The melanin-concentrating hormone (MCH) precursor encodes MCH and a second peptide named neuropep... more The melanin-concentrating hormone (MCH) precursor encodes MCH and a second peptide named neuropeptide EI (NEI) in mammals, neuropeptide EV (NEV) in salmonids and MCH gene-related peptide (Mgrp) in other fish. The primary structure of the putative Mgrp of the cichlid fish tilapia (Oreochromis mossambicus) appears to be very different from mammalian NEI and salmonid NEV. To investigate the processing and release of tilapia Mgrp (tMgrp), in the present study an antiserum was raised against synthetic tMgrp. By immunocytochemistry, tMgrp immunoreactivity was colocated with MCH immunoreactivity in the tilapia hypothalamus and pituitary. In addition, a tMgrp enzyme-linked immunosorbent assay in combination with reversed phase HPLC was used to demonstrate the presence of processed tMgrp in tilapia hypothalamus and pituitary. The release of tMgrp from neuro-intermediate lobes (NILs) of tilapia pituitaries was demonstrated after in vivo incubation of chopped NILs. Depolarizing concentrations of potassium significantly stimulated tMgrp release. Six weeks of adaptation of tilapia to white or black backgrounds had no effect on in vitro tMgrp release or on the tMgrp content of NIL and hypothalamus. Tilapia Mgrp, unlike MCH, had no effect on tilapia scale melanophores, nor did it modulate the melanin-concentrating effect of MCH. We conclude that tMgrp is processed from the MCH preprohormone, that it is released in vitro, and that the peptide has no direct role in the melanin concentration of fish scale melanophores. Therefore a neuroendocrine or neuromodulatory function is proposed for tMgrp.
In this study it was shown- that dark coloured post-larvae of Senegalese sole Solea senegcilensis... more In this study it was shown- that dark coloured post-larvae of Senegalese sole Solea senegcilensis, at two different ages. had elevated cortisol concentrations compared with lighter coloured individuals. As melanophore-stimulating hormone levels were not elevated in dark coloured fish. it is possible that this hormone may not be the main melanotropic hormone involved in stress-related skin darkening.
The responses of rainbow trout and brown trout to the same stressor were compared by measuring pr... more The responses of rainbow trout and brown trout to the same stressor were compared by measuring primary and secondary stress responses during and after a 5.5-h net confinement. Basal levels of adrenocorticotropic hormone (ACTH), alpha-melanocyte-stimulating hormone (alpha-MSH), and glucose were higher in brown trout than in rainbow trout. While confinement induced transient increases in plasma ACTH and cortisol levels in both species, the magnitude of these responses, but not the time course, was greater in brown trout. Brown trout, but not rainbow trout, showed a reduction in plasma alpha-MSH levels after 5.5 h confinement before returning to control values, and the glucose levels in the brown trout were elevated throughout the confinement and recovery periods. Confinement also resulted in increased hematocrit values and reduced plasma sodium and chloride levels in both species. Rainbow trout appeared to recover faster from the confinement, as glucose and hematocrit values in the brown trout remained elevated and ionoregulatory disturbances persisted even after 46 h. During recovery effects on the immune system were more pronounced in brown trout than in rainbow trout. Circulating white blood cell numbers were reduced in both species following 23 h recovery, but remained low in the brown trout. Elevated alternative complement activity and oxygen radical production were found after 23 h recovery, and reduced lysozyme activity was found after 46 h, in brown trout only. Results indicate that differences in the stress response of these closely related species, as illustrated by the intensity of the cortisol response, originate at the level of the pituitary and are also manifested through secondary stress responses.
The stress response of the euryhaline tilapia Oreochromis mossambicus adapted to either fresh Ž. ... more The stress response of the euryhaline tilapia Oreochromis mossambicus adapted to either fresh Ž. Ž Ž .. water FW or salt water Instant Oceane, 950 mosm; SW was investigated to establish the influences of ambient salinity in this species. The fish were considered to be adapted to the salinities as pre-confinement plasma cortisol and glucose levels were typical for unstressed fish. Two hour net confinement increased plasma cortisol and glucose to a similar extent in both FW and SW. Individual plasma sodium and chloride levels were unaffected by confinement, although plasma Na:Cl ratio increased in FW. Confinement increased intestinal Na q rK q-ATPase activity in FW, but not in SW. In contrast, kidney Na q rK q-ATPase activity increased in SW only. Branchial Na q rK q-ATPase activity decreased with confinement in SW, but not in FW. In SW, confinement reduced the numbers of opercular chloride cells. Increased aging of the branchial Ž. chloride cell CC population of SW-confined fish was indicated by large numbers of apoptotic CCs in the interlamellar areas. This effect on the CC population was absent in FW-confined fish. Overall, confinement in SW-adapted fish had a more profound impact than confinement in FW-adapted fish. This is likely to have associated energetic consequences in terms of branchial oxygen and ATP consumption. Therefore, results suggest the possibility of different effects of confinement on subsequent growth in FW and SW.
