Feasibility of ranching coastal cod (Gadus morhua) compared with on-growing, full-cycle farming and fishing

The feasibility of ranching wild cod in ‘herds’ was compared with three other scenarios: on-growing of wild cod in sea cages, full-cycle cod farming with hatchery produced juveniles, and commercial cod fishery. In the calculations it was assumed that an existing fishing company could either fish, ranch or on-grow 200 tons of cod quota to increase the quota yield or sell it to invest in full-cycle farming. The results indicate ranching to be the most profitable, fishing as the second and on-growing as the third, whereas full-cycle farming appears to be unrewarding. The net present value (NPV) of the four scenarios was €754 000, €532 000, €198 000 and €−95 000, respectively. Ranching based on aggregating and growing wild cod in a reserved coastal area with anthropogenic feeding thus has the potential of decreasing the cost of fishing, improving growth rate and enhancing quota yield without the investments required in conventional farming. As cod ranching is in the initial stages of development the risks are higher than in the well established cod fishery.     

Influence of water temperature and oxygenation on the aerobic metabolic scope of Atlantic cod (Gadus morhua)

Environmental influences (temperature and oxygenation) on cod metabolism and their impact on the ecology of this species were investigated. Limiting oxygen concentration curves (O₂ level ranging between 15 and 100% air saturation) were established at 2, 5 and 10°C. The standard metabolic rate (SMR), the maximum metabolic rate and the metabolic scope were then modelled as functions of temperature and/or oxygen saturation. The mean SMR at 2, 5 and 10°C were 19.8±4.9, 30.8±6.1 and 54.3±4.1 mg O₂ h⁻¹ kg⁻¹, respectively. Between 2 and 5°C, the active metabolic rate of cod almost doubled from 65 to 120 mg O₂ h⁻¹ kg⁻¹, to reach 177 mg O₂ h⁻¹ kg⁻¹ at 10°C. In terms of metabolic scope (MS), the temperature rise from 2 to 5°C resulted in a two-fold increase from 45 to 89 mg O₂ h⁻¹ kg⁻¹, with MS reaching 123 mg O₂ h⁻¹ kg⁻¹ at 10°C. Our proposed model describing the impact of temperature and oxygen level provides new insight into the energetic interactions which govern the relationship between Atlantic cod and its environment. We re-examined published experimental and field studies from the angle of the regulation of metabolic power. We suggest that, when faced with heterogeneous or unstable hydrological conditions, cod tend to behaviourally maximise their metabolic scope. Through this adaptive response, fish reduce energy budgeting conflicts and presumably increase the probability of routinely operating away from lethal boundaries.     

Candidate biomarker discovery in plasma of juvenile cod (Gadus morhua) exposed to crude North Sea oil, alkyl phenols and polycyclic aromatic hydrocarbons (PAHs)

In this study we have investigated protein changes in plasma of juvenile Atlantic cod (Gadus morhua) induced by crude North Sea oil and North Sea oil spiked with alkyl phenols and polycyclic aromatic hydrocarbons, a surrogate produced water composition. Using a proteomic approach, we identified 137 differentially expressed proteins at different levels of crude oil exposure. Many of the induced protein changes occurred at low levels of exposure. The results obtained with protein expression profiles after exposure to oil and surrogate produced water indicate effects on fibrinolysis and the complement cascade, the immune system, fertility-linked proteins, bone resorption, fatty acid metabolism as well as increased oxidative stress, impaired cell mobility and increased levels of proteins associated with apoptosis. Although the number of individuals and samples in this study is limited within each treatment group, the protein changes observed in this study represent a first screening for potential biomarker candidates in cod plasma reflecting potential effects of crude oil and produced water exposure on fish.     

