Stress affects reproduction

A short account of how stress interferes with reproduction in farmed fish

Changes in water quality within anglers' keepnets during the confinement of fish

The influence of mesh size and loading density on conditions within keepnets during the confinement of fish was examined. The performance of a mixed-mesh net was also evaluated. Confinement of fish within nets of a standard diameter and length and of three different mesh sizes for 5 hours resulted in no deleterious changes in levels of dissolved oxygen, unionized ammonia, carbon dioxide, or pH at any of three sample points within each net. Transfer of fish to similar nets at a similar, and a higher, loading for 5 hours resulted in a depletion of oxygen, and accumulation of ammonia, in the high-load nets. No changes in carbon dioxide levels or pH were observed in nets containing either moderate or high loads. Confinement of fish in mixed-mesh nets for 5 hours resulted in a depletion of dissolved oxygen in the lower section of the net and an accumulation of unionized ammonia. There were no changes in carbon dioxide, or pH. These results are discussed with reference to the water quality requirements of freshwater fish. It is concluded that changes in water quality within anglers keepnets during the confinement of fish are not of sufficient magnitude to adversely affect the confined fish

Changes in blood cortisol, glucose and lactate in carp retained in anglers' keepnets

Capture of carp from holding tanks by dip-net, or from semi-natural conditions by rod and line, elicits a physiological stress response characterised by elevation of plasma cortisol levels. The transfer of carp to keepnets subsequent to capture does not increase or reduce the magnitude or duration of this response and in both cases plasma cortisol levels have returned to pre-stress levels within 24 hours of the initial disturbance. The post-capture plasma cortisol elevation is accompanied by disturbances in plasma glucose and lactate levels but these are less consistent in severity and duration than the cortisol response. These data suggest that the retention of fish in keepnets following capture, does not represent a source of stress additional to that imposed by capture and has no effect on the rate of recovery of the fish from the initial capture stress

Pheromone reception in salmonid fish: identification and characterization of putative steroid receptors in olfactory tissue of brown and rainbow trout

Specific binding sites for testosterone have been detected in three compartments of olfactory tissue from brown and rainbow trout. Binding of 3H-testosterone to the membrane fraction of olfactory tissue is of high affinity (Kd = 0.5 - 1.9 nM) and limited capacity (Nmax= 30 - 60 fmol mg-1 protein). Binding is reversible, and is eliminated by protease treatment. The binding site exhibits a high degree of ligand specificity, 11β-hydroxytestosterone, 11-ketotestosterone, 17α-hydroxyprogesterone, 17α, 20β-dihydroxy-4-pregnen-3-one, cortisol, and estradiol-17β all fail to displace testosterone at 20-fold excess. These attributes are characteristic of specific steroid receptor proteins. Binding of testosterone within the cytosol fraction is of moderate affinity (Kd = 9.0 - 23.0 nM) and high capacity (Nmax = 0.5 - 2.9 pmol mg-1 protein) and binding of testosterone is more readily displaced by a number of steroid competitors than is the case for the membrane site. The rate of association and dissociation of testosterone from the cytosolic binding site is markedly more rapid than the equivalent processes in the membrane fraction. Binding of testosterone to the nuclear extract is of high affinity (Kd ~ 3.0 nM) and limited capacity (Nmax ~ 50 fmol mg-1 protein). There are no marked differences between species or between sexes in the affinity or capacity of testosterone-binding sites in nuclear extract or membrane fraction. However, cytosolic testosterone-binding sites are three- to four-fold more abundant in rainbow trout than in brown trout, and female rainbow trout have more cytosolic binding sites than male rainbow trout, but a lower affinity for testosterone than male sites. Preliminary evidence supports the involvement of the membrane-associated testosterone-binding site in olfactory processes. Rainbow trout display an EOG response to testosterone at a concentration (10-9 M) which is consistent with the equilibrium dissociation constant (Kd) of the membrane-associated testosterone-binding site. The concentration of ligand at which half the binding sites are saturated (Kd) is in the range 0.5 - 2.0 . 10-9 M for membrane-associated testosterone binding. Binding of 3H-testosterone to the membrane-associated site shows a pH dependency which is comparable to the effects of pH on the EOG response to testosterone in intact fish. The data concerning the attributes of the membrane associated testosterone-binding site are consistent with the olfactory tissue of salmonids possessing the capability to respond to testosterone present in the aquatic environment. The intracellular testosterone-binding sites show characteristics common to testosterone receptors in other fish tissues which are known androgen target tissues. This suggests that the development and/or function of salmonid olfactory tissue may be open to influence by endogenous testosterone. This is the first report of androgen binding to olfactory tissue in fish, and the first report of a membrane-associated androgen binding site in fish

