Effect of vitamin B12 and taurine on the alleviation of nutritional anaemia in common sole (Solea solea)

Sole fed commercial pellets develop a nutritional anaemia. This study assessed the impact of dietary B12 and taurine on the haematocrit (Hct) and haemoglobin (Hb) level and mineral absorption in anaemic sole. Anaemic sole was fed one of four diets. Diets were equal regarding mineral, amino acid and macronutrient composition and formulated, according to a two by two factorial design: two B12 (0.34 vs. 1.9 mg kg dm^?1) and two taurine levels (3.5 vs. 7.6 mg kg dm^?1). The feeding level was restricted and equal for all diets. Hct and Hb levels in anaemic sole are influenced by dietary B12. A “high” level of B12 increases the Hct and Hb level. An increasing level of taurine suppresses the stimulating effect of the “high” level of B12. The applied B12 and taurine levels were unable to completely alleviate the anaemia in sole. Nevertheless, sole needs high dietary levels of B12 to alleviate anaemia. The impact of B12 and taurine on Hb and Hct was not related to a change in the absorption of iron. A “high” level of B12 positively affected the absorption of chromium and a high level of taurine negatively affected the absorption of cobalt in sole.     

The acute stress response in fed and food deprived Atlantic cod, Gadus morhua L.

The aim of the present study was to evaluate the effect of stress and nutritional state (fed vs food deprived) on the generalized stress response and intestinal integrity in Atlantic cod (Gadus morhua L.). Cod in feeding or food deprived states were subjected to 15 min of acute stress (exhaustive exercise). Blood was collected at 9 intervals from before stress (t = 0), to t = 48 h post stress and analysed for blood haematocrit and haemoglobin, and plasma cortisol, lactate, glucose, osmolality, chloride, as well as the tissue damage indicators glutamate oxaloacetate transaminase, glutamate pyruvate transaminase and thiobarbituric acid reactive substances. Intestinal segments were prepared for histology with the same intervals, while assessment of intestinal integrity and microbiology was performed at t = 0, 4 and 48 h post stress.Subjecting cod to exhaustive stress initiated a standard stress response including increased blood Hct and plasma cortisol, glucose, chloride, osmolality and lactate. Food deprived fish did in general have reduced stress resistance compared to fed fish. For many parameters, cod returned slowly to basal levels. Cellular indicators of tissue damage and oxidative stress increased in a biphasic manner following stress. Stress did not affect gut histology but did transiently increase gut permeability. Furthermore, stress had no effect on the adherent bacterial population level in midgut, but did cause a small decrease in hindgut (non-significant) and hindgut chamber (p < 0.05). Isolates belonging to Carnobacterium were predominant but not affected by stress.In conclusion, food deprived cod are less resistant to stress than fed cod. The magnitude of the response is less than in salmonids, but the effects are persistent (including tissue damage indicators and oxidative stress) and may have negative long term consequences. The gut is relatively resistant to stress, there is however a transient increase in the intestinal permeability and alterations in microbiota that may indicate lower protection against invading pathogens.     

Tolerance of Atlantic salmon (Salmo salar) to dietborne endosulfan assessed by haematology,biochemistry, histology and growth

The inclusion of plant‐based ingredients in commercial fish feeds may pose a challenge because of the presence of undesirable substances, such as the pesticide endosulfan. Waterborne endosulfan is highly toxic to fish, whereas dietborne exposure has varied toxicity in different species. To investigate the systemic effects of endosulfan exposure, quadruplicate groups of Atlantic salmon (Salmo salar) were fed either 0 (control), 0.005 mg kg^?1; the European Union's maximum limit, or 10 or 20 times this level (0.05 and 0.1 mg kg^?1 respectively) for 95 days. There were no significant differences (P > 0.05) in liver somatic index, spleen somatic index, condition factor or growth among treatments. There were no indications of liver damage in fish from any of the groups in the biomarkers measured: plasma aspartate aminotransferase, plasma alanine aminotransferase and histopathology. Similarly, there were no apparent treatment‐related effects on the haematological parameters Hct, Hb, mean corpuscular volume, mean corpuscular haemoglobin concentration and mean corpuscular haemoglobin, and blood sodium, potassium, calcium and chloride levels were not significantly (P > 0.05) different among groups. Lipid digestibility, but not energy, protein, or glycogen digestibility, was significantly (P < 0.05) reduced at the highest exposure concentration. However, no significant differences were observed in lipid production value or lipid efficiency ratio. In contrast to previous studies, clinical histological abnormalities were not observed in the intestine, liver or spleen of endosulfan‐treated fish.     

