Haddock Larvae Research Articles

Static magnetic fields reduce swimming activity of Atlantic cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) larvae

Abstract Static magnetic fields (B-fields) are introduced in marine ecosystems by anthropogenic sources such as subsea power cables. Larvae of the gadoids Atlantic haddock (Melanogrammus aeglefinus) and Atlantic cod (Gadus morhua) disperse over the continental shelf and may encounter B-fields, which could alter their behavior. We tested the behavior of 184 gadoid larvae while they were being exposed to a B-field (22–156 μT), which is in the intensity range of that produced by a high-voltage direct current cable, for a duration of 10 min in a raceway tank. We present a reanalysis of published data on 92 haddock larvae combined with newly collected data on 92 cod larvae tested under the same settings. Exposure did not affect the spatial distribution of the larvae. Both species displayed the same proportion of nonexploratory (78%) and exploratory (22%) individuals. Exposure significantly reduced the average swimming speed of the nonexploratory larvae by 32% and the average acceleration by 30%. Exploratory larvae were not affected. These results indicate that the swimming behavior of a high proportion of gadoid larvae would be reduced by weak static B-fields. Consequences of exposure on dispersal and survival at the population scale awaits further work using biophysical-coupled models.

Magnetic fields produced by subsea high-voltage direct current cables reduce swimming activity of haddock larvae (Melanogrammus aeglefinus).

High-voltage direct current (HVDC) subsea cables are used to transport power between locations and from/to nearshore and offshore facilities. HVDC cables produce magnetic fields (B-fields) that could impact marine fish. Atlantic haddock (Melanogrammus aeglefinus) is a demersal fish that is at risk of exposure to anthropogenic B-fields. Their larvae drift over the continental shelf, and use the Earth's magnetic field for orientation during dispersal. Therefore, anthropogenic magnetic fields from HVDC cables could alter their behavior. We tested the behavior of 92 haddock larvae using a setup designed to simulate the scenario of larvae drifting past a B-field in the intensity range of that produced by a DC subsea cable. We exposed the larvae to a B-field intensity ranging from 50 to 150 µT in a raceway tank. Exposure to the B-field did not affect the spatial distribution of haddock larvae in the raceway. Larvae were categorized by differences in their exploratory behavior in the raceway. The majority (78%) of larvae were nonexploratory, and exposure to the artificial B-field reduced their median swimming speed by 60% and decreased their median acceleration by 38%. There was no effect on swimming of the smaller proportion (22%) of exploratory larvae. These observations support the conclusion that the swimming performance of nonexploratory haddock larvae would be reduced following exposure to B-field from HVDC cables. The selective impact on nonexploratory individuals, and the lack of impact on exploratory individuals, could have population-scale implications for haddock in the wild.

Ontogeny-Specific Skeletal Deformities in Atlantic Haddock Caused by Larval Oil Exposure

Bone deformities are one of the main effects of crude oil exposure in marine fish larvae. Craniofacial and jaw deformities, if severe enough, may restrict feeding and ultimately kill the developing larvae. This study aimed to examine the impact of dispersed crude oil on bone development in Atlantic haddock (Melanogrammus aeglefinus) larvae, a fish species spawning in areas approached for oil and gas exploration in the North Atlantic Ocean. Atlantic haddock larvae were exposed to low (60 μg oil/L), high (600 μg oil/L), or pulsed (0–600, average 60 μg oil/L over time) dispersed crude oil from 0 to 18 days post hatch (dph). Endpoints included survival and growth, bone integrity, and transcriptional parameters, which were assessed during (0–18 dph) and after exposure until the fish reached 8 months of age (243 dph). The results showed that the larvae in the high treatment group had reduction in growth at 2–19, 44, 134, and 243 dph. Craniofacial abnormalities were most severe at 8 and 19 dph. These deformities were not present at 44 dph, possibly because the larvae with deformed jaws failed to feed properly and died. Higher prevalence of spinal deformities was observed in haddocks that survived for 243 dph. Three genes encoding proteins critical for osteoblast function, sp7, postn, and col10a1, were downregulated in the high treatment group larvae. We discuss possible mechanisms of action in the developing larvae after oil exposure. In conclusion, this study shows that larval exposure to oil can potentially have long-term effects on growth and bone integrity in Atlantic haddock.

