can be used to study simultaneously the relative bioavailability of several individual AA in fish larvae. In larval gilthead seabream ( Sparus aurata) fed on rotifers, relative bioavailabilities (a combined measure of absorption efficiency and rate of catabolism) vary between AA being high for aspartate, glutamate and lysine and low for threonine. These estimates of relative biovailability of individual AA together with the IAA profiles of the larval seabream indicate that rotifers are deficient in threonine and leucine for larval seabream, threonine being the first limiting AA for protein synthesis. In order to define ideal IAA profiles for larval fish, further studies are needed on the factors affecting the relative bioavailability of IAA, such as species, age, developmental stage, temperature and the dietary nitrogen molecular form(s). Estimates of relative bioavailability of individual AA together with the IAA profile of the larval protein allow to determine the ideal dietary IAA profile for a given species.

Photoenhanced toxicity of aqueous phase and chemically dispersed weathered Alaska North Slope crude oil to Pacific herring eggs and larvae

The photoenhanced toxicity of weathered Alaska North Slope crude oil (ANS) was investigated in the eggs and larvae of Pacific herring (Clupea pallasi) with and without the chemical dispersant Corexit 9527. Oil alone was acutely toxic to larvae at aqueous concentrations below 50 microg/L total polycyclic aromatic hydrocarbons (tPAH), and median lethal (LC50s) and effective concentrations (EC50s) decreased with time after initial oil exposure. Brief exposure to sunlight (approximately 2.5 h/d for 2 d) significantly increased toxicity 1.5- to 48-fold over control lighting. Photoenhanced toxicity only occurred when oil was present in larval tissue and increased with increasing tPAH concentration in tissue. Ultraviolet radiation A (UVA) treatments were less potent than natural sunlight, and UVA + sunlight caused greater toxicity than sunlight alone. The toxicity of chemically dispersed oil was similar to oil alone in control and UVA treatments, but oil + dispersant was significantly more toxic in the sunlight treatments. The chemical dispersant appeared to accelerate PAH dissolution into the aqueous phase, resulting in more rapid toxicity. In oil + dispersant exposures, the 96-h no-observed-effect concentrations in the UVA + sunlight treatment were 0.2 microg/L tPAH and 0.01 microg/g tPAH. Exposure of herring eggs to oil caused yolk sac edema, but eggs were not exposed to sun and UVA treatment did not cause phototoxicity. These results are consistent with the hypothesis that weathered ANS is phototoxic and that UV can be a significant and causative factor in the mortality of early life stages of herring exposed to oil and chemically dispersed oil.