Juvenile Atlantic Cod Gadus Morhua Research Articles

Condition, size, and winter duration affect winter survival probability of juvenile Atlantic cod Gadus morhua in a coastal subarctic ecosystem

Juvenile Atlantic cod Gadus morhua in coastal Newfoundland, Canada, settle in nearshore habitats in 3-6 pulsed events each year, from mid-summer to early winter, creating a broad size range of age-0 fish within each year-class, with potentially different survival trajectories entering their first winter. We hypothesized that early-arriving pulses, high autumn body condition, and low winter severity would contribute to high first-winter survival of age-0 cod. To test these hypotheses, we examined juvenile cod catch data, archived samples, and winter temperature records to determine the impact of winter duration, body condition, and settlement time on winter survival from 2001 to 2019. Settlement pulse, pre-winter condition, and winter duration had an interactive effect on survival. Fish condition did not vary across pulses within a given year-class, but we observed improved winter survival during long winters when body condition was high, with highest survival among the larger, early-arriving pulses of fish. Late-arriving pulses of fish were small-sized before winter onset, but these pulses unexpectedly survived better than pulses settling earlier in the season during short winters when body condition was high. However, all settlement pulses had a survival advantage when settlement occurred earlier on average (associated with warmer autumns), suggesting that increased growth and size within a pulse can also contribute to overwintering success. Our findings challenge some assumptions of overwintering ecology (e.g. ‘bigger is better’, low temperature stress) but illustrate the importance of cohort effects for overwintering survival in a sub-arctic marine ecosystem in a changing climate.

High site-fidelity and low mortality of juvenile Atlantic cod (Gadus morhua) in subarctic coastal habitat during their first winter

Abstract In subarctic Newfoundland, age-0 juvenile Atlantic cod (Gadus morhua) settle into coastal habitats in several summer and fall pulses, yielding a broad length-frequency distribution prior to their first winter. The first winter is often associated with physiological and metabolic stress and has been considered a critical survival period determining cohort strength. We evaluated size-structured overwinter mortality and movement using mark–recapture and condition metrics by marking 226 cod in two batches one week apart, in October 2016. We estimated fall and overwinter mortality, and documented movement of fish recaptured in May 2017 using Cormack–Jolly–Seber models. We recaptured 30 marked juveniles. High fall mortality characterized late settling cohorts relative to earlier settling cohorts (16.6%∙d−1 vs. 4.5–7.7% ∙d−1). Overwinter mortality was unexpectedly low (0.0052 and 0.0022% ∙d−1). Individual condition (Fulton’s K) of juvenile cod remained high throughout winter across all size groups. We expected higher mortality of juvenile cod and broad dispersal of juveniles over winter (32 weeks). In contrast, our results indicated low mortality and high site-fidelity in their first winter. This study indicates the period leading up to winter is important for survival, suggesting winter is not a survival bottleneck and may even provide a refuge compared to the rest of the year.

Susceptibility and Pathology in Juvenile Atlantic Cod Gadus morhua to a Marine Viral Haemorrhagic Septicaemia Virus Isolated from Diseased Rainbow Trout Oncorhynchus mykiss.

