Physiological responses of pink abalone Haliotis corrugata (Gray, 1828) exposed to different combinations of temperature and salinity

Physiological responses of pink abalone Haliotis corrugata were determined under different temperature and salinity conditions. Oxygen consumption rate was not affected by temperature and salinity. Ammonium excretion of pink abalone was inversely related to salinity. The O:N ratio indicated that abalone maintained in lower salinities had an interval of 4.9–7.7, which is indicative of a protein‐dominated metabolism, whereas the O:N in 35‰ was 28.8–35.5 for both temperatures, suggesting that carbohydrates were used as energy substrate. Haemolymph osmolality of abalone exposed to 20 and 24 °C was slightly hyperiso‐osmoconformic in salinity ranges of 20–35‰. The results of this study suggested that for optimized culture, pink abalone should be cultivated at 24 °C at a salinity of 35‰.     

The effects of a sudden salinity change on cortisol, glucose, lactate, and osmolality levels in grouper Epinephelus malabaricus

Grouper Epinephelus malabaricus (weighing 46.37?±?5.10?g) previously maintained in 24‰ seawater were transferred to 14, 19, 24 (control), 29, and 34‰ seawater. Serum cortisol, glucose, lactate, and osmolality levels were measured at 7 time points during 240?min. Serum cortisol and glucose levels of fish transferred to 29 and 34‰ seawater significantly increased to the highest after 10 and 20?min, respectively. No significant differences in serum cortisol and glucose levels were observed for the fish after 30?min among all treatments. Serum lactate level of fish transferred to 14, 19, 29, and 34‰ seawater was significantly lower than that of the control fish after 10-30?min. However, no significant differences in serum lactate were observed 60?min among five treatments. The serum osmolality of the fish following 240-min transfer increased directly with salinity, whereas the osmoregulatory capacity value (medium osmolality-plasma osmolality) of the fish following 240-min transfer was inversely related to salinity. It is concluded that grouper showed strong osmoregulation in 14-34‰ seawater. Serum cortisol and glucose levels of fish transferred to 29 and 34‰ seawater increased rapidly in 10-30?min, indicating an early stress response.     

Osmoregulation,growth and moulting cycles of the giant freshwater prawn (Macrobrachium rosenbergii) at different salinities

The giant freshwater prawn, Macrobrachium rosenbergii, is a species with a high commercial value in aquaculture. Two experiments were performed to determine the effects of salinities on the osmoregulation, growth and molting cycles of M. rosenbergii during growout. The first experiment was designed to determine whether these animals are capable of adapting to the changes in salinity seen in salinity intrusions in tropical deltas, with an incremental increase in salinity of 3‰ per day from 0‰ to 30‰ Haemolymph osmolality was rapidly regulated up to salinities of 15‰ , whereas animals conformed at higher salinities. The second experiment determined the growth, moulting cycle, osmolality, muscle water content and mortality during a 4‐month experiment at 0‰, 15‰ or 25‰ salinity. The weight gains in 0‰ and 15‰ were not significantly different and were comparable to the growth rates achieved in production farms with body mass increases of 2.6 and 2.3‐fold their initial body mass, respectively, after 4 months. The 25‰ group suffered from low growth, high mortality and a significantly lower moulting frequency. These data show that this species can be reared in brackish water up to 15‰, allowing for farming in the large areas impacted by salt water intrusions in tropical deltas.     

Survival, growth, food conversion efficiency and plasma osmolality of juvenile Siganus guttatus (Bloch, 1787): experimental analyses of salinity effects

We studied the effects of salinity on survival, growth, food conversion efficiency and plasma osmolality of juvenile Siganus guttatus in two independent experiments. In the first experiment, fish were transferred from 30 ‰ salinity to freshwater, 5, 10, 20 and 30 ‰ salinities for 192 h. No fish died when transferred directly from 30 ‰ to salinities >5 ‰. However, all fish died in the freshwater treatment. In the second experiment, survival, growth, feeding rate, food conversion efficiency and plasma osmolality of fish were analyzed during 6 weeks in salinities of 5, 10, 20 and 30 ‰ (control). At the end of this experiment, the final weight and the specific growth rate of fish were significantly greater at 10 ‰ than fish in all other treatments. Feeding rate increased significantly with decreasing salinity: 10 ‰ > 20 ‰ > 30 ‰. However, the food conversion efficiency was not significantly different between fish in any treatment. Plasma osmolality of fish in 20 and 30 ‰ salinity was significantly greater than fish reared at 10 or 5 ‰. A salinity of 13.95 ‰ (411.88 mOsmol/kg) was the point of isosmolality for juvenile S. guttatus.     

