The compensatory growth response of the Atlantic cod: effects of nutritional history

The effects of different combinations of nutritional background, feeding regimes and dietary compositions on growth responses of the Atlantic cod have been examined. Alternating short periods (1–3 weeks) of food deprivation with unlimited provision of food depressed growth below that of controls, but cod that were fed on alternate weeks (1:1) were larger than those that were exposed to 2 or 3 week periods of deprivation and feeding (2:2 or 3:3). Thus, periods of food deprivation of short duration were insufficient to induce any marked compensatory growth response. When cod were deprived of food for longer periods a compensatory growth response was observed. On receiving excess food supplies following 8 weeks of food deprivation the fish grew more rapidly than the controls and had completely recovered body weight within 12 weeks. The greatest compensatory growth response was shown by cod in poor condition (lowest condition factor), because at the end of an 18 week growth trial there were no differences in body weight between fish irrespective of their initial condition. Both sexes displayed a compensatory growth response.     

Plasma FITC-dextran exchange between the primary and secondary circulatory systems in the Atlantic cod, <Emphasis Type="Italic">Gadus Morhua</Emphasis>

Fluorescein isothiocyanate dextran (FITC-dextran) exchange between the primary (PCS) and secondary (SCS) circulatory systems in the Atlantic cod, Gadus morhua (Linnaeus, 1752), were studied using 20-kDa (n = 4) and 500-kDa (n = 4) FITC-dextran. In order to give a qualitative perspective of the general connection between the PCS and SCS, distribution of plasma-borne tracers (FITC-dextran) in the PCS and SCS were examined. In this study, a total of eight cod were cannulated in the ventral aorta (PCS) and dorsal cutaneous vessel (SCS), for investigation of FITC-dextran disappearance in the PCS and its subsequent appearance in the SCS. FITC-dextran of both sizes was found to be in equilibrium between the PCS and SCS in less than 20 min. This indicates a profound connection between the PCS and SCS in the Atlantic cod, and rapid mixing of tracers between the PCS and SCS. The destination of the injected 500-kDa FITC-dextran was also examined, and it was observed that of the 500-kDa FITC-dextran lost from the primary and secondary vascular systems, 63.0 ± 9.2% could be recovered from the liver     

A system for model-based biomass estimation of larvae in intensive cod larvicultures

High and unpredictable mortality rates are observed in the larval rearing of cod (Gadus morhua). As a means of addressing this problem, we present a model-based estimator system which can be used to indirectly measure the larval density through monitoring the live food dynamics and larval growth. The estimator has been evaluated in a conceptual context using a preliminary model formulation, and the observability of the process has been investigated. It was found that the two parameters, live food dynamics and larval growth, contain enough information for the larval density to be estimated under noisy conditions, given the correct model. When the system is applied practically, the estimation error will depend on the measurement and model accuracy; this is especially true with respect to the predictability of the feed intake rate of the fish.     

Higher food abundance reduces the catchability of cod (Gadus morhua) to longlines on the Faroe Plateau

The cod fishery at the Faroes has been managed since 1996 by an effort management system where it is assumed that there is a direct relationship between fishing mortality and fishing effort. We show that this relationship is weak. Due to a factor five variation in the primary production on the Faroe Plateau, the annual growth rate of cod may vary by a factor of five. Commercial catch-per-unit-effort data in combination with stock assessment estimates showed that there was a negative correlation between the annual growth rate of cod and their catchability with longlines, as well as with the total fishing mortality of cod on the Faroe Plateau. Furthermore, mark-recapture experiments showed that longline-caught cod in comparison with trawl-caught cod had a lower condition factor, a lower stomach content of natural prey, and a higher content of longline baits. During the feeding season in September–December, longline-caught cod exhibited a larger displacement distance than trawl-caught cod. These results were largely confirmed by storage tag data. Consequently, during low-productive periods, (i) the longline-dominated cod fishery at the Faroes exerted fishing mortalities that by far exceeded safe biological limits, and (ii) longline catch-per-unit-effort series might overestimate stock size considerably.     