Simple SummaryVHSV (viral haemorrhagic septicaemia virus) is a globally important group of viruses, infecting a wide range of fish species, in both marine and freshwater. New initiatives are now being taken to re-establish Atlantic cod as an aquaculture species. Any susceptibility to diseases would be relevant for this industry. Atlantic cod was experimentally infected with a strain of VHSV originating from a disease outbreak of farmed rainbow trout in Norway. The fish infected by injection did develop the disease, as verified by investigations of tissue samples. However, no transmission of the virus to cohabitant fish (i.e., individuals sharing the tank with infected fish) was found. This indicates that, despite the fact that the virus is capable of causing disease in Atlantic cod, the degree and ability to infect the fish is limited.The first known outbreak caused by a viral haemorrhagic septicaemia virus (VHSV) strain of genotype III in rainbow trout occurred in 2007 at a marine farm in Storfjorden, Norway. The source of the virus is unknown, and cod and other marine fish around the farms are suspected as a possible reservoir. The main objective of this study was to test the susceptibility of juvenile Atlantic cod to the VHSV isolate from Storfjorden. As the pathology of VHS in cod is sparsely described, an additional aim of the study was to give a histopathological description of the disease. Two separate challenge experiments were carried out, using both intra peritoneal (ip) injection and cohabitation as challenge methods. Mortality in the ip injection experiment leveled at approximately 50% three weeks post challenge. Both immunohistochemical and rRT-PCR analysis of organs sampled from diseased and surviving fish confirmed VHSV infection. No VHSV was detected in the cohabitants. The results indicate that Atlantic cod has a low natural susceptibility to this VHSV genotype III strain. One of the most extensive pathological changes was degeneration of cardiac myocytes. Immunohistochemistry confirmed that the lesions were related to VHSV. In some fish, the hematopoietic tissue of spleen and kidney showed degeneration and immunostaining, classical signs of VHS, as described in rainbow trout. Positive immunostaining of the capillaries of the gills, suggests this organ as a useful alternative when screening for VHSV.

Personality‐dependent inter‐ and intraspecific foraging competition in the invasive round goby, Neogobius melanostomus

This study examines the impact of boldness on foraging competition of the highly invasive round goby Neogobius melanostomus Pallas 1815. Individual risk tolerance, or boldness, was measured as the time to resume movement after a simulated predation strike. Fish that resumed movement faster were categorized as "bold," fish that took more time to resume movement were categorized as "shy" and those that fell in between these two categories were determined to have "intermediate" boldness. Competitive impacts of boldness in N. melanostomus were determined in a laboratory foraging experiment in which interspecific (juvenile Atlantic cod Gadus morhua Linnaeus 1758) and intraspecific (intermediate N. melanostomus) individuals were exposed to either bold or shy N. melanostomus competitors. G. morhua consumed fewer prey when competing with bold N. melanostomus than when competing with shy N. melanostomus, whereas intermediately bold N. melanostomus foraging was not affected by competitor boldness. Bold and shy N. melanostomus consumed similar amounts of prey, and the number of interactions between paired fish did not vary depending on the personality of N. melanostomus individuals. Therefore, intraspecific foraging competition was not found to be personality dependent. This study provides evidence that individual differences in boldness can mediate competitive interactions in N. melanostomus; nonetheless, results also show that competition is also governed by other mechanisms that require further study.

Atlantic cod Gadus morhua save energy on stone reefs: implications for the attraction versus production debate in relation to reefs

Reefs are structurally complex habitats that are degraded in numerous coastal areas. Structural complexity is often associated with elevated fish abundance, and recent studies have indicated that such structural complexity (e.g. reefs) not only acts as a fish aggregator, but also increases fish production. The objective of this study was to advance this knowledge by investigating if an underlying mechanism of the observed productivity is related to reduced metabolic rates (proxy for energy use) of fish in reef habitats. Using juvenile Atlantic cod Gadus morhua, we tested the hypothesis that fish energy use differs between fish occupying stone reef and sand bottom habitats. Metabolic rate (MO2) was estimated using intermittent flow respirometry in simulated stone reef and sand bottom habitats over 24 h. Results revealed that G. morhua in the stone reef habitat exhibited significantly reduced accumulated MO2 compared to G. morhua in the sand bottom habitat. Likewise, there was a tendency for lower mean standard metabolic rates of the fish in stone reefs, although this pattern was not statistically significant. There are many mechanisms that may underpin elevated productivity in structurally complex habitats such as reefs, including better access to shelter and increased food availability. Our study adds to these mechanisms by showing that G. morhua save energy when occupying stone reefs as compared to sandy bottoms, energy which may be allocated to somatic and gonadal growth.