A dietary modification approach to improve the osmoregulatory capacity of Litopenaeus vannamei cultured in the Arizona desert

A modified diet was formulated for Arizona inland shrimp farming and tested as a method for reducing moult‐associated mortalities presumed due to trace mineral deficiencies. The experimental diet was supplemented with additional dietary magnesium, potassium, phospholipids and cholesterol to a commercial shrimp feed (Rangen 45/10, which was also used as the control diet). The modified diet was tested at Arizona Mariculture Associates (AMA), while the control diet was used at a nearby inland shrimp farm, Desert Sweet Shrimp Farm (DSSF). Both feeds were used throughout the culture season of 2001. Earthen pond‐reared Litopenaeus vannamei at intermoult stages (C‐D₀) and ranging from 7 to 30 g were sampled at intervals for determination of haemolymph osmolality (HO). Results showed that the modified diet had not only resulted in larger size shrimp at harvest, but also improved osmoregulatory capacity (OC). HO of DSSF shrimp decreased as shrimp grew bigger, whereas HO of AMA shrimp was maintained at a stable level, or showed a slightly positive linear relationship with weight. The hyper‐OC of shrimp from AMA (462 mOsm kg^?1) was greater than that from DSSF (398 mOsm kg^?1). Shrimp at AMA fed the experimental diet presented no mass moult‐associated mortalities. To further investigate the iso‐osmotic point of shrimp reared in AMA, a group of six salinity gradients were designed by mixing oceanic salts into the well water to form 5, 8.5, 11.4, 14.4, 17.8, 20.7 p.p.t. medium. HO of subadult shrimp (25 g in average) were then evaluated 48 h after they had been transferred from 5 p.p.t. pond water to the medium. Shrimp HO increased with external salinity, and a plateau formed as salinity reached at 11.4 p.p.t. and higher. The iso‐osmotic point of shrimp was estimated to be 695.5 mOsm kg^?1, equivalent to 26.1 p.p.t. in AMA well water.     

Effect of dietary sodium chloride acclimation on growth and plasma thyroid hormones in tilapia Oreochromis niloticus (L.) in relation to sex

This trial was conducted in order to test the effect of supplemental dietary sodium chloride on growth and plasma thyroid hormone levels of male and female monosex groups of tilapia Oreochromis niloticus (L.) reared in fresh water and 10‰ brackish water. At the end of the experiment. the gonadal development of females was observed. A high‐salt diet (8% NaCl) was fed to female and male tilapia for a period of 3 weeks. After this time. both groups were transferred directly to fresh water and 10‰ brackish water, and a growth trial was conducted over 90 days. The results indicate that dietary supplementation with NaCl improved the growth of females and males at 30 days, except for females maintained in fresh water. Females reared in 10‰ brackish water showed an increase in growth rates that was accompanied by the highest plasma T3 levels. In contrast, males did not exhibit the same relationship in 10‰ brackish water, showing lower plasma T3 levels than in fresh water. Histological sections of O. niloticus ovaries revealed that female groups contained oocytes at different stages of development. At 90 days, females reared in 10‰ brackish water showed oocytes in maturation, while in fresh water, they showed the highest proportion of vitellogenic oocytes and no mature oocytes. The highest proportion of mature oocytes observed in brackish water was associated with the better growth rate in relation to fresh water. These results confirm that tilapia breed freely in low‐salinity brackish water as well as in fresh water.     