The effect of dietary chitin on the autochthonous gut bacteria of Atlantic cod ( Gadus morhua L.)

In the present study the impact on autochthonous (adherent) bacteria in proximal intestine (PI) and distal intestine (DI) of Atlantic cod ( Gadus morhua L.) was evaluated following feeding of a control diet and a diet supplemented with 5% chitin. The autochthonous gut bacteria were investigated using denaturing gradient gel electrophoresis (DGGE). Analysis of the microbiota associated with PI and DI of Atlantic cod indicate that dietary chitin modulate the intestinal bacterial community. For example, band 25 ( Escherichia coli–like), band 14 ( Anaerorhabdus furcosa–like) and band 29 (uncultured bacterium–like) in PI were depressed by dietary chitin (P < 0.05). The number of bands (23.7 ± 5.4) in DI of fish fed chitin was marginally higher than the control fish (16.7 ± 2.1) (P = 0.065), and the relative abundances of band 6 (swine faecal bacterium–like) were marginally stimulated by dietary chitin (P = 0.095). Furthermore, the present study reports several novel sequences not previously reported in the gastrointestinal tract of Atlantic cod. Whether the dietary effect of chitin on gut bacterial community has any positive effect of fish health merits further investigations.     

Unmethylated CpG oligodeoxynucleotides activate head kidney leukocytes of Atlantic cod, <Emphasis Type="Italic">Gadus morhua</Emphasis>

Bacterial DNA and synthetic oligodeoxynucleotides (ODNs) that contain unmethylated CpG motifs are strong inducers of immune response in most mammalian organisms. The use of these synthetic CpG motifs in fish, particularly in salmonids and carp, resulted in the modulation of their immune system. However, much less is known in other species of fish such as gadoids including Atlantic cod, Gadus morhua. Using head kidney (HK) leukocytes of cod in an in vitro study, we determined the effects of some established CpG-ODNs on the cellular responses of the fish immunocytes. Incubation of the HK leukocytes with 2 μM concentration of the CpG-ODNs resulted in enhanced respiratory burst. There were differential effects on the activities of acid phosphatase and cellular myeloperoxidase. Only CpG-ODN 1826 triggered a significant increase in the level of both enzymes. On the other hand, the supernatants derived from the HK leukocytes after incubation with different CpG-ODNs did not possess bactericidal activity against Vibrio anguillarum and Aeromonas salmonicida. This study has shown that CpG-ODNs at low concentrations are able to stimulate respiratory burst in cod but have minimal effects on cellular enzymatic activities and antibacterial action.     

Effects of replacing fish meal and oil with plant resources in on‐growing diets for Atlantic cod Gadus morhua L

The present paper gives an overview on the use of plant protein and plant oils as replacers for fish meal and fish oil in diets for Atlantic cod Gadus morhua L. In focus are effects on growth, feed utilization, digestibility, gut health, muscle and liver uptake and retention of nutrients, and muscle quality. Plant oil can replace fish oil without affecting growth provided that the requirement of marine long chain (LC) n‐3 fatty acids is met, but the altered dietary fatty acid profile in diet will be reflected in both muscle and liver. This can reduce the value of cod liver as an oil source for cod liver oil production. For the fish itself, there are more challenges replacing fish meal than fish oil, due to the amount of fibre and antinutrients in plant protein meals. However, A. cod seems to tolerate a wide range of plant types and their inclusion levels provided that the amino acids requirements are met. It is our view that there is sufficient knowledge to be able to design an A. cod diet based on a mixture of plant and marine ingredients and be able to predict performance such as growth, feed utilization, digestibility, liver size and fish health in general.     