Effects of Exposure to Low Concentrations of Oil on the Expression of Cytochrome P4501a and Routine Swimming Speed of Atlantic Haddock (Melanogrammus aeglefinus) Larvae In Situ.

Exposure to environmentally relevant concentrations of oil could impact survival of fish larvae in situ through subtle effects on larval behavior. During the larval period, Atlantic haddock (Melanogrammus aeglefinus) are transported toward nursery grounds by ocean currents and active swimming, which can modify their drift route. Haddock larvae are sensitive to dispersed oil; however, whether exposure to oil during development impacts the ability of haddock larvae to swim in situ is unknown. Here, we exposed Atlantic haddock embryos to 10 and 80 μg oil/L (0.1 and 0.8 μg ∑PAH/L) of crude oil for 8 days and used a novel approach to measure its effect on the larval swimming behavior in situ. We assessed the swimming behavior of 138 haddock larvae in situ, in the North Sea, using a transparent drifting chamber. Expression of cytochrome P4501a (cyp1a) was also measured. Exposure to 10 and 80 μg oil/L significantly reduced the average in situ routine swimming speed by 30–40% compared to the controls. Expression of cyp1a was significantly higher in both exposed groups. This study reports key information for improving oil spill risk assessment models and presents a novel approach to study sublethal effects of pollutants on fish larvae in situ.

Atlantic Haddock (Melanogrammus aeglefinus) Larvae Have a Magnetic Compass that Guides Their Orientation.

SummaryAtlantic haddock (Melanogrammus aeglefinus) is a commercially important species of gadoid fish. In the North Sea, their main spawning areas are located close to the northern continental slope. Eggs and larvae drift with the current across the North Sea. However, fish larvae of many taxa can orient at sea using multiple external cues, including the Earth's magnetic field. In this work, we investigated whether haddock larvae passively drift or orient using the Earth's magnetic field. We observed the behavior of 59 and 102 haddock larvae swimming in a behavioral chamber deployed in the Norwegian North Sea and in a magnetic laboratory, respectively. In both in situ and laboratory settings, where the magnetic field direction was modified, haddock larvae significantly oriented toward the northwest. We conclude that haddock larvae orientation at sea is guided by a magnetic compass mechanism. These results have implications for retention and dispersal of pelagic haddock larvae.

Offshore Crude Oil Disrupts Retinoid Signaling and Eye Development in Larval Atlantic Haddock

The aim of this study was to examine the impact of dispersed crude oil on retinoid metabolism and signaling in developing haddock larvae (Melanogrammus aeglefinus). Retinoids and its active metabolites are involved in the regulation of several developmental processes as cell differentiation, growth and limb patterning. Thus, disruption of retinoid signaling, especially during early developmental stages, may have detrimental effects on the organism. In the present study, crude oil exposure during embryonic development and early larvae development disrupted vitamin A signaling by affecting retinoid levels and genes involved in retinoid metabolism. The disruption of retinoid signaling was also evident when looking at the gene expression pattern at several time-points during and after exposure, demonstrating the complexity and temporal factor of retinoid signaling disruption. Exposure during the embryonic period (pre hatch) resulted in reduced eye size and increased incidence of abnormal eye morphology. The observed changes in expression of retinoid metabolic genes related to the visual cycle indicates that there is a link between the modulated retinoid levels (all-trans retinoic acid and retinol) and increased incidence of abnormal eye development as a result of crude oil exposure. This is the first study to demonstrate disrupted retinoid signaling in fish following crude oil exposure at environmental relevant levels, giving novel insight in to the mechanism of toxicity.

Embryonic exposure to produced water can cause cardiac toxicity and deformations in Atlantic cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) larvae

Regular discharges of produced water from the oil and gas industry represents the largest direct discharge of effluent into the marine environment worldwide. Organic compound classes typically reported in produced water include saturated hydrocarbons, monoaromatic and polyaromatic hydrocarbons (MAHs, PAHs) as well as oxygenated compounds, such as phenols, acids and ketones. This forms a cocktail of known and suspect toxicants, but limited knowledge is yet available on the sub-lethal toxicity of produced water to cold-water marine fish species. In the present work, we conducted a 4-day exposure of embryos of Atlantic cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) to produced water extracts equivalent to 1:50, 1:500 and 1:5000 times dilutions of raw effluent. No significant reduction in survival or hatching success was observed, however, for cod, hatching was initiated earlier for exposed embryos in a concentration-dependent manner. During recovery, significantly reduced embryonic heart rate was observed for both species. After hatch, larvae subjected to embryonic exposure to produced water extracts were smaller, and displayed signs of cardiotoxicity, jaw and craniofacial deformations. In order to improve risk assessment and regulation of produced water discharges, it is important to identify which produced water components contribute to these effects.