Salinity a significant environmental factor for Vibrio harveyi virulence in Fenneropenaeus indicus

The effect of ambient salinity on the haemolymph variables of Fenneropenaeus indicus and its susceptibility to Vibrio harveyi infection under salinity stress has been studied. Adult shrimps were acclimated to 5‰ (hypo osmotic), 25‰ (iso osmotic) and 35‰ (hyper osmotic) salinity levels and the animals were injected with a mid logarithmic culture of V. harveyi at sub lethal level and haemolymph parameters were analysed. Haemolymph proteins, intracellular superoxide anion production, phenoloxidase (PO), alkaline phosphatase (ALP) and acid phosphatase (ACP) activity were found to be at elevated level both at 5‰ and 35‰ post challenge. The haematological responses showed a progressive increase (P < 0.05) up to post challenge day 5 (PCD 5) followed by a considerable decline at all salinities with the lowest being at 35‰. The alterations in the variables were higher in shrimps held at 5‰. However, the V. harveyi infection was severe in animals held at 35‰. The reduction in the parameters could be correlated with the decrease in survival rate of shrimps at 35‰ with a concurrent increase in V. harveyi at this salinity. Multiple regression analysis revealed that ACP (P < 0.001), haemocyte protein HCP (P < 0.001) and PO (P < 0.05) could explain 91% variability in the shrimp survival. These parameters may be used as effective shrimp health indicators. It is evident from the study that ambient salinity alters the haemolymph variables, modulates the virulence in V. harveyi and makes the shrimps more vulnerable to infection at higher salinity. The virulence of V. harveyi is increased at 35‰ salinity as being evidenced from the high mortality at this salinity. The study emphasizes the importance of salinity as an important environmental factor both in terms of host susceptibility and virulence of the pathogen.     

淡化对南美白对虾存活率、渗透压和Na~+/K~+-ATP酶活力的影响

采用微型冰点渗透压仪、荧光定量PCR和酶活力测定的方法分析淡化对南美白对虾(Penaeus vannamei)存活率、体内渗透压及Na~+/K~+-ATPase基因表达和酶活力的影响。结果表明,养殖水体盐度由12‰下降到0‰过程中,虾苗存活率和活力始终维持一个较高的水平。对虾体内渗透压随着水体盐度的降低而降低,但没有显著差异。渗透压调节关键基因Na~+/K~+-ATPase mRNA表达水平和酶活力在水体盐度12‰下降到9‰过程中显著升高,之后随着水体盐度的下降表达量显著降低,最后在6‰下降到0‰过程中趋于平缓。     

Evaluation of an alternative salt mixture to culture Pacific white shrimp (Litopenaeus vannamei) in inland aquaculture

Pacific white shrimp, Litopenaeus vannamei, exhibit a remarkable ability to tolerate low‐salinity environments, facilitating its culture far from coastal areas using various production systems at salinities less than 15 g/L. Recirculating aquaculture systems (RAS) and biofloc systems are usually operated using reconstituted sea salt (RSS), which is a considerable financial burden to commercial producers due to its higher price. Current study was carried out with the objective of testing the efficacy of a low‐cost salt solution to replace expensive RSS to grow shrimp under laboratory conditions. Low‐cost salt mixture (LCSM) was formulated to yield sodium, potassium, calcium and magnesium concentrations closely comparable to that of diluted seawater using agriculture grade sodium chloride, magnesium chloride, magnesium sulphate, potassium oxide, calcium chloride and sodium bicarbonate. Growth trials were conducted at three different salinities of 3, 6 and 15 g/L, incrementally replacing RSS with LCSM (0, 2.5, 25, 50, 75 and 100%) at four replicates per treatment. Twenty juvenile shrimp were reared for 42 days in 150 L polyethylene tanks. Ionic profile of water, ionic profile and osmolality of shrimp haemolymph were determined to justify growth and survival data through analysing ionic variations and osmoregulatory capacity of shrimp. At the conclusion, no significant differences were observed in survival, growth, osmoregulation and levels of cations in shrimp haemolymph between RSS and LCSM treatments at all salinities examined. Results reflect the potential use of LCSM to replace RSS which could be an excellent solution to bring down the cost of production in inland shrimp aquaculture.     

