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.     

The role of temperature in the prey capture probability of drift‐feeding juvenile brown trout (Salmo trutta)

Abstract – Cold water temperatures are widely supposed to reduce the food intake of stream salmonids. Although cold temperatures have been documented to reduce swimming ability, digestion and gastric evacuation rates, little is known about how temperature influences the ability of fish to capture prey. We examined the effects of water temperature on the prey capture probability of drift‐feeding juvenile brown trout (Salmo trutta) in a laboratory stream. Temperatures ranged between 5.7 °C and 14 °C. We found significant effects of water temperature on prey capture probability and capture manoeuvre time. The mean capture probability dropped from 96% at 14 °C to 53% at 5.7 °C. At 8 °C and higher temperatures, foraging performances did not differ much among treatments. We suggest that reduced swimming ability could be one of the most important mechanisms for the observed pattern of reduced prey capture probability at cold water temperatures, but prey detection limitations and predator avoidance may play a role. Our results will be of use for bioenergetics‐based drift‐foraging models, which to date have not incorporated a temperature‐dependent prey capture function.     

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.     

The effect of water pH on swimming performance in rainbow trout (Salmo gairdneri,Richardson)

A Brett-type respirometer was used to measure the effect of water pH on swimming performance of rainbow trout (Salmo gairdneri). Variations in water pH between 6 and 9 had no measurable effect on maximum aerobic swimming speed. At water pH 4, 5, and 10, however, the critical velocity was only 55, 67, and 61% respectively of that recorded for fish in water of pH 7. Exposure to acid conditions increased coughing and breathing frequency. Acid exposure resulted in a decrease whereas alkaline exposure resulted in an increase in both whole blood and red blood cell pH. Blood gas and acid-base characteristics showed little change during swimming at 2.0 BL/second, but exhaustive swimming resulted in a marked and immediate drop in blood pH in fish in acid, alkaline and neutral water. The blood acid-base status was restored to resting levels after exercise in neutral and alkaline water, but the acidosis was maintained following exercise in acid water. Fatigue occurred earlier and blood lactate levels increased to a higher level in fish swum to exhaustion in acid or alkaline water, compared with fish in neutral water.     

Gill pathology caused by infestations of adult and preadult Dissonus manteri Kabata (Copepoda: Dissonidae) on coral trout, Plectropomus leopardus (Lacépède), (Serranidae)

Adult and preadult Dissonus manteri attached to the gills of Plectropomus leopardus cause significant pathology in the form of large hyperplastic nodules on the afferent (leading) edges of gill filaments. Nodules result from the dual actions of parasite attachment and feeding. The host response is characterized by severe epithelial hyperplasia, supplemented by fibroplasia and inflammation. Parasites attach close to the gill arch near the base of filaments. They have little effect on gill vasculature as the maxillipeds penetrate the filament superficial to the efferent filament artery and do not interfere with the blood vessels of the secondary lamellae. Tissue proliferation is limited to the wide portion of filament 'edge' epithelium in the proximal third and also does not extend to the secondary lamellae. Nodules are most numerous towards the ends of hemibranchs and are generally absent from the central regions. Leading hemibranchs bear significantly more nodules than their trailing counterparts. Of the total number of nodules, 20.5% are located on the pseudobranchs. Distribution patterns are considered to be primarily the result of D. manteri avoiding strong water currents, although this cannot explain the difference between numbers on leading and trailing hemibranchs.     

Physiological responses associated with capture and crowding stress in matrinxãBrycon cephalus (Gunther, 1869)

The dynamics of plasma cortisol, blood glucose, plasma chloride and liver glycogen were investigated in matrinxã (Brycon cephalus) submitted to capture and various periods of crowding. A total of 400 fish (700±22 g weight) were distributed in four ponds divided into four 50‐m² squares (25 fish/square, 350 g L^?1), where they were acclimated for 30 days. On the sampling day, after 24 h without food, all fish from three squares were transferred to the fourth square. Six fish were sampled before the procedure (control group, zero time) and 1, 3, 6 and 24 h after the capture and crowding. Each sampling was performed in a different pond to prevent additional stress. Fish were anaesthetized and blood and liver collected for biochemical analysis. Water temperature, pH, dissolved oxygen, alkalinity, ammonia and nitrite levels were within acceptable levels for matrinxã rearing. Slight but not significant increases were verified in plasma cortisol and blood glucose levels, as were decreases in plasma chloride and liver glycogen levels. The results suggest that matrinxã is highly tolerant to the procedures of capture and short‐term crowding.     

