Haematology and leucocyte morphology of wild caught Thunnus maccoyii

The haematology of wild southern bluefin tuna Thunnus maccoyii was described using blood samples collected from fish immediately after they were caught. Cytology and cytochemistry revealed that the blood in peripheral circulation is comprised of erythrocytes, reticulocytes, ghost cells, lymphocytes, thrombocytes, eosinophilic granulocytes, neutrophilic granulocytes and monocytes. Reference ranges established were 41·09–55·50% for haematocrit, 0·62–3·00% for leucocrit, 13·25–17·92 g dl⁻¹ for haemoglobin and 2·1–2·9 million erythrocytes μl⁻¹ for erythrocyte count. Differential cell counts showed 94·58 ± 2·15% erythrocytes, 3·99 ± 1·44% leucocytes and 1·43 ± 1·03% thrombocytes (mean ±  s . d .). Normal ranges for differential leucocyte counts were 0·00–5·45% for neutrophils, 0·69–12·06% for eosinophils, 0·00–5·03% for monocytes, 46·97–74·32% for lymphocytes and 14·47–43·92% for thrombocytes. Erythrocyte indices, leucocyte types and cytochemistry were comparable to other species of scombrids. Packed cell volume was sensitive to the physiological state of the fish and to sample handling technique.     

Stress and survival of small pike-perch Sander lucioperca (L.) after trawling and chilling

The mortality and stress responses (plasma cortisol concentration) of undersized (total length, L _T, <370 mm) pike-perch Sander lucioperca caught as by-catch in a trawl fishery were assessed. The effects of three different holding methods on pike-perch caught by trawl were compared: (1) fish that were transferred to ambient-temperature water (15·0–21·4° C) immediately after capture and not exposed to chilling water, (2) fish held in chilling water for 10 min and (3) fish exposed to chilling water for 2 h. The sample fish were held and monitored in individual plastic restrainers at ambient-water temperature for 48 h after each of the handling procedures. Total mortality was similar for fish held in chilling tanks for 10 min (27·2% total mortality) compared to fish that were only held in ambient-temperature water (28·2% mortality). Total mortality reached 91·3% when fish were held in chilled water for 2 h. Mortality and plasma cortisol concentrations correlated inversely with size (96–368 mm L _T) and directly with lake-water temperature (15·0–21·4° C) after treatment. In addition, the effect of chilling was observed in elevated cortisol concentration and delayed start of recovery. The results show that quickly removing (<10 min) undersized pike-perch from chilled water could markedly improve the survival of released fish. Due to delayed recovery, however, fish should be allowed to recover (30–40 min) in a deck tank before release.     

Plasma cortisol and 17β-oestradiol levels in roach exposed to acute and chronic stress

Plasma cortisol levels were measured as an indicator of physiological stress in roach subjected to brief handling, or to a 14-day period of confinement, and in undisturbed control fish, during winter (water temperature 5° C) and summer (16° C), at which time plasma 17 β-oestradiol levels were also determined. Cortisol levels in undisturbed roach were low (mean 8·1 ng ml⁻¹ at 5° C; 1·4 ng ml⁻¹ at 16° C) and both handling and handling+confinement elevated blood cortisol levels significantly to 400 and 140 ng ml⁻¹, respectively (at 5° C) and 700 and 600 ng ml⁻¹, respectively (at 16) C). Blood cortisol levels had almost returned to baseline within 4 h following handling alone but in fish subjected to handling and prolonged confinement cortisol levels remained elevated for up to 168 h. Differences in baseline and poststress levels of cortisol, and in the rate of recovery from acute stress, were observed at the two different temperatures and the possible factors underlying these differences are discussed. Circulating levels of 17 β-oestradiol were reduced significantly within 24 h of exposure to either acute handling or chronic confinement indicating that the reproductive endocrine system in roach is sensitive to disruption by stressors.     

Serum parameters of Adriatic sturgeon Acipenser naccarii (Pisces: Acipenseriformes): effects of temperature and stress

Data on the concentrations of some blood constituents of captive Adriatic sturgeon, Acipenser naccarii, a primitive bony fish, are reported. Serum osmolality, Na⁺, K⁺, Cl⁻, Ca²⁺, cortisol, glucose and total protein concentrations were measured. The effects of anaesthesia, temperature, crowding and prolonged handling stress were tested on a group of 12 4-year-old sturgeons sampled repeatedly. The anaesthetic dose of MS 222 (140 mg l⁻¹) induced significant osmolality elevation in the sturgeon. After exposure to colder temperature (17 versus 25°C), cortisol and Cl⁻ concentrations significantly decreased. The cultured sturgeon did not seem susceptible to crowding and prolonged handling stress, since neither the serum cortisol and glucose levels nor the other blood parameters were affected by these stressors. Results are compared with the few available data on other chondrostean fish and with those on teleosts.     

