Cod Gadus Morhua Larvae Research Articles

Modelling larval haddock Melanogrammus aeglefinus and cod Gadus morhua densities and mortality rates in hatchery mesocosms

The numbers and instantaneous mortality rate Z of haddock Melanogrammus aeglefinus and cod Gadus morhua larvae in a hatchery from 0 to 50 days post hatch (dph) were estimated directly and non-destructively. A small mesh plankton net was raised vertically in the water column from the tank base to the water surface and larvae were examined and counted. Using this direct sampling method Z was assessed through the larval period. A semi-log plot described the relationship of larval numbers on time. The Z of M. aeglefinus larvae from 0 to 50 dph was consistent between tanks, from 11.2 to 14.8% d−1 in seven rearing tanks sampled, with a common regression coefficient of 12.7%. The Z was lower for the period 10–50 dph, from 5.5 to 11.8% d−1 with a calculated common slope for all tanks giving a Z of 9.6%. Restricted data for G. morhua suggested lower mortality of Z of 7.8% d−1 from 0 to 50 dph with 4.2% solely for the period 10 to 50 dph. Avoidance of the net sampler by larvae was generally not recorded until >50 dph. The Z in both M. aeglefinus and G. morhua larvae was similar to Z calculated for these species in sea fisheries surveys. Advantages of the technique for estimating Z in hatchery mesocosms and examining causes and timing of larval mortality are discussed. Care in sampling larvae without removal from water, minimizing tank disturbance by sampling after tank cleaning, sampling across tank locations, and thorough disinfection of sampling nets are essential.

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.

Feeding of Plankton in a Turbulent Environment: A Comparison of Analytical and Observational Results Covering Also Strong Turbulence

The present studies address feeding of plankton in turbulent environments, discussed by a comparison of analytical results and field data. Various models for predator-prey encounters and capture probabilities are reviewed. Generalized forms for encounter rates and capture probabilities in turbulent environments are proposed. The analysis emphasizes ambush predators, exemplified by cod larvae Gadus morhua L. in the start-feeding phase (stage 7 larvae) collected in shallow waters near Lofoten, Norway. During this campaign, data were obtained at four sites with strongly turbulent conditions induced by tidal currents and long-wave swells, and one site where the turbulence had a lower level in comparison. The guts of the selected cod larvae were examined in order to determine the number of nauplii ingested. Analytically obtained probability densities for the gut content were compared with observations and the results used for estimating the rate of capture of the nauplii. This capture rate was then compared with analytical results using also data for the surroundings, such as measured prey densities and turbulence conditions, as quantified by the specific energy dissipation rate. Different from earlier studies, the presented data include conditions where the turbulence exceeds the level for optimal larval encounter-capture rates.

Dying from the lesser of three evils: facilitation and non‐consumptive effects emerge in a model with multiple predators

Prey modify their behaviour to avoid predation, but dilemmas arise when predators vary in hunting style. Behaviours that successfully evade one predator sometimes facilitate exposure to another predator, forcing the prey to choose the lesser of two evils. In such cases, we need to quantify behavioural strategies in a mix of predators. We model optimal behaviour of Atlantic codGadus morhualarvae in a water column, and find the minimal vulnerability from three common predator groups with different hunting modes; 1) ambush predators that sit‐and‐wait for approaching fish larvae; 2) cruising invertebrates that eat larvae in their path; and 3) fish which are visually hunting predators. We use a state‐dependent model to find optimal behaviours (vertical position and swimming speed over a diel light cycle) under any given exposure to the three distinct modes of predation. We then vary abundance of each predator and quantify direct and indirect effects of predation. The nature and strength of direct and indirect effects varied with predator type and abundance. Larvae escaped about half the mortality from fish by swimming deeper to avoid light, but their activity level and cumulative predation from ambush predators increased. When ambush invertebrates dominated, it was optimal to be less active but in more lit habitats, and predation from fish increased. Against cruising predators, there was no remedy. In all cases, the shift in behaviour allowed growth to remain almost the same, while total predation were cut by one third. In early life stages with high and size‐dependent mortality rates, growth rate can be a poor measure of the importance of behavioural strategies.