Hormones and the behavioural ecology of stress Respiratory and cardiovascular systems during stre... more Hormones and the behavioural ecology of stress Respiratory and cardiovascular systems during stress Impact of stress on animal intermediate metabolism The impact of stress on animal reproductive activities Histological and histopathological effects of stress Stress-induced immune-endocrine interaction Impact of stress on animal toxicology References Index .
Although hypothalamic corticotropin-releasing hormone (CRH) is involved in the stress response in... more Although hypothalamic corticotropin-releasing hormone (CRH) is involved in the stress response in all vertebrate groups, only a limited number of studies on this neuroendocrine peptide deals with non-mammalian neuroendocrine systems. We determined the cDNA sequence of the CRH precursor of the teleost Oreochromis mossambicus (tilapia) and studied the biological potency of the CRH peptide in a homologous teleost bioassay. Polymerase chain reaction (PCR) with degenerate and specific primers yielded fragments of tilapia CRH cDNA. Full-length CRH cDNA (988 nucleotides) was obtained by screening a tilapia hypothalamus cDNA library with the tilapia CRH PCR products. The precursor sequence (167 amino acids) contains a signal peptide, the CRH peptide and a motif conserved among all vertebrate CRH precursors. Tilapia CRH (41 aa) displays between 63% and 80% amino acid sequence identity to CRH from other vertebrates, whereas the degree of identity to members of the urotensin I/urocortin lineage is considerably lower. In a phylogenetic tree, based on alignment of all full CRH peptide precursors presently known, the three teleost CRH precursors (tilapia; sockeye salmon, Oncorhynchus nerka; white sucker, Catostomus commersoni) form a monophyletic group distinct from amphibian and mammalian precursors. Despite the differences between the primary structures of tilapia and rat CRH, maximally effective concentrations of tilapia and rat CRH were equally potent in stimulating adrenocorticotropic hormone (ACTH) and alpha-MSH release by tilapia pituitaries in vitro. The tilapia and salmon CRH sequences show that more variation exists between orthologous vertebrate CRH structures, and teleost CRHs in particular than previously recognized. Whether the structural differences reflect different mechanisms of action of this peptide in the stress response remains to be investigated.
Abstract Common carp (at 20 °C) and rainbow trout (at 15 °C) were fitted with an indwelling cannu... more Abstract Common carp (at 20 °C) and rainbow trout (at 15 °C) were fitted with an indwelling cannula in the dorsal aorta. The fish were exposed to a controlled decline of water pO2 followed by 90 min deep hypoxia at 0.3 kPa (carp) or 4.8 kPa (trout). Thereafter, nor-moxic recovery was ...
SYNOPSIS. In rainbow trout the magnitude of the cortisol response to stress shows both consistenc... more SYNOPSIS. In rainbow trout the magnitude of the cortisol response to stress shows both consistency over time and a moderate to high degree of heritability, and high responding (HR) and low responding (LR) lines of rainbow trout have been generated by individual selection for consistently high or low post-stress cortisol values. Using 2nd and 3rd generation fish, we tested the hypothesis that differential stress responsiveness is associated with behavioral alterations in the HR-LR trout model. LR fish showed a tendency to become socially dominant, a rapid recovery of food intake after transfer to a novel environment, and a reduced locomotor response in a territorial intrusion test. Furthermore, stress induced elevation of brain stem and optic tectum concentrations of the monoamine neurotransmitters serotonin, dopamine, and norepinephrine and their metabolites suggests that both synthesis and metabolism of these transmitters were elevated after stress to a larger degree in HR than in LR trout. A divergent pattern was seen in the hypothalamus, where LR fish displayed elevated levels of 5-hydroxyindoleacetic acid (a serotonin metabolite) and 3-methoxy-4-hydroxyphenylglycol (a norepinephrine metabolite). Thus, selection for a single trait, cortisol responsiveness, in rainbow trout is associated with concurrent changes in both behavior and central signaling systems. The apparent parallel to genetically determined stress coping styles in mammals, and the existence of similar trait associations in unselected populations of rainbow trout, suggests an evolutionarily conserved correlation between multiple traits. Continuing studies on the HR and LR trout lines are aimed at providing the physiological and genetic basis for new marker-assisted selection strategies in the rapidly developing finfish aquaculture industry, as well as increased knowledge of the function and evolution of central neuroendocrine signaling systems.
