Physiological Responses Of Rainbow Trout Research Articles

The Influence of Water Nitrate Concentration Combined with Elevated Temperature on Rainbow Trout Oncorhynchus mykiss in an Experimental Aquaponic Setup

Intensive recirculating systems are a fast-developing sector of aquaculture. While several warm-water fish have been reared in aquaponics, almost no data are available for cold-water species. The determination of nitrate toxicity thresholds in recirculating aquaculture is crucial. Different pollutants are typically more toxic at elevated temperatures. We investigated the performance of Oncorhynchus mykiss under two different nitrate levels and two temperatures. We applied a 2 × 2 factorial design, where fish (9.78 ± 0.51 g) were exposed to nitrate concentrations of 40 or 110 mg/L NO3− and to temperatures of 17 °C or 21 °C for 20 days. This study focused on understanding the physiological responses of rainbow trout to relatively low nitrate levels under heat stress in order to investigate the feasibility of integrating this species into commercial aquaponics. The growth, condition, and expression of genes involved in metabolism, heat shock, antioxidant, and immune response were assessed in the liver, together with the activities of enzymes related to glucose and fatty acid metabolism. High nitrate levels at 17 °C affected the condition but did not alter growth, leading to increased glycolytic potential and, occasionally, a greater reliance on lipid oxidation. Antioxidant defense was mainly induced due to high nitrates and the similar expression patterns of antioxidant genes observed under high nitrate at both 17 °C and 21 °C. Warm exposure decreased condition and growth, leading to greatly reduced glucokinase transcription, irrespective of the nitrate levels. Exposure to 21 °C and high nitrate led to equivalent growth and condition as well as to a milder inflammatory response combined with metabolic readjustments (enhancement of glycolytic and lipid oxidation pathways) compared to the low nitrates at 21 °C. Based on the results, rearing at a temperature close to 21 °C should be avoided for fingerling growth, while NO3− concentration until 110 mg/L may not have severe impacts on fingerling health and growth at 17 °C. In addition, rainbow trout fingerlings can tolerate a 20-day exposure at 21 °C and NO3− up to 110 mg/L. Additional factors should always be considered, such as specific water quality parameters, for a comprehensive approach to assessing the feasibility of rainbow trout aquaculture in aquaponics.

Repeated hypoxic episodes allow hematological and physiological habituation in rainbow trout.

Introduction: Under climate change, the increase in temperature in aquatic environments may induce oxygen depletion. In extreme cases, low oxygen may become a limiting factor for fish, thus generating stress. In addition, consecutive hypoxic episodes may complicate the recovery of individuals and hinder their ability to modulate physiological and biochemical responses to maintain homeostasis. Thus, the aim of this study was to determine the hematological and physiological responses of rainbow trout under a condition of repeated hypoxic and manipulation stresses at three different time points. Methods: Every hypoxic episode consisted of exposing the fish to low dissolved oxygen concentrations (2 mgO2/L for 1 h). Following the exposure, the fish were allowed to recover for 1 h, after which they were sampled to investigate hematological and physiological parameters. Results and discussion: The results showed a pattern of habituation reflected by values of hematocrit, hemoglobin, and mean corpuscular volume, indicating a certain ability of rainbow trout to resist this type of repeated hypoxic events, provided that the fish can have some recovery time between the exposures.

Effects of dietary vitamin E and C co-supplementation on growth performance, hemato-immunological indices, digestive enzymes activity, and intestinal histology of rainbow trout fed diet contained spoiled fish meal and oil