The growth of larval cod and haddock in the Irish Sea: a model with temperature, prey size and turbulence forcing

AbstractWe applied a physiological individual‐based model for the foraging and growth of cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) larvae, using observed temperature and prey fields data from the Irish Sea, collected during the 2006 spawning season. We used the model to estimate larval growth and survival and explore the different productivities of the cod and haddock stocks encountered in the Irish Sea. The larvae of both species showed similar responses to changes in environmental conditions (temperature, wind, prey availability, daylight hours) and better survival was predicted in the western Irish Sea, covering the spawning ground for haddock and about half of that for cod. Larval growth was predicted to be mostly prey‐limited, but exploration of stock recruitment data suggests that other factors are important to ensure successful recruitment. We suggest that the presence of a cyclonic gyre in the western Irish Sea, influencing the retention and/or dispersal of larvae from their spawning grounds, and the increasing abundance of clupeids adding predatory pressure on the eggs and larvae; both may play a key role. These two processes deserve more attention if we want to understand the mechanisms behind the recruitment of cod and haddock in the Irish Sea. For the ecosystem‐based management approach, there is a need to achieve a greater understanding of the interactions between species on the scale a fish stock is managed, and to work toward integrated fisheries management in particular when considering the effects of advection from spawning grounds and prey–predator reversal on the recovery of depleted stocks.

Seasonal trends in mortality and growth of cod and haddock larvae result in an optimal window for survival

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 405:57-69 (2010) - DOI: https://doi.org/10.3354/meps08503 Seasonal trends in mortality and growth of cod and haddock larvae result in an optimal window for survival L. J. Buckley1,*, R. G. Lough2, D. Mountain2 1University of Rhode Island, Graduate School of Oceanography, South Ferry Road, Narragansett, Rhode Island 02882, USA 2NOAA/NMFS, Northeast Fisheries Science Center, 166 Water Street, Woods Hole, Massachusetts 02543, USA *Email: lbuckley@gso.uri.edu ABSTRACT: Changing climate and global depletion of fish stocks have added urgency to the century- old quest to understand the factors controlling fish production. The leading hypotheses advanced to explain the large (orders of magnitude) inter-annual variability in recruitment of young fish emphasize rapid growth and a match to prey production in the first weeks after hatching, although avoiding predators may be of equal or greater importance. Here we show for 2 important North Atlantic groundfish (Atlantic cod Gadus morhua and haddock Melanogrammus aeglefinus) that seasonal patterns in growth (G) and mortality (M) rates of young larvae combine in some years to yield a window of opportunity when M falls below G within days after hatching and cohort biomass increases rapidly possibly leading to high recruitment. Contrary to expectations, this window occurs early in the seasonal production cycle (February to March) when temperatures are near their annual minimum, fish larvae and their prey are relatively scarce, and G is low. In most cases examined, later, faster-growing cohorts appear to be rapidly lost to a suite of vertebrate and invertebrate predators whose abundance, metabolism, and consumption increase through the spring with increasing water temperature. In this seasonally varying environment, size on year day may be critical to minimizing M/G. Our data demonstrate the importance of rapid growth throughout the season cycle, but particularly early in the season when temperatures, potential prey, and predators are at seasonal low levels. These findings reinforce the importance of management practices protecting larger, older females that begin spawning earlier in the season and produce larger, more viable eggs and larvae. KEY WORDS: Transition size . Vital rates . Photoperiod . Seasonal trends . Atlantic cod . Haddock Full text in pdf format PreviousNextCite this article as: Buckley LJ, Lough RG, Mountain D (2010) Seasonal trends in mortality and growth of cod and haddock larvae result in an optimal window for survival. Mar Ecol Prog Ser 405:57-69. https://doi.org/10.3354/meps08503 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 405. Online publication date: April 29, 2010 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2010 Inter-Research.