The ability of clove oil and MS-222 to minimize handling stress in rainbow trout (Oncorhynchus mykiss Walbaum)

The effects of 60‐mg L^?1 clove oil and 60‐mg L^?1 tricaine methanesulphonate (MS‐222) on the blood chemistry of rainbow trout were compared after exposure to handling stress via caudal puncture blood sampling. Fish sampled by caudal puncture and subsequently exposed to anaesthetics showed a typical handling stress response over a 48‐h period. There were no significant differences between the responses of fish exposed to equal concentrations of clove oil and MS‐222, with the following exceptions: the blood glucose at full anaesthesia, and lactate at full recovery increased significantly in the clove oil‐exposed fish. In a subsequent experiment, the stress response observed in fish sampled by caudal puncture and exposed to clove oil and MS‐222 was compared with a non‐anaesthetized control group. The increases in plasma cortisol levels were significantly lower at recovery in fish treated with either anaesthetic compared with the control fish. Fish exposed to MS‐222 had significantly higher cortisol levels at 1 h. These findings show that few differences exist between the anaesthetic effects of clove oil and MS‐222 on the physiological response of fish to stress. However, clove oil is more effective at reducing the short‐term stress response induced by handling and blood sampling, and is recommended as an alternative fish anaesthetic.     

The physiological response to capture and handling stress in the Atlantic sharpnose shark, Rhizoprionodon terraenovae

Secondary effects of capture and handling stress in the Atlantic sharpnose shark, Rhizoprionodon terraenovae, were investigated in this study. Twenty-four sharks were serially bled and changes in several hematological parameters were monitored over a 1-h time period, following capture by hook-and-line. Blood samples were obtained from each shark at 0, 15, 30, 45 and 60 min. All 0-min (initial) blood samples were obtained within 3 min of capture. Blood glucose (9.2–13.1 mmol l^–1), lactate (1.5–28.9 mmol l^–1), and plasma osmolality (871–929 mOsm kg^–1) all increased after capture, whereas blood pH (6.86–6.78) declined. Hematocrit values (initial = 25.1%) remained unchanged throughout the 1-h stress period. Due to the short amount of time it took to obtain the initial sample and the lack of a significant relationship between the initial time and the initial parameter levels, all initial samples are considered the best approximation of the predisturbance resting levels. The use of repeated measures in this study enables us to describe the dynamics of the secondary stress response in the Atlantic sharpnose shark.     

Effects of size and fragmentation of marine reserves and fisher infringement on the catch and biomass of coral trout, Plectropomus leopardus, on the Great Barrier Reef, Australia

Abstract  A spatially structured simulation model of the population dynamics and line fishing exploitation of common coral trout, Plectropomus leopardus Lacepède, was used to evaluate the effects of infringement and different amounts and arrangements of marine reserves on the Reef Line Fishery of the Great Barrier Reef, Australia. With no marine reserves and under a constant future effort level equal to that for 1996, the size of the population was reduced and the biomass stabilised at about 40% of pre-exploitation levels. Marine reserves were ineffective at conserving biomass when limited infringement was allowed throughout an entire reserve. When infringement was absent altogether or limited to the edges of reserves, larger marine reserves lead to lower total catches and higher overall biomass. When infringement was limited to reserve edges, a single large closure was more effective at conserving biomass than more fragmented arrangements. Simulations suggested that marine reserves might lead to better conservation of a fishery-targeted species if infringement is negligible or limited to reserve margins. Even where infringement occurred only at the edges of reserves, a network of small reserves may be less effective at conserving a targeted species than a smaller number of larger reserves.     

