Actions of epinephrine on the contractility of fast and slow skeletal muscle fibres in teleosts

Fast and slow muscle fibers were isolated from the myotomes of atlantic cod (Gadus morhua L.) and sculpin (Myoxocephalus scorpius L.). Epinephrine was found to have no effect on twitch or sub-tetanic contractions in fast muscle fibres. Isoprenaline (10^–6M) had no effect on the contractility of slow muscle fibres. In contrast, epinephrine elicited a dose-dependent decrease in the half-time for twitch relaxation (t_1/2r), and in most cases a decrease in twitch amplitude. The maximum decrease in t_1/2r was around 5–20% of control values (at 10^–6M epinephrine), with a half maximal response at about 30 nmol l^–1. Responses to epinephrine were unaffected by propranolol and reversed by phentolamine, consistent with the stimulation of -adrenoreceptors. 10^–6M epinephrine produced a rise in cAMP levels from 1.8 to 3.1 pmol mg dry wt^–1 in cod slow fibres. However, the cellular mechanism underlying the action of epinephrine is unclear since forskolin, a potent activator of adenylate cyclase activity, where it has been investigated, was found to increase not decrease twitch duration and amplitude. The responses of fast and slow fibres to epinephrine and its antagonists were similar in summer (13°C) and winter acclimatized (5–6°C) sculpin.It is suggested that epinephrine may act to modulate the active state of slow muscle fibres at high cruising speeds and thereby increase swimming performance.     

Balanced exploitation and coexistence of interacting,size‐structured,fish species

This paper examines some effects of exploitation on a simple ecosystem containing two interacting fish species, with life histories similar to mackerel (Scomber scombrus) and cod (Gadus morhua), using a dynamic, size‐spectrum model. Such models internalize body growth and mortality from predation, allowing bookkeeping of biomass at a detailed level of individual predation and growth and enabling scaling up to the mass balance of the ecosystem. Exploitation set independently for each species with knife‐edge, size‐at‐entry fishing can lead to collapse of cod. Exploitation to achieve a fixed ratio of yield to productivity across species can also lead to collapse of cod. However, harvesting balanced to the overall productivity of species in the exploited ecosystem exerts a strong force countering such collapse. If balancing across species is applied to a fishery with knife‐edge selection, size distributions are truncated, changing the structure of the system and reducing its resilience to perturbations. If balancing is applied on the basis of productivity at each body size as well as across species, there is less disruption to size‐structure, resilience is increased, and substantially greater biomass yields are possible. We note an identity between the body size at which productivity is maximized and the age at which cohort biomass is maximized. In our numerical results based on detailed bookkeeping of biomass, cohort biomass reaches its maximum at body masses <1 g, unlike standard yield‐per‐recruit models, where body growth and mortality are independent externalities, and cohort biomass is maximized at larger body sizes.     

The innervation pattern of fast myotomal muscle in the teleostMyoxocephalus scorpius: A reappraisal

The pattern of polyneuronal innervation in the sculpinMyoxocephalus scorpius was examined. The majority of fast fibres in sculpin are innervated by both adjacent nerves, and <15% receive input from sub-adjacent myotomes. Stimulation through both adjacent and sub-adjacent nerves results in muscle action potentials. Each adjacent nerve supplies 2–5 axons to a given fibre. A typical fibre is probably innervated by around 4–6 axons, and pre-terminal branching accounts for the 8–20 endplates present on these fibres.     

Development of a continuous cell line from larval Atlantic cod (Gadus morhua) and its use in the study of the microsporidian,Loma morhua