Distributions of copepod nauplii and turbulence on the southern flank of Georges Bank: implications for feeding by larval cod (Gadus morhua)

The vertical distributions of copecod nauplii and water properties were sampled at well-mixed and stratified sites on Georges Bank using a pumping system, CTD and in vivo fluorometer during a four day period in late May 1992. At each stratified station at least one sample was taken within the thermocline and the fluorescence maximum, which usually co-occurred. Well-mixed sites had low average concentrations of nauplii, ca 41⁻¹, and showed little variation of abundance with depth. Stratified sites had from 4 to 16 times the integrated (0–50 m) abundance of nauplii compared to well-mixed sites and showed strong vertical patterns of distribution. Maximum concentrations of nauplii, up to 1601⁻¹, were associated with the thermocline at 7 of the 9 stratified stations. At the two remaining stratified sites the naupliar maximum was in the upper mixed layer, sampled at 5 m depth. The encounter rate between early feeding cod (Gadus morhua) larvae and their naupliar prey was calculated with and without turbulence. Turbulence was estimated from two sources: wind stress in the upper layer (calculated from wind observations during our cruise) and tidal shear in the lower layer (estimated initially from a tidal mixing equation). We ultimately replaced the lower layer estimates with turbulence data from a series of measurements made in 1995. The latter are more robust and had the advantage of providing dissipation rates for the pycnocline as well as the lower layer. Theory predicts an increase in encounters between a predator and its prey with the addition of turbulence parameters into standard models of encounter. We combined turbulence profiles with the vertical distribution of nauplii to examine the potential contribution of turbulent kinetic energy to predator-prey encounter rates at various depths in stratified and mixed water columns. Our calculations suggest the following increases due to turbulence at stratified sites on Georges Bank during our cruise: from 34 to 219% in the upper mixed layer, depending on wind speed and depth; approximately 8% in the pycnocline; and approximately 110% below the pycnocline. Mixed sites experience increases of at least 110% (tide only), but greater increases (118–192% in this study) occur when the wind blows because of the combined (spatially overlapped) effects of wind and tidal mixing at these sites. The absolute values for encounter rates and their modification by turbulence are sensitive to a number of assumptions in the models. We used a series of stated assumptions to generate estimates that range from 0.6 to 26.5 prey h⁻¹, depending on geographical location, physical forcing and depth.     

Toxicity of sea-surface microlayer: Effects of hexane extract on baltic herring (Clupea harengus) and atlantic cod (Gadus morhua) embryos

This study was designed to determine whether contaminated sea-surface microlayer was toxic to marine fish embryos in its ntaive form and as a hexane extract. Developing embryos of Atlantic cod (Gadus morhua) and Baltic herring (Clupea harengus) were exposed to hexane extracts of sea-surface microlayer collected from five locations in the North Sea and Baltic Sea. Extracts from two of these locations produced significant embryos mortality as well as severe deformities in live hatched larvae. A control sample of bulk water collected from 20 cm under the surface and extracted in the same way produced no significant mortality or deformities. Significaant changes in timing of hatching were also observed in those samples which produced embryo toxic effects. A comparison of these data with those obtained from code embryos exposed to unextracted microlayer showed a similar biological effect with both unextracted samples and hexane extracts.Chemical analyses revealed the greatest biological effect in samples with petroleum hydrocarbon concentrations between 180 and > 200 μg liter⁻¹. The bulk water control had 1 μg liter⁻¹ while the three samples that showed no biological activity had 3 to 8 μg liter⁻¹ petroleum hydrocarbons. Phthalic acid esters were detected in four samples and chlorinated hydrocarbons in one, but could not be positively correlated with any of the toxic responses. No other chemical contaminants were detected in the five samples.The data presented here show that some sites contain sea-surface microlayer which can be toxic to marine fish embryos: that Baltic herring and Atlantic cod embryos respond similarly to the toxic effects of contaminated microlayer: and that unextracted microlayer and hexane extract of microlayer produce essentially the same toxic effect(s) if only organic contaminants are considered.     

Cytochromes P-450 in cod (Gadus morhua): Effects of induces on regiospecificity of phenanthrene metabolism and immunochemical properties

The metabolism of some xenobiotics can lead to the formation of reactive intermediates with mutagenic/carcinogenic properties. With the carcinogenic PAH these have been identified as bay-region diol-epoxides.¹ Phenanthrene, a non-carcinogenic, bay-region containing model PAH, is metabolised in vivo by bony fish at the proximate bay-region position, whereas mammals and other marine organisms mainly form the K-region metabolite 9,10-dihydro-9,10-dihydroxy-phenanthrene.² We wanted to investigate this difference more closely by studying the regiospecificity of phenanthrene metabolism in vitro both with microsomes from differently pretreated cod and with isolated cytochrome P-450 isozymes from BNF-induced cod.³ Secondly, by preparing antibodies to the major isozyme isolated (called cod P-450c), we investigated the immunochemical properties of the variously treated cod liver microsomes.     