Juvenile gadoid habitat and ontogenetic shift observations using stereo-video baited cameras

Understanding habitat variables affecting species distribution and survival is essential to their protection. This is especially important in areas where anthropogenic pressures can have a significant direct impact on not only the survival of the species but also damage their habitat. The Firth of Clyde, southwestern Scotland, was an important commercial fishing area for a variety demersal fish species up until 1973. However, stocks have since declined to near-zero despite fisheries measures put in place to aid recovery. Here we report on Stereo Baited Remote Underwater Video (SBRUV) surveys in the Firth of Clyde between June and September in 2013 and 2014 to determine the habitat of juvenile Atlantic cod Gadus morhua, haddock Melanogrammus aeglefinus, and whiting Merlangius merlangus. Habitat predictor variables explored included substratum type, depth, wave fetch, and bentho-demersal species diversity. G. morhua were most abundant in shallow, sheltered areas composed of gravel-pebble containing maerl. Ontogenetic shifts and density dependence were also observed. M. aeglefinus, and M. merlangus predominated over deeper sand and mud. Relative abundances of all three species were positively related to bentho-demersal diversity. This work demonstrates the potential of SBRUV as a non-destructive survey tool under northern-temperate conditions. Our results indicate that spatial conservation measures to benefit demersal fish should be advised by patterns of bentho-demersal diversity as well as physical substratum types.

An assessment of juvenile Atlantic cod Gadus morhua distribution and growth using diver operated stereo-video surveys.

Stereo‐video scuba transects were conducted during daylight hours from June to September 2013 within a proposed marine protected area (MPA) in the Firth of Clyde, west of Scotland. More juvenile Atlantic cod Gadus morhua of fork length (L F) range 6–11 cm were observed in substrata containing mixed gravel, including maerl, than in boulder‐cobble substrata with high algal cover, or sand with low density seagrass. Community composition was significantly different between substratum types. A decrease in G. morhua abundance was observed over the period of data collection. Over time, mean and variance in G. morhua L F increased, indicating multiple recruitment events. Protecting mixed gravel substrata could be a beneficial management measure to support the survival and recruitment of juvenile G. morhua; other substrata might be important at night given their diel migratory behaviour. Stereo‐video cameras provide a useful non‐destructive fisheries‐independent method to monitor species abundance and length measurements.

The measurement of specific dynamic action in fishes.

Specific dynamic action (SDA) is the postprandial increase in oxygen uptake. Whereas it is easy to measure in fishes that remain calm and motionless during the entire digestion period, spontaneous locomotor activity is a frequent problem that leads to overestimation of SDA amplitude and magnitude (area under the curve, bound by the standard metabolic rate, SMR). Few studies have attempted to remove the effect of fish activity on SDA. A new method, non-parametric quantile regression, is described to estimate SDA even when pronounced circadian activity cycles are present. Data from juvenile Atlantic cod Gadus morhua are used to demonstrate its use and advantages compared with traditional techniques. Software (scripts in the R language) is provided to facilitate its use.

The effect of temperature and body size on metabolic scope of activity in juvenile Atlantic cod Gadus morhua L.

Changes in ambient temperature affect the physiology and metabolism and thus the distribution of fish. In this study we used intermittent flow respirometry to determine the effect of temperature (2, 5, 10, 15 and 20°C) and wet body mass (BM) (~30–460g) on standard metabolic rate (SMR, mgO2h−1), maximum metabolic rate (MMR, mgO2h−1) and metabolic scope (MS, mgO2h−1) of juvenile Atlantic cod. SMR increased with BM irrespectively of temperature, resulting in an average scaling exponent of 0.87 (0.82–0.92). Q10 values were 1.8–2.1 at temperatures between 5 and 15°C but higher (2.6–4.3) between 2 and 5°C and lower (1.6–1.4) between 15 and 20°C in 200 and 450g cod. MMR increased with temperature in the smallest cod (50g) but in the larger cod MMR plateaued between 10, 15 and 20°C. This resulted in a negative correlation between the optimal temperature for MS (Topt) and BM, Topt being respectively 14.5, 11.8 and 10.9°C in a 50, 200 and 450g cod. Irrespective of BM cold water temperatures resulted in a reduction (30–35%) of MS whereas the reduction of MS at warm temperatures was only evident for larger fish (200 and 450g), caused by plateauing of MMR at 10°C and above. Warm temperatures thus seem favourable for smaller (50g) juvenile cod, but not for larger conspecifics (200 and 450g).