In vitro cell culture methods are crucial for the isolation, purification and mass propagation of intracellular pathogens of aquatic organisms. Cell culture infection models can yield insights into infection mechanisms, aid in developing methods for disease mitigation and prevention, and inform commercial‐scale cultivation approaches. This study details the establishment of a larval cell line (GML‐5) from the Atlantic cod (Gadus morhua) and its use in the study of microsporidia. GML‐5 has survived over 100 passages in 8 years of culture. The line remains active and viable between 8 and 21°C in Leibovitz‐15 (L‐15) media with 10% foetal bovine serum and exhibits a myofibroblast phenotype as indicated by immuno‐positive results for vimentin, α‐smooth muscle actin, collagen I and S‐100 proteins, while being desmin‐negative. GML‐5 supports the infection and development of two microsporidian parasites, an opportunistic generalist (Anncaliia algerae) and cod‐specific Loma morhua. Using GML‐5, spore germination and proliferation of L. morhua was found to require exposure to basic pH and cool incubation temperatures (8°C), in contrast to A. algerae, which required no cultural modifications. Loma morhua‐associated xenoma‐like structures were observed 2 weeks postexposure. This in vitro infection model may serve as a valuable tool for cod parasitology and aquaculture research.     

Temperature‐based targeting in a multispecies fishery under climate change

Temperature controls important physiological processes in fish and determines aspects of their niches. In an effort to inform selective fishing and spatiotemporal management in the U.S. Northeast Multispecies fishery, we used 16 years of data from the Northeast Fisheries Science Center Spring and Fall Scientific Trawl Surveys to determine if bottom temperature can be used to differentiate the distribution of Atlantic cod (Gadus morhua) from other species within the fishery management plan (FMP). We identified two separate regimes in spring temperatures and used empirical cumulative distribution functions to calculate biomass availability by temperature for each species. We applied a bagged approach to find optimum thermal threshold values that maximize the difference in cod biomass from each of the other species. For our study area, 38% to 54% of the species considered were well separated from cod by temperature in spring, whereas only 17% were separable in the fall. This study suggests that temperature targeting can be used seasonally to separate cod from many other species in the FMP including top catches and no‐retention species. The use of temperature targeting may allow fishermen to better meet multiple quotas while avoiding choke species. Our results also suggested increasing thermal overlap between cod and species inhabiting higher median temperatures (e.g., spiny dogfish, Squalus acanthias) under the current warming temperature regime. These results indicate that the ability to selectively fish in the US Northeast Multispecies fishery will become more difficult under a warming ocean.     

The Effect of Photoperiod on Sexual Maturation,Appetite and Growth in Wild Atlantic Cod (Gadus morhua L.)

An experiment was conducted to examine (a) the effects of photoperiod on timing of sexual maturation (b) the relationship between plasma steroid levels, appetite and growth in male and female Atlantic cod (Gadus morhua L.). Wild caught Norwegian coastal cod were subjected to either a 6L/18D photoperiod typical of January at 60° N-(Short day group) or a simulated natural photoperiod (Normal day group) from June 2000 until spawning started. Appetite of individual fish were measured twice weekly, while weight, length and plasma levels of the sex steroids testosterone (T), 11 keto-testosterone (11-KT) and estradiol-17β (E2) were monitored bimonthly. Cod in the Short day group matured 3 months ahead of the cod in the Normal day group and started spawning in early November. Appetite decreased in both sexes 2–3 months prior to spawning in both groups, but this reduction was stronger among males. In both sexes, length growth was reduced concurrently with the appetite loss. Overall, females had significantly higher somatic growth, put relatively less energy into length growth and had developed larger livers compared to males at the time of spawning in the Short day group. Plasma steroid levels increased in both groups throughout the experiment, reaching peak levels of ca 10 ng ml⁻¹ (T) and 15–20 ng ml⁻¹ (11-KT) in males, and 1.5–2 ng ml⁻¹ (T) and 12–18 ng ml⁻¹ (E2) in females at the onset of spawning. Steroid levels increased more rapidly among Short day cod verifying the earlier onset of maturation. These results confirm that photoperiod is a major cue to maturation in cod and imply that the high cost of spawning for females incur differences in appetite between the sexes.     