Comparison of DNA damage in the early life stages of cod, Gadus morhua, originating from the Barents Sea and Baltic Sea

DNA adducts in cod embryos and larvae were analysed by ³²P-postlabeling to test the hypothesis that anthropogenic substances, which could form reactive intermediates, are involved in the reproductive failure of cod (Gadus morhua) from the Baltic Sea. A comparison with cod from the Barents Sea was performed. The mean value of DNA adducts in cod embryos/larvae from the Baltic Sea was 2.3 nmol of adducts/mol nucleotides, compared to 0.12 nmol of adducts/mol nucleotides in the embryos/larvae from the Barents Sea.     

Influence of diet on growth, condition and reproductive capacity in Newfoundland and Labrador cod (Gadus morhua): Insights from stable carbon isotopes (δC)

Cod populations in Newfoundland and Labrador waters have shown differing growth, condition and recruitment since near-universal declines in these properties during the cold period of the late 1980s and early 1990s. To assess the influence of variable prey communities on these parameters, we compared cod energetics and diet in populations off Labrador and the northeast and south coasts of Newfoundland. Many properties were highest in the southern group(s) and lowest in the northern group(s), including growth, somatic condition, liver index and age-at-maturity. Most differences could be explained by variations in diet, as measured by stomach contents and stable carbon isotopes (δ¹³C). The diet of Labrador cod consisted almost entirely of northern shrimp (Pandalus borealis), and these cod displayed the most benthic δ¹³C signatures. Northeast cod had a more varied diet that included capelin and other fish, but still had mostly benthic δ¹³C signatures, suggesting the importance of benthic prey like shrimp in this population. South coast cod exhibited the most varied diet, including capelin (Mallotus villosus), zooplankton, crabs and other fish, and had the most pelagic δ¹³C signatures. Among and within populations, the benefits of a more pelagic diet in medium-sized (30–69 cm) cod included higher somatic condition, higher liver index (lipid stores) and greater spawning potential (decreased incidence of atresia). It is hypothesized that major rebuilding of Newfoundland and Labrador cod stocks will require a return to a system that supports mostly pelagic feeding (i.e. capelin) in cod.     

Comparison of the response of Atlantic cod (Gadus morhua) in the high-latitude regions of the North Atlantic during the warm periods of the 1920s–1960s and the 1990s–2000s

Concern about future anthropogenic warming has lead to demands for information on what might happen to fish and fisheries under various climate-change scenarios. One suggestion has been to use past events as a proxy for what will happen in the future. In this paper a comparison between the responses of Atlantic cod (Gadus morhua) to two major warm periods in the North Atlantic during the 20th century is carried out to determine how reliable the past might be as a predictor of the future. The first warm period began during the 1920s, remained relatively warm through the 1960s, and was limited primarily to the northern regions (>60°N). The second warm period, which again covered the northern regions but also extended farther south (30°N), began in the 1990s and has continued into the present century. During the earlier warm period, the most northern of the cod stocks (West Greenland, Icelandic, and Northeast Arctic cod in the Barents Sea) increased in abundance, individual growth was high, recruitment was strong, and their distribution spread northward. Available plankton data suggest that these cod responses were driven by bottom-up processes. Fishing pressure increased during this period of high cod abundance and the northern cod stocks began to decline, as early as the 1950s in the Barents Sea but during the 1960s elsewhere. Individual growth declined as temperatures cooled and the cod distributions retracted southward. During the warming in the 1990s, the spawning stock biomass of cod in the Barents Sea again increased, recruitment rose, and the stock spread northward, but the individual growth did not improve significantly. Cod off West Greenland also have shown signs of improving recruitment and increasing biomass, albeit they are still very low in comparison to the earlier warming period. The abundance of Icelandic cod, on the other hand, has remained low through the recent warm period and spawning stock biomass and total biomass are at levels near the lowest on record. The different responses of cod to the two warm events, in particular the reduced cod production during the recent warm period, are attributed to the effects of intense fishing pressure and possibly related ecosystem changes. The implications of the results of the comparisons on the development of cod scenarios under future climate change are addressed.     