Gene regulation of lipid and phospholipid metabolism in Atlantic cod (Gadus morhua) larvae.

The mechanism of essentiality of dietary phospholipid (PL) for larval fish is not clear. The main objective of the present study was to determine if the PL requirement of Atlantic cod larvae was due to any genetic impairment caused by functional immaturity. Cod larvae were sampled at 1, 3, 8, 13, 17, 18, 30, 42 and 60 days post hatch (dph) for transcriptome analysis using a recently developed microarray. The fatty acid profile and gene expression levels of cod larvae at 17 dph were compared after feeding differently enriched rotifers, which contained different DHA levels in PL. No significant differences (p<0.05) were found for the two rotifer diets in the overall gene expression level of cod larvae, their growth and survival, and their DHA levels in total lipid and PL fraction. The fatty acid data suggested that dietary EPA was elongated to DPA by cod larvae, and a threshold DHA level in PL to maintain membrane fluidity and other functions may exist. There appeared to be no major effect of development on the expression of key genes of PL biosynthesis suggesting no genetic constrain in early developmental stages. Our overall data suggested that besides the possible limited de novo PC synthesis ability in the intestine, other metabolic constraints should also be considered, especially the possible low input of bile PC as a result of immature liver. Further studies are needed to elucidate the gene expression level and enzyme activity in the PL biosynthesis pathways for specific tissue or cells.

The stress hormone corticosterone in a marine top predator reflects short-term changes in food availability.

In many seabird studies, single annual proxies of prey abundance have been used to explain variability in breeding performance, but much more important is probably the timing of prey availability relative to the breeding season when energy demand is at a maximum. Until now, intraseasonal variation in prey availability has been difficult to quantify in seabirds. Using a state-of-the-art ocean drift model of larval cod Gadus morhua, an important constituent of the diet of common guillemots Uria aalge in the southwestern Barents Sea, we were able to show clear, short-term correlations between food availability and measurements of the stress hormone corticosterone (CORT) in parental guillemots over a 3-year period (2009–2011). The model allowed the extraction of abundance and size of cod larvae with very high spatial (4 km) and temporal resolutions (1 day) and showed that cod larvae from adjacent northern spawning grounds in Norway were always available near the guillemot breeding colony while those from more distant southerly spawning grounds were less frequent, but larger. The latter arrived in waves whose magnitude and timing, and thus overlap with the guillemot breeding season, varied between years. CORT levels in adult guillemots were lower in birds caught after a week with high frequencies of southern cod larvae. This pattern was restricted to the two years (2009 and 2010) in which southern larvae arrived before the end of the guillemot breeding season. Any such pattern was masked in 2011 by already exceptionally high numbers of cod larvae in the region throughout chick-rearing period. The findings suggest that CORT levels in breeding birds increase when the arrival of southern sizable larvae does not match the period of peak energy requirements during breeding.

Probiotic strains introduced through live feed and rearing water have low colonizing success in developing Atlantic cod larvae