Experimental study of the susceptibility of Atlantic cod, Gadus morhua (L.), to infection with an IPNV strain pathogenic for Atlantic salmon, Salmo salar L

Intraperitoneal (IP) injection, cohabitation and immersion routes of infection were used to determine if Atlantic cod, Gadus morhua (L.), of 1 and 3 g are susceptible to infectious pancreatic necrosis (IPN). Mortalities of cod injected IP were significantly higher when challenged with infectious pancreatic necrosis virus (IPNV) than with phosphate buffered saline. This is the first report of Atlantic cod mortalities caused by IPNV. Fish challenged by cohabitation had significantly higher mortalities than the controls, but mortalities of Atlantic cod challenged with IPNV by immersion were not significantly different from controls. Titres of IPNV in the tissues of infected fish were sometimes very high (range 10²–10¹⁰ infectious units per gram of tissue) suggesting virus replication and titres of fish that died were generally higher than those of fish which survived. However, the relatively low mortality rates when challenged by cohabitation and immersion (20% and 17%, respectively), compared to the IP injection challenge (100%) suggest that 1 and 3 g cod have low susceptibility to IPN when challenged by more natural routes. These data strongly suggest that the cause of death of experimentally challenged cod was IPNV and further histological evidence for this came from 1 g cod challenged IP with IPNV in which the pancreas showed severe necrosis and heavy immunostaining for IPNV coincidentally with the peak of mortalities.     

Yersiniosis in Atlantic cod,Gadus morhua (L.), characterization of the infective strain and host reactions

A disease outbreak in farmed Atlantic cod caused by Yersinia ruckeri is reported. Mortality started following vaccination of cod reared in two tanks (A and B). The accumulated mortality reached 1.9% in A and 4.8% in B in the following 30 days when treatment with oxytetracycline was applied. Biochemical and molecular analysis of Y. ruckeri isolates from the cod and other fish species from fresh and marine waters in Iceland revealed a high salinity‐tolerant subgroup of Y. ruckeri serotype O1. Infected fish showed clinical signs comparable with those of Y. ruckeri ‐infected salmonids, with the exception of granuloma formations in infected cod tissues, which is a known response of cod to bacterial infections. Immunohistological examination showed Y. ruckeri antigens in the core of granulomas and the involvement of immune parameters that indicates a strong association between complement and lysozyme killing of bacteria. Experimental infection of cod with a cod isolate induced disease, and the calculated LD₅₀ was 1.7 × 10⁴ CFU per fish. The results suggest that yersiniosis can be spread between populations of freshwater and marine fish. Treatment of infected cod with antibiotic did not eliminate the infection, which can be explained by the immune response of cod producing prolonged granulomatous infection.     

Infectious haemolytic anaemia causes jaundice outbreaks in seawater-cultured coho salmon, Oncorhynchus kisutch (Walbaum), in Chile

In the last 9 years, epizootics of an icterus condition has affected coho salmon, Oncorhynchus kisutch (Walbaum), reared in seawater cages in southern regions of Chile. At necropsy, fish from field cases exhibited signs of jaundice accompanied by pale light-brown livers and dark spleens. Histopathological and haematological results indicated that these fish presented haemolytic anaemia. After microbiological examination no bacterial or viral agents could be identified as aetiological agents of this disease. In an infectivity trial, coho salmon, Atlantic salmon, Salmo salar L., and rainbow trout, Oncorhynchus mykiss (Walbaum), were inoculated intraperitoneally with a filtrate of an organ homogenate (0.45 microm) from a diseased coho salmon and held for 60 days in tanks supplied with fresh water. The disease was only reproduced in coho salmon in which mortalities, beginning at day 23 post-inoculation (p.i.), reached a cumulative value of 24% at day 27 p.i. This condition was transmitted to non-inoculated cohabiting coho salmon suggesting that it is a waterborne disease. Thus, this icteric condition is caused by an infectious form of haemolytic anaemia, probably of viral aetiology, and coho salmon are more susceptible than either Atlantic salmon or rainbow trout.     