Modeling larval Calanus finmarchicus on Georges Bank: time‐varying mortality rates and a cannibalism hypothesis

AbstractThroughout the North Atlantic, the copepod Calanus finmarchicus dominates the zooplankton biomass, linking primary production and higher trophic levels. On Georges Bank, the peak abundance of larval (naupliar) stages occurs in March–April and represents a potential source of prey for cod and haddock larvae. Following this maximum, naupliar abundance declines dramatically, reaching a minimum in May and increasing again in June. Explaining the naupliar seasonal cycle is critical for predicting climate effects on C. finmarchicus dynamics, including whether environmental variability may lead to a mismatch with larval fish. Here, an age‐within‐stage population dynamics model is used to investigate the factors controlling the temporal variation of C. finmarchicus nauplii in three Georges Bank sub‐regions. The model incorporates temperature‐ and food‐dependent development and egg production, as well as female abundance derived from the US Global Ocean Ecosystem Dynamics (GLOBEC) program. Use of field‐estimated constant mortality rates overestimates May abundances by as much as an order of magnitude. These data/model discrepancies can not be explained by temperature or food‐limitation effects on physiological rates. Instead, accurate simulation requires use of time‐varying early stage mortalities, which differ from published estimates in both magnitude and trend. These mortality rates are correlated with C. finmarchicus female abundance, implying cannibalism as a possible regulatory factor. Thus, the biological control of predation (including cannibalism) must be considered to predict the effects of climate on C. finmarchicus and associated larval fish populations.

Use of differently enriched rotifers,Brachionus plicatilis, during larviculture of haddock,Melanogrammus aeglefinus: effects on early growth, survival and body lipid composition

We evaluated the effects of enriched rotifers on growth, survival and on the lipid composition of haddock larvae. The treatments tested were (1) AlgaMac 2000®, (2) AquaGrow® Advantage and (3) Pavlova sp. paste and AlgaMac 2000®. The treatments did not influence larval growth rate throughout the experimental period (P = 0.70). Larvae from all treatments grew approximately 8% of their dry weight per day between 1 and 29 days post hatch (dph). Treatment 3 resulted in the best survival, estimated to be 3 on a scale from 0 to 5, whereas for the two other groups the survival estimates were 0 and 2. Rotifers from treatment 1 had low sterol concentrations, high eicosapentaenoic acid/arachidonic acid ratio and their feeding resulted in high larval mortality. Rotifers enriched with Pavlova sp. had the lowest proportions of the sum of saturated fatty acids, docosahexaenoic acid and sum of ω3 and the highest proportions of the sum of monounsaturated fatty acids (ΣMUFA). This was partially reflected in larvae from treatment 3 in that they had the highest proportions of ΣMUFA and the lowest proportions of Σω3 (P < 0.0001 for both analyses). In addition, these larvae had the highest and lowest ΣC20 and ΣC22 polyunsaturated fatty acids (PUFA) respectively (P < 0.0001 for both analyses). We suggest that more research with ω3 and ω6 PUFA can lead to improvements in the rearing of haddock larvae produced in hatcheries.

Persistent effects of incubation temperature on muscle development in larval haddock (Melanogrammus aeglefinusL.)

Muscle development and growth were investigated in haddock larvae (Melanogrammus aeglefinus L.) incubated under controlled temperatures (4, 6, 8 degrees C) and reared post-hatch through yolk-dependent and exogenous-feeding stages in a 6 degrees C post-hatch environment. Changes in cell number and size in superficial and deep myotomes within the epaxial muscle were investigated for 28 days following hatch. Distinct and significant differences in muscle cellularity following separate developmental strategies were observed in superficial and deep myotomes. The number of superficial myofibres increased with time and, although not in a manner proportional to temperature during the first 21 days post hatch (d.p.h.), there was observed a trend during the final 7 days of greater mean cell size that was strongly associated with increased temperature. In addition, there was an apparent correspondence between increased temperature and increased size between 21 and 28 d.p.h. Among all temperature groups the superficial myotome not only demonstrated a consistent unimodal myofibre-size distribution but one that increased in range proportional to temperature. In the deep muscle, myotomes from higher incubation temperatures had a broader range of fibre sizes and greater numbers of myofibres. The onset of a proliferative event, characterized by a significant recruitment of new smaller myofibres and a bimodal distribution of cell sizes, was directly proportional to incubation temperature such that it occurred at 14 d.p.h. at 8 degrees C but not until 28 d.p.h. at 4 degrees C. The magnitude of that recruitment was also directly proportional to temperature. Following hatch, those embryos from the greatest temperature groups had the largest mean deep muscle size but, as a result of the proliferative event, had the smallest-sized cells 28 days later. The muscle developmental and growth strategy as indicated by sequential changes in cellularity and cell-size distributions between myotomes in response to temperature are also discussed in light of whole animal growth and development.