Salinity increases total body prolactin and gill and skin prolactin receptor expression in the Chinese edible frog,Hoplobatrachus rugulosus,tadpole

Water salinity has effects on growth and metamorphosis of anuran species, including Hoplobatrachus rugulosus. Previously, we reported that cultured H. rugulosus tadpoles at low salinities (2–4‰) were of bigger size and grew faster than those in fresh water (FW). However, at a higher salinity level of 6‰, their sizes were reduced and the metamorphosis was delayed. It was therefore hypothesized that high salinity‐induced osmotic stress affected secretion of prolactin (PRL), which acts as osmoregulatory hormone and a regulator of metamorphosis in amphibians. In this study, transferring tadpoles into 4‰ and 6‰ brackish water increased the PRL levels by ~1.2‐ and ~twofold, respectively, as compared to FW group. These osmotic challenges also increased the total body fluid osmolality and levels of Na⁺, Cl^? and Ca²⁺. The contents of triiodothyronine (T₃) were significantly reduced in 4‰ and 6‰ groups, but not 2‰ group. Three sizes (49, 29 and 23 kDa) of H. rugulosus PRL receptors (PRLRs) were detected, and their protein expression was found in the skin, gill, tail fin, brain, intestine, heart, liver and kidney. The expression of PRLR‐49k protein was significantly higher in both skin and gills in 2–4‰ groups, whereas that of PRLR‐29k and PRLR‐23k were higher in gills and lower in skin of the 6‰ group than FW group. In conclusion, salinity challenge, particularly 4‰ and 6‰, increased the levels of PRL, while decreasing the T₃ levels, which could explain why salinity markedly modulated growth, metamorphosis and survival of tadpoles.     

Short-term responses of adult kuruma shrimp Marsupenaeus japonicus (Bate) to environmental salinity: osmotic regulation, oxygen consumption and ammonia excretion

The effects of salinity on haemolymph osmolality, oxygen consumption and ammonia excretion were investigated in adult kuruma shrimp, Marsupenaeus japonicus (Bate), at salinities of 20, 25, 30 and 35 g L^?1. Haemolymph osmolality showed a positive linear relationship (r²=0.9854) with medium osmolality. The isosmotic point calculated from this relationship was 1039 mOsm kg^?1, which corresponds to a salinity of approximately 35 g L^?1. The slope of the regression equation was very high (0.81), suggesting that M. japonicus adults are poor osmoregulators compared with the adults of other penaeids and to conspecific young. The difference between haemolymph and medium osmolality (D_OP) was lowest at 35 g L^?1 and highest at 20 g L^?1. Thus, the minimum D_OP coincided with the isosmotic point of the shrimp. The respiration rate was significantly lower at 30 g L^?1 than at the other salinities. Ammonia excretion rates were inversely related with salinity and therefore were minimal at 35 g L^?1. The results of this study suggest that the optimum salinity for adult kuruma shrimp is around 30–35 g L^?1 and that even minor (e.g. 5 g L^?1) deviations from this optimum cause significant physiological changes. Further, the observed increases in oxygen consumption and ammonia excretion during exposure to low salinities, which indicate higher energy expenditure and amino acid catabolism for osmoregulation, respectively, suggest that the growth efficiency of M. japonicus adults may be severely compromised by hypohaline water inflow into the rearing ponds.     

Effect of iodophor disinfection of non‐hardened Salmo trutta eggs on their bacterial and fungus load

This study investigated the efficiency of iodophor disinfection (135 ppm active iodine for 15–30 min) of non‐hardened Salmo trutta eggs against different groups of bacteria and against fungus. Egg samples were taken from non‐disinfected and from disinfected eggs, microorganisms were cultured on specific nutrient media and their mass was measured by turbidimetric methods. Bacteria and fungus mass of non‐hardened eggs could be reduced but not eliminated by iodophor disinfection with 135 ppm active iodine for 15 min. The extent of reduction was 47–65% (Experiment 1). The efficiency of disinfection increased with disinfection time as the reduction in bacteria and fungus mass was 40–55% after 15 min and 58–74% after 30 min (Experiment 2). Disinfection efficiency of iodophor solution diluted in water (reduction 49–57%) and of iodophor solution diluted in sodium chloride solution iso‐osmolar to the oocytes (reduction 52–61%) was similar (Experiment 3). The reduction in bacteria and fungus mass was persistent as it was 39–72% lower in embryos deriving from disinfected eggs than in embryos deriving from non‐disinfected ones (Experiment 4). In conclusion, the tested disinfection method is inadequate to eliminate pathogens completely but it could positively influence immune defence of eggs and embryos.     