An eight-week feeding trial was conducted to elucidate the effects of diets containing oxidized fish oil (OFO) and/or spoiled fish meal (SFM) supplemented with various contents of vitamins E (VE: 100 and 200 mg/kg) and C (VC: 200 and 400 mg/kg) on some selected physiological parameters of juvenile rainbow trout, Oncorhynchus mykiss. The growth indices were affected by OFO and SFM-contained diets; the lowest values were observed in those fish raised on diet containing OFO and high levels of the vitamins. In all experimental groups, the hematological parameters (erythrocytes, leukocytes, hematocrit, and hemoglobin) were increased compared to the control group, and higher values were recorded in group fed OFO+VE (200 mg/kg) +VC (400 mg/kg)-supplemented diet (P < 0.05). A significant increase in serum lysozyme activity, immunoglobulin content, and complement pathway, was observed in fish fed OFO or SFM-contained feeds compared to the control group (P < 0.05). Digestive enzyme activities were mainly affected by dietary OFO contents, where the highest activities were detected in fish fed contained OFO and the vitamins (P < 0.05). According to the histological results, vitamin supplementation of OFO or SFM contained diets, especially at higher concentration, effectively reduced intestinal tissue damage (P < 0.05). In conclusion, VE and VC supplementation could mitigate the adverse effects of dietary OFO or SFM (e.g., decreased fish performance or health) by improving physiological responses of rainbow trout.

Effects of stress conditions on plasma parameters and gene expression in the skin mucus of farmed rainbow trout (Oncorhynchus mykiss).

The aim of this study was to investigate the physiological response of rainbow trout (Oncorhynchus mykiss) before slaughtering in the last phase of farming analyzing skin mucus and plasma. Two groups of rainbow trout were considered: Group UN ("unstressed"), represented by fish randomly captured from raceways, in the last phase of a standard fattening cycle; Group S ("stressed"), collected at the end of the pre-slaughtering tank, soon after slaughtering. The fish skin mucus was swabbed from head to tail using a sterile plastic spatula and the blood was collected through an endocardial puncture. qRT-PCR was used to study the gene expression in skin mucus. The mRNA expression levels of the IL-6 and IgD genes were higher in the S than in the Group UN. The plasma analysis showed an only a decrease in the glucose plasma levels in the Group S when compared to the Group UN. The present results indicated that the procedures adopted after slaughtering only affected changes in plasma glucose and skin mucus activity in rainbow trout suggesting that management protocol was compatible with non-stressful farming conditions.

Effect of dietary antioxidant supplements (selenium forms, alpha-tocopherol, and coenzyme Q10) on growth performance, immunity, and physiological responses in rainbow trout (Oncorhynchus mykiss) using orthogonal array design

Dietary supplements containing antioxidants play an important role in reducing the risk of peroxidative attack in aquatic animals. In this work, an orthogonal array design (L9: 34) was used to evaluate the effect of four dietary antioxidant supplements on the physiological responses of rainbow trout at three levels. The supplements included different (A) selenium (Se) forms (inorganic, organic, and nanoparticle), (B) Se content (0, 0.3, & 0.5 mg/kg feed), (C) vitamin E (VE) content (0, 100, & 150 mg/kg feed), and (D) coenzyme Q10 (CoQ10) content (0, 10, & 20 mg/kg feed). Fish with an average body weight of 8.35 ± 0.33 g were randomly allocated to different experimental groups. According to the results, the antioxidant supplements included in the diet had no significant effects on the growth performance of fish (P > 0.05). Immunological and antioxidant parameters were mainly improved by the Se form (Nano-Se) and dietary CoQ10 supplementation. In addition, Se form and VE were more effective in digestive enzyme activities and hematology indices in comparison to other dietary antioxidants. Additionally, diets supplemented with nano-Se along with CoQ10 and VE improved fish resistance/stamina against stress. In conclusion, a more effective combination of the four antioxidant supplements was A2/3B2/3C3D3 (i.e., 0.5 mg/kg organic/nano-Se, 150 mg/kg VE, and 20 mg/kg CoQ10), which could mainly improve the physiological responses of rainbow trout.