Ontogenetic and seasonal trends in recent growth rates of Atlantic cod and haddock larvae on Georges Bank: effects of photoperiod and temperature

Growth rate is a key demographic factor affecting survival and recruitment of marine fishes. Yet in the field, the patterns of change in growth rate with development and the effects of environmental variability on growth are poorly understood. We examined several factors that may contribute to the observed variability in recent (i.e. 2 to 4 d before sampling) growth and survival of Atlantic cod Gadus morhua and haddock Melanogrammus aeglefinus larvae on the southern flank of Georges Bank for the years 1995 through 1999. For both species, strong ontogenetic and seasonal trends in larval growth rates were apparent. A rapid initial increase in specific growth rate with lar- val size was observed in both species, followed by a stanza with little change in specific growth rate and finally a gradual increase with size to a maximum specific growth rate. For larva of any given size, growth rate increased as the season progressed. A variety of models were used to explore and describe the relations among growth rate, larval size, photoperiod, temperature and other variables. Generalized additive models (GAMs) with both larval size (protein content) and photoperiod terms explained 48% and 61% of the variability observed in recent growth of cod and haddock, respec- tively. Residuals from these models were used to examine the effects of other factors on estimated growth rates. Salinity, water density (sigma-t, σt), distance along the Bank, bottom depth, tempera- ture (T) and residual T (observed T minus the long-term mean for a given day of the year) explained small but significant portions of the residual variability in larval growth rates. These data and other considerations suggest that, while both increasing photoperiod and temperature contribute to the increase in larval growth rates observed each spring, photoperiod rather than temperature was the better proxy for the seasonal trend in larval growth rates between March and May on Georges Bank. Feeding conditions and growth of larval Atlantic cod and haddock were poor during the late winter and spring of 1995 compared with those from 1997 to 1999.

Seasonal and inter-annual trends in the zooplankton prey and growth rate of Atlantic cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) larvae on Georges Bank

Abstract The combination of two data sets compiled as part of the US GLOBEC NW Atlantic Georges Bank Program afforded us the opportunity to examine prey abundance and larval growth rates over extended spatial and temporal scales. These data demonstrate a strong correlation between larval growth rates and estimated prey biomass concentration. The dominant copepod taxa on Georges Bank were monitored between January and June of 1995 through 1999, using a pump sampler and a 1-m MOCNESS. Between March and May of these years over 10,000 cod and haddock larvae were collected and recent growth rates of individual larvae estimated using RNA/DNA ratio analysis. The zooplankton sampling was completed on monthly broadscale cruises covering much of the Bank, while most of the larval collections were made on process cruises concentrated on the southern flank. Indices of prey abundance on the southern flank were estimated for different size-classes of larvae. Prey counts (# m−3) and prey biomass concentration (μg dry weight m−3) increased between February and May of each year. Following a similar trend, larval growth rates increased between March and May. Particularly strong correlations were observed between the biomass of Pseudocalanus spp. and larval growth rates. These correlations persisted when the seasonal trend was removed from the estimates of prey biomass concentration, and the seasonal and ontogenetic trends were removed from the estimated growth rates. The spring of 1995 and to a lesser extent 1996 appeared to be periods of low prey availability and poor growth of cod and haddock larvae on Georges Bank. Although no large year class of cod was produced during the study period, the 1998 year-class of haddock was among the largest produced over the previous 20 years on Georges Bank. The data suggest that rapid larval growth maybe a necessary but not sufficient requirement for production of a strong year class. The strong correlations observed between prey biomass concentration and larval growth rates provide additional support for the “growth–mortality” hypothesis that links favorable feeding conditions to rapid growth, reduced stage duration and enhanced survival and recruitment.