Osmoregulatory ability and stress responses during freshwater adaptation of black porgy (Acanthopagrus schlegeli) treated with exogenous prolactin

The effects of ovine prolactin (oPRL) on osmoregulatory ability (electrolyte balance, plasma osmolality and activity of gill chloride cells and gill Na⁺/K⁺‐ATPase) and stress responses (plasma cortisol, glucose, aspartate aminotransferase: AST and alanine aminotransferase: ALT) were investigated in black porgy transferred to freshwater (FW). Fish in seawater (SW) were injected twice at a 24 h interval with oPRL (at 1, 3, or 5 μg g^–1 body weight) or vehicle (0.9% NaCl) and then transferred to FW. They were sampled 3 days after the transfer. With oPRL at 5 μg g^–1, levels of plasma Na⁺ and Cl^? and osmolality were significantly higher than in saline‐treated fish, whereas gill CCs number and Na⁺/K⁺‐ATPase activity were lower. Also, the 5 μg g^–1oPRL treatment led to significantly lower plasma cortisol levels than did saline treatment. However, there were no significant differences in plasma AST and ALT between groups. These results support the positive osmoregulatory role of PRL in black porgy during FW adaptation.     

Chemical composition and osmolality of seminal fluid of Acipenser persicus; their physiological relationship with sperm motility

Determination of semen quality is necessary to understand the basic biochemical processes occurring during motility of sperm and during fertilization to evaluate the reproductive ability of different fish species and to create an optimal environment for storage of spermatozoa; in this regard less information is available for Acipenseridae compared with Cyprinidae and Salmonidae. The aim of the present study is to determine chemical composition and osmolality of seminal fluid and their relationship with sperm motility in Acipenser persicus. The results obtained show that sodium (Na⁺), chloride (Cl^?) and potassium (K⁺) were predominant ions in the seminal plasma and the average of osmolality of seminal plasma was 82.56 mOsm kg^?1. The higher chemical contents and osmolality compared with other sturgeon species reveal species‐specific characteristics and high secretory activity of spermatic duct in A. persicus. Significant positive correlations were observed between osmolality‐Cl^?, Na⁺‐osmolality and Na⁺–Cl^? (P<0.05, P<0.001 and P<0.05 respectively). But statistically significant correlation was not observed between seminal plasma parameters and sperm motility. Probably, the Na⁺ and Cl^? are the main electrolytes playing a major role in maintaining the osmolality of the seminal plasma and the viability of the spermatozoa in vivo.     

Observations on salinity tolerance and osmoregulation in laboratory-reared Macrobrachium rosenbergii post-larvae (Crustacea: Caridea)

The tolerance of postlarval Macrobrachium rosenbergii to gradual and rapid increases in salinity was determined. Mortalities occurred at salinities around 25‰ and increased rapidly at levels ≥30‰ in both cases. However, acclimation substantially increased survival time at 35‰.Freezing point depressions of blood were measured from laboratory-reared M. rosenbergii postlarvae and juveniles exposed to various salinities from fresh water to approximately 35‰. The blood concentration was hyperosmotic to the medium at salinities from fresh water to about 17–18‰ and hypoosmotic at higher salinities. Postlarvae maintained a nearly constant blood concentration (freezing point depression = ?0.89 ± 0.13°C) over a wide range of external salinities (fresh water to about 27–30‰). The animals' osmoregulatory mechanisms failed at salinities ≥30‰, and thereafter the blood concentration paralleled that of the medium. The blood concentrations of juvenile shrimp grown for 5 months at salinities from fresh water to about 15‰ (freezing point depression = ?0.88 ± 0.07°C) closely resembled those of postlarvae.The osmoregulatory performance of young M. rosenbergii is generally similar to that of other brackishwater animals, but in their ability to hyperosmoregulate effectively in fresh water they more closely resemble fresh water species. It is suggested that M. rosenbergii may be able to conserve salt in dilute media by producing blood-hypoosmotic urine.An interesting stress symptom often preceded death of postlarvae in high salinities. The animals changed gradually from nearly transparent to opaque white and then died, usually within a day or so.     