Cellular responses to temperature stress in steelhead trout (Onchorynchus mykiss) parr with different rearing histories

This study compared the heat-shock response and metabolic energy status in hatchery-raised and two groups of wild-caught steelhead trout parr collected from the Navarro River watershed, California. Wild parr were from coastal and inland sites with different thermal regimes. Fish were exposed in the laboratory to 25 ± 0.2°C for 2-h and the heat-shock response was assessed in muscle tissue via induction of heat-shock proteins (hsps) 63, 72, 78, and 89. Metabolic measurements included muscle phosphocreatine (PCr), ATP, ADP, and AMP, and hepatic glycogen. Inland and coastal fish overlapped considerably with regard to their hsp responses and energetic endpoints, but hatchery fish were distinct in the biochemical patterns they exhibited. Hsp expression levels after temperature shock were significantly lower in hatchery than in wild fish. Hatchery fish also had significantly lower hepatic glycogen and higher muscle ADP, ATP, and PCr concentrations than wild fish. Coastal and inland steelhead did not differ significantly with regard to peak hsp72 and hsp89 levels or to concentrations of energy metabolites. However, fish from the warm-water, inland site expressed significantly less hsp63, maintained higher basal levels of hsp72, and induced hsp89 more slowly than fish from the cold-water, coastal site. Discriminant function analysis revealed that hatchery fish can be distinguished from wild Navarro River fish with 84.9% certainty using the following function: f(x) = − 43.6 + 0.14(Gly) + 4.1(PCr) + 186.4(AMP) + 80.8(ADP) − 0.14(hsp63) + 0.005(hsp72). This study demonstrates that within a single species, rearing conditions or genetic variation can influence an organism’s disposition and cellular response to thermal stress. Extrapolation of results from laboratory studies on hatchery fish to wild fish may therefore not be possible, and caution must be used when interpreting hsp data obtained for wild fish with different thermal histories.     

Cortisol,glucose and hematocrit changes during acute stress,cohort sampling,and the diel cycle in diploid and triploid brook trout (Salvelinus fontinalis Mitchill)

In this study, groups of diploid (control) and triploid brook trout were subjected to a 5 min acute handling/confinement stress. Blood samples were collected from equal numbers of diploid and triploid fish at regular predetermined intervals, beginning prior to confinement and continuing for up to 3h after confinement. These blood samples were used for the measurement of hematocrit and plasma cortisol and glucose concentrations. The effects of cohort sampling and the diel cycle on these variables were also analysed. Except for minor differences, both groups responded similarly to the acute stress, with short-term elevations in plasma cortisol and hematocrit levels, and a more sustained increase in plasma glucose levels. No significant differences were found between diploid and triploid fish in their reactions to cohort sampling. However, the act of removing an individual from a tank caused significant changes in plasma cortisol levels in cohorts remaining in that tank (p < 0.001). Significant diel effects were observed for both ploidy groups in plasma cortisol (p < 0.05) but not in plasma glucose or hematocrit. To whom correspondence should be addressed     

Use of garlic, Allium sativum, to control Aeromonas hydrophila infection in rainbow trout, Oncorhynchus mykiss (Walbaum)

Garlic, Allium sativum , which was fed at 0, 0.05, 0.1, 0.5 and 1.0 g per 100 g of feed for 14 days to rainbow trout, Oncorhynchus mykiss (Walbaum), led to control of experimental infection with Aeromonas hydrophila. At doses of 0.5 and 1.0 g garlic per 100 g of feed, there was a reduction in mortalities to 4% compared with the controls (88%). Moreover, there was a significant increase in growth, feed conversion and protein efficiency. There was stimulation of the number of erythrocytes and leucocytes, a significantly higher haematocrit, enhancement of phagocytic activity, respiratory burst, lysozyme, anti-protease and bactericidal activities following feeding with garlic.     