Effect of nutritional status and sampling intensity on recovery after dorsal aorta cannulation in free-swimming Atlantic salmon (Salmo salar L.)

Recovery from implantation of a cannula in the dorsal aorta (DA) of Atlantic salmon (Salmo salar) was studied in relation to nutritional status and sampling intensity. The incentive for the study was the inconsistency between published reports and our own experience of recovery and longevity of fish exposed to this protocol. In two studies using starved fish, blood (0.3 ml) was sampled 0, 1 and 24 h after DA-cannulation, and thereafter at 48 and 72 h and thereafter once weekly for four weeks. In a third study using fed fish, four consecutive samples (0, 3, 6 and 12 h after a meal) were obtained twice a week over a four-week period. All fish displayed a sharp increase in pCO₂ and haematocrit (Hct) during surgery, followed by a marked raise in cortisol, glucose, sodium and potassium (1 h). pCO₂, pH and Hct approached baseline levels as early as the 1 h post-surgery sample, while this was not the case for cortisol and electrolytes before the 24 h post-surgery sample. Glucose did not display any significant changes post surgery. From then on, all variables displayed minor but non-significant (P > 0.05) changes indicating a steady state close to baseline values for unstressed fish. This pattern was independent of sampling procedure, i.e. repeated single or multiple samples and thus volume of blood removed. Nutritional status (fed vs. starved) did not affect post-surgical recovery pattern. Only K⁺ and Hct displayed consistent and significant post-prandial patterns. We found marked differences between baseline level of cannulated fish and uncannulated control fish, in pH, K⁺ and Hct indicating that cannulation may be the preferred method to obtain representative resting values in fish.     

Anesthesia induces stress in Atlantic salmon (<Emphasis Type="Italic">Salmo salar</Emphasis>), Atlantic cod (<Emphasis Type="Italic">Gadus morhua</Emphasis>) and Atlantic halibut (<Emphasis Type="Italic">Hippoglossus hippoglossus</Emphasis>)

Stress in response to anesthesia with benzocaine, MS-222, metomidate and isoeugenol was studied in Atlantic salmon (Salmo salar), Atlantic halibut (Hippoglossus hippoglossus), and Atlantic cod (Gadus morhua) with no concomitant stress from handling or confinement in association with anesthesia or sampling. All of the anesthetics tested induced a stress response in all species, displayed by a release of cortisol to the water. MS-222 anesthesia elicited the highest cortisol release rates, reaching maximum levels 0.5 h post-exposure and returning to basal levels after 3–4 h. Benzocaine anesthesia caused a bimodal response where the initial peak in cortisol release rate was followed by a second increase lasting towards the end of the trial (6 h). This bimodality was more profound in Atlantic salmon than in Atlantic halibut and Atlantic cod. Metomidate anesthesia induced the lowest release of cortisol of the agents tested in both Atlantic halibut and Atlantic cod, but resulted in a bimodal response in Atlantic salmon where the initial increase in cortisol release was followed by a larger increase peaking at 2–2.5 h post exposure before returning to basal levels after 5 h. The stress induced in Atlantic salmon by isoeugenol anesthesia resembled that of MS-222, but did not reach the same elevated level. Overall, the cortisol release was most profound in Atlantic salmon followed by Atlantic halibut and Atlantic cod.     

Inclusion of size fractionated fish hydrolysate in high plant protein diets for Atlantic cod, Gadus morhua