Examination of fine‐scale spatial‐temporal overlap and segregation between two closely related congeners Gadus morhua and Gadus ogac in coastal Newfoundland

The spatial and temporal movement patterns of sympatric juvenile Atlantic cod Gadus morhua and Greenland cod Gadus ogac were studied using high-resolution radio-acoustic positioning in a coastal area of Newfoundland during the summers of 2009 and 2010. A total of 20 fish (10 G. ogac and 10 G. morhua) were equipped with acoustic transmitters and monitored for periods up to 23 days. Most fishes showed high site fidelity with mean residence times of 12·4 (G. morhua) and 14·4 days (G. ogac). A few individuals showed a transient use of the study area, ranging distances up to c. 4 km. Mean daily home ranges [95% kernel utilization distributions (KUDs)] and core activity areas were significantly larger for G. morhua (3·8 and 0·5 ha) than for G. ogac (2·7 and 0·3 ha). Home ranges were not related to total length (LT ) for G. morhua but showed a weak positive relationship for G. ogac. Gadus morhua occupied larger areas during the day while G. ogac occupied slightly larger areas at night. Mean rates of movement for G. ogac and G. morhua ranged from 0·83 to 1·24 and 0·76 to 1·76 LT s(-1) , respectively, and were highest during crepuscular periods. Overall, G. morhua were wider ranging, moved at faster rates and were active throughout the diel cycle compared to G. ogac of the same size. It is suggested that differential use of space and activity periods plays an important role in the successful coexistence of these two species.

Habitat complexity affects how young of the year Atlantic codGadus morhuaperceive predation threat from older conspecifics

The response of age 0+ year juvenile Atlantic cod Gadus morhua to the presence of age 1+ and age 3+ year conspecifics was measured with and without cover available. Juveniles reacted by aggregating more closely and maintaining distance from older conspecifics in an experimental setting without cover but only to age 3+ year conspecifics when cover was available. The results indicate that prior residence of older juveniles can affect age 0+ year juveniles during benthic settlement and highlights the conservation value of structurally complex nursery habitats.

Post-escape dispersal of juvenile Atlantic cod Gadus morhua from Norwegian fish farms and their potential for recapture

AEI Aquaculture Environment Interactions Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections AEI 3:107-116 (2013) - DOI: https://doi.org/10.3354/aei00051 Post-escape dispersal of juvenile Atlantic cod Gadus morhua from Norwegian fish farms and their potential for recapture R. M. Serra-Llinares1,2,*, R. Nilsen1,2, I. Uglem3, P. Arechavala-Lopez4, P. A. Bjørn1,2, C. Noble1 1Nofima, Muninbakken 9-13, 9291 Tromsø, Norway 2Institute of Marine Research, PO Box 6404, 9294 Tromsø, Norway 3Norwegian Institute of Nature Research, Tungasletta 2, 7485 Trondheim, Norway 4Department of Marine Science and Applied Biology, University of Alicante, PO Box 99, 03080 Alicante, Spain *Email: rosa.maria.serra.llinares@imr.no ABSTRACT: The escape of fish from sea-based aquaculture facilities is regarded as a potential environmental threat and is one of the biggest challenges the industry has faced in recent years. In addition to preventing escapes by improving farming operations and procedures, effective and operational routines are needed for recapturing fish should an escape occur. This study investigated the post-escape dispersal of juvenile Atlantic cod Gadus morhua L. from commercial sea cages in coastal Norway using acoustic telemetry. It also assessed the efficacy of different techniques (e.g. cod pots, fyke nets, and gill nets) for recapturing escaped fish. Results suggest that escaped juvenile cod can experience a high size-related predation pressure immediately after escape due to high numbers of large fish aggregating around the cages. Consequently, the escapees rapidly disperse from the farms and seek shelter in littoral areas. Once in shallower waters, they stay relatively close (<10 km) to the farm during the first 2 mo following an escape. This suggests a high potential for recapture if the effort is focused on the littoral area and not in the immediate vicinity of the farm. No escapees were caught using live recapture methods, and a low number of recaptures (<5%) were achieved with gill nets deployed in littoral areas. Moreover, high by-catch rates and a subsequent high workload suggest this method may be inappropriate for the recapture of escapees. KEY WORDS: Atlantic cod · Fish escape · Aquaculture · Telemetry · Recapture Full text in pdf format PreviousNextCite this article as: Serra-Llinares RM, Nilsen R, Uglem I, Arechavala-Lopez P, Bjørn PA, Noble C (2013) Post-escape dispersal of juvenile Atlantic cod Gadus morhua from Norwegian fish farms and their potential for recapture. Aquacult Environ Interact 3:107-116. https://doi.org/10.3354/aei00051 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AEI Vol. 3, No. 2. Online publication date: January 30, 2013 Print ISSN: 1869-215X; Online ISSN: 1869-7534 Copyright © 2013 Inter-Research.