Food consumption and growth of two piscivorous fishes, the mandarin fish and the Chinese snakehead

Rates of maximum food consumption and growth were determined for immature mandarin fish Siniperca chuatsi (47·2—540·2 g) and Chinese snakehead Channa argus (45·0—546·2 g) at 10, 15, 20, 25, 30 and 35) C. The relationship between maximum rate of food consumption ( C max), body weight ( W ) and temperature ( T ) was described by the multiple regression equations: In C max=−4·880+0·597 In W +0·284 T −0·0048 T ² for the mandarin fish, and In C max=−6·718+ 0·522 In W +0·440 T −0·0077 T ² for the Chinese snakehead. The optimum temperature for consumption was 29·6) C for the mandarin fish and 28·6) C for the Chinese snakehead. The relationship between growth rate ( G ), body weight and temperature was ln( G +0·25)=−0·439−0·500 ln W +0·270 T −0·0046 T ² for the mandarin fish, and ln( G +0·25)=−6·150+ (0·175−0·026 T ) ln W +0·571 T −0·0078 T ² for the Chinese snakehead. The weight exponent in the growth–weight relationship was −0·83 for the mandarin fish, but decreased with increasing temperature for the Chinese snakehead. The optimum temperature for growth was 29·3) C for the mandarin fish, but tended to decrease with increasing weight for the Chinese snakehead, being 30·3) C for a 45-g fish, and 26·1°C for a 550-g fish.     

Upper thermal limits for feeding and growth of 0+ Arctic charr

When Arctic charr Salvelinus alpinus from two diVerent stocks were fed live Neomysis integer , the upper thermal limits for feeding and growth were established in the range 21·5–21·8° C. These critical temperatures might have been underestimates, because fish tend to show increased sensitivity to handling at high experimental temperatures. In the second experiment, the proportion of feeding undisturbed charr from four stocks decreased initially as temperature was raised in steps from 18 to 22° C. At the lower temperatures, 18 and 20) C, almost all fish resumed feeding, but the recovery time was longer and more fish ceased to feed at 20) C than at 18° C. When the temperature was increased to 21° C, 50% of the fish ceased feeding permanently, and all fish ceased feeding within 2 days at 22° C. It is concluded that 0+ charr cease to feed and grow at c .21·5) C and that the critical temperatures for feeding and growth coincide.     

Cortisol and glucose responses after acute stress by net handling in the sparid red porgy previously subjected to crowding stress

In red porgy Pagrus pagrus subjected to 3 weeks of chronic stress by crowding, plasma cortisol remained significantly higher in crowded fish compared to controls. There was no significant effect of crowding on plasma glucose levels. When the crowded fish were subjected to an acute handling the plasma cortisol response was similar to that of the uncrowded fish. No significant differences were found between the groups. The changes in plasma glucose following acute handling were also similar in both crowded and uncrowded fish.     

Host-pathogen-environment interactions predict survival outcomes of adult sockeye salmon (Oncorhynchus nerka) released from fisheries

Incorporating host-pathogen(s)-environment axes into management and conservation planning is critical to preserving species in a warming climate. However, the role pathogens play in host stress resilience remains largely unexplored in wild animal populations. We experimentally characterized how independent and cumulative stressors (fisheries handling, high water temperature) and natural infections affected the health and longevity of released wild adult sockeye salmon (Oncorhynchus nerka) in British Columbia, Canada. Returning adults were collected before and after entering the Fraser River, yielding marine- and river-collected groups, respectively (N = 185). Fish were exposed to a mild (seine) or severe (gill net) fishery treatment at collection, and then held in flow-through freshwater tanks for up to four weeks at historical (14°C) or projected migration temperatures (18°C). Using weekly nonlethal gill biopsies and high-throughput qPCR, we quantified loads of up to 46 pathogens with host stress and immune gene expression. Marine-collected fish had less severe infections than river-collected fish, a short migration distance (100 km, 5–7 days) that produced profound infection differences. At 14°C, river-collected fish survived 1–2 weeks less than marine-collected fish. All fish held at 18°C died within 4 weeks unless they experienced minimal handling. Gene expression correlated with infections in river-collected fish, while marine-collected fish were more stressor-responsive. Cumulative stressors were detrimental regardless of infections or collection location, probably due to extreme physiological disturbance. Because river-derived infections correlated with single stressor responses, river entry probably decreases stressor resilience of adult salmon by altering both physiology and pathogen burdens, which redirect host responses toward disease resistance.     