Feed preferences in juvenile cod estimated by inert lanthanid markers – effects of moisture content in the feed

There are indications that low ingestion ratesof formulated feed may limit the growth ofearly juvenile fish, including cod. This hasparticularly been observed during the weaningperiod, when the fish must change from apresumably palatable live prey to usually a drydiet. The study of the physical properties ofthe diet seems to be an underestimated area ofresearch, compared to studies on thenutritional properties of the diet. In thisstudy we used lanthanide markers as a tool inestimating diet preferences for examining theeffect of dietary moisture content on ingestionrates in juvenile cod (0.8 g). Fishmeal-baseddiets were produced with five levels of water,giving diets with 35, 42, 54, 65 or 95% dryweight. Each diet was marked with a smallamount of a lanthanide or yttrium oxide. Thefish were hand fed on a mixture of these fivediets. Ingestion rates where then estimated bykilling 1/2 of the fish after one day and therest after four days of feeding. The whole fishwith gut content was homogenized and markercontent was measured by ICP-MS. The amountingested of each of the five diets could thenbe calculated from these figures. Despite thehigh variation in diet selection betweenindividuals the results clearly indicate ahigher intake of moist feed. This could becaused by a better palatability or to a higheravailability caused by a lower sinking rate ofthe moist feed.     

Purification and physicochemical properties of deoxyribonuclease from pyloric caeca of Atlantic cod (Gadus morhuaL.)

A deoxyribonuclease (DNase) of pancreatic origin has been purified from extracts of the pyloric caeca from Atlantic cod (Gadus morhua L.). The crude extract was prepared by mincing frozen caeca tissue in equal volumes of buffer. The enzyme was isolated from the supernatant after streptomycin sulfate precipitation and centrifugation. The purification scheme further included chromatography on Q-Sepharose Fast Flow and hydroxyapatite columns. Affinity adsorption chromatography of the hydroxyapatite fraction on 8-(6-aminohexyl)-amino-5′-AMP-Sepharose, revealed an apparently homogeneous protein with molecular weight of 35,000 Da as judged by NaDodSO₄-PAGE. In sum a 644-fold enzymatic enrichment and 3.5% total enzyme recovery was achieved. The cod enzyme resembles DNase I-type enzymes with an alkaline pH activity optimum and shows dependency for Mg²⁺. The pI of the enzyme is 6.5 as determined by isoelectric focusing and DNase-zymography. Our findings suggest that the nuclease is a member of the cod's digestive enzymes secreted from the connective tissue surrounding the caeca.     

Short-term crowding stress in Atlantic cod, Gadus morhua L. modulates the humoral immune response

Considering overcrowding as a stressor, the effects of a short-term exposure on the immune responses of Atlantic cod, Gadus morhua L. were determined at 2, 24 and 72 h post-crowding. While plasma glucose and total antioxidant capacity were quantified as stress responses, immune responses were based on humoral indices. Bactericidal capacity of plasma was also assessed. There was a significant increase in plasma glucose and total antioxidant capacity at 2 h post-crowding, however the former returned to pre-stress levels 24 h later and the latter remained elevated until 72 h. The plasma protein did not reveal any significant change, but there was a transient upregulation of globulin at 24 h post-crowding. The myeloperoxidase activity increased at 2 h after the stress, but returned to its pre-stress levels at 24 h. The lysozyme activity was upregulated even from the first time point after stress, although the differences were significant only at 24 and 72 h compared to the activity prior to stress. At 72 h post-crowding there was a significant increase in alkaline phosphatase activity while haemolytic activity showed a significant decrease. An increase in the proliferation of the bacterial pathogens, Vibrio anguillarum and Aeromonas salmonicida was seen from 24 h in the plasma of the stressed fish. Thus, our finding suggests that short-term crowding stress modulates the immune responses in Atlantic cod and therefore husbandry procedures should consider these effects while addressing better management strategies.     

Changes in tissue and plasma free amino acid concentrations after feeding in Atlantic cod

Atlantic cod, Gadus morhua, were maintained on a diet of sandeel and after a 6-day fast were refed a single meal. Concentrations of free amino acids (AAs) were measured in hepatic portal and cardiac blood as well as in the stomach and white muscle at intervals of 6h up to 24h post-feeding. The appearance of both essential and non-essential AAs in the hepatic portal blood was significantly correlated, up to 12h after feeding, to their abundance in the diet. There was a significant decline in total AA concentration in cardiac blood after 6h, followed by a significant increase at 12h. No significant changes in total AA concentration were observed in the other tissues, although mean concentration increased at 12 or 18h. At a more detailed level, the post-prandial changes in concentration of some essential AAs were consistent with their having a role in the stimulation of protein synthesis after feeding.     