Abstract The use of probiotic bacteria is a strategy suggested to overcome microbial problems during early stages of farmed animals, including fish. However, few studies have investigated the efficiency in the establishment of probiotics in the fish and how lasting such treatments are. The objective of this study was to evaluate whether the microbiota of Atlantic cod larvae Gadus morhua L can be steered by introduction of selected probiotic candidates, and if there are particular developmental stages where this is more easily obtained. Cod larvae were given a mixture of 4 candidate probiotic strains (Microbacterium (ID3-10), Ruegeria (RA4-1), Pseudoalteromonas (RA7-14) and Vibrio (RD5-30)) through the live feed and the water during a treatment period of 24 h. The strains originated from reared cod larvae and are proven to have probiotic properties. The larvae were treated at seven different ages, namely days 0, 2, 4, 8, 16, 30 and 45 post-hatching, with one new experimental group started each time. A real-time PCR strategy was developed to quantify the relative amounts of the four added bacterial strains in live feed, and in water and cod larvae during 10 days after exposure. Only ID3-10 was measured to constitute considerable fractions of the larval microbiota for most of the treatments, despite the fact that all the probiotic candidates originated from cod larvae intestines. In most cases, the amounts of the added strains decreased to approximately background levels after a maximum of 4 days, indicating only a transient presence in the larvae. The results indicate that probiotic treatment aiming for colonization with new strains in the cod larvae is difficult, and challenges the probiotic concept for the larval stage unless continuous or repeated addition to the fish larvae is used.

Climate-Driven Ichthyoplankton Drift Model Predicts Growth of Top Predator Young

Climate variability influences seabird population dynamics in several ways including access to prey near colonies during the critical chick-rearing period. This study addresses breeding success in a Barents Sea colony of common guillemots Uria aalge where trophic conditions vary according to changes in the northward transport of warm Atlantic Water. A drift model was used to simulate interannual variations in transport of cod Gadus morhua larvae along the Norwegian coast towards their nursery grounds in the Barents Sea. The results showed that the arrival of cod larvae from southern spawning grounds had a major effect on the size of common guillemot chicks at fledging. Furthermore, the fraction of larvae from the south was positively correlated to the inflow of Atlantic Water into the Barents Sea thus clearly demonstrating the mechanisms by which climate-driven bottom-up processes influence interannual variations in reproductive success in a marine top predator.

Effect of food deprivation on distribution of larval and early juvenile cod in experimental vertical temperature and light gradients

How and when food limits the growth and survival of larval fish are essential ques- tions which link oceanography and fisheries science, and theory suggests that food availability may affect survival through behavioural responses. We tested the effect of food deprivation on the vertical distribution of larval cod Gadus morhua in light and temperature gradients during larval and early juvenile stages. Groups of fed (ad lib) and unfed (16 h) larval cod at 16, 30 and 37 d post hatch (dph) and early juvenile cod at 44 dph were repeatedly observed in experimental columns with temperature gradients (110 × 15 cm, 6 to 8°C) for a period of 3 h while the directionality of the light was manipulated. At earlier stages (16 and 30 dph), larvae were distributed mainly in the upper part of the column regardless of the water stratification. The presence of a thermocline reduced the likelihood of cod being observed in the lower part of the column at 37 and 44 dph, but this response was not affected by feeding history. Unfed larvae distributed deeper in the column than fed larvae, but this effect was small (on average, 4.3 cm difference in a 115 cm column). Video analysis of individual swimming behaviour at 44 dph indicated that, while unfed cod would not stay longer or swim deeper into the columns than fed cod, there was an increased number of fish swimming up and down in the column, suggesting an increased motivation to sample new environments. We conclude that short-term food deprivation (16 h) has a small but significant effect on larval vertical distribution, most likely as a consequence of increased prey-search behav- iour, but that temperature and ontogeny were the key factors in determining distribution patterns.

Nucleotide Enrichment of Live Feed: A Promising Protocol for Rearing of Atlantic Cod Gadus morhua Larvae