The effects of a 21 day infestation with the ectoparasite Argulus foliaceus on the response of ra... more The effects of a 21 day infestation with the ectoparasite Argulus foliaceus on the response of rainbow trout Oncorhynchus mykiss to an acute stressor (confinement) were investigated. Fish were divided into a control and two parasitized groups, with one parasitized group having received cortisol feeding 72 and 24 h before infection. Prior to confinement only control fish showed a significant increase in
Plasma levels of ACTH, alpha-MSH, and N-ac-beta-END, and in vitro interrenal ACTH sensitivity wer... more Plasma levels of ACTH, alpha-MSH, and N-ac-beta-END, and in vitro interrenal ACTH sensitivity were investigated in rainbow trout (Oncorhynchus mykiss) stressed by confinement and in unstressed fish treated with exogenous cortisol. Within 3 hr after the onset of confinement, plasma cortisol and ACTH levels were significantly elevated above control values, while plasma alpha-MSH, but not N-ac-beta-END, levels were significantly decreased compared with those of unstressed fish. At 3 hr, sensitivity of the interrenal tissue to ACTH stimulation in vitro was reduced in stressed fish compared to that of unstressed controls. This hyposensitivity cannot be due to the intervention of alpha-MSH or N-ac-beta-END, because after 48 hr of confinement levels of both POMC-derived peptides were significantly lower than in controls, whereas interrenal tissue of stressed fish still responded significantly less to an ACTH challenge than tissue from control fish. Plasma cortisol and ACTH levels in confined fish at this time point were similar to those at 3 hr. Within 96 hr of the onset of confinement, plasma ACTH levels in stressed fish had returned to baseline levels. Plasma cortisol levels in stressed fish at 96 hr had also declined significantly, but were still higher than those in controls. The circulating cortisol level cannot be the regulatory factor responsible for the ACTH hyposensitivity observed after 3 and 48 hr of stress, because treatment of unstressed fish with exogenous cortisol (which resulted in elevated plasma cortisol and lower plasma ACTH and alpha-MSH levels compared to those of controls) did not induce a reduction in interrenal sensitivity to ACTH. It is suggested, instead, that these data support the contention that not only the initiation of the interrenal stress response, but also the habituation of the response, are regulated at the level of the hypothalamus via circulating ACTH levels.
Canadian Journal of Fisheries and Aquatic Sciences, 1993
Two strains of rainbow trout (Oncorhynchus mykiss) were exposed to soft water at pH 4.0 for 14 da... more Two strains of rainbow trout (Oncorhynchus mykiss) were exposed to soft water at pH 4.0 for 14 days, after ambient pH was reduced gradually. Several parameters, either indicators of acid stress, or reportedly involved in the adaptive response to low pH, were monitored. No mortality occurred during the exposure period; feeding behavior, haematocrit, and plasma protein levels were not affected. A transient depression of leucocrit was observed. A minor, but significant, hypochloremia and perturbations in plasma glucose levels occurred in acid-exposed fish from one strain only. There was no evidence of activation of the pituitary-interrenal axis in acid-exposed fish. Baseline plasma ACTH and Cortisol levels were indistinguishable from those of control fish, and there was no evidence of sensitization to additional stress in acid-exposed fish, in vitro baseline and ACTH-stimulated Cortisol secretion was not significantly different in the two groups. Ultrastructural evidence indicated an i...
Red porgy Pagrus pagrus were placed and maintained in white, grey and black background fibreglass... more Red porgy Pagrus pagrus were placed and maintained in white, grey and black background fibreglass tanks for 2 weeks. Additionally, fish kept in white and black background tanks were then subjected to crowding stress. After 2, 9, 16 and 23 days, blood samples were taken and plasma cortisol, alpha melanocyte stimulating hormone (α-MSH) and glucose values were analysed and compared
Melanin-concentrating hormone (MCH) is a true advocate for comparative endocrinology. Originally ... more Melanin-concentrating hormone (MCH) is a true advocate for comparative endocrinology. Originally postulated and identified in the teleost hypothalamus-pituitary complex, 1 it subsequently appeared that MCH also has a wide array of functions in the mammalian brain, 2 including the regulation of feeding behavior. 3 Some of these central functions of the peptide appear to be antagonistic to those of another neuropeptide, α-MSH. 4 From a comparative perspective this is of interest, because the phylogenetically old action of MCH on the fish skin also opposes that of α-MSH. 5 This review focuses on studies on MCH in fish, which appeared after the latest comparative review on MCH, 2 and discusses recent data and perspectives for future research.