Bioavailability of PAH in effluent water from an aluminium works evaluated by transplant caging and biliary fluorescence measurements of Atlantic cod (Gadus morhua L.)

Fixed wavelength fluorescence (FF) of bile was used as a biomarker for PAH exposure in fish caged adjacent to an aluminium works. After 30 days of caging, a 20–50 fold increase of pyrene fluorescence was found in groups caged adjacent to the works as compared to two control groups. The PAH uptake occurred mainly from suspended particles rather than from PAH contaminated sediments at the caging sites. Our results demonstrates the combined use of fish caging and bile-fluorescence measurements as a powerful field model for the monitoring of coastal waters subjected to PAH pollution.     

Aspects of larval,post-larval and juvenile ecology of Macrobrachium petersi (Hilgendorf) in the Keiskamma estuary,South Africa

Although Macrobrachium petersi has nine larval stages, only stage I and a minimal number of stage II M. petersi larvae were caught in the Keiskamma estuary. Stage I larvae undergo a vertical migration at night which is markedly influenced by salinity, especially under stratified conditions. Larvae remain in the water column on the ebb tide, a behavioural pattern which effectively carried them to favourable salinities for growth and development. Stage I larvae show an association with salt front regions. The sudden decline in larval abundance from stage I to stage II downstream from the front suggests a change from a pelagic to an epibenthic existence. Later larval stages failed to appear in the plankton. However, post-larvae were caught in the estuary and a juvenile migration from the estuary to freshwater was monitored.     

鞍带石斑鱼仔稚幼鱼骨骼发育与生长特性研究

骨骼发育对于养殖鱼类苗种培育至关重要,骨骼畸形会影响仔稚幼鱼的外部形态及功能需求。作者利用骨骼染色技术和显微测量的方法对鞍带石斑鱼(Epinepheluslanceolatus)仔稚幼鱼的骨骼发育及生长特性进行连续观察和测量。实验结果表明:鞍带石斑鱼初孵仔鱼不存在骨与软骨结构,鞍带石斑鱼在变态前期和变态早期(长棘期)仔鱼的全长、颅骨长度、脊柱长度及尾鳍复合物的长度增加缓慢,骨骼发育过程中与摄食、呼吸及游泳功能相关的骨骼优先发育,如颅骨(颌骨、鳃)和鳍元件,且骨化顺序与发育顺序基本一致。进入变态晚期(收棘期),营养摄取及利用的器官发育趋于完善,稚鱼进入快速生长阶段。此外,在仔稚鱼发育早期,颅骨、脊柱以及尾鳍复合物中存在异速生长特性,呈现为在变态前期和变态早期(长棘期)颅骨和尾鳍复合物为正异速生长,而脊柱为负异速生长;在变态晚期(收棘期)和变态后期,颅骨为负异速生长,而脊柱和尾鳍复合物为近等速生长。因此,鞍带石斑鱼仔稚幼鱼的颅骨、脊柱及尾鳍复合物骨骼发育的异速生长现象与摄食、呼吸及游泳功能相适应。     

Variability in scale growth rates of chum salmon (Oncorhynchus keta) in relation to climate changes in the late 1980s

Fish scales were used to investigate the interannual variability in chum salmon growth rates at specific ages in relation to climatic/environmental changes during the 1980s–1990s. Scales were obtained from adult salmon returning to the east coast of Korea between 1984 and 1998. Assuming proportionality between scale size increments and fish length, distances between scale annuli were regarded as the growth conditions in different habitat areas with respect to the life stages of chum salmon. In estuarine and coastal areas, growth rates of fingerling salmon were higher in the 1990s than in the 1980s. Zooplankton abundance off the east coast of Korea increased after the late 1980s, which may have provided favorable growth conditions for young salmon in the 1990s. Growth of juvenile chum salmon during the first summer (Okhotsk Sea) was relatively stable, and neither SST nor zooplankton biomass fluctuated significantly during the study period. However, in the Bering Sea, salmon growth rates between age-2 and age-4 (i.e. ocean-phase immature salmon) were higher in the 1980s than in the 1990s. Variability in salmon growth in the Bering Sea was correlated to zooplankton biomass. These results suggest that the climate regime shift of 1988/1989 in the subarctic North Pacific affected salmon growth mediated by changes of zooplankton biomass, revealing a bottom-up process.     