We investigated the effect of two commercial nucleotide products (NT1 and NT2), administered through live feed, on growth and stress tolerance of Atlantic cod larvae. Expression of genes related to muscle growth (igf-1, igf1r, igf-2, fst, fgf6, myod, and myhc) and nucleotide metabolism (uox, hprt, ndk, and uck) was evaluated during larval development. In addition, the expression of genes related to stress (hif-1α, hif-2α, hif-3α, and mb) was studied after an air exposure stress test. The enrichment of rotifers with nucleotides did not reveal any difference in nucleotide profiles, the exception being the RNA level of the NT1-enriched group that was significantly higher than the unenriched rotifer. Unenriched Artemia showed poor nucleotide profiles compared to enriched Artemia since 5' UMP, 5' GMP, and 5' AMP were observed only in the nucleotide groups. At 38days post-hatch (dph), NT1 group had significantly higher dry weight (3.1 ± 0.1mg) than the control (CON; 2.3 ± 0.1mg). The treatments did not produce any significant differences in the expression of the key myogenic genes. Among the genes associated with nucleotide metabolism, ndk was down-regulated in NT1 at 38 dph. In the air exposure test, survival was significantly higher in the CON (77 ± 6%) than in NT1 (48 ± 3%) and NT2 (50 ± 3%). After air exposure, mb was expressed at lower levels in NT2 group, hif-2α was induced in NT1 group, and hif-3α was upregulated in all groups. Our findings indicate that the improvement in the nucleotide profile of Artemia upon nucleotide enrichment could eventuate in the rapid growth of larvae.

Model of optimal behaviour in fish larvae predicts that food availability determines survival, but not growth

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 432:207-219 (2011) - DOI: https://doi.org/10.3354/meps09148 Model of optimal behaviour in fish larvae predicts that food availability determines survival, but not growth Øyvind Fiksen1,2,*, Christian Jørgensen2 1Department of Biology, University of Bergen, Pb 7803, 5020 Bergen, Norway 2Uni Research, 5020 Bergen, Norway *‑Email: oyvind.fiksen@bio.uib.no ABSTRACT: How do growth and survival of larval fish depend on the availability of zooplankton prey? This question connects plankton ecology to fisheries science and is typically answered by the classical ‘match/mismatch’ hypothesis for explaining recruitment variability to fish populations. In field and experimental data, however, the effects of food abundance on growth are not always unequivocal. Here, we present a detailed state-dependent optimality model of larval cod Gadus morhua in a water column with environmental gradients and circadian light cycles. Larval feeding rates and predation risk both depend on ambient light, body size, swimming activity and depth position, which together describe trade-offs between growth and survival from realistic mechanisms. The model finds the optimal depth (vertical migration) and swimming activity that maximize survival probability to a given size (15 mm). These optimal behaviours in turn determine food intake, gut fullness, growth and survival over time. The model predicts that increasing food leads to increasing survival, whereas growth remains high except when food availability is very low. When food is more abundant, larvae select deeper and safer habitats and are less active to avoid predation. This can explain why prey abundance and larval fish growth are often not strongly correlated in field studies, although there is still an important effect of prey abundance on recruitment success through its effect on predation rates. KEY WORDS: Larval fish · Behaviour · Growth · Mortality · Recruitment · Trade-off Full text in pdf format Supplementary material PreviousNextCite this article as: Fiksen Ø, Jørgensen C (2011) Model of optimal behaviour in fish larvae predicts that food availability determines survival, but not growth. Mar Ecol Prog Ser 432:207-219. https://doi.org/10.3354/meps09148 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 432. Online publication date: June 27, 2011 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2011 Inter-Research.

Spatio-temporal overlap of the alien invasive ctenophore Mnemiopsis leidyi and ichthyoplankton in the Bornholm Basin (Baltic Sea)

In 2007 the alien invasive ctenophore Mnemiopsis leidyi A. Agassiz 1865 was recorded for the first time in the Bornholm Basin, an area which serves as important spawning ground for Baltic fish stocks. Since M. leidyi is capable of preying upon early life stages of fish and further might act as food competitor for fish larvae, it is of major concern to investigate the potential threat that this non-indigenous species poses to the pelagic ecosystem of the Baltic Sea. The present study investigates the temporal and spatial overlap of M. leidyi with eggs and larvae of Baltic cod (Gadus morhua L.) and sprat (Sprattus sprattus L.) in order to assess the potential impact of this new invader on two of the most important Baltic fish stocks. Results show variable inter-seasonal distribution and overlap dynamics and thus different seasonal threat-scenarios for the early life stages of cod and sprat. The spatial overlap between M. leidyi and ichthyoplankton was low for most of the period observed, and we conclude that M. leidyi presently does not have a strong impact. However, we detected situations with high overlaps, e.g. for sprat larvae and cod eggs in spring. As the population dynamics of M. leidyi in the central Baltic are not yet fully understood, a future population explosion of the alien ctenophore with possible effects on fish recruitment cannot be ruled out. Furthermore, a possible shift in peak spawning of cod to the early season, when ctenophore abundances were relatively high, might increase the impact of M. leidyi on cod.