SUMMARYIn salmonid fish, a darker skin colour has been suggested to signal social subordination. ... more SUMMARYIn salmonid fish, a darker skin colour has been suggested to signal social subordination. Substratum colour is another factor affecting skin pigmentation in fish; in the present experiment, juvenile Arctic charr (Salvelinus alpinus) were acclimated and allowed to interact in pairs for 5 days on a pale or dark background colour. Skin darkness was quantified prior to and following social interaction. Furthermore, agonistic behaviour and skin darkness were quantified, together with plasma levels of cortisol,adrenocorticotropin (ACTH) and α-melanocyte-stimulating hormone(α-MSH), and brain levels of monoamines and monoamine metabolites. The results show that fish interacting on a white background were more aggressive than those interacting on a black background. Social subordination resulted in skin darkening in fish kept on a white background, but not in fish kept on a black background. Furthermore, subordinate fish on a white background showed an elevation of brain norepinephric...
The effect of cortisol on Na(+)/K(+)-ATPase expression in the gill chloride cells of tilapia Oreo... more The effect of cortisol on Na(+)/K(+)-ATPase expression in the gill chloride cells of tilapia Oreochromis mossambicus was studied by immunocytochemistry at the light and electron microscope levels. One of three doses of cortisol (low, 125 mg kg(−1)food; middle, 375 mg kg(−1)food; high, 750 mg kg(−1) food) was administered via the food (at a ration of 1.5 % of body mass) and the fish were sampled after 5 days. Plasma osmolality and Na(+) levels were elevated in the middle- and high-dose groups, and plasma cortisol levels in the high-dose groups. Hematocrit values were not affected by the treatments. Opercular membrane chloride cell density increased by 94 % and 286 % in the middle- and high-dose fish, respectively, whereas the gill chloride cell frequency increased by up to 28 % maximally in the high-dose fish. Lamellar gill chloride cells were absent in the control and low-dose groups, but were observed in the middle- and high-dose groups. Cortisol increased the volume of the tubular...
levels are normal, but prolactin secretion remains high. T h i c k « « * and mucocyte density of ... more levels are normal, but prolactin secretion remains high. T h i c k « « * and mucocyte density of the epidermis are Increased, uhich Bay repr*«*At » structural correlate of the reducing effect of prolactin on tha permeability to water and ion of this epithelium. Chronic expotur* to pH 4.0 does not increase the resistance of the fish to a further d«cre»s* of water pH. The effects of acidification of the ambient vater on fish «.re multiple and complicated. Laboratory observations indicate that disturbed acid-base balance and vater-and ion regulation are the primary deleterious effects, that may be lethal under conditions of severe acid stress (McWilliams, 1580; McDonald, 1903; tfendelaar Bonga et al., 198lta). From field studies it has been concluded that it is not increased mortality of adult fish, but recruitment failure caused by reduced reproductive activity in combination with limiting hatching success that are the main causes of the reduction and and often disappearance of fish populations from acidified vater (Hainea, 1981; Frenette and Dodson, 1981*)• This discrepancy between the conclusions from laboratory and field studies are partially caused by differences in the parameters detorroined, and partially b y differences in the conditions investigated. Most field studies are dealing with the effects of chronic but sublethal acidification, and attention is usually concentrated on population structure and reproductive success. However, under field conditions the effects of acidity of the vator are difficult to separate fro» those of other variables such as the presence D«p«rtmant of Anlmit Physiology, Ttcultyof S d tn ct,. Unlvenity of Nljmsgan, 8525 ED Nljm*g*n. Th* Ntttwnwidt
This study deals with the regulation of pituitary-interrenal axis activity in the freshwater tele... more This study deals with the regulation of pituitary-interrenal axis activity in the freshwater teleost Oreochronis mossatnblcus (tilania) exposed to low environmental pH for 2 of 5 days. nie~"5timulaCion of the cortisol producing interrenal cells which occurs under these stressful conditions was not reflected in increased plasma cortisol levels. However, increased sensitivity of the interrenal cells of 5 days acid treated tilapia to 2 pituitary secretagoguea could be demonstrated in vitro. First to ACTH and secondly to a product with alpha-MSH iimunoreactivity, which has been detected in tilapia plasma, and was purified from pars intermedia tissue. An electron microscopical survey demonstrated the concurrent activation of both the ACTH and MSH cells of fish acclimating to the low pH stress. Future'studies will have to determine the relative contribution of ACTH and alpha-MSH to the interrenal hyperactivity under these conditions.