Physiological response of rainbow trout (Oncorhynchus mykiss) to graded levels of novel Chlorella sorokiniana meal as a single fishmeal alternative or combined with black soldier fly larval meal

Chlorella meal is a potential single-cell protein source for fishmeal replacement in aquafeed. However, it is still challenging to incorporate Chlorella meal in diets of carnivorous fish at high inclusion level due to its rigid cell wall and lower nutritional quality compared with fishmeal. This study was conducted to investigate novel cell wall-ruptured Chlorella sorokiniana GT-1 meal alone or combined with black soldier fly larval meal (BSFM) as substitute ingredient to dietary fishmeal for rainbow trout, Oncorhynchus mykiss. Nine isonitrogenous (43% crude protein) and isolipidic (17% crude lipid) diets were formulated: a control diet (fishmeal-based) and eight experimental diets replacing fishmeal by 25%, 50%, 75% and 100% with C. sorokiniana meal; 25%, 50%, 75% and 100% with C. sorokiniana meal + BSFM blended with 50:50 ratio (C. sorokiniana meal + BSFM). A total of 540 fish (initial body weight of 67.65 g) were randomly distributed to 27 tanks (20 individuals/tank) with the nine diets in triplicate. The fish were hand-fed experimental diets to apparent satiation twice daily for 8 weeks. The results showed improved growth performance and feed intake in rainbow trout fed a C. sorokiniana meal-based diet (C5). The C. sorokiniana meal-based diet also resulted in higher villi height and greater muscular layer thickness of the proximal intestine, improved intestinal barrier integrity, and healthier gut microbiota with increased Lactobacillus and decreased Acinetobacter compared with the controls. There was no improvement in growth performance of rainbow trout fed a diet based on a mixture of C. sorokiniana meal and BSFM (C9), and no significant difference was observed between C9 and the control group. However, decrease in intestinal inflammation and improvement of bacterial diversity were observed by blending C. sorokiniana meal and BSFM. In addition, shifts in amino acid metabolism and elevation of fatty acid metabolism were found in C5 and C9. Upregulation of mechanistic target of rapamycin (mTOR) pathway-related genes in liver and intestine was also observed in C5 and C9. The findings suggest that the novel C. sorokiniana meal as a single substitute ingredient or combined with BSFM has the potential to replace dietary fishmeal at high inclusion levels in rainbow trout.

Physiological response of rainbow trout (Oncorhynchus mykiss) to graded levels of Hermetia illucens or poultry by-product meals as single or combined substitute ingredients to dietary plant proteins

In the last decades, processed animal proteins, such as poultry by-product meal (PBM) and insect meals have received great attention as sustainable and nutritious aquafeed ingredients. The aim of the present study was to evaluate growth performances, liver and gut histology, macromolecular composition and inflammatory response in rainbow trout (Oncorhynchus mykiss) fed diets deprived of fish meal, where graded levels of vegetable protein-rich ingredients, were replaced by defatted Hermetia illucens pupae meal (HM) or PBM, singly or in combination. To this end eight grossly iso‐proteic (45% DM), isolipidic (26% DM) and isoenergetic (23.5 MJ/kg DM) were offered each to triplicated groups of juveniles' fish in a 91 days feeding trial. A diet rich in vegetable protein derivatives high in soybean meal (CV) was prepared to have a 10:90 and 20:80 fish to vegetable protein and lipid ratios respectively. By contrast, a fish-based diet (CF) was formulated with opposite fish to vegetable protein and lipid ratios. Six more diets, were obtained by replacing graded levels of protein (10, 30 and 60%) of diet CV, by protein from a defatted Hermetia illucens pupae meal and/or poultry by-product meal, singly or combined, while maintaining the same vegetable to fish lipid ratio as in the CV diet.Relative to diets CV and CF, a medium to high substitution (30 and 60%) of dietary vegetable protein-rich ingredients, with HM and/or PBM resulted in improved growth performance as well as in a minor incidence of distal intestine morphological alterations. The diet including both the test animal proteins led to nearly the best overall response in terms of growth and gut/liver health. Both HM and PBM when included at moderate or high levels in the diet, resulted in a downregulation of the expression of inflammatory-related genes relative to diet CV. This effect was greater with HM than that observed with PBM and goes beyond the parallel reduction of vegetable protein and SBM levels in the same diets, suggesting a beneficial role of insect meal that warrant further investigation.The results obtained so far, provide support to a reliable use of alternative/underexploited protein and lipid sources [(HM) or (PBM)] in developing a new generation of sustainable and healthy trout diets that meet the circular economy principles.

