Diel changes in plasma arginine vasotocin, isotocin, and melatonin in rainbow trout (Oncorhynchus mykiss)

The diel changes in plasma AVT, IT and Mel in rainbow trout (Oncorhynchus mykiss) were studied to assess potential relationships. Blood was sampled at 05:00, 11:00, 16:00, 22:30 and 05:00 in freshwater-adapted fish and at 22:30 in brackish water-adapted fish maintained under natural photoperiod. A few of the FW-acclimated fish were assigned to one of two experimental groups and adapted to DD or LL lighting regimes. Blood samples were taken at 11:00 and 22:30. Hormones were extracted from plasma by solid phase extraction and determined by high-performance liquid chromatography. Marked diel variations in AVT and Mel were detected in fish maintained under natural photoperiod. Plasma AVT (fmol ml^–1) increased during the light to reach the maximal level at the end of that phase (261.7±23.1). Thereafter, AVT concentration decreased and became minimal at 05:00 (68.9±11.5) 3 h before the sunrise. Plasma Mel (pmol ml^–1) increased between 16:00 and 22:30 when a peak value was reached (1204.0±55.5). Thereafter, Mel levels decreased and were minimal after the onset of the light phase (242.8±37.0). IT levels displayed no significant diel changes. Linear regression analysis indicated the negative correlation between plasma Mel and AVT for five collecting times of the daily 24 h cycle in freshwater fish and at 22:30 in brackish water fish. A similar correlation occurred at 11:00 in the DD group and at 22:30 in the LL group. To elucidate the character of the Mel-AVT relationships further studies are required.     

Pituitary and plasma AVT content in the flounder (Platichthys flesus)

Radioimmunoassay measurement of pituitary AVT content and plasma AVT concentration indicated comparable levels in fully adapted sea water (SW) and fresh water (FW) flounders. Circulating AVT represented less than 0.1% of the pituitary AVT reserve. The urophysis contained AVT but the total content was only 2 or 3 fold that of circulating AVT. In fish adapted to hypertonic media, there was a close correlation between plasma AVT concentration and plasma Na⁺ concentration or osmolality. The present study examined the effects of acute osmotic challenge, associated with FW to SW transfer, and the influence of extracellular fluid volume status on AVT secretion. Short-term transfer of fish from FW to SW (up to 3 days) did not evoke a clear change in plasma AVT levels, though pituitary content was reduced at 24 h. During the first 3 days after transfer to SW, only small increments in plasma tonicity were apparent. The sensitivity of AVT secretion to osmotic stimuli may only be expressed when plasma osmolality has exceeded a specific threshold, which was probably not reached in these transfer studies. Fish in hypotonic media showed no relationship between plasma osmolality/tonicity and plasma AVT concentration. Acute extracellular fluid volume expansion of SW adapted fish also abolished the normally observed relationship between plasma osmolality and AVT concentration in these hypertonic media fish. This trend indicates that volume status may modulate the sensitivity of AVT secretion to osmotic stimuli as occurs in tetrapods.     

Neuropeptides isotocin and arginine vasotocin in urophysis of three fish species

In this study, for the first time, both neuropeptides isotocin (IT) and arginine vasotocin (AVT) have been identified and measured in urophysis, the neurohaemal organ of the caudal neurosecretory system of teleost fish. So far, AVT, but not IT, was quantified by radioimmunoassay (RIA) in urophysis of several fish species. We have used high-performance liquid chromatographic assay with fluorescence detection (HPLC-FL) preceded by solid-phase extraction (SPE) and liquid chromatography-electrospray ionization triple-quadrupole tandem mass spectrometry (LC-ESI MS/MS) technique to determine both neuropeptides in urophysis of three fish species. The efficiency of peptide’s SPE extraction was 79–85 %. In HPLC-FL method, the limits of detection (LOD) and quantification (LOQ) were estimated as 1.0 and 3.4 pmol/mL for IT and 0.25 and 2.20 pmol/mL for AVT. In LC–MS/MS method, LOD and LOQ were estimated as 0.4 and 1.2 pmol/mL for IT and 0.06 and 0.2 pmol/mL for AVT. The chromatographic methods are good alternative for RIA, because enable to measure both nonapeptides simultaneously in one sample. In round goby (Neogobius melanostomus), three-spined stickleback (Gasterosteus aculeatus) and sea bream (Sparus aurata), urophysial IT concentrations ranged between 0.056 and 0.678 pmol/mg tissue and AVT concentrations ranged between 0.0008 (or even below detection threshold) and 0.084 pmol/mg tissue.     