The melanin-concentrating hormone (MCH) precursor encodes MCH and a second peptide named neuropep... more The melanin-concentrating hormone (MCH) precursor encodes MCH and a second peptide named neuropeptide EI (NEI) in mammals, neuropeptide EV (NEV) in salmonids and MCH gene-related peptide (Mgrp) in other fish. The primary structure of the putative Mgrp of the cichlid fish tilapia (Oreochromis mossambicus) appears to be very different from mammalian NEI and salmonid NEV. To investigate the processing and release of tilapia Mgrp (tMgrp), in the present study an antiserum was raised against synthetic tMgrp. By immunocytochemistry, tMgrp immunoreactivity was colocated with MCH immunoreactivity in the tilapia hypothalamus and pituitary. In addition, a tMgrp enzyme-linked immunosorbent assay in combination with reversed phase HPLC was used to demonstrate the presence of processed tMgrp in tilapia hypothalamus and pituitary. The release of tMgrp from neuro-intermediate lobes (NILs) of tilapia pituitaries was demonstrated after in vivo incubation of chopped NILs. Depolarizing concentrations of potassium significantly stimulated tMgrp release. Six weeks of adaptation of tilapia to white or black backgrounds had no effect on in vitro tMgrp release or on the tMgrp content of NIL and hypothalamus. Tilapia Mgrp, unlike MCH, had no effect on tilapia scale melanophores, nor did it modulate the melanin-concentrating effect of MCH. We conclude that tMgrp is processed from the MCH preprohormone, that it is released in vitro, and that the peptide has no direct role in the melanin concentration of fish scale melanophores. Therefore a neuroendocrine or neuromodulatory function is proposed for tMgrp.
In this study it was shown- that dark coloured post-larvae of Senegalese sole Solea senegcilensis... more In this study it was shown- that dark coloured post-larvae of Senegalese sole Solea senegcilensis, at two different ages. had elevated cortisol concentrations compared with lighter coloured individuals. As melanophore-stimulating hormone levels were not elevated in dark coloured fish. it is possible that this hormone may not be the main melanotropic hormone involved in stress-related skin darkening.
The responses of rainbow trout and brown trout to the same stressor were compared by measuring pr... more The responses of rainbow trout and brown trout to the same stressor were compared by measuring primary and secondary stress responses during and after a 5.5-h net confinement. Basal levels of adrenocorticotropic hormone (ACTH), alpha-melanocyte-stimulating hormone (alpha-MSH), and glucose were higher in brown trout than in rainbow trout. While confinement induced transient increases in plasma ACTH and cortisol levels in both species, the magnitude of these responses, but not the time course, was greater in brown trout. Brown trout, but not rainbow trout, showed a reduction in plasma alpha-MSH levels after 5.5 h confinement before returning to control values, and the glucose levels in the brown trout were elevated throughout the confinement and recovery periods. Confinement also resulted in increased hematocrit values and reduced plasma sodium and chloride levels in both species. Rainbow trout appeared to recover faster from the confinement, as glucose and hematocrit values in the brown trout remained elevated and ionoregulatory disturbances persisted even after 46 h. During recovery effects on the immune system were more pronounced in brown trout than in rainbow trout. Circulating white blood cell numbers were reduced in both species following 23 h recovery, but remained low in the brown trout. Elevated alternative complement activity and oxygen radical production were found after 23 h recovery, and reduced lysozyme activity was found after 46 h, in brown trout only. Results indicate that differences in the stress response of these closely related species, as illustrated by the intensity of the cortisol response, originate at the level of the pituitary and are also manifested through secondary stress responses.
The stress response of the euryhaline tilapia Oreochromis mossambicus adapted to either fresh Ž. ... more The stress response of the euryhaline tilapia Oreochromis mossambicus adapted to either fresh Ž. Ž Ž .. water FW or salt water Instant Oceane, 950 mosm; SW was investigated to establish the influences of ambient salinity in this species. The fish were considered to be adapted to the salinities as pre-confinement plasma cortisol and glucose levels were typical for unstressed fish. Two hour net confinement increased plasma cortisol and glucose to a similar extent in both FW and SW. Individual plasma sodium and chloride levels were unaffected by confinement, although plasma Na:Cl ratio increased in FW. Confinement increased intestinal Na q rK q-ATPase activity in FW, but not in SW. In contrast, kidney Na q rK q-ATPase activity increased in SW only. Branchial Na q rK q-ATPase activity decreased with confinement in SW, but not in FW. In SW, confinement reduced the numbers of opercular chloride cells. Increased aging of the branchial Ž. chloride cell CC population of SW-confined fish was indicated by large numbers of apoptotic CCs in the interlamellar areas. This effect on the CC population was absent in FW-confined fish. Overall, confinement in SW-adapted fish had a more profound impact than confinement in FW-adapted fish. This is likely to have associated energetic consequences in terms of branchial oxygen and ATP consumption. Therefore, results suggest the possibility of different effects of confinement on subsequent growth in FW and SW.