花鲈仔、稚、幼鱼摄食习性与生长的研究

分析了花鲈仔、稚、幼鱼的摄食习性与生长.结果表明,在水温为15.5～16.5℃时,花妒仔鱼孵出约140h左右开口摄食,开口饵料为小型臂尾轮虫.全长10mm左右的仔鱼可摄食卤虫幼体,全长11mm左右的个体可摄食枝角类.对431尾仔、稚、幼鱼观察结果,在实验条件下其摄食率高达99.1%,胃饱满系数波动于2.38%～16.48%之间,日摄食指数在45%～60%.其摄食强度具明显的昼夜节律,以16:00～20:00胃饱满度最高.仔、稚鱼夜间基本不摄食,部分幼鱼个体少量摄食.仔、稚、幼鱼个体间生长速度具有一定的差异性.其体重与摄食量的关系符合直线方程y=0.1018+8.3261×10-2x;全长与体重的相关关系可用ω=1.6473×10-3L3.4743表示,全长与日龄的关系式为L_t=5.5242e1.9681×10-2D;体重与日龄的回归方程为ω=0.5836e6.9208×10-2D.     

Do bigger fish arrive and spawn at the spawning grounds before smaller fish: Cod (Gadus morhua) predation on beach spawning capelin (Mallotus villosus) from coastal Newfoundland

A relationship between body size and time of spawning has often been described for both pelagic and non-pelagic fish species that migrate for the purpose of spawning. The present study investigates this relationship for capelin (Mallotus villosus), a pelagic smelt-like species that spawns on the beaches of Newfoundland. Simple linear regressions were carried out separately for three groups of capelin: ovid females, spent females and males in three successive years (1982–1984). Bigger fish arrived near the spawning grounds first, for all three groups in all three years and was most obvious for female capelin. Analyses of stomach contents of Atlantic cod (Gadus morhua), an important predator of capelin in the Newfoundland area, showed a similar decrease in mean size of capelin throughout the capelin spawning season in June, July and August. Furthermore, analyses strongly suggest that early in the spawning seasons, when capelin abundance was high, cod selected for bigger capelin, whereas towards the end of the spawning seasons, when capelin abundance was low, cod did not show any size preference.     

Trophic relations of capelin Mallotus villosus and polar cod Boreogadus saida in the Barents Sea as a factor of impact on the ecosystem

The purpose of the study is to assess the role of trophic relations of the dominant pelagic fishes capelin and polar cod in the Barents Sea with regard to distribution and accessibility as prey for the Atlantic cod in warm years (2004–2005). Unlike in the previous period, during these warm years a dramatic increase of the polar cod population resulted in a northwards expansion of the feeding grounds where overlapping of polar cod and capelin concentrations was observed. This caused an increased competition for copepods, which are the main food item for young fish. In the areas dominated by polar cod the shortage of copepods forced immature capelin to switch to the chaetognath Sagitta, which affected their fatness negatively.During the warm years the feeding grounds of Atlantic cod also expanded, to a large degree caused by the shortage of their main food, the capelin. In 2004–2005 the cod formed feeding concentrations in the north and northeast Barents Sea where they fed on the capelin. In this area the consumption of polar cod by cod increased, and in some local areas the polar cod practically replaced the capelin in the diet of cod. In general polar cod in the diet of Atlantic cod were more important in the northern than in the southern part of the Barents Sea. The fatness of cod was extremely low during the whole spring–summer period (until August), and after the feeding period the fatness index of the Atlantic cod became lower than the average long-term autumn value.