The influence of first‐feeding diet on the Atlantic cod Gadus morhua phenotype: survival, development and long‐term consequences for growth

Atlantic cod Gadus morhua larvae reached four-fold (at low larval density) to 11 fold higher body mass (high larval density) at 50 days post hatch (dph) when fed zooplankton rather than enriched rotifers. A short period (22-36 dph) of dietary change affected larval growth positively if changed from enriched rotifers to natural zooplankton and negatively if prey type changed vice versa. Overall survival did not differ between the two larval groups at low larval density, but at high density the rotifer group had a higher overall survival (10.8% v. 8.9%). Long-term growth was affected significantly by larval diet in favour of the zooplankton diet; juveniles reached a 23% higher mass in a 12 week growth period. No difference in growth performance was found between juveniles fed natural zooplankton during the larval period for 36, 22 or 14 days, but all these juveniles performed significantly better compared with the rotifer-fed group. These findings suggest that optimal diet during a short period in the larval period can result in improved growth in both the larval and juvenile period. Improved rotifer quality may, therefore, hold a large potential for growth improvement in this species.

Transcriptional effects on glutathione S-transferases in first feeding Atlantic cod ( Gadus morhua) larvae exposed to crude oil

Polycyclic aromatic hydrocarbons (PAHs) and other oil compounds are known to induce stress and impact health of marine organisms. Water-soluble fractions of oil contain components known to induce glutathione S-transferases (GSTs), one of the major classes of phase II detoxifying enzymes present in essentially all eukaryotic organisms. In this study, the transcriptional responses of six GSTs (GST pi, GST mu, GST omega, GST theta, GSY zeta and GST kappa) were examined in early larvae of Atlantic cod Gadus morhua exposed to five concentrations of dispersed oil (containing oil droplets and water-soluble fraction) and water-soluble fractions (WSF) of oil. When Atlantic cod larvae were exposed to WSF (containing 1.31 ± 0.31 μg ∑PAH/L for 4 days), expression of GSTM3 and GSTO1 was significantly increased, whereas no differences in GST expression were observed in larvae exposed to a corresponding 50% lower amount of dispersed oil (containing 0.36 ± 0.10 μg ∑PAH/L for 4 days). The study suggest that although the oil clearly had severe negative effects on the larvae (i.e. concentration-dependent lethality and growth reduction), only minor effects on GST transcription could be observed using RNA obtained from pooled whole-larvae homogenates. This result indicates that the expression of these important detoxification enzymes is only moderately inducible at such an early developmental stage either reflecting low tolerance of cod larvae to dispersed oil or alternatively that using whole-larvae homogenates may have masked tissue-specific mRNA induction.

Ribosomal RNA gene sequences confirm that protistan endoparasite of larval cod Gadus morhua is Ichthyodinium sp.

An enigmatic protistan endoparasite found in eggs and larvae of cod Gadus morhua and turbot Psetta maxima was isolated from Baltic cod larvae, and DNA was extracted for sequencing of the parasite's small subunit ribosomal RNA (SSU rRNA) gene. The endoparasite has previously been suggested to be related to Ichthyodinium chabelardi, a dinoflagellate-like protist that parasitizes yolk sacs of embryos and larvae of a variety of fish species. Comparison of a 1535 bp long fragment of the SSU rRNA gene of the cod endoparasite showed absolute identity with I. chabelardi, demonstrating that the 2 parasites are very closely related, if not identical. This finding is discussed in relation to some morphological differences that appear to exist between I. chabelardi and the cod endoparasite.