The biliary accumulation of corticosteroids in rainbow trout,Oncorhynchus mykiss,during acute and chronic stress

The accumulation of immunoreactive corticosteroids in the bile of rainbow trout during stress was monitored by radioimmunoassay and GUMS. Although plasma cortisol levels were elevated by confinement for 1 hour, biliary levels of free and conjugated steroids in the bile were unaffected. However, after 24 hours confinement, in addition to elevated plasma cortisol levels, free and conjugated steroids in the bile were also significantly higher than in control, unstressed fish. The time-course of change in plasma and biliary corticosteroid levels was determined in rainbow trout subject to 96 hours confinement stress. Free steroid levels in the bile of stressed fish were elevated within 2 hours of the onset of stress, while levels of conjugated steroids were significantly elevated within 4 hours of the onset of confinement. Analysis of bile from stressed fish, by GC/MS, established the major conjugated steroids present to be tetrahydrocortisone (230 g ml^–1 bile), tetrahydrocortisol (75 g ml^–1), cortisone (33.5 g ml^–1), cortisol (25 g ml^–1) and -cortolone (5 g ml^–1). The data are discussed with reference to the role of cortisone and conjugating enzymes in the clearance of cortisol, and further data are presented to suggest that the analysis of biliary steroid content may provide a suitable means of identifying stressed fish under conditions in which an additional sampling stress is unavoidable.     

Antioxidant processes are affected in juvenile rainbow trout (Oncorhynchus mykiss) exposed to ozone and oxygen-supersaturated water

Two groups of juvenile rainbow trout (Oncorhynchus mykiss) were exposed for 4 h to either hyperoxic (>40 mg O₂/l) or ozonised (5.2 μg O₃/l) water containing supersaturated oxygen. Gill, liver, blood cells and plasma were taken 1, 5, 12, 24 and 48 h following the exposure periods and antioxidant responses and oxidative damage studied in terms of, respectively, antioxidant enzyme activities/glutathione status and lipid peroxidation. Observed biochemical changes were significant at p<0.05. Ozonation elevated oxidised glutathione (GSSG) levels, increased lipid peroxidation and decreased reduced glutathione (GSH) levels in gills 1 h following exposure, which indicate oxidative stress. However, the longer-term effects (48 h) following ozone exposure resulted in increased GSH levels in both gills and liver and, measured as oxidative stress index (OSI), were indicative of enhanced potential of tissues to resist oxidative stress. Ozonation also resulted in elevated activity of superoxide dismutase (SOD) at 5–12 h following exposure in gills compared to 24–48 h in liver, indicating either differential regulation and time-courses of response, or an earlier impact of ozonolysis products on gills than liver. In contrast, catalase activity was elevated in both gills and liver at 24 h by the effects of hyperoxia alone. Hyperoxia also decreased GSSG levels in both gills and liver, but had no effect on lipid peroxidation. Increases were seen in the activities of selenium-dependent glutathione peroxidase as a result of ozonation (gills; 5 and 24 h) and hyperoxia (liver; 1 h), and in total GPX (Se-dependent and independent) as a result of ozonation (both tissues; 48 h), but no effects were seen on glutathione reductase (GR) in either tissues. Levels of GSH were increased in blood cells at various times following hyperoxia. Overall, the results show (i) differential antioxidant and pro-oxidant effects of ozonation compared to hyperoxia, (ii) gills and possibly blood as the first line of impact and defence, with later effects on liver, and (iii) that even after 24–48 h following ozone exposure, all antioxidant defences had not returned to pre-exposure values.     