Effect of some repetitive factors on turbot stress response

The stress response of the turbot, Scopthalmus maximus (L.), to repetitive factors including netting, air exposure, blood sampling and hand-stripping, were tested using two different tank sizes as well as two blood sampling techniques. Exposure of juvenile fish to air for 1-4 min had no immediate effect on plasma cortisol concentrations or haematocrit values. Similarly, the serial netting of immature fish from tanks did not significantly modify plasma cortisol concentrations, haematocrit or osmolarity values. Hand-stripping of mature males was more disturbing than air exposure. The cumulative effect on plasma cortisol levels and osmolarity of stress factors such as netting, air exposure, blood sampling and stripping applied simultaneously to mature males in a 16 m3 tank and repeated twice daily for several days was recorded. The level of cortisol increased from 5 ng ml-1 to 300 ng ml-1 after 10 days of treatment, while an osmoregulatory imbalance and fish death were observed. Moreover, adaptation of fish to smaller tanks seemed to improve the increased plasma cortisol levels and death rate. Reduction in the number of stress factors applied greatly decreased both the range of physiological responses and the death rate. In order to avoid a cumulative stress response, handling of fish should therefore be reduced to a minimum.     

Capture and handling stress affects the endocrine and ovulatory response to exogenous hormone treatment in snapper, Pagrus auratus (Bloch & Schneider)

Sexually mature female hatchery‐reared snapper, Pagrus auratus (Bloch & Schneider) were captured from sea cages by handline and injected at first capture (control) or 24 h after capture, transport and subsequent confinement (delayed injection) with either saline, luteinizing hormone releasing hormone analogue, human chorionic gonadotropin, or 17α‐hydroxyprogesterone. Blood was sampled before hormone treatment and again after 168 h, and fish were checked daily for ovulation. Plasma levels of 17β‐estradiol (E2), testosterone (T), 17α, 20β dihydroxy‐4‐pregnen‐3‐one (17, 20βP) and cortisol were determined by radioimmunoassay. The ovulatory response was assessed from the proportion of fish ovulating, ovulation volume, egg quality and fertility. A delay in injection resulted in significantly lower plasma E2 and T levels in response to hormone treatment, smaller ovulation volumes, and poorer egg quality than in control fish. The results are consistent with the generally inhibitory effects of stress on reproduction in fish, and confirm the requirement to treat fish with hormones designed to induce ovulation, as soon as possible after capture and disturbance.     

Anaesthetic efficacy and biochemical effects of 1,8‐cineole in rainbow trout (Oncorhynchus mykiss,Walbaum, 1792)