Distribution of cholecystokinin‐immunoreactive cells in the gut of developing Atlantic cod Gadus morhua L. larvae fed zooplankton or rotifers

One of the main gastrointestinal hormones, cholecystokinin (CCK), was studied in order to advance understanding of the control of the digestive process in Atlantic cod Gadus morhua larvae after onset of first feeding. Larvae were fed either natural zooplankton or enriched rotifers in similar rearing systems and sampled from hatching to 22 days post-hatch (dph). CCK was visualized by immunohistochemistry and the first CCK-immunoreactive (IR) cells were detected at 8 dph corresponding to 6 days after first feeding. The CCK-IR cells were mostly found in the anterior midgut, and the number of CCK-IR cells was lower in the posterior midgut. They were also present in the hindgut of some of the larvae, but not in the foregut. No clear differences were found in the ontogenetic appearance and the distribution pattern of CCK-IR cells between the two dietary treatments. This indicates that the onset of CCK production in the gut as well as the spatial distribution of the CCK-IR cells is not differentially affected by these diets. To what extent the hormone production itself is influenced by dietary factors needs to be studied by more sensitive methods.

Effects of egg size, parental origin and feeding conditions on growth of larval and juvenile cod Gadus morhua

An experimental study was performed to disentangle parental and environmental effects on the growth of Atlantic cod Gadus morhua larvae and juveniles. Eggs were collected during the spawning season from spawning pairs (families) kept separately in specially designed spawning compartments. Newly hatched larvae were released simultaneously into two mesocosms of 2,500 and 4,400 m(3). Larval growth was monitored by sampling over a 10 week period, after which juveniles were transferred to on-growing tanks, where they were tagged and kept for up to 2 years. Maternal origin was determined by individual microsatellite genotyping of the larvae (n = 3949, 24 families) and juveniles (n = 600). The results showed significant positive correlations between egg size and larval size during the whole mesocosm period. Correlations, however, weakened with time and were no longer significant at the first tank-rearing sampling at an age of 9 months. Significant family-specific differences in growth were observed. The coefficient of variation (c.v.) was calculated in order to examine variation in standard length of larvae during the mesocosm period. Inter-family c.v. was on average 69% of intra-family c.v. Differences in zooplankton densities between the two mesocosms were reflected in larval growth, condition factor and c.v. Low food abundance appeared to reduce c.v. and favour growth of larvae that showed relatively slow growth at high food abundance. It is suggested that genetically determined variation in growth potential is maintained by environmental variability.

Effects of female spawning experience and larval size on feeding and growth of cod larvae Gadus morhua L. reared in mesocosms

The viability, defined in terms of growth and feeding success, of cod larvae from first-time and repeat spawners of similar sizes was studied in two mesocosms. The growth rate of larvae from first-time and repeat spawners were similar from hatching through to 41 days old, when the experiment was terminated. Larvae from first-time spawners were heavier throughout the experiment than larvae of repeat spawners, a difference that might be explained by a difference (although non-significant) in egg size between the two groups. There was a significant difference in growth rate between the two mesocosms, which may be explained by the difference in temperature between the mesocosms. In both mesocosms larvae fed mainly on copepod nauplii during the first weeks of life and started to actively select copepodites at age 20 days post hatch. There was no significant difference in the energy content of the ingested prey at a given age between offspring of first-time and repeat spawners, although there was a significant difference between the two mesocosms. The dry mass of the ingested prey items compared to larval dry mass increased until age 17–27 days post hatch and decreased thereafter.