An acute increase in water temperature can decrease the swimming performance and energy utilization efficiency in rainbow trout (Oncorhynchus mykiss).

In order to evaluate the effects of acute temperature exposure on the swimming performance of rainbow trout (Oncorhynchus mykiss), the critical swimming speed (Ucrit) and oxygen consumption rates (MO2) were determined at different temperatures (13.2, 18.4, and 22.5°C). The Ucrit and MO2 of different body mass (109.44, 175.74, and 249.42g) fish were also obtained at 13.4°C. The Ucrit first increased as the temperature increased from 13.2 to 15.2°C, which was calculated to be the optimal temperature for the Ucrit, and then decreased with increasing temperature. The optimal swimming speed (Uopt) showed a similar trend to the Ucrit. At a given swimming speed, the MO2 and cost of transport (COT) were significantly higher at 22.5 than at 13.2°C, suggesting the energy utilization efficiency decreased with increasing temperature. The absolute values of Ucrit and Uopt increased as the body mass increased from 109.44 to 249.42g, whereas the relative values decreased. Although not statistically significant, the maximum metabolic rate (MMR) tended to increase with temperature but decrease with body mass. Results can be of value in understanding the behavioral and physiological response of rainbow trout to acute temperature change.

Using acoustic telemetry to assess behavioral responses to acute hypoxia and ammonia exposure in farmed rainbow trout of different competitive ability

As other vertebrates, fish differ on an individual basis in their responses to disturbance (i.e. stress) and in their capacity for adaptation to environmental change. This individual stress-coping style (SCS) might have an impact on the individual welfare in aquaculture facilities. However, most of the studies about the behavioral and physiological stress responses of fish with different SCS were performed under conditions very unlike usual rearing conditions. Therefore, we aimed in the current study at investigating the behavioral and physiological responses of rainbow trout (Oncorhynchus mykiss) of different SCS to common aquaculture stressors (exposure to hypoxia or high ammonia) under realistic conditions. We first screened the fish according to their competitive ability, as a proxy of SCS, separating the best and worst competitors (winners, W, and losers, L, respectively). Then, we evaluated the behavioral (using both telemetric and video-monitoring approaches) and physiological response of both groups upon exposure to increasing levels of hypoxia and ammonia. Overall, increasing hypoxia induced a slight but progressive decrease in fish activity, independently of the fish SCS. High concentrations of total ammonia induced an increase of certain behavioral displays, such as swimming bursts or approaches to the surface, the latter being overall more frequent in W than in L fish. At the specific stress levels tested (hypoxia: 50 % oxygen saturation; total ammonia: 2.91 mM), the physiological stress markers showed that the behavioral response to ammonia was probably driven by stress, while the behavioral response of the fish to hypoxia was just a behavioral adjustment to accommodate the decrease in oxygen availability. In conclusion, our data show that fish of different competitive ability showed similar activity patterns in routine conditions or when adapting to non-stressful conditions (50 % oxygen saturation) in an aquaculture-like setup, but differed in their behavioral response when exposed to stress (high water ammonia). In addition, our data support the use of acoustic accelerometer transmitters as a promising tool for real-time monitoring of fish welfare in commercial fish farms.