The aim of the present study was to investigate the anaesthetic efficacy and biochemical effects of 1,8‐cineole (cineole) in rainbow trout (Oncorhynchus mykiss). The fish were exposed to 200, 300, 400, 500, 600 and 800 μl/L cineole and time of induction of anaesthesia and recovery from anaesthesia were recorded. Thereafter, the fish haematological and biochemical responses to anaesthesia with different concentrations of cineole were studies. Moreover, the haematological and biochemical response of fish anaesthetized for 300 s with either cineole (283 μl/L) or eugenol (25 μl/L) were compared. Cineole at the concentrations of 200–800 μl/L induced stages 2, 3 and 4 anaesthesia within 109‐29.3, 226‐59 and 418‐117 s respectively. Increase in anaesthesia induction time led to higher stress responses and enzymes’ activity characterized by elevation in red blood cell (RBC), white blood cell (WBC), blood haematocrit and haemoglobin, and plasma cortisol, glucose and lactate levels, and aspartate aminotransferase (AST), alkaline phosphatase (ALP), lactate dehydrogenase and creatine phosphokinase (CPK) activities. However, cineole concentrations had no significant effects on plasma alanine aminotransferase (ALT) activity and ions levels. Comparison of cineole with eugenol showed that cineole showed less change in blood RBC and plasma AST, ALP, CPK, cortisol and glucose levels compared to eugenol. In conclusion, cineole is efficient to anaesthetize trout at concentrations of 200–800 μl/L. Increase in cineole concentration shortens anaesthesia induction time, stress response and probably tissue damage. The concentrations of 600–800 μl/L cineol is recommended for rapid sampling as it causes the least stress and enzymatic responses. The present results suggest that cineole causes slightly lower side effects in trout compared to eugenol.     

Stress responses and disease resistance in salmonid fish: Effects of chronic elevation of plasma cortisol

Basal levels of plasma cortisol in unstressed salmonid fish are normally in the range 0–5 ng ml⁻¹. An acute stress such as handling or 1 h confinement caused a temporary elevation of the plasma cortisol levels of both brown trout,Salmo trutta L., and rainbow trout,Salmo gairdneri Richardson, in the range 40–200 ng ml⁻¹ with a return to basal levels within 24–48 h. The extent of the cortisol elevation in response to an acute stress was dependent upon both the species and strain of trout. Chronic stresses, such as prolonged confinement or crowding, resulted in an elevation of plasma cortisol levels to approximately 10 ng ml⁻¹. Under these circumstances, blood cortisol levels remained elevated for periods of up to 4 weeks before acclimation finally occurred. It is shown, by means of intraperitoneal implantation of cortisol, that chronic elevation of plasma cortisol levels in the brown trout results in a dose-dependent increase in mortality due to common bacterial and fungal diseases. This effect is apparent at plasma cortisol levels as low as 10 ng ml⁻¹, levels below those often reported as being representative of ‘unstressed’ fish. These findings are discussed in relation to the known immunosuppressive effects of corticosteroids in teleost fish.     

Effects of iodized feed on stress modulation in steelhead trout, Oncorhynchus mykiss (Walbaum)

In the aquaculture industry, the physiological systems of fish can be chronically stressed by various biological, chemical and physical factors. Chronic stress leads to a decrease in the overall health and growth of the fish, making them more prone to diseases. Dietary iodine has been shown to reduce this stress response in chickens and increase disease resistance in dairy cattle, but the mechanisms by which iodine affects stress resistance and immunocompetency is not completely understood and has not been extensively studied in fish. This study investigated the effects of iodized feed as a nutritional supplement in relation to stress modulation in steelhead trout (Oncorhynchus mykiss). We investigated effects on primary, secondary and tertiary stress responses by measuring plasma levels of cortisol, glucose and thyroid hormones as well as haematocrit percentage and average growth rate in steelhead trout. Iodine‐supplemented fish, on average, had lower levels of plasma cortisol and glucose and lower packed cell volumes than fish fed with regular commercial feed (P<0.05). Iodine‐supplemented fish also showed higher levels of thyroid hormones and exhibited better growth over the period of the experiment (P<0.05). It was concluded that, used with other husbandry practices, use of iodine‐supplemented feed could lead to better host defence, growth and survival in fish raised in the aquaculture industry.     