Properties of cod metallothionein,its presence in different tissues and effects of Cd and Zn treatment

One isoform of the low-molecular-weight metal-binding protein metallothionein (MT) has been isolated from the liver of Atlantic cod by size-exclusion and ion-exchange chromatography. Cod MT contained 33% cysteine, no aromatic amino acids or arginine. As is the case for other piscine MTs, the N-terminus of cod MT lacked the asparagine in position 4 which is present in mammalian MTs. In addition, cod MT differed from all other vertebrate MTs described in that the N-terminal methionine was not acetylated. Antibodies were raised in rabbits against hepatic MT from cod by repeated injections of native protein mixed with adjuvant. Anti-cod MT antisera cross reacted with similarly-sized proteins in liver, brain, anterior kidney, posterior kidney, spleen, intestine, gills and ovaries. The putative MT in cod brain migrated differently to that of the other tissues in native gel electrophoresis. Intraperitoneally injected Cd (1 mg/kg) was nearly entirely associated with the MT-peak in hepatic and renal cytosols, whereas a single injection of Zn (10 mg/kg) resulted in increases in all cytosolic Zn pools of the liver and no apparent change in cytosolic Zn, Cu, Ni or Cd in kidney.     

Characterization of a pancreatic DNase from pyloric caeca of atlantic cod (Gadus morhua L.)

An alkaline deoxyribonuclease (DNase) from cod pancreatic tissue has been characterized. The enzyme is a DNase I type endonuclease and hydrolyzes effectively both native and denatured DNA. Monomeric actin inhibits the enzyme reaction. The enzyme obeys Michaelis-Menten kinetics and the apparent K_m value for native linear duplex DNA is 33 µg/ml. The cod DNase opens supercoiled plasmid DNA, by introducing adjacent nicks in both strands, possibly separated by 5–10 nucleotides. DNA hydrolyzed by cod DNase functions as substrates both for DNA polymerase and ligase, and the nicks therefore contain 5-phosphoryl and 3-hydroxyl groups. Optimum concentrations of divalent cations are 5 mM Mg²⁺, 0.63 mM Mn²⁺ and 0.075 mM Ca²⁺. However, Ca²⁺ is apparently not essential for the enzymatic functions. The enzyme has a narrow temperature optimum at 42°C and is thermolabile above 50°C; however, Mn²⁺ shifts the optimum slightly to 45°C by causing increased temperature stability. The cod DNase reaction is inhibited by the DNA intercalating compounds actinomycin D and ethidium bromide. Histidine-modifying reagents such as tosyl phenylalanyl chloromethylketone and diethyl pyrocarbonate inhibit the enzyme activity, but the cod DNase is insensitive to disulfide-reducing agents.     

Effects of vasoactive intestinal polypeptide,substance P, 5-hydroxytryptamine,met-enkephalin and neurotensin on the swimbladder smooth muscle of two teleost species,Gadus morhua andAnguilla anguilla

The effects of vasoactive intestinal polypeptide (VIP), substance P (SP), 5-hydroxytryptamine (5-HT), neurotensin (NT) and met-enkephalin (mEnk) on the smooth muscles of the teleost swimbladder were studied in two teleost species, the Atlantic cod (Gadus morhua) and the eel (Anguilla anguilla). The study was made on isolated strip preparations of the muscularis mucosae, using putative transmitters corresponding to the immunoreactive materials that have previously been localized by immunohistochemical methods in nerves or endocrine/paracrine cells of the teleost swimbladder and/or the gastrointestinal canal. VIP was relaxatory on both cod and eel swimbladder smooth muscle, SP and 5-HT were constrictory in both species, and mEnk was excitatory on the eel swimbladder smooth muscle. Clear effects of these agents were usually seen at a concentration ofca. 10 nM in cumulative concentration/effect experiments. NT had no effect in either species. In the eel, the effects on the pneumatic duct were generally greater than on the swimbladder proper. The study indicates that the 5-HT and peptides previously observed by immunohistochemistry have physiological functions in the swimbladder.     

Growth variation and fin damage in Atlantic cod (Gadus morhua L.) fed at graded levels of feed restriction

Atlantic cod (initial weight 55, 250 and 450 g) were deprived of feed for 1 month or fed one of two diets differing in crude protein and lipid levels at rations corresponding to about 25, 50, 75 or 130% of group satiation for two months. The fish were individually weighed at the start, mid and end of the experiment and growth variation and fin damage were registered. The fin damage patterns differed between size groups; 55 g cod had most wounds on the dorsal fins whereas the pectoral fins were the most damaged in the 250 g fish. The incidence of damage in these groups was high and increased significantly when feeding was restricted. In the 450 g cod there was little fin damage and the incidence did not seem to depend on diet treatment.In the 55 and 250 g cod groups, fast growing fish had lower incidence of fin damage than fish that grew slowly, suggesting that the fish that received most aggression were prevented from feeding. However, a similar trend was registered in non-fed fish, showing that the recipients of aggression also suffered other disadvantages.The variation in individual growth rates increased when feeding was restricted and the distribution was differently skewed depending on feeding level. The data provide evidence that competition is an important factor limiting growth of individual cod held in groups in culture.     