Alteration of the haemocyte parameters,expression of immune‐related and neurohormone bursicon genes of giant river prawn Macrobrachium rosenbergii (de Man) in the response to salinity stress and ammonia stress

We examined the effects of salinity stress and ammonia stress on alteration of the haemocyte count, phenoloxidase activity, expressions of immune‐related genes including prophenoloxidase (proPO), crustin, heat shock protein 70 (HSP70), and expressions of stress‐responsive neurohormone (Bur‐α and Bur‐β) in the thoracic and abdominal ganglia of giant river prawn Macrobrachium. These parameters of prawn that subjected to salinity stress (transferred from 0‰ to 5‰ and 10‰), and subjected to ammonia‐nitrogen (ammonia‐N) stress (transferred from 0 to 0.262 mg/L and 0.786 mg/L) were examined after 0, 3, 6, 24, 72 and 168 hr respectively. During the initial period of 3, 6 and 24 hr, granulocyte haemocyte (granular and semi‐granular hemocyte) count and PO activity significantly decreased, while expressions of Bur‐α and Bur‐β significantly increased. After 24 hr, granulocyte haemocyte count and PO activity significantly increased, whereas expressions of Bur‐α and Bur‐β significantly decreased. The expressions of proPO, crustin and HSP70 were significantly downregulated in the prawn that subjected to salinity stress and ammonia‐N stress at all time periods of 3–168 hr. In conclusion, changes in the granulocyte haemocyte count of M. rosenbergii following salinity stress and ammonia‐N stress are closely associated with the changes of Bur‐α and Bur‐β expressions.     

Low-salinity tolerance of juvenile fugu <Emphasis Type="Italic">Takifugu rubripes</Emphasis>

ABSTRACT:   To study the adaptability of juvenile fugu Takifugu rubripes to low-salinity environments, fish were transferred from full-strength seawater (100% SW) to freshwater (FW) and 25, 50, 75 and 100% SW, and checked for mortality over 3 days. No mortality was observed in 25–100% SW, whereas all fish died in FW. In fish transferred to 25–100% SW, blood osmolality was maintained within a physiological range. To further explore the lower limit of salinity that fugu could tolerate, fish were transferred from 100% SW to FW and 1, 5, 10, 15 and 25% SW. All fish survived in 5–25% SW, but fish died in FW and 1% SW. In fish surviving transfer to FW and 1 and 5% SW, blood osmolality was decreased to a near sublethal level of approximately 300 mOsm/kg·H₂O. Therefore, the lower limit of salinity tolerance is estimated to lie between 5 and 10% SW. Preacclimation in 25% SW for 7 days did not essentially affect the survival salinity range. Although survival rates and blood osmolality were slightly improved by preacclimation in 25% SW, blood osmolality was markedly decreased in salinities less than 10% SW, as was seen in the direct transfer. Neither chloride cell morphology nor sodium-potassium adenosinetriphosphatase activity in the gills showed a significant change following transfer to low salinities. These findings indicate that fugu can be adapted to hypoosmotic environments to some extent, exerting hyperosmoregulatory ability, although chloride cells are less likely to absorb ions in hypoosmotic environments.     

Salinity effects on osmoregulation and gill morphology in juvenile Persian sturgeon (<Emphasis Type="Italic">Acipenser persicus</Emphasis>)

The effect of abrupt and 5-day gradual salinity transfers from freshwater (FW) to 11 ‰ Caspian Sea brackish water (BW) was investigated in juvenile Persian sturgeon Acipenser persicus with three different weight groups: 1–2 g (1.62 ± 0.27 g), 2–3 g (2.55 ± 0.41 g) and 3–5 g (4.28 ± 0.76 g). Mortality rates, blood osmotic pressure, gill morphology and branchial Na⁺, K⁺-ATPase (NKA) activity were measured 4 and 10 days after abrupt transfer and 9 and 15 days after the initial gradual transfer (i.e. 4 and 10 days after reaching Caspian Sea salinity). Fish under 3 g could not survive increased salinity, and the blood osmotic pressure of the remaining surviving fish increased and remained elevated. However, heavier fish were able to survive and successfully acclimate, even to rapid salinity change with osmotic pressure reduced to Caspian Sea osmolality levels. At the gill level, the developmental increase in chloride cell volume and a higher NKA content most probably allow juveniles weighing more than 2 g to sharply increase NKA activity if the fish are transferred to BW. The rapid chloride cell proliferation occurring with increased salinity should strengthen this acclimation response. Therefore, a drastic physiological change occurs when fish weigh more than 2 g that allows migration to higher salinities. The triggering signal on chloride cells must be further investigated in order to optimize this functional step.     