Growth performance, plasma parameters and liver antioxidant enzymes activities of Rainbow trout (Oncorhynchus mykiss) juvenile fed on Spirulina platensis extract

The purpose of this study was to evaluate the physiological responses of Rainbow trout fed on diets supplemented with methanolic extract of Spirulina platensis. 150 fish with a mean initial weight of 12.6±0.3 g were randomly divided into five groups. The juveniles were fed for 8 weeks with the diets containing 0, 250, 500, 1000 and 2500 mg of S. platensis extract per kg of diet. After eight weeks, 12 fish from each treatment were subjected to confinement stress. It has been shown that 250 mg of the algae extract per kg of diet resulted in the highest final weight and lowest feed conversion ratio in fish. There was no significant difference between treatments in fat, protein and moisture contents. The results showed that three hours after the air exposure and confinement stress, minimum (2.42 mg dl-1) and maximum (6.18±2.5 mg dl-1) levels of plasma cortisol were observed in 2500 and 500 mg kg-1 treatments, respectively. Moreover, the minimum (66±14 mg dl-1) and maximum (168±18 mg dl-1) level of glucose has been observed in 0 and 500 mg kg-1 treatments, respectively. After eight hours, Plasma cortisol and glucose have showed the highest level in 500 mg kg-1 treatment. There was no difference in lysozyme and catalase enzyme activities, but higher Spirulina extract in diet led to an increase in superoxide dismutase enzyme activity in the liver of Rainbow trout. This study suggests that addition of 250 mg kg-1 of Spirulina extract to Rainbow trout diet can improve growth performance and stress condition.

Moderate stocking density does not influence the behavioural and physiological responses of rainbow trout ( Oncorhynchus mykiss ) in organic aquaculture

Welfare in farmed fish got particular attention during the last decades from both governmental and public sides. In aquaculture context, welfare concerns are mainly related to handling procedures, water quality and stoking densities. In Europe, authorities had to clarify the threshold limits of stocking densities to maintain fish good welfare, including for organics aquaculture through the EC regulation 710/2009. However, effects of stocking density on fish welfare are complex and sometimes contradictory. Moreover, there is a lack of knowledge about the impact of density on fish welfare in organic aquaculture. Thus, the aim of the study is to asses welfare state of rainbow trout (Oncorhynchus mykiss) at two initial stocking densities (low density, LD: 12 kg/m³ and high density, HD: 17 kg/m³) fed using organic feed by combining the monitoring of growth performances, behaviour (swimming activity) and physiological indicators (i.e. cortisol, glucose, lactate, hematocrit, red blood cellule count and lysozyme). At the end of experiment, the stocking density reached 21 kg/m³ and 30 kg/m³ for the LD and HD respectively. Overall, growth performances, swimming activity and level of physiological indicators of stress and welfare were similar between HD and LD over the experiment duration. To conclude, we observed no alteration of fish welfare between the two stocking densities monitored. This study suggests that a final stocking density of 30 kg/m³ can be considered for organic aquaculture of rainbow trout respecting welfare.

The effects of strain and ploidy on the physiological responses of rainbow trout (Oncorhynchus mykiss) to pH 9.5 exposure.

We characterized the physiological effects of exposure to pH9.5 on one domesticated and four wild strains of diploid and triploid juvenile rainbow trout (Oncorhynchus mykiss) over two consecutive years. In the first year, 35-70% of the individuals from the wild strains showed a loss of equilibrium (LOE) at 12 h exposure to pH9.5, with all fish from wild strains experiencing a LOE by 48 h. In contrast, <20% of the domesticated strain showed LOE over the 48 h exposure to pH9.5. In our second experiment, similar strain effects were observed, but far fewer fish showed LOE (≤50% in all strains) over 72 h at pH9.5. In both experiments, there was no effect of ploidy on time to LOE. In the fish that did not show LOE, high pH exposure resulted in significant increases in plasma, brain and muscle ammonia, with no effect of strain or ploidy on the extent of ammonia accumulation. Glutamine accumulated in the brain during high pH exposure, with a stoichiometric decrease in glutamate, but no differences were noted among strains or ploidies. Lactate also accumulated in the plasma to a similar extent in all trout strains and ploidies. Plasma chloride decreased at 24h exposure in all trout strains and ploidies, but recovered by 72 h. No change was observed in plasma sodium. Overall, our data suggest that the domesticated strain of trout is more tolerant of pH9.5 than the wild strains, but these differences in tolerance cannot be explained by our sub-lethal assessment of ammonia balance or ion regulation.