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.     

Genetic comparison of experimental farmed strains and wild Icelandic populations of Atlantic cod (Gadus morhua L.)

Microsatellite DNA loci and the Pantophysin locus (Pan I) were used to investigate levels of genetic diversity within farmed strains of Atlantic cod Gadus morhua and to compare them with the wild source population. A total of 282 farmed samples originating from a spawning ground off the south-west coast of Iceland were sampled in the years 2002 and 2003, and 258 wild cod were collected at the same spawning ground in the same years. The farmed strains exhibited a lower mean number of alleles and allelic diversity than the wild samples at the microsatellite loci. Significant differences were observed between wild and farmed samples both in allele and genotype frequencies at the Pan I locus. We argue that the genetic divergence of wild and farmed samples of Atlantic cod may be due to a small number of effective founding breeders contributing to the genetic variation of the farmed strains, inducing a reduction in allelic diversity. We discuss the potential effect of breeding practices on the genetic diversity of Atlantic cod.     

Effects of serotonin, adrenaline and other vasoactive drugs on the branchial blood vessels of the Antarctic fish Pagothenia borchgrevinki

Myography and an isolated, perfused gill arch preparation were used to investigate the actions of drugs on the gill vasculature of an Antarctic teleost fish, Pagothenia borchgrevinki. Serotonin produced a dose-dependent vasoconstriction of the afferant branchial arteries, the gill arch and the efferent branchial arteries, and was the most potent vasoconstrictor tested. Acetylcholine, at concentrations exceeding 1 × 10^-6M, vasoconstricted the gill arch, but had a negligible effect on the branchial arteries. The responses to adrenaline, with and without the -adrenergic blocking drug, sotalol and the effects of the -adrenergic agonist drug isoprenaline indicated the presence of both -adrenergic and -adrenergic receptors in the gill vasculature, with the vasoconstrictory action of the former predominating in the efferent vasculature. Angiotensin II was without effect in either preparation. The results are a further demonstration of the dominance of vasoconstrictory responses in the control of gill cular resistance in P. borchgrevinki: which has been associated previously with the sub-zero temperatures at which the animals are found.     

Digestive capacity, intestinal morphology, and microflora of 1-year and 2-year old Atlantic cod (Gadus morhua) fed standard or bioprocessed soybean meal

The objectives of this work were to evaluate how dietary soybean meal (SBM) or a soy meal made by bioprocessing the SBM (BPSBM) to remove anti-nutritional factors affected hydrolytic capacity, amino acid absorption, intestinal morphology, and microflora along the intestinal tract of Atlantic cod at two life stages. Three fish meal based standard cod diets were formulated to contain no soy (FM control), 25% SBM, or 22% BPSBM. Prior to sampling the diets were fed to duplicate groups of 0.5 kg (1-year old) and 1.7 kg (2-year old) cod for a period of 3 months, and the groups reached 0.9 and 2.5 kg, respectively. Digesta was then sampled from different intestinal sections for analyses of trypsin and amylase activity as well as absorption of amino acids, nitrogen, and sulphur. Gastrointestinal sections were sampled for measurements of relative weight (kg^− 1 body weight), and tissues from these sections were sampled for analyses of brush border enzyme (alkaline phosphatase (ALP), leucine aminopeptidase (LAP), and maltase) activity and histological examination. Microflora was sampled from both digesta and the intestinal wall. The SBM diet stimulated relative growth of all gastrointestinal sections except the distal intestine in both age classes. Relative growth of the pyloric intestine was also stimulated by BPSBM. The pyloric caeca and the upper mid intestine were found to be the major sites for enzymatic hydrolysis of protein and starch and for amino acid absorption. Dietary SBM and BPSBM did not alter the activity of trypsin and LAP, but the activity of these enzymes in the proximal intestine was affected by age, being higher in 1-year old than in 2-year old cod. The rate of amino acid, nitrogen, and sulphur absorption along the gastrointestinal tract was not affected by SBM, but was slowed by BPSBM. Dietary SBM or BPSBM did not alter the morphology of the intestinal mucosa in any sections of the cod intestine. The distal-most structure of the intestine, a compartment with inlet and outlet (anus) valves, showed very high microbial colonisation in the mucosal brush border. Inclusion of SBM in the diet changed the intestinal microflora, increasing the population level of transient bacteria in the pyloric and mid intestine, but reducing the population level of adherent bacteria throughout the intestine. To conclude, Atlantic cod appeared to have a robust and flexible digestive system able to adjust to high dietary levels of soy protein meals.     