Physiological effects of ice‐angling capture and handling on northern pike,Esox lucius

Understanding how released fish recover following capture is vital information for researchers examining the effects of angling on exploited populations. This information is virtually non‐existent for fish angled through the ice in winter, despite the popularity of ice‐angling in many northern areas. To address this gap, 60 northern pike, Esox lucius L., were angled through the ice from an impoundment in eastern Wisconsin, USA, and subjected to one of ten combinations of handling and recovery duration. Plasma samples were collected and analysed for cortisol, lactate and glucose. The results showed a delayed response in the elevation of plasma variables, and a significant interaction between air exposure and recovery time for plasma lactate. No fish suffered mortality during the period of holding. Collectively, these data suggest that northern pike are physiologically resilient to ice‐angling capture stress as long as air exposure times are kept at 4 min or less.     

Increased stocking density influences the acute physiological stress response of common carp Cyprinus carpio (L.)

The physiological response of common carp, Cyprinus carpio (L.) to increased stocking density and an additional acute net confinement stressor was investigated. Stocking densities were increased from 28.4 to 56.8 or 113.6 kg m^?3 by the use of crowding screens and fish were sampled from the crowded groups after 15, 39 and 87 hours of crowding (hc). A transient elevation of plasma cortisol was found in the higher density group after 15 hc before values returned to control levels. Increased stocking density also increased plasma levels of glucose, free fatty acids (FFA) and lactate during the experimental period. No effect was found on oxygen radical production in the blood, haemoglobin or haematocrit levels, but leucocrit values were lower after 39 hc in both groups. Net confinement resulted in a significant increase in plasma cortisol levels in all groups. However, after 15 hc, cortisol and FFA levels in both crowded plus confinement groups were higher than in the control and confined groups. Confinement resulted in increased oxygen radical production in the crowded plus confined groups at all times. Results indicate that although carp responded with a mild stress response to increased stocking density and adaptation occurred by 87 hc, the crowded fish were more sensitive to an additional acute stressor.     

Effects of acute thermal stress on acid–base regulation,haematology, ion‐osmoregulation and aerobic metabolism in Channel Catfish (Ictalurus punctatus)

The Channel Catfish Ictalurus punctatus is an important ecological, recreational and aquaculture species. In both natural and pond culture systems, Channel Catfish are periodically exposed to acute increase in temperature, especially in the summer, which may induce a stress response. With the effects of global climate change, the impact of rising temperatures on aquatic systems is expected to be exacerbated in the future. Hence, there is the need to understand the physiological mechanisms controlling the thermal stress response in fish. Acid–base, haematological, osmotic and metabolic regulations were investigated following acute temperature increase from 28°C to either 32°C or 36°C at a rate of 2°C/hr to assess the physiological response of Channel Catfish to temperature increase. Blood was sampled 1 hr after treatment temperatures were reached. When temperature increased from 28 to 32°C, blood bicarbonate () decreased while cortisol, partial pressure of carbon dioxide (pCO₂) and glucose increased. When temperature increased from 28 to 36°C, blood pH, , chloride, total proteins and mean corpuscular haemoglobin concentration decreased while cortisol, pCO₂, haematocrit, haemoglobin, glucose, lactate, mean corpuscular volume and mean corpuscular haemoglobin all increased. The changes observed are characteristic of acute stress responses in fish and suggest that acute temperature increases to both 32 and 36°C are physiologically stressful to Channel Catfish.     

Stress and metabolic indicators in a relatively high (European sea bass,Dicentrarchus labrax) and a low (meagre,Argyrosomus regius) cortisol responsive species,in different water temperatures

The aim of this study was to examine species‐specific differences in pre‐ and post‐stress concentrations of haematological, metabolic and hormonal parameters in two Mediterranean fish species, one with relatively high (European sea bass, Dicentrarchus labrax) and the other with low (meagre, Argyrosomus regius) basal and post‐stress blood cortisol concentrations, in relation to different water temperatures. Fish were reared in net‐pen sea cages and exposed to an identical acute stressor (crowding and chasing with a net for 5 min) in three different periods of the year. Results indicated that inter‐specific differences occurred in most of the examined parameters. In addition, within each species, differences between sampling periods existed in plasma cortisol, glucose, osmolarity, blood pH and muscle glycogen concentration. Glucose, lactate and osmotic pressure showed a constant pattern of change, with maxima at half an hour post stress in both species, while cortisol, and blood and muscle pH, were significantly altered only in E. sea bass. No alterations were observed in liver and muscle glycogen concentrations in E. sea bass, while a significant reduction was evident only in the coldest temperature in meagre. It is concluded that there are important species‐specific differences in the magnitude of hormonal and metabolic response to acute stress and that both basal and post‐stress blood cortisol concentrations are affected by the sampling period.     