Secretion of hatching enzyme and its proteolytic activity in coregoninae (Coregonus albula L andC. lavaretus L) embryos

After the electrial stimulation Coregoninae embryos secreted the hatching enzyme (chorionase) within 0.1–0.5 h, and the dissolution of their chorions lasted 1.2–2.0 h, depending on embryo's developmental stage (DS 13 or DS 14) and water temperature (5.2 or 9.6–9.8°C).Crude chorionase (hatching liquid) ofCoregonus albula andC. lavaretus was collected in large quantities by means of the electric stimulation of eggs. In both species the temperature optimum of proteolytic activity of the crude chorionasc was 30°C; the activity was lost at temperatures < 3-2°C and > 35–40°C. The maximal proteolytic activity was observed at pH 8.5; a rapid decrease in enzyme activity was evident at pH < 7.0, and the activity was zero at pH 6.The temperature-activity curve of chorionase may reflect the adaptation of Coregoninae to hatching immediately after the ice cover recedes from lakes, whereas the rapid decrease of enzyme activity at pH 7 -pH 6 can affect adversely the process of hatching in acidified lakes.     

Loads applied to aquaculture nets by the biting behaviour of Atlantic cod (Gadus morhua)

Atlantic cod (Gadus morhua) bite at netting materials in sea-cages, which is known to weaken and destroy net materials, contribute to the formation of net holes and lead to escapes. We determined the lateral pulling forces applied to nets through biting by cod in a laboratory set-up. A sensor for automatic logging of the lateral pulling force was used to obtain data for over 1000 undisturbed, objectively collected biting events. Lateral pull force varied between cod of different size (180 and 610 g) and different net types, ranging from 0.9 to 9.4 N. Further, pull forces were on average 1.5–2.5 times stronger during lengthy biting events compared to single, brief bites. Maximum lateral pulling forces exerted by 610 g cod were similar to their body weight in air, while 180 g fish were able to pull with a force equivalent to twice their own weight in air. All recorded lateral pull strengths significantly exceeded the known force needed to break single nylon fibres of the netting material. Our results advance understanding of mechanisms and forces involved when cod interact with sea-cage nets and provide important baseline data for the design and production of more bite-resistant netting.     

Environmental influences on melatonin secretion in Atlantic cod (Gadus morhua L.) and their relevance to commercial culture

This study investigated the effects of photoperiod and temperature on plasma melatonin secretion in Atlantic cod (Gadus morhua L.). Initial work confirmed the presence of a diel profile of melatonin synthesis, with elevated levels during the dark phase. Unusually for fish, the peak in plasma melatonin occurred towards the end of the dark phase, which is indicative of a type `A' melatonin profile. When exposed to 60 hours of continuous darkness a clear endogenous rhythm of melatonin synthesis was observed, which continued for 4 cycles with a periodicity which, approximated to 24 h. When acclimated to varying temperatures (4, 8, 12 or 16 °C) no variation in melatonin production was seen, however, body size appeared to be an important influence, with the smallest fish exhibiting significantly higher levels of dark phase melatonin. Finally, the application of additional night-time illumination to cod maintained in sea cages i.e. without blackout, did not significantly reduce dark phase plasma melatonin, suggesting that cod are less sensitive to photoperiod manipulation in cages than salmonids.     

The fate of noradrenaline and adrenaline in the perfused cod spleen

The time course of appearance of catecholamine metabolites was studied in the spleen of cod,Gadus morhua, during perfusion with radioactively labelled noradrenaline and adrenaline at 10°C. The t_lag for appearance of the metabolites ranged between 1.78 and 6.76 min after onset of perfusion for both amines, indicating a rapid disposition of catecholamines. Perfusion with noradrenaline resulted in mainly MOPEG, VMA and DOMA formation, while perfusion with adrenaline additionally resulted in MN formation. There was still formation of deaminated metabolites after denervation, which indicates an additional non-neuronal site of deamination. It is concluded from the study that the fate of noradrenaline and adrenaline within the cod spleen depends on their affinities for the two uptake mechanisms and an extraneuronal site of deamination of great importance cannot be excluded.     

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

We 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.     