Fish hydrolysate was evaluated as feed ingredient in high plant protein diets in an 89 days feed experiment with Atlantic cod (Gadus morhua). The fish hydrolysate was size fractionated by ultra- and nano-filtration and the various fractions were tested specifically as feed ingredients to trace any effect observed with the hydrolysate. All diets contained 68% of total protein as plant protein, added as a mixture of corn gluten, full-fat soy bean meal, soy protein concentrate and extracted soy bean meal. The diets were equal in protein, lipid and energy. The control diet contained 21.8% fish meal. Fish hydrolysate was tested in another diet where one third of the fish meal protein was exchanged with the fish hydrolysate. Retentate after ultra-filtration of fish hydrolysate and retentate and permeate after nano-filtration were used in three separate diets at dietary inclusion levels corresponding to the absolute dry matter level of the fractions in the hydrolysate. The cod tripled in weight during the experimental period. No significant differences were observed for growth or feed intake for any groups. The diets containing retentate from ultra- and nano-filtration showed lower feed efficiency than the control diet with fish meal or the diet containing fish hydrolysate or permeate after nano-filtration. In conclusion the results show that fish hydrolysate may successfully be used as a protein source in high plant protein diets for Atlantic cod in exchange of fish meal. Removal of small molecules from the fish hydrolysate by filtration reveals poorer feed utilization indicating that this marine fraction of small compounds is important for optimal growth of Atlantic cod. This may be important in the discussion of increased dietary utilization of plant protein sources in feed for fish.     

Element concentrations in meals from krill and amphipods, — Possible alternative protein sources in complete diets for farmed fish

In the marine environment, organisms from lower trophic levels seem as a good alternative to the traditional meal and oil sources. In the present study, meals were produced from Antarctic krill (Euphausia superba), Arctic krill (Thysanoessa inermis) and the Arctic amphipod Themisto libellula. Diets were then prepared for Atlantic salmon and Atlantic cod where up to 100% of the fish meal protein was replaced by protein from these organisms. Concentrations of copper (Cu), zinc (Zn), arsenic (As), cadmium (Cd), mercury (Hg) and lead (Pb) were determined by ICP-MS in the various krill and amphipod meals, complete diets and muscle samples from fish fed these diets. The element concentrations were related to growth and general fish health as well as present EU legislations on feed ingredients and complete diets. The cod showed no difference in growth during the trial, while salmon fed diets where 40% of the fish meal protein was replaced with Arctic krill or amphipod meal shoved improved SGR during the first period of feeding (first 100 days). No adverse effects on growth rate or fish health were observed in any fish species or treatment. Nevertheless, high levels of Cu were found in the meal from Antarctic krill (46 mg kg^− 1 dry matter (dm)) resulting in a dietary level of Cu exceeding the upper limit for complete feedingstuff set by EU. Furthermore, the Cd level found in the meal from amphipod (12 mg kg^− 1 dm) was 6 times higher than EU's upper limit. This indicates limitations for the use of certain zooplanktons as alternative protein sources in feed for farmed fish, unless future processing methods yield lower levels of these unwanted elements.     

Rotifers enriched with iodine,copper and manganese had no effect on larval cod (Gadus morhua) growth,mineral status or redox system gene mRNA levels

It currently remains unclear if rotifers contain sufficient mineral levels to meet larval fish requirements. In this study, rotifers were enriched with a commercial enrichment (control), or with additional iodine, iodine and copper, or iodine, copper and manganese, and the effects of feeding these rotifers to Atlantic cod (Gadus morhua) larvae from 3 to 18 days post hatch were investigated. Rotifer enrichment with minerals was successful, but Mn enrichment also increased rotifer zinc levels. No differences were observed between treatments in larval growth or survival, or in the mRNA levels in the majority of the redox system genes analysed. Only Zn levels increased in cod larvae in response to mineral enrichment of rotifers. Apart from Zn, little evidence was found to suggest that cod larvae require increased concentrations above the control rotifer levels of the essential elements studied here.     

Host tropism of infectious salmon anaemia virus in marine and freshwater fish species

The aquatic orthomyxovirus infectious salmon anaemia virus (ISAV) causes a severe disease in farmed Atlantic salmon, Salmo salar L. Although some ISA outbreaks are caused by horizontal transmission of virus between farms, the source and reservoir of the virus is largely unknown and a wild host has been hypothesized. Atlantic salmon are farmed in open net‐pens, allowing transmission of pathogens from wild fish and the surrounding environment to the farmed fish. In this study, a large number of fish species were investigated for ISAV host potential. For orthomyxoviruses, a specific receptor binding is the first requirement for infection; thus, the fish species were investigated for the presence of the ISAV receptor. The receptor was found to be widely distributed across the fish species. All salmonids expressed the receptor. However, only some of the cod‐like and perch‐like fish did, and all flat fish were negative. In the majority of the positive species, the receptor was found on endothelial cells and/or on red blood cells. The study forms a basis for further investigations and opens up the possibility for screening species to determine whether a wild host of ISAV exists.     