Ontogenetic variations in lipid class and fatty acid composition of haddock larvae Melanogrammus aeglefinus in relation to changes in diet and microbial environment

This study examined the ontogenetic variations in lipid class composition and fatty acid partitioning between neutral and polar lipids of haddock ( Melanogrammus aeglefinus) larvae in relation to changes in diet and microbial environment. Three groups of larvae were exposed to the candidate probiotic bacterium Arthrobacter sp. (RSXII) and three equivalent control groups were left unexposed. Larvae were fed rotifers between 2 and 31 days post hatch (dph), which were gradually replaced by Artemia until 45 dph and progressively weaned from live feed to a dry diet between 45 and 56 dph. Overall, the larvae grew exponentially during the course of the experiment as reflected by rates of increase in dry mass and accumulation of lipid. Proportions of arachidonic acid (20:4 n-6, ARA) in haddock larvae were 3–7× higher than observed in the diets, suggesting the selective incorporation of this fatty acid in both lipid reserves and membranes. The initial proportion of docosahexaenoic acid (22:6 n-3, DHA) in haddock larvae was 4.6× higher than the dietary values. However, DHA in the neutral lipids decreased markedly during larval ontogeny to proportions that reflected the dietary values. Regarding polar lipids, the proportions of DHA were markedly less variable than those recorded for neutral lipids, which supports the notion that phospholipids in fish are generally higher in polyunsaturated fatty acids (PUFA) and more resistant to changes in diet than are neutral lipids. During the transition from a diet of rotifer to a diet of Artemia, haddock larvae showed an arrested accumulation of triacylglycerols and a marked increased in ARA, presumably attributable to stimulation of immune functions due to an increase in the bacterial load in the rearing system. Finally, larvae exposed to RSXII showed a superior rate of increase in dry mass and lipid accumulation compared to control groups, suggesting that RSXII enhanced the general health of haddock larvae by modifying their bacterial microflora.

RAG-1 and IgM genes, markers for early development of the immune system in the gadoid haddock, Melanogrammus aeglefinus, L.

The full sequence of the heavy chain of Immunoglobulin M (IgM) and a partial fragment of the recombination activating gene-1 (RAG-1) gene were sequenced in haddock, Melanogrammus aeglefinus, L. The complete transcript of haddock IgM consisted of 1865 bp and translated into a 572-aa peptide. The RAG-1 fragment was 1776 bp and was identified as the core region of RAG-1. These two immune genes were used in expression studies as markers of early development in haddock larvae. A DIG labelled oligoprobe of the RAG-1 gene was used in whole-mount in situ hybridisation (WISH). A hybridisation signal for RAG-1 was first detected in larvae at 25 days post-hatching (dph) in two bilateral symmetric regions of the head identified as the thymus. Further expression studies were carried out by RT-PCR analysis of RAG-1 and IgM on larval samples obtained during early development, i.e. from fertilisation to weaning. Haddock RAG-1 expression was detected after 21 days post-fertilisation (dpf) whilst IgM transcripts were not detected until 40 dpf, equivalent to day 29 post-hatching. These results suggest that the immune system in haddock starts to develop in larvae of 6–7 mm in length (25–29 dph).

Development of the digestive capacity in larvae of haddock ( Melanogrammus aeglefinus) and Atlantic cod ( Gadus morhua)

Using biochemical and molecular biological techniques, we describe the expression of several key digestive enzymes throughout the ontogeny of larval haddock and Atlantic cod. The pattern of activity of general proteases (GP), trypsin-like enzymes (TLE), pepsin-like enzymes (PLE), general lipase (GL), bile salt-activated lipase (BAL), alkaline phosphatase (AP) and α-amylase were studied in larvae of both species using colourometric techniques. All enzymes were detected as early as hatch, except for α-amylase. Activity of GP generally increased from 0 to 144 degree-days (DD), decreased until 333 DD and then increased again in the oldest larvae of both species. Activity of TLE in haddock was high at hatch and generally showed an inverse pattern to that of Atlantic cod. Using zymography, we detected serine proteases, particularly trypsin, in the protein digestion of both species. Using RT-PCR, trypsinogen transcripts were detected as early as hatch. For both species, in situ hybridization analysis showed localization of trypsinogen expression to the pancreas during larval development. Although activity of PLE was detected as early as hatch in both species, pepsinogen transcripts were detected by RT-PCR only in the oldest larvae sampled, and after the gastric glands were identified morphologically. Atlantic cod BAL activity showed no significant differences over time. Activity of GL remained constant over time in larvae of both species. Levels of AP activity in haddock larvae showed no significant differences from hatch to 333 DD, except at 66 and 401 DD when there was a significant increase compared to other time points. In Atlantic cod, AP activity remained relatively constant until 476 DD, when a significant increase was detected. α-Amylase activity could not be detected in either species, except at 43 and 60 DD for Atlantic cod and 144 DD for haddock when large numbers of live prey were present in the gut. The estimated contribution of Pavlova lutheri-enriched rotifers to the total larval digestion was negligible, except for α-amylase, for which their contribution was estimated to be 100%. Our results suggest that both Atlantic cod and haddock larvae are capable of digesting protein and lipids at the time of mouth opening and that they have a limited capacity to digest carbohydrates.