The physiological response of the turbot to multiple net confinements

The effects of multiple net confinements on the physiological stress response of the turbot (Scophthalmus maximus L.) were investigated. To allow for repeated blood sampling from individuals, fish were cannulated in the afferent branchial artery and were exposed to multiple 9 min net confinement episodes separated by either 4 h or 24 h. In fish stressed twice 4 h apart cumulative effects in plasma cortisol, glucose and free fatty acid concentrations were evident after the second handling stress. Although plasma Na⁺ and Cl⁻ concentrations were not increased further by the second net confinement, the elevation in plasma concentrations were more sustained compared to turbot handled only once. In a second experiment where turbot were net confined five times, with a 24 h recovery period between each net confinement episode, there was no evidence of any physiological accommodation with repeated exposures. For most circulatory parameters, there was also no evidence of any cumulative effect apparent. Plasma glucose concentrations were, however, elevated to a significantly higher degree with repeated net confinements. Although turbot were tolerant to the handling procedures, with no mortalities recorded, episodes of multiple handling of this species should be separated by at least 24 h if cumulative physiological disturbances are to be avoided. The significance of cumulative increases in plasma glucose concentrations is discussed. Present address: Aquaculture Associates International, The Firs, Glasshouse Hill, Codnor, Derbyshire, DE5 9QT, UK     

The effects of dietary long‐chain essential fatty acids on growth and stress tolerance in pikeperch larvae (Sander lucioperca L.)

The nutritional requirements of pikeperch larvae have been sparsely examined. Dietary polyunsaturated fatty acids, arachidonic acid (ARA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) may affect growth and physiological stress response in marine fish larvae, but these mechanisms have not received as much attention in freshwater fish. Pikeperch larvae were reared on Artemia from day 3 until 21 days posthatch. Artemia were enriched with six formulated emulsions, with inclusion of either fish oil, pure olive oil (POO) or olive oil supplemented with various combinations of ARA, EPA and DHA. Larval tissue FA was significantly related to the content in the diets, but larval growth was similar for all treatments. When exposed to stress by confinement in small tanks with culture tank water or saline water (15 g L^?1.), mortality in larvae treated with POO was significantly higher than in the remaining treatments while tissue cortisol contents in these fish seemed lower. The findings of a lower stress response in larvae fed POO may be related to the lower tissue content in these larvae of essential fatty acids especially DHA but also EPA and ARA.     

Physiological stress responses in spotted wolffish (Anarhichas minor) subjected to acute disturbance and progressive hypoxia