Hormones and the behavioural ecology of stress Respiratory and cardiovascular systems during stre... more Hormones and the behavioural ecology of stress Respiratory and cardiovascular systems during stress Impact of stress on animal intermediate metabolism The impact of stress on animal reproductive activities Histological and histopathological effects of stress Stress-induced immune-endocrine interaction Impact of stress on animal toxicology References Index .
Although hypothalamic corticotropin-releasing hormone (CRH) is involved in the stress response in... more Although hypothalamic corticotropin-releasing hormone (CRH) is involved in the stress response in all vertebrate groups, only a limited number of studies on this neuroendocrine peptide deals with non-mammalian neuroendocrine systems. We determined the cDNA sequence of the CRH precursor of the teleost Oreochromis mossambicus (tilapia) and studied the biological potency of the CRH peptide in a homologous teleost bioassay. Polymerase chain reaction (PCR) with degenerate and specific primers yielded fragments of tilapia CRH cDNA. Full-length CRH cDNA (988 nucleotides) was obtained by screening a tilapia hypothalamus cDNA library with the tilapia CRH PCR products. The precursor sequence (167 amino acids) contains a signal peptide, the CRH peptide and a motif conserved among all vertebrate CRH precursors. Tilapia CRH (41 aa) displays between 63% and 80% amino acid sequence identity to CRH from other vertebrates, whereas the degree of identity to members of the urotensin I/urocortin lineage is considerably lower. In a phylogenetic tree, based on alignment of all full CRH peptide precursors presently known, the three teleost CRH precursors (tilapia; sockeye salmon, Oncorhynchus nerka; white sucker, Catostomus commersoni) form a monophyletic group distinct from amphibian and mammalian precursors. Despite the differences between the primary structures of tilapia and rat CRH, maximally effective concentrations of tilapia and rat CRH were equally potent in stimulating adrenocorticotropic hormone (ACTH) and alpha-MSH release by tilapia pituitaries in vitro. The tilapia and salmon CRH sequences show that more variation exists between orthologous vertebrate CRH structures, and teleost CRHs in particular than previously recognized. Whether the structural differences reflect different mechanisms of action of this peptide in the stress response remains to be investigated.
Abstract Common carp (at 20 °C) and rainbow trout (at 15 °C) were fitted with an indwelling cannu... more Abstract Common carp (at 20 °C) and rainbow trout (at 15 °C) were fitted with an indwelling cannula in the dorsal aorta. The fish were exposed to a controlled decline of water pO2 followed by 90 min deep hypoxia at 0.3 kPa (carp) or 4.8 kPa (trout). Thereafter, nor-moxic recovery was ...
SYNOPSIS. In rainbow trout the magnitude of the cortisol response to stress shows both consistenc... more SYNOPSIS. In rainbow trout the magnitude of the cortisol response to stress shows both consistency over time and a moderate to high degree of heritability, and high responding (HR) and low responding (LR) lines of rainbow trout have been generated by individual selection for consistently high or low post-stress cortisol values. Using 2nd and 3rd generation fish, we tested the hypothesis that differential stress responsiveness is associated with behavioral alterations in the HR-LR trout model. LR fish showed a tendency to become socially dominant, a rapid recovery of food intake after transfer to a novel environment, and a reduced locomotor response in a territorial intrusion test. Furthermore, stress induced elevation of brain stem and optic tectum concentrations of the monoamine neurotransmitters serotonin, dopamine, and norepinephrine and their metabolites suggests that both synthesis and metabolism of these transmitters were elevated after stress to a larger degree in HR than in LR trout. A divergent pattern was seen in the hypothalamus, where LR fish displayed elevated levels of 5-hydroxyindoleacetic acid (a serotonin metabolite) and 3-methoxy-4-hydroxyphenylglycol (a norepinephrine metabolite). Thus, selection for a single trait, cortisol responsiveness, in rainbow trout is associated with concurrent changes in both behavior and central signaling systems. The apparent parallel to genetically determined stress coping styles in mammals, and the existence of similar trait associations in unselected populations of rainbow trout, suggests an evolutionarily conserved correlation between multiple traits. Continuing studies on the HR and LR trout lines are aimed at providing the physiological and genetic basis for new marker-assisted selection strategies in the rapidly developing finfish aquaculture industry, as well as increased knowledge of the function and evolution of central neuroendocrine signaling systems.