Effects of salinity and temperature on growth, plasma ions, cortisol and immune parameters of juvenile Atlantic cod (Gadus morhua)

The effects of salinity and temperature on growth, plasma ions, cortisol and immune parameters were investigated in two experiments. In the first experiment small, medium and large juvenile Atlantic cod Gadus morhua (initial average weights of 1.9, 8 and 83g, respectively) were reared at four constant salinities (6 to 32‰) for a short period (19–57days, depending on size), then returned to seawater (32‰) without acclimation and reared for another period (20–391days). The highest growth rates were found at 10‰ in all size-classes. After the fish were returned to seawater the growth rates were inversely related to the salinity change in all size-classes and long-term rearing of the medium-sized fish revealed that abrupt salinity increase from 6 and 10‰ to seawater may permanently reduce the growth capacity of juvenile cod. In another long-term experiment, there was no significant difference in the growth rate of cod (initial average weight 3.4g) reared at either 13.5 or 32‰ for 187days. Rearing at 13.5‰ neither enhanced growth rate at 6.3°C nor at 10°C in larger juveniles (>245g) compared with rearing in seawater. The study shows that rearing salinity and abrupt salinity changes have limited or no effects on stress and immune-related parameters, and there are no indications of ion regulatory disturbances at salinities as low as 6‰. This shows that the Atlantic cod is an extremely euryhaline marine teleost species, and indicates that commercial Atlantic cod aquaculture can just as well be carried out in locations with low as with high environmental salinity.

Settling-depth vs. genotype and size vs. genotype correlations at the Pan I locus in 0-group Atlantic cod Gadus morhua

We sampled 0-group juvenile Atlantic cod Gadus morhua L. within fjords and off- shore in northern Norway from 1994 to 2008 using different gears for the 3 sampling depths: shore seine (0�3 m), pelagic trawl (various depths), and bottom trawl (>80 m). Frequencies of alleles at the Pan I locus (4218 fish analysed) showed highly significant differences among samples col- lected in the different habitats. The Pan I A allele showed a mean frequency of ~80% in the shore seine samples, 12% in the bottom trawl samples, and between 5 and 57% in the pelagic samples. These differences are thought to reflect the co-occurrence of different populations of cod in the area with different settling regimes. Shallow-water settlers are thought to represent the stationary Norwegian coastal cod (NCC), the deep-water settlers represent the migratory Arcto-Norwegian cod (ANC), and the non-settled individuals represent a variable mixture of the 2 populations. For designated samples, we analyzed 16 microsatellites (non-neutral and neutral) that supported a genetic divergence between shallow-water and deep-water settlers. Correlations between length and Pan I genotypes within selected samples showed that the Pan I BB homozygotes (typical of ANC) were significantly longer than the Pan I AA homozygotes (typical of NCC). This could reflect differences in spawning time and growth conditions between ANC and NCC, just as well as one genotype being superior to the others in terms of growth performance. Finally, we argue that the Pan I difference between 0-group NCC and ANC is not caused by contemporary selection but reflects adaptation on an ecological post-glacial time scale.