The spotted wolffish (Anarhichas minor) is considered a promising species for coldwater aquaculture. It is a sedentary, bottom-dwelling fish which exhibits a calm and “non-stressed” behaviour in captivity. There are, however, no reports on the physiological responses to stressors in this species. In the present study we investigated primary (cortisol secretion) and secondary (glucose mobilization) responses to common aquaculture stressors like disturbance and hypoxia. Pre-stress plasma cortisol levels were within those generally considered representative for unstressed fish (~ 10 ng ml^− 1), whereas basal glucose levels were unusually low (0.3–0.4 mM). After exposure to a short, but severe disturbance challenge (emptying the tank of water for 10 min), the increase in plasma cortisol level was slow and relatively weak, reaching a peak level of 25 ng ml^− 1 4 to 8 h after disturbance. When the fish were exposed to a gradually decreasing oxygen level in the tank, a significantly elevated plasma cortisol level (35 ng ml^− 1) was seen in the fish that remained in the tank until oxygen saturation had decreased to 20% oxygen saturation after 2.5 h. However, a two-fold higher plasma cortisol level (~ 70 ng ml^− 1) was seen in all fish exposed to reduced oxygen levels (60, 40 and 20% oxygen saturation) after 3.5 h recovery in normoxic water. Plasma glucose levels showed only moderate increases (~ 70%) following disturbance and hypoxia challenges. An in vivo injection of ACTH caused a strong elevation of plasma cortisol (peak level ~ 170 ng ml^− 1), demonstrating a high capacity for interrenal steroidogenesis in the spotted wolffish. The slow and relatively weak cortisol response to stressors, and low plasma glucose levels, may relate to the sedentary lifestyle of the spotted wolffish. The stress-response is characterised by a passive (reactive) coping style, which is considered adaptive for farming of this species.     

Plasma growth hormone levels in fed and fasted rainbow trout (Oncorhynchus mykiss) are decreased following handling stress

Plasma growth hormone concentrations of rainbow trout,Oncorhynchus mykiss, fasted for six weeks, were significantly (p < 0.01) higher than in comparable fed animals; in the fasted fish, the levels fell progressively following acute stress (by displacing the fish within their home aquarium), with significant differences from pre-stressed fish evident between one and thirty-two hours after application of the stressor. Plasma growth hormone concentrations also fell significantly in the fed group, but differences were evident only between two and eight hours after stressor application.Plasma cortisol concentrations in pre- and post-stressed fed and fasted fish were similar. There was a bimodal response to stressor application in both groups, with significantly higher values relative to the pre-stressed sample evident one and eight hours after disturbance, but not after two, four or thirty-two hours. The changes in plasma cortisol levels between the initial (09:00h) sample and the sample taken eight hours later resembles the diet pattern seen in trout given access to self-demand feeders.Plasma glucose concentrations in pre-stressed fed animals were higher than in pre-stressed fasted fish. This relationship was also evident between one and four hours and thirty-two hours after stressor application. The post-stress rise in plasma glucose concentration was evident between one and four hours in the fed group, and between four and eight hours in fasted fish.The diel changes in plasma growth hormone and glucose concentrations could not be attributed to normal circadian patterns, and there was no apparent correlation between changes in plasma growth hormone and cortisol concentrations. There was a significant inverse correlation between plasma glucose and growth hormone concentrations when the total data set were analyzed, but these correlations were not apparent when the treatment groups were analyzed separately.     

Clove oil attenuates stress responses in lambari,Astyanax altiparanae

The effects of clove oil anaesthetic on mitigating the physiological responses to air exposure, a stressful and routine situation in fish farming, laboratory conditions and sport fishing (catch and release), were evaluated in lambari (A. altiparanae). Adult females (n = 80) were randomly sorted to receive one of four treatments: control, anaesthesia (clove oil 50 mg/L), stress (5 min air exposure) and pre‐anaesthesia associated to stress. Their cortisol, glucose, lactate and haematocrit levels, the hepatosomatic index (HSI), liver and muscle glycogen, lipid peroxidation and the enzymatic activity of lactate dehydrogenase (LDH), catalase (CAT) and glutathione reductase (GR), were recorded. Glucose levels increased (53.9%) after anaesthesia and/or stress. The stress situation increased plasma cortisol (146.6%), lactate (294.6%) and lipid peroxidation in white muscle (45%) and decreased glycogen in white muscle (40.1%). The haematocrit increased after stress or anaesthesia (7.9%) while the liver glycogen and HSI did not change. Anaesthesia or stress did not affect the LDH but reduced the activity of CAT (46.1%) and GR (30.3%). We concluded that the anaesthetic clove oil in the concentration 50 mg/L modulates the physiological responses to air exposure stress improving the welfare; air exposure and clove oil affect the antioxidant defences of lambari; the activity of CAT and GR and the concentration of MDA can be used as biomarkers of stress in A. altiparanae.     