Influence of spawning on swimming performance and muscle contractile properties in the short-horn sculpin

The total distance travelled during the first two kinematic stages of the escape response of short-horn sculpin was significantly greater in post spawning fish (0·41 L) than in gravid fish (0·23 L). The maximum velocity of the snout during the C-bend was significantly higher (5·6 L s⁻¹) in postspawning fish than in gravid fish (3·8 L s⁻¹). To investigate some of the mechanisms underlying changes in swimming performance, the contractile properties of fast muscle fibres were determined in fish of similar body length. The rate of tetanic force relaxation (time from last stimulus to 50% peak force) was 34% faster in gr avid than in postspawning fish. Maximum contraction velocity, determined by the slack-test method, was significantly higher in gravid than in postspawning fish (6·8 v . 5·9 muscle lengths s⁻¹). In contrast, both maximum isometric stress and power output (determined from the force–velocity relationship) were >50% higher in fibres from postspawning than from gravid fish, even though myofibrillar protein and water contents were similar (120 mg g⁻¹ wet mass and 86% of body mass, respectively). The results show that swimming performance and the contractile properties of fast muscle fibres vary with the reproductive cycle in short-horn sculpin acclimated to the same photoperiodic and temperature regime.     

Heat stress‐induced alterations of antioxidants in the freshwater fish Channa punctata Bloch

The effect of elevated temperature on the antioxidants in the freshwater fish Channa punctata was investigated. Fish stressed with an elevated temperature of 12° C, range ± 1° C over the ambient temperature for 3 h showed a significant ( P  < 0·05–0·01) reduction in the levels of antioxidants: reduced glutathione (GSH) and non‐protein thiols. Activity of glutathione reductase was also reduced in all the tissues (liver, kidney and gills) after 3 h of heat stress and 24 h recovery. Catalase (CAT) showed enhanced activity in liver in both the conditions while gills and kidney showed a decreased CAT activity. Glutathione S‐transferase (GST) activity in kidney and liver decreased significantly ( P  < 0·05–0·01) after 3 h of heat stress. At 24 h GST activity showed a tendency to normalize in all the tissues along with a concomitant increase in the GSH level in the kidney. Total and protein thiols in heat stressed fish when matched with controls, showed significant ( P  < 0·05) reduction in the kidney only with a transient increase in liver and gills. Heat shock also induced lipid peroxidation in 3 h heat‐treated and recovery groups when compared with controls. Elevated temperature therefore resulted in tissue specific and time‐dependent alterations of antioxidants in the fish. It also induced lipid peroxidation in various tissues.     

Stress caused by the 'mark-recapture' method to Coregonus albula (L)

The aim of this study was to establish if capture and marking caused stress to C. albula , and if a 'mark-recapture' method was suitable for the estimation of a population of C. albula . The blood lactate and glucose levels and the liver and muscle glycogen content were determined during the initial handling and subsequent recovery of the fish in the autumn and spring.
The blood lactate content did not increase to the critical level. Usually the values were distinctly less than 100 mg %, but the blood glucose content increased throughout the whole experiment (24 h) until it reached 250 mg %. The glycogen content in liver and muscle decreased. The liver glycogen of female C. albula was below 0·3 % in autumn, while the values for males were 3–5 %. In spring, the corresponding values were about 0·5 % in both sexes. During handling, the critical period was when the glycogen reserves in the liver became negligible, and female C. albula in autumn had the greatest risk of dying because of their low liver glycogen content.
Spring seemed to be a better season for marking than the autumn. A steady increase in blood glucose indicated there was also stress in spring and the marking time in both seasons should be less than two hours.     

Effects of handling and electrofishing on plasma glucose and whole blood lactate of Leuciscus cephalus

Chub Leuciscus cephalus exposed to simulated pulsed direct current electrofishing operations exhibited rapid elevations in plasma glucose and blood lactate levels. Plasma glucose levels were significantly higher 0·5 h after simulated electrofishing operations, and peaked 2 h after treatment. Glucose levels remained high for up to 4 h. No changes in plasma glucose were evident following handling. Simulated electrofishing operations and handling induced an immediate lactacidosis in chub. Initial responses to both treatments were similar except that blood lactate was significantly higher in fish exposed to simulated electrofishing operations than in handled fish 5 and 15 min after treatment. Blood lactate remained elevated in fish exposed to simulated electrofishing operations for 2 h, while blood lactate of handled fish returned to levels similar to those in the control fish within 0·5 h post‐treatment.     