Prey selectivity by juvenile Atlantic cod Gadus morhua in three coastal habitat types

Coastal habitats are heavily subjected to eutrophication and commercial fisheries, and such alterations can affect organism interaction strengths and potentially influence trophic dynamics. A key species inhabiting coastal environments in temperate waters is the Atlantic cod Gadus morhua, which utilises coastal areas for food and shelter. We used an experimental mechanistic approach to assay prey selectivity by juvenile cod when foraging on grass shrimp Palaemon elegans and brown shrimp Crangon crangon, under light and dark conditions, in 3 of the most abundant habitat types in temperate coastal environments-sand, eelgrass (artificial vegetation mimicking Zostera marina), and bladderwrack Fucus vesiculosus. Using functional response relationships from single-prey experiments, we calculated the energetically best foraging strategy for cod in the 3 habitats, i.e. feeding selectively on either of the shrimp species or on a combination of both. These predictions were tested in experiments where the cod predator was offered both prey species. Cod selected both prey species in accordance with our predictions in eelgrass and in bladderwrack under light conditions, but a lower than predicted consumption of grass shrimp was found in sand and in bladderwrack under dark conditions. Cod decreasingly selected grass shrimp with increasing habitat complexity, i.e. the highest selectivity was in sand and the lowest selectivity was in bladderwrack. As the 2 shrimp species have different trophic roles, cod selective predation may have effects on lower trophic levels. We provide a quantitative prediction of cod selective predation in habitat types that undergo degradation, and suggest that such predation can influence the trophic consequences from environmental change. (Less)

Chronic CO2 exposure markedly increases the incidence of cataracts in juvenile Atlantic cod Gadus morhua L.

A study was undertaken to test the affect of chronic exposure to elevated dissolved carbon dioxide on juvenile Atlantic cod. The CO2 treatment concentrations were designated as low (1–2mgL−1, 1000μatm), medium (8mgL−1, 3500μatm) and high (18mgL−1, 8500μatm), and the fish were reared at 10°C and 20‰ salinity. A marked observation at the end of the 55day trial was that an increase in the incidence of eye lesions correlated with increasing CO2 concentration. Typical lesions included unilateral and bilateral exopthalmos, gas bubbles under the sclera and cataracts, and these were quantified in all fish (n=757 individuals) using field methods. The most notable difference between CO2 treatments was the prevalence and intensity of lenticular cataracts, which were primarily diffuse rather than nucleated. Nearly 75% of all fish from the high CO2 treatment were found to have some degree of cataractous lesion, compared with 10–13% for the other treatments. The severity of the cataract was most pronounced at the highest CO2 concentration, with many fish presenting complete bilateral cataracts. These data indicate that chronic exposure to high CO2 concentrations can cause cataracts in juvenile Atlantic cod. To our knowledge this is the first report of CO2 as a causative agent or aggravating factor for cataracts.

Tissue-specific turnover rates and trophic enrichment of stable N and C isotopes in juvenile Atlantic cod Gadus morhua fed three different diets

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 461:197-209 (2012) - DOI: https://doi.org/10.3354/meps09871 Tissue-specific turnover rates and trophic enrichment of stable N and C isotopes in juvenile Atlantic cod Gadus morhua fed three different diets Torben Ankjærø, Jens Tang Christensen, Peter Grønkjær* Department of Bioscience, Marine Ecology, Aarhus University, 8000 Aarhus C, Denmark *Email: peter.groenkjaer@biology.au.dk ABSTRACT: A 150 d laboratory diet-shift study was conducted on juvenile Atlantic cod Gadus morhua L. to examine (1) stable nitrogen and carbon isotope turnover rates, (2) the tissue-specific relative contribution of metabolism and growth to isotopic change, and (3) diet−tissue enrichment of the isotopes in white muscle, heart, whole blood, and cranial bone collagen. Time- and growth-based models described the change in δ15N and δ13C of the tissues following a diet shift from pelleted food to either blue mussels Mytilus edulis L., sandeel Ammodytes marinus Raitt., or whiting Merlangius merlangus L. diets. Cod growth rates ranged from 1.5 to 2.0% d−1, with the exception of whiting-fed cod that experienced a cessation in growth after Day 86. Isotope turnover rates, expressed as half-lives (T½), differed little between tissues as expected in fast-growing fish. For δ15N, heart tissue had the shortest T½ while muscle had the longest (30.7 to 34.8 versus 35.7 to 77.9 d−1; range among diets). Heart tissue also had the shortest δ13C T½, whereas blood had the longest (25.5 to 38.5 versus 49.5 to 60.3 d−1; range among diets). Diet-tissue enrichment varied between 0.8 and 5.1‰ (Δδ15N) and between 0.7 and 2.2‰ (Δδ13C). Growth accounted for most of the isotopic change, except in heart tissue of all cod and in all tissues of whiting-fed cod, where there was a significant effect of metabolism on isotopic change. Despite variability in enrichment among diets and tissues, fish feeding on the 3 diets could be distinguished based on their tissue-specific isotopic signatures. KEY WORDS: Isotopic turnover · Diet shift · 15N · 13C · Nitrogen · Carbon · Growth · Metabolism Full text in pdf format PreviousNextCite this article as: Ankjærø T, Christensen JT, Grønkjær P (2012) Tissue-specific turnover rates and trophic enrichment of stable N and C isotopes in juvenile Atlantic cod Gadus morhua fed three different diets. Mar Ecol Prog Ser 461:197-209. https://doi.org/10.3354/meps09871 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 461. Online publication date: August 08, 2012 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2012 Inter-Research.