The effects of a 21 day infestation with the ectoparasite Argulus foliaceus on the response of ra... more The effects of a 21 day infestation with the ectoparasite Argulus foliaceus on the response of rainbow trout Oncorhynchus mykiss to an acute stressor (confinement) were investigated. Fish were divided into a control and two parasitized groups, with one parasitized group having received cortisol feeding 72 and 24 h before infection. Prior to confinement only control fish showed a significant increase in
Plasma levels of ACTH, alpha-MSH, and N-ac-beta-END, and in vitro interrenal ACTH sensitivity wer... more Plasma levels of ACTH, alpha-MSH, and N-ac-beta-END, and in vitro interrenal ACTH sensitivity were investigated in rainbow trout (Oncorhynchus mykiss) stressed by confinement and in unstressed fish treated with exogenous cortisol. Within 3 hr after the onset of confinement, plasma cortisol and ACTH levels were significantly elevated above control values, while plasma alpha-MSH, but not N-ac-beta-END, levels were significantly decreased compared with those of unstressed fish. At 3 hr, sensitivity of the interrenal tissue to ACTH stimulation in vitro was reduced in stressed fish compared to that of unstressed controls. This hyposensitivity cannot be due to the intervention of alpha-MSH or N-ac-beta-END, because after 48 hr of confinement levels of both POMC-derived peptides were significantly lower than in controls, whereas interrenal tissue of stressed fish still responded significantly less to an ACTH challenge than tissue from control fish. Plasma cortisol and ACTH levels in confined fish at this time point were similar to those at 3 hr. Within 96 hr of the onset of confinement, plasma ACTH levels in stressed fish had returned to baseline levels. Plasma cortisol levels in stressed fish at 96 hr had also declined significantly, but were still higher than those in controls. The circulating cortisol level cannot be the regulatory factor responsible for the ACTH hyposensitivity observed after 3 and 48 hr of stress, because treatment of unstressed fish with exogenous cortisol (which resulted in elevated plasma cortisol and lower plasma ACTH and alpha-MSH levels compared to those of controls) did not induce a reduction in interrenal sensitivity to ACTH. It is suggested, instead, that these data support the contention that not only the initiation of the interrenal stress response, but also the habituation of the response, are regulated at the level of the hypothalamus via circulating ACTH levels.
Canadian Journal of Fisheries and Aquatic Sciences, 1993
Two strains of rainbow trout (Oncorhynchus mykiss) were exposed to soft water at pH 4.0 for 14 da... more Two strains of rainbow trout (Oncorhynchus mykiss) were exposed to soft water at pH 4.0 for 14 days, after ambient pH was reduced gradually. Several parameters, either indicators of acid stress, or reportedly involved in the adaptive response to low pH, were monitored. No mortality occurred during the exposure period; feeding behavior, haematocrit, and plasma protein levels were not affected. A transient depression of leucocrit was observed. A minor, but significant, hypochloremia and perturbations in plasma glucose levels occurred in acid-exposed fish from one strain only. There was no evidence of activation of the pituitary-interrenal axis in acid-exposed fish. Baseline plasma ACTH and Cortisol levels were indistinguishable from those of control fish, and there was no evidence of sensitization to additional stress in acid-exposed fish, in vitro baseline and ACTH-stimulated Cortisol secretion was not significantly different in the two groups. Ultrastructural evidence indicated an i...
Red porgy Pagrus pagrus were placed and maintained in white, grey and black background fibreglass... more Red porgy Pagrus pagrus were placed and maintained in white, grey and black background fibreglass tanks for 2 weeks. Additionally, fish kept in white and black background tanks were then subjected to crowding stress. After 2, 9, 16 and 23 days, blood samples were taken and plasma cortisol, alpha melanocyte stimulating hormone (α-MSH) and glucose values were analysed and compared
Melanin-concentrating hormone (MCH) is a true advocate for comparative endocrinology. Originally ... more Melanin-concentrating hormone (MCH) is a true advocate for comparative endocrinology. Originally postulated and identified in the teleost hypothalamus-pituitary complex, 1 it subsequently appeared that MCH also has a wide array of functions in the mammalian brain, 2 including the regulation of feeding behavior. 3 Some of these central functions of the peptide appear to be antagonistic to those of another neuropeptide, α-MSH. 4 From a comparative perspective this is of interest, because the phylogenetically old action of MCH on the fish skin also opposes that of α-MSH. 5 This review focuses on studies on MCH in fish, which appeared after the latest comparative review on MCH, 2 and discusses recent data and perspectives for future research.