Individual-based modeling of feeding ecology and prey selection of larval cod on Georges Bank

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 376:227-243 (2009) - DOI: https://doi.org/10.3354/meps07796 Individual-based modeling of feeding ecology and prey selection of larval cod on Georges Bank Trond Kristiansen1,4,*, R. Gregory Lough2, Francisco E. Werner1,5, Elisabeth A. Broughton2, Larry J. Buckley3 1Marine Sciences Department, University of North Carolina, Chapel Hill, North Carolina 27599-3300, USA 2Northeast Fisheries Science Center, NMFS, NOAA, Woods Hole, Massachusetts 02543, USA 3University of Rhode Island/NOAA CMER Program, Graduate School of Oceanography, Narragansett, Rhode Island 02882, USA 4Present address: Institute of Marine Research, PO Box 1870 Nordnes, 5817 Bergen, Norway 5Present address: Institute of Marine and Coastal Sciences, Rutgers University, New Brunswick, New Jersey, United States *Email: trond.kristiansen@imr.no ABSTRACT: Understanding larval fish survival dynamics is essential to determining variability in future adult population structure. Realistic modeling of larval fish feeding ecology depends on incorporating both the biotic and abiotic conditions that affect predator–prey interactions. We used an individual-based model (IBM) to test which variables drive Atlantic larval cod Gadus morhua feeding preferences. The IBM included a bioenergetics component that incorporated metabolic parameters and growth and a mechanistic prey selection component that depended on larval development and behavior, prey size and behavior, depth, light, and physical oceanographic conditions. We applied our model to Georges Bank and incorporated high-resolution field data on environmental conditions and prey abundance to analyze larval cod feeding ecology. Based on simulated selectivity indices, we found that cod prey selection was determined by differential encounter of prey due to the abundance of suitably sized prey, their visibility, and larval cod ability to capture these prey items. The model suggested that Pseudocalanus spp. were the dominant prey species for larval cod because of their abundance in the water column and their large image area. Centropages spp. were also modeled to be an important part of larval diet, but no copepodite stages of this taxon were found in gut samples. Lack of Centropages spp. in the gut samples indicated that they are more elusive in their behavior than Pseudocalanus spp. Overall our results suggest larval cod feeding ecology on Georges Bank is a consequence of the physical and biological conditions rather than active prey selection. KEY WORDS: Feeding ecology · Individual-based model · Cod · Larval fish · Georges Bank · Gadus morhua · Prey selection Full text in pdf format PreviousNextCite this article as: Kristiansen T, Lough RG, Werner FE, Broughton EA, Buckley LJ (2009) Individual-based modeling of feeding ecology and prey selection of larval cod on Georges Bank. Mar Ecol Prog Ser 376:227-243. https://doi.org/10.3354/meps07796 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 376. Online publication date: February 11, 2009 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2009 Inter-Research.

Determination of apparent protein digestibility of live Artemia and a microparticulate diet in 8-week-old Atlantic cod Gadus morhua larvae

A technique was developed to determine apparent digestibility coefficients (ADCs) of protein in microparticulate and live feeds for marine fish larvae. The technique is analogous to methods used for larger fish and allows for an in vivo measurement of protein digestibility by employing a spectrophotometric protein assay for protein determination and rare earth oxides as inert digestibility markers. Either a microbound microparticulate diet developed in our laboratory or Artemia nauplii were fed to 8-week-old Atlantic cod as a single 30-min feeding and fecal solids collected 6 h later. Protein ADCs for the two diets were significantly different (P=0.016) with determined ranges of 47 to 58% and 76 to 86%, (Artemia and microparticulate diets, respectively). Measured ADCs are presented as a range to account for the possibility of leaching of protein from the microparticulate diet, and the evacuation (loss) of marker from the live prey during the 30-min feeding. It is suggested that this new technique will assist researchers in selecting experimental larval feeds with the most nutritive potential for extended feeding studies. Detection limits for this technique were determined to be 8.6 μg for protein and 0.020 and 0.038 μg for yttrium (Y2O3) and dysprosium (Dy2O3) markers, respectively, in collected fecal solids.