Indicators of reproductive performance in rainbow trout Oncorhynchus mykiss (Walbaum) selected for high and low responsiveness to stress

A number of indicators of reproductive performance were assessed in rainbow trout divergently selected on the basis of their plasma cortisol response to a standardised stressor. For both male and female rainbow trout, body weight was significantly related to stress responsiveness. High-responding (HR) females were significantly heavier than low-responding (LR) females overall and HR males were significantly heavier than LR males overall. There was no significant difference in the SGR of HR and LR female fish during the experimental period while in contrast the mean SGR of HR males was significantly greater than that of LR males. The divergent confinement-induced levels of blood cortisol in HR and LR groups were stable for more than one year after selection. There was no significant difference in the extent to which confinement stress reduced blood estradiol-17 levels in HR and LR females despite the large difference in relative blood cortisol levels. The onset and rate of ovulation was similar within the HR and LR groups. Differences in fecundity, relative fecundity and egg volume and weight were wholly attributable to the different mean body weights of the HR and LR fish. There was no difference between the sperm counts of HR and LR males. There was significantly higher mortality among eggs derived from HR parents overall between fertilization and hatch but maximum mean mortality did not exceed 12%. Mean time to eyeing in the HR groups was 224 degree days and in the LR groups was 244 degree days. Hatching commenced at 344 and 347 degree days in the HR and LR groups respectively and was complete within 412 and 416 degree days respectively. Overall, selection for stress responsiveness was associated with no significant benefits or costs in reproductive performance

A comparison of plasma glucose and plasma cortisol as selection markers for high and low stress-responsiveness in female rainbow trout

Two groups of female rainbow trout displaying consistently divergent plasma cortisol responses to a 3 h period of confinement were identified following five separate confinement episodes at monthly intervals. High-responding (HRC) and low-responding individuals (LRC) continued to display divergent cortisol responses to confinement up to 21 months after the start of the study (342 ± 34 ng ml-1 and 208 ± 21 ng ml-1 respectively at the final sample; p<0.01). HRC fish were significantly larger than LRC fish throughout the study period (533 ± 13 g and 422 ± 10 g respectively overall; p<0.001), although significant differences in specific growth rate (SGR) were apparent only at the start of the study. Individual fish were also selected from the same population on the basis of their plasma glucose levels following confinement (HRG: 189 ± 6; LRG 121 ± 3 mg dl-1; p<0.001). However, the two selection traits (cortisol and glucose) identified separate subsets of the experimental population. HRG fish were also significantly larger than LRG fish although this difference was not so pronounced as for the cortisol-selected fish. There was no reciprocal relationship between body weight and stress responsiveness; fish selected from the population on the basis of high or low body weight displayed no divergence in either cortisol or glucose responses to confinement. Differences in size and SGR may indicate that HR fish adapted more rapidly to changes in environmental and social factors at the start of the study than LR fish did

Characterization of putative steroid receptors in the membrane, cytosol and nuclear fractions from the olfactory tissue of brown and rainbow trout