Efficacy of clove solution on blood sampling and hematological study in Beluga, Huso huso (L.)

Two experiments were conducted to evaluate the efficacy of clove solution on anesthesia and hematological parameters in Beluga, Huso huso (L.). In the experiment 1, fish were exposed to concentrations of 300, 500, 700, 1,800 and 3,000 ppm clove solution and induction (stage 3 and 4) as well as recovery period lengths were recorded. These concentrations were led to induction and recovery time between 42–365 and 125–235 s, respectively, in dose-dependent manner. There was negative correlation between induction and recovery time (R ² = 0.92). In the experiment 2, fish were exposed to each aforementioned concentrations and let to reach stage 4 anesthesia and then blood-sampled. Control group was sampled without anesthesia. Hematological studies between groups showed no significant changes in white blood cell (WBC) and differential leukocyte count (P > 0.05). Hematocrit (Hct), hemoglobin (Hb), red blood cell (RBC) and mean corpuscular hemoglobin concentration levels were significantly high in concentrations of 300–700 ppm compared to control, 1,800 and 3,000 ppm. Control and 500–3,000 ppm groups have similar mean corpuscular volume values and significantly higher than 300 ppm. Lower values of mean corpuscular hemoglobin were related to control, 3,000 and 1,800 ppm and higher values were observed in the others. Strong positive correlation were observed between induction periods and Hct, Hb and RBC levels (R ² = 0.095, 0.99 and 0.92, respectively). Results suggested that anesthesia with low concentrations of clove solution over a long period is stressful compared to high concentrations over short period.     

The study of some haematological and serum biochemical parameters of juvenile beluga (<Emphasis Type="Italic">Huso huso</Emphasis>) fed oligofructose

A study was conducted to investigate the effects of dietary oligofructose (1, 2 and 3%) on the blood profiles of beluga (Huso huso) juveniles (18.77 ± 0.76 g) compared to fish fed an un-supplemented diet. After 7 weeks of feeding on the experimental diets, haematological parameters, metabolic products (cholesterol, glucose and total protein) and serum enzymes (lactate dehydrogenase, alkaline phosphatase, alanine aminotransferase and aspartate aminotransferase) were measured. Compared to the control group (0% oligofructose), dietary oligofructose had no effect on red blood cell counts (RBC), mean corpuscular volume (MCV), mean cellular haemoglobin (MCH) or mean cell haemoglobin concentration (MCHC) (P > 0.05). However, haemoglobin (Hb) concentration, leucocyte (WBC) levels and the proportion of lymphocytes were significantly higher (P > 0.05) in the 2% oligofructose fed fish than in the 3% oligofructose fed fish. Additionally, haematocrit (Hct) values (P = 0.049) and the proportion of lymphocytes (P ≤ 0.01) were significantly higher in the 2% oligofructose group than in the control group. Although serum glucose and total protein remained unaffected, serum cholesterol was significantly lower in the 2% oligofructose group than in the control and 3% oligofructose group (P < 0.05). The results of the present study showed that oligofructose had no significant effects on serum lactate dehydrogenase, alkaline phosphatase, alanine aminotransferase and aspartate aminotransferase. These results indicate that fish blood profiles could be affected by prebiotics, which should be taken into account in future studies.     