Low social status impairs hypoxia tolerance in rainbow trout (Oncorhynchus mykiss)

In the present study, chronic behavioural stress resulting from low social status affected the physiological responses of rainbow trout (Oncorhynchus mykiss) to a subsequent acute stressor, exposure to hypoxia. Rainbow trout were confined in fork-length matched pairs for 48-72h, and social rank was assigned based on behaviour. Dominant and subordinate fish were then exposed individually to graded hypoxia (final water PO(2), PwO(2)=40Torr). Catecholamine mobilization profiles differed between dominant and subordinate fish. Whereas dominant fish exhibited generally low circulating catecholamine levels until a distinct threshold for release was reached (PwO(2)=51.5Torr corresponding to arterial PO(2), PaO(2)=24.1Torr), plasma catecholamine concentrations in subordinate fish were more variable and identification of a distinct threshold for release was problematic. Among fish that mobilized catecholamines (i.e. circulating catecholamines rose above the 95% confidence interval around the baseline value), however, the circulating levels achieved in subordinate fish were significantly higher (459.9±142.2nmolL(-1), mean±SEM, N=12) than those in dominant fish (130.9±37.9nmolL(-1), N=12). The differences in catecholamine mobilization occurred despite similar P(50) values in dominant (22.0±1.5Torr, N=6) and subordinate (22.1±2.2Torr, N=8) fish, and higher PaO(2) values in subordinate fish under severely hypoxic conditions (i.e. PwO(2)<60Torr). The higher PaO(2) values of subordinate fish likely reflected the greater ventilatory rates and amplitudes exhibited by these fish during severe hypoxia. At the most severe level of hypoxia, subordinate fish were unable to defend arterial blood O(2) content, which fell to approximately half (0.60±0.13mLO(2)g(-1) haemoglobin, N=9) that of dominant fish (1.08±0.09mLO(2)g(-1) haemoglobin, N=9). Collectively, these data indicate that chronic social stress impacts the ability of trout to respond to the additional, acute stress of hypoxia.

Physiological Response of Rainbow Trout to Sediment Released during Open-Cut Pipeline Water Crossing Construction

Abstract The physiological response of rainbow trout exposed to elevated suspended sediment concentrations downstream of two open-cut pipeline water crossings was investigated. Trout held in cages downstream of construction had increased respiration rates and shorter times till loss of equilibrium during sealed jar bioassays. Differences in blood hematocrit levels between experiments and transects is attributed to sediment concentration and particle size. Sediment exposure did not result in gill damage or fish mortality. The observed level of physiological effect was consistent with the predictions of the sediment-effects dose-response equation for salmonids.

Effects of altering freshwater chemistry on physiological responses of rainbow trout to silver exposure

AbstractThe influence of different water Cl− (50–600 μM), Ca2+ (50–1, 500 μM), Na+ (50–1, 500 μM), or dissolved organic carbon (DOC, 0.31–5 mg/L) levels on silver‐induced physiological and biochemical perturbations of rainbow trout were investigated. Fish were acclimated to soft water (50 μM; Cl−, Ca2+, and Na+), then exposed to 3.7 μg/L Ag (as AgNO3) for 6 h, which resulted in a reduction in Na+ influx from the water, an inhibition of gill sodium‐ and potassium‐activated adenosine triphosphatase (Na+/K+‐ATPase) activity, and an accumulation of silver on the gills. Increasing the water Cl− or DOC levels ameliorated the silver toxicity. However, increasing water Ca2+ or Na+ concentration did not reduce the silver‐induced physiological and biochemical perturbations. The free silver ion (Ag+) concentrations (calculated from MINEQL+, a geochemical speciation computer program) showed a negative correlation with the Na+ influx rates and gill Na+/K+‐ATPase activity. However, gill silver levels did not correlate to Ag+ concentrations and no correlation was found between gill silver levels and either Na+ influx rates or gill Na+/K+‐ATPase activity. These results support the notion that the [Ag+] concentration is of major importance when assessing silver toxicity in fish, and that this should be taken into account in regulatory strategies for silver in the natural environment.