The persistence of infectivity of Tetracapsulabryosalmonae-infected water for rainbow trout, Oncorhynchus mykiss (Walbaum)

Proliferative kidney disease (PKD) is caused by the infection of susceptible salmonid fish with spores of the myxozoan Tetracapsula bryosalmonae , a parasite harboured and released by several species of bryozoans. Under natural conditions, PKD is a water-borne infection of fish, whose outcome and spatio-temporal dissemination depend on the viability of spores present in the water. In order to evaluate the duration of parasite infectivity, juvenile rainbow trout, Oncorhynchus mykiss , were exposed for 20 h to T. bryosalmonae -infected water at various times post-water collection or after different filtration procedures. When infected water was held in a temperature range of 14.5–17 °C for up to 14 days, PKD was transmitted to the fish only between 0 and 12 h post-water collection and its infectivity vanished between 12 and 24 h. Similarly, the infectivity of water passed through 25 μm but not through 1 μm mesh filters, and was lost in the material eluted from the 1 μm filtration membrane although the parasite's DNA was amplified from this material. The parasitic infectivity in water appears to be fragile and this may offer opportunities to decrease the impact of PKD in trout farms by the implementation of management procedures aimed at reducing the number of the bryozoan-holding surfaces located in the river, immediately upstream from these farms.     

Response of resident brown trout, Salmo trutta L., and rainbow trout, Oncorhynchus mykiss (Walbaum), to the stocking of hatchery-reared brown trout

Two strains of hatchery-reared adult brown trout, Salmo trutta L., [208–334 mm total length (TL); n =  591] were individually marked and released into a limestone stream. The estimated survival after one month (86%; n =  508) was comparable to that for resident brown trout and rainbow trout, Oncorhynchus mykiss (Walbaum), (89%; n =  771), but declined to 14% ( n =  83) after 8 months compared with 52% ( n =  451) for resident trout. The movement of resident trout out of stocked stretches was higher (14%) than from control sites (5%), but the population size in both individual sites and the overall study area were unaffected. The growth of resident brown trout was unaffected by stocking, but rainbow trout showed lower growth rates in stocked versus unstocked stretches both one and 8 months after stocking ( P <  0.002).     

The garlic component,allicin, prevents disease caused by Aeromonas hydrophila in rainbow trout,Oncorhynchus mykiss (Walbaum)

Allicin was fed at 0 (= control), 0.5 and 1.0 mL of Allimed^® liquid 100 g^?1 of feed for 14 days to rainbow trout, Oncorhynchus mykiss (Walbaum), fingerlings before infection with Aeromonas hydrophila with a resultant reduction in mortalities from 80% in the controls to 8% [relative percentage survival (RPS) = 90%] and 0% (RPS = 100%) among the treated fish. Allicin was strongly antibacterial compared to the control, with a minimum inhibitory concentration (MIC) of >400 μL mL^?1 of Allimed^® liquid. Use of allicin led to a lower number of white blood cells (132.0 ± 0.4 × 10³) compared to 175.0 ± 0.1 × 10³ in the controls, but elicited increased phagocytic activity, i.e. a phagocytic value of 39.2% compared to 13.6% in the controls, and serum lysozyme activity, which showed significant (P > 0.05) differences compared to the control at 15 and 30 min after the first reading at 0 min of incubation.     

Digestibility, growth and excretion response of rainbow trout (Oncorhynchus mykiss Walbaum) to feeds of different ingredient particle sizes

The effects of feed ingredient particle size on apparent digestibility, growth and excretion responses of rainbow trout were investigated in pilot production systems. Particle size of the feed ingredients (ground using a hammer mill with 0.6 and 3.0 mm screen sizes) had no significant effect (P > 0.05, d.f. = 1/6) on the apparent digestibility of dry matter, phosphorus and crude protein in cold‐extruded diets. Feed ingredient particle size had an impact on the feed conversion ratio over an 85‐day feeding trial when key ingredients (78.65% of diet) were ground using a pulverizer and a hammer mill with 3.0 mm screen size and heat extruded. No significant differences (P > 0.05, d.f. = 1/12) were observed in the excretion ratios of TAN (total ammonia nitrogen), TKN (total Kjeldahl nitrogen), TP (total phosphorus), BOD₅ (5‐day biochemical oxygen demand) and TSS (total suspended solids) among three feed types, which included a wide ingredient particle size distribution.