Ontogenetic changes in temperature preference of Atlantic cod

Final thermal preferendum ( T ) experiments were conducted in a horizontal thermal gradient tank from the beginning of August 2001 to mid‐November 2001 using Atlantic cod Gadus morhua from 6·5 to 79·0 cm fork length ( L _F). The value of T varied significantly ( P  < 0·005) with L _F( T  = 7·23–0·054 L _F), with smaller (younger) fish choosing higher temperatures than larger (older) fish. The preferendum varied from 6·9° C for fish of 6·5 cm to 3·0° C for those of 79·0 cm. Experiments comparing fish positions in the gradient tank between thermal gradients of 0·5–11·0 and 4·5–14·5° C demonstrated that fish positions were determined by temperature selection instead of undesirable tank effects. This study is the first to demonstrate the effect of ontogeny on temperature preferences of a marine fish species.     

Survival and reproductive performance of the desert pupfish, Cyprinodon n. nevadensis (Eigenmann and Eigenmann), in acid waters

Desert pupfish, Cyprinodon n. nevadensis , were exposed to pH levels of 8·3 (control), 7·0, 6·5, 6·0, 5·5 and 5·0 to determine the effects of acidity on reproduction. Egg production was significantly reduced at every pH level tested below the control. Egg-laying virtually ceased at pH 5·0, while egg viability was reduced to less than 50% of the control value at pH 6·5, when eggs were tested at the same pH at which they were laid. The 96 h LC₅₀ for this species was pH 4·56, considerably below that for successful reproduction. Larvae were less tolerant to acid stress than were adults.
Acclimation of reproductive performance to increased acid levels did not occur. Reproductive performance did not fully recover to control levels when the fish were placed in more favourable conditions after prolonged exposure to low pH.
Reduction in the number and development of oocytes was observed in the ovaries of acid stressed fish resulting in the decreased reproductive potential.     

Thermally induced phenotypic plasticity of swimming performance in European sea bass Dicentrarchus labrax juveniles

The vulnerability of embryonic and larval stages of European sea bass Dicentrarchus labrax to environmental temperature and the longer-term consequences for the early juveniles was demonstrated. This phenotypic plasticity was highlighted by subjecting D. labrax at 15·2 ± 0·3 or 20·0 ± 0·4° C (mean ± s . d .) up to metamorphosis and then at the same temperature (18·5 ± 0·7° C). After 4–6 weeks at the same temperature, the measurement of critical swimming speed at four exercise temperatures (15, 20, 25 and 28° C) showed a significantly higher swimming capacity in the fish initially reared at 15° C than for fish initially reared at 20° C. This performance was correlated with significant differences in the phenotype of red muscle. Thermally induced phenotypic plasticity was clearly demonstrated as an important mechanism controlling swimming performance in early juveniles of D. labrax .     

Health management during handling and live transport of crustaceans: a review

Best practice approaches used in the live transport of commercial crustacean species groups are reviewed and the physiological responses to handling practices are described. Codes of practice aimed at providing technological guidelines in handling and transportation of live prawns, lobsters, crabs and freshwater crayfish are examined. While some handling and transport practices are common across species groups, for example purging and chilling, recommended practices vary with species group. The influence of stress responses on health and survival during live transport is discussed and research investigations on the effect of stressors, in particular air exposure, handling and physical disturbances and temperature fluctuations on physiological processes are reviewed for the six species groups, crabs, freshwater crayfish, clawed and spiny lobsters, freshwater prawns and marine prawns. Investigations on the assessment of immune responses to live transport stressors using haemograms, clotting times, phenoloxidase activity, phagocytic activity, bacteremia and antibacterial activity and haemolymph protein concentration are described. A combination of physiological parameters is desirable in the assessment of stress response or health status in crustacean species transported live to seafood markets.     

Thermal tolerance of a northern population of striped bass Morone saxatilis

Thermal tolerance of age 0+ year Shubenacadie River (Nova Scotia, Canada) striped bass Morone saxatilis juveniles (mean ± s . e . fork length, L _F, 19·2 ± 0·2 cm) acclimated in fresh water to six temperatures from 5 to 30° C was measured by both the incipient lethal technique (72 h assay), and the critical thermal method ( C _m). The lower incipient lethal temperature ranged from 2·4 to 11·3° C, and the upper incipient lethal temperature ( I _U) from 24·4 to 33·9° C. The area of thermal tolerance was 618° C². In a separate experiment, the I _U of large age 2+ year fish (34·4 ± 0·5 cm L _F) was 1·2 and 0·6° C lower ( P < 0·01) than smaller age 1+ year fish (21·8 ± 0·5 cm L _F) at acclimation temperatures of 16 and 23° C. Using the C _m, loss of equilibrium occurred at 27·4–37·7° C, loss of righting response at 28·1–38·4° C and onset of spasms at 28·5–38·8° C, depending on acclimation temperature. The linear regression slopes for these three responses were statistically similar (0·41; P > 0·05), but the intercepts differed (25·3, 26·0 and 26·5° C; P < 0·01). The thermal tolerance of this northern population appears to be broader than southern populations.     