Foraging performance of juvenile Atlantic cod Gadus morhua and profitability of coastal habitats

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 456:245-253 (2012) - DOI: https://doi.org/10.3354/meps09705 Foraging performance of juvenile Atlantic cod Gadus morhua and profitability of coastal habitats Anders Persson*, Peter Ljungberg, Magnus Andersson, Elin Götzman, P. Anders Nilsson Department of Biology, Aquatic Ecology, Lund University, Ecology Building, 223 62 Lund, Sweden *Email: anders.persson@biol.lu.se ABSTRACT: Overfishing and eutrophication affects coastal communities worldwide, leading to dwindling fish stocks and deteriorated habitats. Hence, attempts to rebuild overfished stocks to past fish productivities need to account for functional relations between habitat types and fish performance. Here we quantified resource availability, foraging performance, and anti-predator behavior of juvenile Atlantic cod Gadus morhua (hereafter ‘cod’) to assess the costs and benefits associated with different coastal habitats. In the laboratory, cod foraged more efficiently in sand habitats compared to the structurally more complex habitats of eelgrass Zostera marina and the canopy forming bladderwrack Fucus vesiculosus. Presence of chemical cues from a cannibal reduced cod consumption rates in all habitats, but most strongly in the sand habitat. Field observations in the 3 habitats showed highest resource density in the bladderwrack habitat and lowest in the sand habitat, irrespective of season. Habitat profitability, calculated by combining data from field estimates of prey density and experimental quantifications of foraging performance, revealed the bladderwrack habitat to be the most profitable, independent of season. The difference in profitability between the complex habitats was relatively small, suggesting that cod in the field contributed to drive habitat profitability towards equalization. The results strengthen the view that the ongoing loss of seagrass and macroalgae habitats may have significant ramifications for juvenile cod performance, which ultimately may lower the productivity of entire stocks. Consequently, future and ongoing rebuilding of commercial fish stocks should revise the expectations of stock productivity (and hence harvesting intensity) accordingly. KEY WORDS: Cod · Habitat choice · Macroinvertebrates · Functional response · Seagrass · Bladderwrack · Fucus vesicolosus · Zostera marina Full text in pdf format PreviousNextCite this article as: Persson A, Ljungberg P, Andersson M, Götzman E, Nilsson PA (2012) Foraging performance of juvenile Atlantic cod Gadus morhua and profitability of coastal habitats. Mar Ecol Prog Ser 456:245-253. https://doi.org/10.3354/meps09705 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 456. Online publication date: June 07, 2012 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2012 Inter-Research.