Stimulation of growth performance without causing stress response in young red sea bream, Pagrus major (Temminck & Schlegel), by photoperiod manipulation

Three photoperiods (12L:12D, 16L:8D and 24L:0D) were used to investigate the growth performance and stress response in red sea bream, Pagrus major (body weight 200–400 g). Fish were fed a commercial diet to apparent satiation, two times a day for 8 weeks. Fish exposed to a 24L:0D photoperiod showed a significantly higher weight gain (%) than those exposed to other photoperiods (P<0.05). The best specific growth rate and feed conversion efficiency were achieved at 24L:0D and 16L:8D, without significant differences among them. Although fish exposed to 16L:8D showed a significantly higher plasma level of cortisol than those exposed to other photoperiods in the third week, there was no major variation in the cortisol level among the treatments either at the sixth week or at the end of this study. There were no significant differences either in the haematocrit level or the plasma levels of glucose, total cholesterol and total protein among the treatments during this study. The results revealed that the growth performance of red sea bream reared from 200 to 400 g can be stimulated significantly using a continuous (24L:0D) photoperiod without any measurable significant stress response in fish.     

Physiological responses to continuous swimming in wild salmon (Salmo salar L.) parr and smolt

Wild salmon (Salmo salar) parr and smolt were forced to swim against constant flow (50 cm.s^–1) for 8 hours. Physiological properties describing the hormonal status, the energy metabolism and the ionic and osmotic balance of fish were measured from the fish prior to and at the end of the swimming test.Plasma cortisol levels were elevated in response to enforced swimming; the response of the smolt was clearly greater than that of the parr. Plasma thyroxine concentration increased in the parr but stayed at the initial level in the smolts. The parr consumed much of their coelomic fat, but the glycogen stores stayed nearly constant. The smolts had very low fat stores, and the glycogen stores were depleted in the test. The ionic and osmotic balance of the parr was stable in the test, but in smolts, the plasma Cl^–1 and osmotic concentrations decreased and muscle moisture increased.The results indicate that downstream migration smolts have markedly lower physiological capacity for continuous swimming than parr.     

Cortisol and Behavioral Response to Handling (Acute) and Confinement (Chronic) Stressors in Juvenile Spotted Wolffish,Anarhichas minor

The purpose of this study was to determine the cortisol response of spotted wolffish (Anarhichas minor) after exposure to air immersion and netting (acute stress) under a range of increasing densities (chronic stressor). In addition, the presence of a cumulative negative impact from chronic stress was assessed by the application of an additional acute stressor following rearing at various densities, and proxies of behavior were evaluated (feeding and aggression data). The stress response to air immersion and netting led to increasing plasma cortisol values at 0.5, 13, and 37 h post-stress, with the highest value achieved after 13 h. At 168 h, cortisol concentrations returned to similar pre-stress value. Changes in cortisol concentrations were relatively low after acute stress (five to six fold increases) and recovery time long lasting (>37 h). Prolonged rearing at 20, 30, and 40 kg m^?2 showed a non-significant trend of increasing cortisol values with increasing density, and the cortisol response after the application of an additional acute stressor was significantly altered, i.e., higher cortisol levels were measured in unstressed (chronic stress only) compared to stressed fish (chronic stress + acute stress). Our results suggest that (1) spotted wolffish is a low responder that additionally displays a long-lasting cortisol elevation following an acute stressor; (2) fixed densities did not lead to significant differences of plasma cortisol concentration or aggression levels, although involved marked changes in daily feed intake and food conversion efficiency were observed; and (3) cortisol levels reached acute stress values after prolonged chronic stress. Although this species displays indications of being relatively resistant to handling disturbances during aquaculture practices, it is nevertheless responsive to chronic stress factors that could alter the physiological response to subsequent acute stressor.