Effects of malachite green on leucocyte abundance in rainbow trout, Salmo gairdneri (Richardson)

Blood counts from more than 1000 young-of-the-year rainbow trout, Salmo gairdneri (Richardson), were examined to determine if static exposure to malachite green at 1·35,13·5, or 21·0 mg/1 for 25–30 min or 42·0 or 72·0 mg/1 for 5 min caused chronic leucopaenia. The major changes in fish exposed for 25–30 min came during the first 24 h. After an initial lag of 3·4 h, total leucocyte-thrombocyte counts in both treated and control fish rapidly declined. Recovery was essentially complete 1·4 days after exposure, and no leucopaenia was noted after 14 or 28 days. Thrombocytosis developed during the first 24 h in fish exposed to the higher concentrations. Lymphopaenia and neutrophilia also developed, but abated after the 4th post-treatment day. Leucocyte numbers in control and exposed groups were virtually the same by the 14th day. The total leucocyte-thrombocyte counts in fish exposed for 5 min declined after 24 h, but counts were not as depressed as those in fish exposed for 30 min.
Because leucocyte changes similar to those in exposed fish were evident in the controls in both experiments, we believe that the leucocyte changes in rainbow trout exposed to malachite green were a result of a nonspecific vertebrate stress syndrome, rather than of specific leucocytotoxic effect of this chemical.     

Short‐term freshwater exposure benefits sea lice‐infected Atlantic salmon

Atlantic salmon Salmo salar were infected with sea lice Lepeophtheirus salmonis (0·08 ± 0·007 sea lice g⁻¹) over a period of 4 h. Both infected and non‐infected fish were swim tested in sea water (SW) and fresh water (FW). The ventral aorta of each fish was fitted with a Doppler cuff in order to measure cardiac output, stroke volume and heart rate during swim testing. Blood samples were taken at rest and after exercise. Critical swimming speed of infected fish in SW (2·14 ± 0·08 body lengths, bl s⁻¹) was significantly lower ( P  < 0·05) than infected fish switched to FW (2·81 ± 0·08 bl s⁻¹) and non‐infected fish in SW (2·42 ± 0·04 bl s⁻¹) and FW (2·61 ± 0·08 bl s⁻¹). Cardiac and blood results indicated infected fish exposed to FW did experience stress, but relief from osmotic and ionic distress probably reduces energy expenditure, allowing the increase in performance. As the performance of sea lice‐infected fish improved upon transfer to FW, it is likely that heavily infected salmonids do return to FW to restore compromised osmotic and ionic balance, and remove sea lice in the process.     

Compensatory growth of juvenile brown flounder Paralichthys olivaceus (Temminck & Schlegel) following thermal manipulation

The compensatory growth of juvenile brown flounder Paralichthys olivaceus (body mass c. 12 g) following different thermal exposure was investigated. Fish were exposed to one of the five temperatures: 8·5 ( T _8·5), 13·0 ( T _13·0), 17·5 ( T _17·5), 22·0 ( T _22·0) and 26·5° C ( T _26·5) for 10 days and fish grew best at 22·0° C. Then the water temperature in all treatments was equably adjusted to 22·0° C over 3 days. At the end of the following 30 days after temperature adjustment, there were no significant differences between body masses of fish in the different treatments (wet body mass at the end of the experiment ranged from 22·13 to 24·56 g). Results indicated that the juvenile P. olivaceus achieved complete compensatory growth. Analysis of the dynamics of the feeding rates and feed conversion efficiencies indicated that compensatory growth of the fish experienced low temperature ( T _8·5, T _13·5 and T _17·5) or high temperature ( T _26·5) exposure was mainly dependent on increasing feed intake (hyperphagia) and possibly by improvement in feed conversion efficiency. The moisture content was not affected by different temperature exposure significantly. The lipid and energy content of juvenile P. olivaceus in T _8·5, however, were significantly lower than other treatment. Results of the current study indicate that a short period of low or high temperature exposure may not affect annual growth, but may affect lipid and energy deposition.