Pre-anaesthetic metomidate sedation delays the stress response after caudal artery cannulation in Atlantic cod (Gadus morhua)

Recovery from caudal artery cannulation with and without pre-anaesthesia metomidate sedation was assessed in Atlantic cod (Gadus morhua). The levels of plasma cortisol, glucose, electrolytes and acid–base parameters were compared between sedated and unsedated cod and to those in uncannulated individuals, where the samples were obtained by sacrificial sampling (reference level). Metomidate sedation delayed the stress response, causing sedated cod plasma cortisol to return to the reference level more slowly [day 4 post surgery (PS)] than in unsedated cod (day 2 PS). Plasma glucose was elevated in both sedated and unsedated cod up to and including day 5 PS. Plasma K⁺ was lower and pH was higher in cannulated cod than in the reference from 24 h PS until the end of experimentation, indicating a stress effect of sacrificial sampling on plasma K⁺ and pH that was likely caused by an acute stress response. Metomidate sedation delayed the stress response following CA cannulation and should therefore not be used as a pre-anaesthetic sedation in Atlantic cod. The caudal artery cannulation can be a useful tool in obtaining repeated blood samples from Atlantic cod given an adequate recovery time, which was determined to be 6 days irrespective of pre-anaesthesia sedation status.     

Multiple dose pharmacokinetic study of oxolinic acid in cod, Gadus morhua L.

The plasma, muscle and liver distribution and elimination of the antibacterial agent oxolinic acid were studied after multiple oral (p.o.) administration of 10 or 20 mg kg⁻¹ day⁻¹ to cod (Gadus morhua) for 6 days. The fish, held in seawater at 6 and 12°C and weighing 150–250 g were sampled 24 h following last medication. The concentrations in plasma and tissues were clearly dosage and temperature dependent. The distribution from plasma to muscle (muscle/plasma ratio) was higher than that from a single dose study and independent of temperature and dosage. The distribution from plasma to liver (liver/plasma ratio) was lower than the muscle/plasma ratio and according to this study dependent of the administered dosage but independent of temperature. The elimination of oxolinic acid from plasma, muscle and liver was considerably faster following multiple administration compared to a single administration.     

Variations in growth in haemoglobin genotypes of Atlantic cod

In the present paper are described the growth properties of three different haemoglobin genotypes of juvenile Atlantic cod (Gadus morhua) reared at 7, 10, 13 and 16 °C. In addition one group was reared under temperature steps i.e. moved successively from 16 to 13 and 10 °C. The genotype Hb-I(2/2)displayed the overall highest growth rate in the temperature range 13–16 °C, whereas the Hb- I(1/1)genotype showed the highest overall growth at the lowest temperature (7 °C). Accordingly, we found a significant interaction between genotype and temperature. The differences in growth were largest when cod were reared under the temperature step regime where the Hb-I(2/2)genotype displayed 17 and 24% higher growth than Hb-I(1/1)and Hb-I(1/2),respectively. Optimal temperature for growth (T_opt.G) varied between the genotypes with the genotype Hb-I(1/2)displaying the highest (mean ± SE) T_opt.G (14.5 ± 1:0.8 °C) and Hb-I(1/1)the lowest (12.5 ± 0.2 °C). The biological significance of this link between biochemical genetic variation and physiological properties might be the influences on growth pattern, ultimate size and age at first maturity.     

Effects of filleting method,stress, storage and season on the quality of farmed Atlantic cod (Gadus morhua L.)

The effects of filleting method, pre‐slaughter stress, storage and season on drip loss, water content, water‐holding capacity, rigour contraction and colour in Atlantic cod, Gadus morhua L., were examined. A total of 182 fish were sampled under commercial conditions. To test the effects of filleting method and stress, stressed (S) and unstressed (C) fish were filleted either pre (Pr) or post rigour (Po) at 1 and 48 h post mortem, receptively. The muscle pH significantly decreased from 0 to 144 h of storage in all groups. The onset of the rigour contraction was more pronounced in the Pr‐S group as compared with the Pr‐C group, but after 144 h of storage, no difference in degree of contraction was observed. Filleting method, stress and storage time influenced the colour of the fillets. Post‐rigour filleting caused a significantly increased in measured Lightness (L*) during storage. Stress caused a significant increase in measured redness (a*). No significant difference was found for water‐holding capacity. The water content was influenced by filleting method, where the Pr‐S group had a significantly lower water content compared with the Pr‐C groups; water content changed also according to season. The findings of this study show that stress, filleting method, time of storage and season had a significant effect on the drip loss, where a combination of all factors will determine the total loss.     