Output of organic material from land-based juvenile Atlantic cod (Gadus morhua) tanks

A mass balance experiment was conducted in which dry mass, dissolved organic carbon, total nitrogen, lipid classes, and fatty acids were quantified in the inflow and outflow of land-based juvenile Atlantic cod (Gadus morhua) tanks. The inflow contained 89.9 ± 15.4 g/day of dry mass that increased to 187 ± 39 g/day in the outflow. Correction for the inflow indicated 96.8 ± 33.8 g/day of excess feed and faeces left the tanks amounting to a feed to waste conversion ratio of 25 %. The amount of feed in the waste was estimated to be 3 %. The breakdown indicator free fatty acid (43.1 ± 9.5 % total lipid), the markers of zooplankton and subsequent indicators of the feed, 20:1ω9 and 22:1ω11, and the essential fatty acid docosahexaenoic acid (DHA) were all significantly higher (p < 0.020) in the outflow compared to the inflow. The output from the entire aquaculture facility was calculated from the experimental tanks and gave 1,060 ± 370 g/day dry mass and 1.5 ± 0.4 g/day DHA, which could support 0.44 tonnes of mussels assuming an average weight of 5.31 g/mussel. Additionally, the output data were calculated per kilogram of fish and used to estimate potential output for operational Atlantic cod farms. An 1,880 tonne farm would produce 3,170 ± 870 kg/day dry mass and 4.7 ± 1.7 kg/day of DHA, which could theoretically support 1,400 tonnes of mussels. Natural mussels and those grown in co-culturing systems could assimilate such valuable compounds that would otherwise be lost.

Neoplasms in the swim bladder of juvenile cod

340 The mariculture of anadromous and marine fish steadily develops in many countries worldwide. The cod is one of promising species for mariculture. The improvement of biotechnology for mass propagation of this species necessitates clarification of the causes of poor quality of juvenile cod. The disturbances of metabolism and growth resulting in the formation of neoplasms in the swim bladder are the factors that may affect survival of juvenile fish. To date, various neo� plasms have been revealed in more than 40 wild and farmed fish species. Neoplasia does not depend on the fish phylogenetic status [1–6]. Some tumors may be of virus origin [7]. The goal of this study was to use histological tech� niques to determine at least some reasons for the low survival rate in juvenile cod. The study was carried out in the framework of the NorthCod International Project sponsored by the European Union. Juvenile Atlantic cod Gadus morhua was studied. Cod larvae were sampled from fish farms in Nor� way, Iceland, and Scotland (United Kingdom). The larvae were fixed at the ages of 1, 3, 5, 7, 10, 15, 20, 30, 40, 50, and 60 days post hatching. Boin’s fixative, 10% neutral formalin, and Karnovski’s fixative were used. Histological specimens were prepared following the commonly accepted routine [8]. The description of the specimens was based on putative histopatholog� ical alterations caused by waterborne pollutants [9]. The swim bladder of adult cod is closed and lacks the air duct connecting the bladder with the digestive tract. However, in juvenile cod, the swim bladder is connected with the esophagus through the air (pneu� matic) duct. Morphogenesis in cod larvae at the stage of the for� mation of the definitive swim bladder is a metamor� phosis and is coupled with immunological changes. Degeneration (apoptosis) of some cells of the pneu� matic duct starts early, between the seventh and the ninth days after hatching. Chronic inflammatory pro� cesses in juvenile fish entailing the proliferation and hyperplastic growth of the swim bladder epithelium are facilitated by the transitional type of the swim bladder epithelium. Normally, this tissue includes the flat, cubic, and prismatic types of epithelium. No alterations were found in the notochord at the prelarval stage before the resorption of the yolk sac. Deformation of the notochord occurs upon the transi� tion from endogenous to exogenous feeding. This begins approximately on the seventh day after hatch� ing and continues for five to eight weeks, when the for� mation of the first bone components of the backbone starts. During this period of time, a curvature of the notochord behind the scull, above the swim bladder, was recorded in most fish. Four types of malformations of the swim bladder development were revealed in juvenile cod from all fish farms in the studied regions. These malformations were expressed in overfilling the bladder with gases both during the initial period of its filling and during various stages of early development (as long as two months) as a result of progressing inflammation. Pre� tumor processes in the swim bladder of juvenile cod consist in an altered proportion of inflammatory reac� tions and regeneration (excessive and atypical prolif� eration) in combination with the initial transudate accumulation (Fig. 1) followed by exudate accumula� tion and inflammatory alterations in the connective tissue surrounding the swim bladder.