Accelerated extractions of North Atlantic cod and herring, 1520–1790

We propose the concept of Accelerated Marine Extraction to signify two periods when rapidly increasing cod (Gadus morhua, Gadidae) and herring (Clupea harengus, Clupeidae) fisheries, c.1540–1600 and c. 1730–1790, exceeded human demographic growth. Total landings vastly exceeded previous assessments and more than doubled between 1520 and 1620 from about 220,000 metric tonnes (t) to 460,000 t. Supplies of cod and herring to the European market peaked in 1788 at more than 1 million t before the unrest connected with the French Revolution brought many fisheries to a temporary halt. Accelerated Marine Extractions increased European food security at times of human demographic growth by almost doubling the supplies of fish protein per capita. While herring was the most important species by 1520, cod dominated through the period 1540–1790, and the trajectories of cod and herring extractions differed significantly. Cod landings increased almost ten-fold between 1520 and 1790, driven by strong and sustained landings in the Northwest Atlantic. Herring landings remained stable through the 16th century but declined severely through the next 150 years. However, from 1750, herring landings quadrupled, largely because of Swedish west coast fisheries. The results fundamentally shift our understanding of the scale of Atlantic fisheries in the past and underline the role of marine resources for European societies.     

The effects of experimental anaemia on CO2 excretionin vitro in rainbow trout,Oncorhynchus mykiss

The effects of severe experimental anaemia on red blood cell HCO₃ ^– dehydrationin vitro were examined in rainbow trout,Oncorhynchus mykiss. After 5 days of anaemia (haematocrit=4.9±1.1%) induced by intraperitoneal injection of phenylhydrazine hydrochloride, fish displayed elevated arterial CO₂ tensions (anaemic PaCO₂=3.19±0.42 torrvs. control PaCO₂=1.35±0.17 torr) and a significant acidosis (anaemic pHa=7.73±0.04vs. control pHa=7.99±0.04). However, after 15–20 days of anaemia (hct=6.6±0.8%) induced by blood withdrawal, the arterial CO₂ tension was significantly lower than the control value, suggesting that physiological adjustments occurred within this time period to compensate for the lowered haematocrit. Compensation probably did not involve alterations in ventilation, which was unaffected by 5 days of anaemia (anaemic ;w=786±187 ml min^–1 kg^–1 vs. control ;w=945±175 min^–1 kg^–1), based on indirect Fick principle measurements.Potential adaptations to longer term anaemia at the level of the red blood cells were investigated using a radioisotopic HCO₃ ^– dehydration assay. Owing to the difference in haematocrits, the HCO₃ ^– dehydration rate for blood from anaemic fish was significantly lower than that for control fish following equilibration at the same CO₂ tension. This difference was eliminated when HCO₃ ^– dehydration rates were measured on blood samples adjusted to the same haematocrit, a result which implies that the intrinsic rate of CO₂ excretion at the level of the red blood cell was not up-regulated during anaemia. The difference was also eliminated by equilibrating the blood samples with CO₂ tensions appropriate for the group from which the sample was obtained,i.e., PCO₂=1.4 torr for control samples and PCO₂=3.2 torr for anaemic samples; each at the appropriate haematocrit. It is concluded that the elevated PaCO₂ helps to reset CO₂ excretion to the control level, but that some additional physiological adjustment occurs to lower the PaCO₂ after 15–20 days of anaemia.     

Enzymes from the gut bacteria of Atlantic cod,Gadus morhua and their influence on intestinal enzyme activity

Gut‐associated bacteria of fish are known to produce enzymes which aid in digestion. The presence and activities of these bacteria in cold‐water fishes like Atlantic cod are less known. Therefore, we have characterized the activities of extracellular enzymes of GP21 (Pseudomonas sp.) and GP12 (Psychrobacter sp.), two bacteria isolated from the gastrointestinal tract of Atlantic cod. Additionally, we examined if these bacteria when delivered through feeds could influence the activity of selected intestinal enzymes. GP21 was able to produce amylase, chitinase, cellulase and protease, whereas GP12 could produce only chitinase and protease. These enzymes were produced extracellularly and they were found to be catalytically active at acidic conditions (pH 2–5) and at temperatures ranging from 15 to 30 °C. Orally delivered bacteria could possibly influence the activity of intestinal enzymes after 40 days, rather than after 20 days of feeding. Thus GP21 and GP12, the potential probiotic organisms, could support digestion in Atlantic cod.