Estimating growth in haddock larvae Melanogrammus aeglefinus from RNA:DNA ratios and water temperature

Five biochemically based variables (RNA, DNA, protein content, RNA:DNA [R:D] ratio, protein:DNA [pro:DNA] ratio) were evaluated as potential indirect measures of growth in larval haddock Melanogrammus aeglefinus. Larvae were reared in the laboratory from hatch to 47 d post-hatch under temperature (T)-controlled conditions (6, 8, and 10°C) and, to produce a variety of growth rates, were starved or reared at 1 of 3 prey levels. The nucleic acid content of the larvae was measured with a spectrofluorometric microplate assay, and the protein-specific growth rate (SGR,% d -1 ) was estimated from the difference in mean protein content between consecutive sampling intervals. Larval haddock growth rate was best described by R:D or pro:DNA ratios. The growth models developed were: SGR=4.61R:D+ 1.18T- 17.31 (R 2 = 0.52) and SGR = 0.92 pro:DNA + 1.10T- 24.97 (R 2 = 0.52). These models can be used to estimate recent growth of larval haddock collected from both the laboratory and field. A combined haddock/Atlantic cod Gadus morhua growth model was calculated as: SGR = 4.67R:D + 0.96T- 15.30 (R 2 = 0.45). This model will be used to estimate recent growth of haddock and cod larvae collected during a multi-year field sampling effort on Georges Bank.

Bile salt-activated lipase expression during larval development in the haddock ( Melanogrammus aeglefinus)

In the present work, we report the characterization of the partial cDNA sequence of a bile salt-activated lipase (BAL) cDNA from haddock. The predicted polypeptide encoded by the cDNA sequence contains the bile salt-binding site characteristic of all BALs at amino acid positions 36–45, and the lipid-binding site thus far only reported in fish BALs starting at position 345. Other features of BAL are also present including: the active site serine motif at positions 111–117, the catalytic triad formed by the residues S 114, D 239 and H 358, and an N-glycosylation site at position 107. The relative levels of BAL gene expression were determined in haddock larvae during ontogeny by reverse transcription–polymerase chain reaction (RT–PCR) with the earliest detectable transcript levels identified at hatch. Using in situ hybridization, the BAL transcripts were localized consistently in the pancreas of haddock larvae from mouth opening until 401 degree days (DD). Using biochemical techniques, the specific activity of BAL was found to decline significantly over time. Our results also suggest that haddock larvae are capable of digesting lipids at the time of mouth opening.

Optimum temperature and food‐limited growth of larval Atlantic cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) on Georges Bank

AbstractWe estimated recent growth of Atlantic cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) larvae collected on the southern flank of Georges Bank in May 1992–94 from the ratio of RNA to DNA (R/D) and water temperature. Growth of both species increased with water temperature to about 7°C and then decreased. The highest growth rates were observed in May 1993 at water temperatures around 7°C. These data confirm an earlier observation of comparable temperature optima for growth of Atlantic cod and haddock larvae in the north‐west Atlantic. Comparisons of field growth rates and temperature optima with data for larvae cultured at high temperatures and prey densities in the laboratory suggest that growth may have been food‐limited at higher temperatures on Georges Bank. Given that 7°C is the long‐term mean water temperature on the southern flank in May and that climate models predict a possible 2–4°C rise in water temperatures for the western North Atlantic, our findings point to a possible adverse effect of global warming on Atlantic cod and haddock.