Recovery from High pH Exposure in the Rainbow Trout: White Muscle Ammonia Storage, Ammonia Washout, and the Restoration of Blood Chemistry

The physiological responses of rainbow trout were followed during 48 h of high pH (pH 9.5) exposure and a further 48 h of recovery at pH 8.0. High pH exposure temporarily inhibited ammonia excretion (JAmm) and led to a sixfold increase in plasma total ammonia (TAmm) concentration. By 24 h at pH 9.5, JAmm had returned to preexposure (control) rates but plasma TAmm concentration remained elevated. The fish also developed a transient metabolic alkalosis (increased metabolic base) and a sustained respiratory alkalosis (decreased plasma CO₂ tension [PaCO₂]). Plasma Na⁺ and Cl⁻ concentrations were reduced by 5% after 48 h at pH 9.5. An "ammonia washout, " of about 5,000 μmol ․ kg⁻¹ occurred during the first 12 h of the recovery period, with fivefold elevations in JAmm during the first few hours. This ammonia washout was accompanied by a return of plasma TAmm concentration to preexposure levels after 3 h. The amount of excess TAmm excreted by the fish during the washout was about 50-fold greater than extracellular fluid (ECF) TAmm stores. Subsequent experiments indicated the white muscle (WM) intracellular fluid (ICF) compartment had stored at least 40% of the excess TAmm. The TAmm concentrations in the WM ICF were 2.5-fold greater in fish held at pH 9.5 for 48 h than in those held at pH 8.0. Estimates of the ECF and WM ICF pH, NH₃ partial pressures (PNH₃), and NH⁺₄ concentrations indicated the development of favorable ECF:ICF electrochemical gradients for NH⁺₄ uptake, and PNH₃ gradients for NH₃ uptake, by the WM during the initial period of high pH exposure. There was a partial return toward steady state by 48 h. Thus, the WM serves as an "ammonia reservoir" for rainbow trout when plasma TAmm increases owing to temporary reductions in branchial ammonia excretion. The rapid return of other physiological indices such as arterial pH (pHa), PaCO₂, and plasma Na⁺ and Cl⁻ to control levels during recovery (in 3-8 h), as well as constant arterial O₂, tension (Pao₂), suggested that high-pH-induced physiological disturbances are reversible and that there is no high-pH-induced gill histopathology during such short-term exposures.

Use of respiratory-cardiovascular responses of rainbow trout (Salmo gairdneri) in identifying acute toxicity syndromes in fish: Part 3. Polar narcotics

The physiological responses of rainbow trout to acutely lethal aqueous concentrations of the suspected polar narcotics phenol, 2,4-dimethylphenol, aniline, 2-chloroaniline and 4-chloroaniline were examined. Visible signs of intoxication included tremors that progressed to whole-organism clonic seizures, followed by general depression and respiratory-cardiovascular collapse. Tremors and seizures were usually initiated with coughs. The most striking changes in the respiratory-cardiovascular parameters for all five toxicants included elevated cough frequency (coincident with seizures), ventilation frequency and hematocrit, and depressed gill oxygen uptake efficiency, arterial pH, total arterial oxygen and total arterial carbon dioxide. The physiological responses noted were attributed to the initial muscular activity associated with seizures followed by respiratory-cardiovascular collapse. Using phenol as a model compound, these effects were found to be reversible when intoxicated fish were exposed to chemical-free water. Principal components analyses of the physiological responses demonstrated that the 11 monitored variables were highly correlated. Interpretation of the principal components showed that responses within each toxicant-exposure group were distinct from those of the control group. The response data sets for the suspected polar narcotics (N = 20 fish) were combined with four fish acute toxicity syndromes (FATS) (N = 32 fish) previously described (respiratory uncoupler syndrome, respiratory irritant syndrome, acetylcholinesterase inhibitor syndrome and narcosis syndrome), and assessed using discriminant function analysis. This analysis showed that all 52 trout could be correctly classified into their respective FATS. As a result, two separate narcosis FATS, narcosis type I (previous work) and narcosis type II (this study), were defined. Identification of a narcosis type II syndrome supports the concept of developing quantitative structure-activity relationship models for polar narcotics in fish.