Effects of chronic confinement on physiological responses of juvenile gilthead sea bream, Sparus aurata L., to acute handling

Understanding how gilthead sea bream, Sparus aurata L., an important Mediterranean Sea species for aquaculture, respond physiologically to stressors commonly encountered in intensive rearing is important for effective production, as managing for stress is a major factor in maintaining healthy fish stocks. Our objective was to determine whether holding juvenile gilthead sea bream at a high density (HD), as a chronic stressor, would affect their physiological responses to a subsequent acute handling stressor. After acclimation at a low density (LD) of 6 kg m^?3 in 200‐L circular tanks containing 33–36 g L^?1 recirculating seawater at 19°C under a normal photoperiod, juvenile 37‐g gilthead sea bream were confined for 14 days at a HD of 26 kg m^?3 and then subjected to 30‐s aerial emersion in a dipnet. Plasma levels of cortisol, glucose, lactate, osmolality and chloride were determined in fish held in separate lots during LD (control) and HD confinement at 0, 1, 2, 7 and 14 days, and then after handling at 0, 1, 2, 4 and 8 h. Although plasma cortisol levels were similar in LD and HD fish groups after 14 d of confinement (15 and 23 ng mL^?1, respectively), the cortisol response in fish from the HD treatment at 1 and 2 h following acute handling (70 and 37 ng mL^?1, respectively) was only about half of that measured in the control group (139 and 102 ng mL^?1); plasma cortisol was similar in both groups by 4 and 8 h. In contrast, plasma glucose elevations in response to handling were higher at 4 and 8 h in the HD‐held fish (94 and 72 mg dL^?1, respectively) than in those from the LD treatment (59 and 51 mg dL^?1); glucose responses were similar in both groups at 1 and 2 h after handling and throughout confinement. Plasma lactate levels were higher in LD fish than in the HD group at the beginning of the experiment but were similar after 14 d confinement and responses to handling were similar (e.g. 33 and 35 mg dL^?1 at 1 h). Plasma osmolality showed increases during the first 2 h after acute handling but no differences were evident between the two density treatments at any time during confinement or posthandling. Plasma chloride levels did not change throughout the experiment. The reduced plasma cortisol response to acute handling likely resulted from negative feedback of mildly but chronically elevated circulating cortisol caused by the confinement stressor on the hypothalamic–pituitary–interrenal axis. While other post‐handling physiological changes also showed differences between treatment groups, the suppressed cortisol response in the HD‐held fish suggests a reduction in the gilthead sea bream's normal capacity to respond to an acute stressor.     

Osmotic adaptation of Oncorhynchus kisutch Walbaum

Coho salmon yearlings, reared in France in a freshwater hatchery, were directly transferred to sea water at three different periods of the year: 14 January, 3 March and 14 April 1976. The last two experiments were realized at three different salinities: 25, 30 and 35‰.The results show important seasonal differences in the osmoregulatory responses. The direct transfer to 35‰ reveals some osmoregulatory problems which are not discernable at lower salinities. Yearlings transferred to a 35‰ sea water present a much higher and faster rise of plasma electrolytes and of branchial Na⁺K⁺ ATPase activity than fish transferred to a 25 or 30‰ sea water.It was found that a physiologically pre-adapted fish, characterized by a high level of branchial Na⁺K⁺ ATPase activity in fresh water (April) will present in sea water a slower and more regular increase in gill Na⁺K⁺ ATPase activity than fish with a low level of enzyme activity in fresh water (January–March). These smolts transferred to 25 and 30‰ sea water in April do not exhibit important variations, whereas a well-marked osmotic disequilibrium appears at 35‰. However, this osmotic stress is much more rapidly controlled than in the previous transfers.Our results suggest that the highest tolerance to sea water is reached only at time of smolting and that the time of transfer may have a direct influence on the intensity of the osmotic stress. These facts might be of considerable importance for the development of marine rearing of coho salmon in coastal areas where the salinities stay usually above 30‰ which constitutes an unusual environment for the species under consideration.