Specific binding sites for testosterone have been detected in three compartments of olfactory tissue from brown and rainbow trout. Binding of 3H-testosterone to the membrane fraction of olfactory tissue is of high affinity (KD = 0.5 - 1.9 nM) and limited capacity (NMAX = 30 - 60 fmol mg-1 protein). Binding is reversible, and is eliminated by protease treatment. The membrane binding site exhibits a high degree of ligand specificity; 11β-hydroxytestosterone, 11-ketotestosterone, 17α-hydroxyprogesterone, 17α, 20β-dihydroxy-4-pregnen-3-one, cortisol, and estradiol-17β all fail to displace testosterone at 20-fold excess while testosterone itself competes successfully. These attributes are consistent with the presence of specific steroid receptor proteins. Binding of testosterone within the cytosol is of moderate affinity (KD = 9.0 - 23.0 nM) and high capacity (Nmax = 0.5 - 2.9 pmol mg-1 protein) and is more readily displaced by a number of steroid competitors than is the case for the membrane site. The rate of association and dissociation of testosterone from the cytosolic binding site is markedly more rapid than the equivalent processes in the membrane fraction. Binding of testosterone to the nuclear extract is of high affinity (KD ~ 3.0 nM) and limited capacity (Nmax ~ 50 fmol mg-1 protein). There are no substantial differences between species or between sexes in the affinity or capacity of testosterone-binding sites in nuclear extract or membrane fraction. However, cytosolic testosterone-binding sites are three- to four-fold more abundant in rainbow trout than in brown trout, and female rainbow trout have more cytosolic binding sites than male rainbow trout, but a lower affinity for testosterone than male sites. Preliminary evidence supports the involvement of the membrane-associated testosterone-binding site in olfactory processes. Rainbow trout display an EOG response to testosterone at a concentration (10-9 M) which is consistent with the equilibrium dissociation constant (KD) of the membrane-associated testosterone-binding site. Binding of 3H-testosterone to the membrane-associated site shows a pH dependancy which is comparable to the effects of pH on the EOG response to testosterone in intact fish. The attributes of the intracellular testosterone-binding sites are common to testosterone receptors in other fish tissues which are known androgen target tissues. This suggests that the development and/or function of salmonid olfactory tissue may be susceptible to influence by endogenous testosterone

The effects of environmental stress on the physiology of growth in rainbow trout, Salmo gairderi Richardson

There is little doubt that both mammalian and teleost growth hormones can accelerate growth and increase food conversion efficiency in all commonly-reared species of salmonid fish. In those vertebrates that have been closely studied (predominantly mammals), the pituitary hormone somatotropin (GH or growth hormone) is a prime determinant of somatic growth. The hormone stimulates protein biosynthesis and tissue growth, enhances lipid utilization and lipid release from the adipose tissues (a protein-sparing effect) and suppresses the peripheral utilization of glucose. The present study is a prerequisite for future work on growth hormone physiology in salmonids and should contribute to our understanding of the mechanisms of growth suppression in stressed fish. Plasma growth hormone (GH) levels were measured in rainbow trout using a radioimmunoassay developed against chinook salmon growth hormone

Stress responsiveness affects dominant-subordinate relationships in rainbow trout

The magnitude by which plasma cortisol levels increase following exposure to a stressor is a heritable trait in rainbow trout. The relative growth in co-culture of F1 lines selected for high-responsiveness (HR) and low-responsiveness (LR) to a confinement stressor suggested that behavioral characteristics related to food acquisition, aggression or competitive ability might differ between the two lines. This hypothesis was tested using the F2 generation of the selected lines. The F2 lines clearly exhibited the characteristics of the F1 parents, displaying significantly divergent plasma cortisol responses to a 1h confinement stressor and a high heritability for the trait. Behavioral differences between the lines were assessed by observing the outcome of staged fights for dominance in size-matched pairs of HR and LR fish. The identification of dominant and subordinate fish within each pair on the basis of their behavior was supported by the levels of blood cortisol in the fish attributed to each group (dominant << subordinate). Fish from the LR line were identified as dominant in significantly more trials than were HR individuals. The results suggest that behavioral attributes that affect the outcome of rank-order fights are closely linked to the magnitude of the plasma cortisol response to stress in rainbow trout. Whether the link is causal or circumstantial is not yet evident

A Saprolegnia parasitica challenge system for rainbow trout: assessment of Pyceze as an anti-fungal agent for both fish and ova

A reproducible Saprolegnia parasitica spore delivery system was developed and demonstrated to be effective in providing a sustained spore challenge for up to 10 days. Treatment of rainbow trout with slow-release intraperitoneal implants containing cortisol resulted in chronically elevated blood cortisol levels and rendered the fish susceptible to infection by S. parasitica when exposed to the spore challenge. Sham-implanted fish were not susceptible to infection. Bronopol (2-bromo-2-nitropropane-1,3-diol), formulated as Pyceze, was effective in protecting predisposed fish from infection by S. parasitica when administered as a daily bath/flush treatment at concentrations of 15 mg l-1 and greater. Pyceze was also demonstrated to protect fertilised rainbow trout ova from S. parasitica challenge when administered as a daily bath/flush treatment at concentrations of between 30 and 100 mg l-1. Pyceze appears to qualify as a safe and effective replacement for malachite green and formalin in the prevention of fungal infections in the aquaculture environment