Is the protected Atlantic cod (Gadus morhua) population in Gilbert Bay,Labrador, nearing a tipping point?

1. The Gilbert Bay Marine Protected Area (MPA), Labrador, was created in 2005 to protect a resident, locally adapted population of Atlantic cod and its habitat. Twenty years of monitoring has shown a 90% decline in this bay-cod population since the creation of the MPA.
2. The decline of large commercial-sized cod in the bay was accompanied with increases in the abundance of other fish species, including rock cod (Gadus macrocephalus ogac), sculpin (Myoxocephlalus scorpius), and winter flounder (Pseudopleuronectes americanus), suggesting loss of strong top-down community control.
3. These changes suggest a positive feedback mechanism leading to a fish community tipping point, which could severely impact the recovery potential of the protected Atlantic cod population in the MPA.
4. We suggest that managers should be including this possibility in their management decisions for the Gilbert Bay MPA.

     

Lactate dehydrogenase isozymes in the trunk and cardiac muscles of an antarctic teleost fish,Notothenia neglecta Nybelin

The distribution and kinetics of lactate dehydrogenase (LDH) isozymes in the red and white trunk muscles, and cardiac muscle of an antarctic teleost fish (Notothenia neglecta Nybelin) have been studied. Pyruvate inhibition of LDH in all three muscle types is very low, being less than 50% even at a concentration of 60mM pyruvate. Activity versus pyruvate concentration profiles are not significantly different for LDH in all three muscle types. The Michaelis constant (Km) for pyruvate was not significantly different for all three LDH's. Raising the assay temperature caused an increase in Km of similar form in all three muscle types, while Km was lowest at the lowest assay temperature (–1°C). When samples were run on a polyacrylamide gel, the bands stained specifically for LDH activity appeared at identical positions as those of the H2M2 band of the standards.It would appear therefore that the LDH isozyme found in the red and white trunk muscle ofN. neglecta is identical to that in cardiac muscle. This fact is discussed in relation to the physiological ecology of antaretic fishes, and the metabolic constraints imposed by their habitat, including their apparent low capacity for utilising glycolytic fuels.     

Water balance in developing eggs of the codGadus morhua L.

Measurements of yolk osmolality from the embryo of codGadus morhua L. revealed significant variations in the hyposmolality during the embryonic development. The embryo proved to have an extremely low water permeability, protecting it from dehydration in the hyperosmotic seawater. The effect of temperature on the water permeability is high, expressed by an exceptionally high activation energy for water transfer. The agreement between embryonic volume decrease and diffusion permeability during the first 8–10 days after fertilization indicates that no water uptake mechanism is present at this time, thus leaving the embryo fully dependent on internal water stores. The cod egg is buoyant in seawater throughout development. The mechanism for providing hydrostatic lift is the large volume of diluted tissue water located in the yolk and subdermal spaces.     

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

We 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.     

Does the aerobic capacity of fish muscle change with growth rates?

To ascertain whether growth rate modifies the oxidative capacity of fish white muscle, we examined the effects of individual growth rate on the activities of four mitochondrial enzymes in white muscle of the fast growing Atlantic cod,Gadus morhua. Growth rates were individually monitored in cod held at three acclimation temperatures during experiments repeated in four seasons. The size dependence of citrate synthase (CS), cytochrome C oxidase (CCO) and β-hydroxyacyl CoA dehydrogenase (HOAD) activities was established using wild cod ranging from 115 to 17,350 g. Given their negative allometry, CS and CCO activities in the experimental cod were corrected to those expected for a 1.2 kg animal. HOAD activities did not change with size. The specific activities of CCO and CS were positively correlated with growth rate. However, for both enzymes, season explained more of the variability than growth rate or temperature. Season was the only factor to significantly affect the activity of HOAD, while temperature and season interacted to determine glutamate dehydrogenase activity. CS activity was positively correlated with the initial condition of the cod, which differed among the seasons. The other enzymes did not show this relationship. The independent changes of these enzymes suggest that mitochondria undergo qualitative modifications with changes in growth rate, season and size. Although growth rate and the activities of CCO and CS are positively correlated, the activity of the mitochondrial enzymes is more affected by size, physical condition and season.