SUMMARYIn salmonid fish, a darker skin colour has been suggested to signal social subordination. ... more SUMMARYIn salmonid fish, a darker skin colour has been suggested to signal social subordination. Substratum colour is another factor affecting skin pigmentation in fish; in the present experiment, juvenile Arctic charr (Salvelinus alpinus) were acclimated and allowed to interact in pairs for 5 days on a pale or dark background colour. Skin darkness was quantified prior to and following social interaction. Furthermore, agonistic behaviour and skin darkness were quantified, together with plasma levels of cortisol,adrenocorticotropin (ACTH) and α-melanocyte-stimulating hormone(α-MSH), and brain levels of monoamines and monoamine metabolites. The results show that fish interacting on a white background were more aggressive than those interacting on a black background. Social subordination resulted in skin darkening in fish kept on a white background, but not in fish kept on a black background. Furthermore, subordinate fish on a white background showed an elevation of brain norepinephric...
The effect of cortisol on Na(+)/K(+)-ATPase expression in the gill chloride cells of tilapia Oreo... more The effect of cortisol on Na(+)/K(+)-ATPase expression in the gill chloride cells of tilapia Oreochromis mossambicus was studied by immunocytochemistry at the light and electron microscope levels. One of three doses of cortisol (low, 125 mg kg(−1)food; middle, 375 mg kg(−1)food; high, 750 mg kg(−1) food) was administered via the food (at a ration of 1.5 % of body mass) and the fish were sampled after 5 days. Plasma osmolality and Na(+) levels were elevated in the middle- and high-dose groups, and plasma cortisol levels in the high-dose groups. Hematocrit values were not affected by the treatments. Opercular membrane chloride cell density increased by 94 % and 286 % in the middle- and high-dose fish, respectively, whereas the gill chloride cell frequency increased by up to 28 % maximally in the high-dose fish. Lamellar gill chloride cells were absent in the control and low-dose groups, but were observed in the middle- and high-dose groups. Cortisol increased the volume of the tubular...
levels are normal, but prolactin secretion remains high. T h i c k « « * and mucocyte density of ... more levels are normal, but prolactin secretion remains high. T h i c k « « * and mucocyte density of the epidermis are Increased, uhich Bay repr*«*At » structural correlate of the reducing effect of prolactin on tha permeability to water and ion of this epithelium. Chronic expotur* to pH 4.0 does not increase the resistance of the fish to a further d«cre»s* of water pH. The effects of acidification of the ambient vater on fish «.re multiple and complicated. Laboratory observations indicate that disturbed acid-base balance and vater-and ion regulation are the primary deleterious effects, that may be lethal under conditions of severe acid stress (McWilliams, 1580; McDonald, 1903; tfendelaar Bonga et al., 198lta). From field studies it has been concluded that it is not increased mortality of adult fish, but recruitment failure caused by reduced reproductive activity in combination with limiting hatching success that are the main causes of the reduction and and often disappearance of fish populations from acidified vater (Hainea, 1981; Frenette and Dodson, 1981*)• This discrepancy between the conclusions from laboratory and field studies are partially caused by differences in the parameters detorroined, and partially b y differences in the conditions investigated. Most field studies are dealing with the effects of chronic but sublethal acidification, and attention is usually concentrated on population structure and reproductive success. However, under field conditions the effects of acidity of the vator are difficult to separate fro» those of other variables such as the presence D«p«rtmant of Anlmit Physiology, Ttcultyof S d tn ct,. Unlvenity of Nljmsgan, 8525 ED Nljm*g*n. Th* Ntttwnwidt
This study deals with the regulation of pituitary-interrenal axis activity in the freshwater tele... more This study deals with the regulation of pituitary-interrenal axis activity in the freshwater teleost Oreochronis mossatnblcus (tilania) exposed to low environmental pH for 2 of 5 days. nie~"5timulaCion of the cortisol producing interrenal cells which occurs under these stressful conditions was not reflected in increased plasma cortisol levels. However, increased sensitivity of the interrenal cells of 5 days acid treated tilapia to 2 pituitary secretagoguea could be demonstrated in vitro. First to ACTH and secondly to a product with alpha-MSH iimunoreactivity, which has been detected in tilapia plasma, and was purified from pars intermedia tissue. An electron microscopical survey demonstrated the concurrent activation of both the ACTH and MSH cells of fish acclimating to the low pH stress. Future'studies will have to determine the relative contribution of ACTH and alpha-MSH to the interrenal hyperactivity under these conditions.
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