The stress‐response of rainbow trout to experimental infection with the blood parasite Cryptobia salmositica Katz, 1951

Physiological responses of rainbow trout, Salmo gairdneri Richardson, to experimental infection with the blood haemoflagellate Cryptobia salmositica were monitored for 7 weeks to determine whether the parasitaemia elicited a classical stress‐response as evidenced by elevated plasma cortisol and glucose levels. There was a progressive anaemia, hepatomegaly, splenomegaly, and depressed plasma T3, T4, protein and glucose concentration, and lowered liver glycogen content in the parasitized fish throughout the study, which clearly indicated that the animals were under physiological duress. Moreover, these hormonal and metabolic indicators showed no indication of recovery with the decline in blood parasite numbers. However, there were no differences in plasma cortisol or glucose levels between infected and control fish throughout the study, suggesting that the parasitaemia did not activate the pituitary‐interrenal axis.

Iron catalyzed oxidation of trout diets and its effect on the growth and physiological response of rainbow trout

Two experiments were conducted to determine 1) the effect of iron supplementation and the quality of fish oils on dietary lipid peroxidation and 2) the concurrent effects of diet rancidity and iron overload on the growth and physiological response of rainbow trout. Semi-purified diets supplemented with graded levels of iron (0-6250 mg/kg diet as ferrous sulphate) were fed to trout for 12-36 weeks. The malonaldehyde (MA) concentration of the test diets increased as the iron levels in the diets increased indicating that iron catalyzed lipid oxidation was occurring. However, when ethoxyquin was added to the oils, the increase in dietary MA level was significantly reduced. Fish oils with an initial high peroxide value were more susceptible to iron-catalyzed lipid oxidation. The concurrent effects of diet rancidity and iron overload (greater than 86 mg/kg) led to the development of unique histopathological signs, poor growth and high mortalities in the trout. In contrast, when diet rancidity was low (less than 10 µg MA/g diet), the toxic level of dietary iron was greater than 1380 mg/kg diet. The concentration of iron in trout tissues, and the hematocrit and hemoglobin concentrations increased as dietary iron levels increased and were not affected by the degree of diet rancidity.

Physiological response of rainbow trout ( Salmo gairdneri) to acute fenvalerate intoxication

The physiological responses of rainbow trout ( Salmo gairdneri) to fenvalerate intoxication during aqueous exposure were examined to provide information about the pyrethroid mode of action in fish. Trout ( n = 4) were exposed to 412 ± 50 μg/liter fenvalerate and died in 10.9 ± 1.5 hr. Brain, liver, and carcass fenvalerate concentrations associated with mortality were 0.16 ± 0.05, 3.62 ± 0.57, and 0.25 ± 0.05 mg/kg, respectively. Visible signs of intoxication included elevated cough rate, tremors, and seizures. Histopathological examination of gill tissue showed damage consistent with irritation. An evaluation of respiratory-cardiovascular and blood chemistry responses indicated an elevated rate of metabolism associated with increasingly severe seizures. A cessation of ventilatory and cardiac activity, occurring with the seizures, was also observed. Finally, urine osmolality, Na + and K + concentrations, and Na + and K + excretion rates were elevated with intoxicated trout. The physiological responses of rainbow trout to fenvalerate intoxication suggest that besides effects on the nervous system, effects on respiratory surfaces and renal ion regulation may be associated with the mechanism of pyrethroid action in fish.