Enhancement of image-based fecundity methods: Gravimetric sampling at sea and safer sample preservation

Collecting accurate fecundity samples in the field is challenging as field scales are often unreliable and inaccurate in rough seas. In addition, the storage and use of caustic preservatives may be difficult and dangerous. Quantifying the efficacy of both a non-caustic alternative to traditional preservatives, and the use of pre-weighed vials in sampling protocols is essential in improving the accuracy and utility of field samples. Streck Tissue Fixative (STF) is a less toxic alternative to traditional preservatives and proved effective in the short- and long-term preservation of haddock (Melogrammus aeglefinus) and cod oocytes (Gadus morhua). We found no time series trend or systematic change in the number of oocytes counted and there was stabilization in size decay by the second month, which is comparable to traditionally used preservatives. In examining the use of pre-weighed vials we compared several different vial types. Plastic vials with an o-ring showed a satisfactory predictable loss and we were able to develop a system of time dependent corrections for evaporative rate. Thermal effect was also examined, with evaporative loss decreasing at low temperatures. The effectual use of an alternative preservative and the validation of the use of pre-weighed vials have the potential to increase the efficiency and accuracy of field sampling.     

Seasonal changes in reproductive condition and plasma levels of sex steroids in the blue cod,Parapercis colias (Bloch and Schneider) (Mugiloididae)

Gonad and plasma samples were taken from blue cod captured throughout the reproductive cycle, gonad condition was assessed, and plasma levels of 17-hydroxyprogesterone (17OHP), 17,20-dihydroxy-4-pregnen-3-one (17,20P), testosterone (T), 17-estradiol (E₂) and estrone (E₁) were measured by radioimmunoassay. It was confirmed that spawning occurred over an extended period in late winter and spring, with individual fish being involved in multiple spawning events. Plasma levels of T were bimodal in both sexes with peaks (maximum of 6.0 ng.ml^–1) occurring 2 months prior to, and also during the early part of the spawning period. 17,20P was elevated in males (2.1 ng.ml^–1) in mid-spermatogenesis coinciding with the first T peak (4.9 ng.m.^–1). 17,20P was detectable but not significantly elevated (0.6–1.2 ng.ml^–1) at any sample time in females. E₂ was elevated in mature females (1.0 ng.ml^–1) early in the spawning period but remained at assay detection limits (0.3 ng.ml^–1) at all other sample times. Neither 17OHP nor E₁ were detectable in the plasma of either sex. It is suggested that bimodal increases in sex steroids prior to spawning may be a feature of species with rapid recrudescence.     

Vasoactivity of prostanoids in the trout (Oncorhynchus mykiss) coronary system: modification by noradrenaline

An isolated non-working trout heart, cannulated through the coronary artery and perfused with oxygenated saline with a coronary pressure head of 3.0 kPa has been used in this study. Effects on the coronar resistance of catecholamines, thromboxanes (TXs) and prostacyclin (PGI₂) were analyzed. The effects of PGI₂ and TXs in presence of noradrenaline were also evaluated. Both adrenaline and noradrenaline vasoconstrict the trout coronary system, noradrenaline being more potent than adrenaline. TXA₂ induces 45% vasoconstriction at 10⁻⁶M, while TXB₂ at the same concentration is a slight vasodilator. PGI₂ acts as a weak vasodilator (about 20% decrease in resistance at 10⁻⁶M). In presence of 10⁻⁷M noradrenaline, 10⁻⁸M TXA₂ reduces the vasoconstriction induced by the catecholamine alone from 60% to about 15%. Under similar conditions, 10⁻⁹M PGI₂ potentiates the vasoconstrictive response induced by noradrenaline while a much higher PGI₂ concentration (10⁻⁶M) completely abolishes the vasoconstriction. The β-receptor antagonist propranolol induces vasoconstriction, and 10⁻⁹M PGI₂ in presence of propranolol further increases the vasoconstriction. The α-receptor antagonist phentolamine induces vasodilation and 10⁻⁹M PGI₂ does not affect coronary resistance induced by phentolamine. These results imply a possible interaction between noradrenaline and prostanoids (TXs and PGI₂) in the vasomotion of trout coronary system.