Respiratory stress in rainbow trout dying from aluminium exposure in soft,acid water,with or without added sodium chloride

Rainbow trout exposed to 32 μM aluminium at pH=5.0 in artificial soft water ([Ca⁺⁺]=50 μM), with or without added sodium chloride (150 mM), suffer from severe respiratory stress characterized by hyperventilation, low Pa_{O 2}, high Pa_{CO 2}, low pHa and high blood lactate concentrations at death. Plasma chloride concentration at death had decreased in the group with no added NaCl, but not in the presence of added NaCl. Median survival times were not significantly different in the two groups. These findings suggest that death under the given conditions is primarily due to impeded gas exchange.     

Effects of prolonged epinephrine infusion on blood respiratory and acid-base states in the rainbow trout: Alpha and beta effects

Rainbow trout were infused continuously for 12h with epinephrine in the presence or absence of alpha-and/or beta-adrenergic blockade to characterize the specific adrenergic mechanisms involved in the control of blood acid-base status and oxygen transport capacity. Infusion of epinephrine, alone, produced a transient respiratory acidosis, as indicated by an increase in carbon dioxide tension and a decrease in whole blood pH, yet arterial oxygen tension was elevated. Red blood cell pH increased by approximately 0.2 pH units during epinephrine infusion and this increase as well as the increase in oxygen tension were prevented by pretreatment with propranolol (a beta-adrenergic antagonist). Epinephrine infusion during alpha-adrenergic blockade caused a prolonged elevation of blood carbon dioxide tension and abolished the increases in hematocrit and hemoglobin concentrations observed during epinephrine infusion alone. Infusion of the alpha-adrenergic agonists phenylephrine (an alpha₁ agonist) or clonidine (an alpha₂ agonist) caused respiratory acidosis (decreased pH, increased CO₂ tension) and a reduction in oxygen tension. Infusion of isoprenaline (a non-specific beta agonist) caused delayed increases in carbon dioxide and oxygen tensions. We speculate that the increased carbon dioxide tension observed during epinephrine infusion is a result of beta-adrenoceptor mediated inhibition of red blood cell bicarbonate dehydration and not branchial convective or diffusive adjustments. The effects of epinephrine on blood O₂ tension, content and carrying capacity are discussed with reference to the participation of alpha- and beta-adrenergic mechanisms at the gill, spleen and red blood cell.     

Morphological responses of the rainbow trout (Oncorhynchus mykiss) gill to hyperoxia,base (NaHCO3) and acid (HCl) infusions

Marked morphological responses occur in the gills of freshwater rainbow trout in response to experimental acid-base disturbance and these responses play an important role in acid-base correction. Compensated respiratory acidosis induced by 70h exposure to environmental hyperoxia (elevated water PO₂) caused a 33% decrease in branchial chloride cell fractional surface area (CCFA). Metabolic alkalosis induced by normoxic recovery (6h) from hyperoxia (72h) caused a 50% increase in CCFA, whereas metabolic alkalosis induced by infusion (19h) of NaHCO₃ caused a 70% rise. However, the largest increase (135%) in CCFA was seen in response to infusion (19h) of HCl. NaCl infusion had no effect. A particular goal was to assess the relative importance of changes in CCFA vs. changes in internal substrate (HCO₃ ^–) availability in regulating the activity of the branchial Cl^–/HCO₃ ^– exchange system. For each of the experimental treatments, the accompanying blood acid-base status and branchial transport kinetics (K_m, J_max) for Cl^– uptake had been determined in earlier studies. In the present study, a positive linear relationship was established between CCFA and J^Cl– _max in individual control fish in the absence of an acid-base disturbance. By reference to this relationship, observed changes in J^Cl– _max during metabolic acid-base disturbances were clearly due to changes in both CCFA and internal substrate levels (plasma [HCO₃ ^–]) with the two factors having approximately equal influence.     

Preservation of trout sperm in liquid or frozen stateFlüssig- und gefrierkonservierung von regenbogenforellensperma

A series of experiments to study the preservation of rainbow trout semen in the liquid and frozen state was carried out.For the preservation of liquid semen both undiluted and diluted semen was stored in total darkness at 20° or 4°C under a number of different gasses (air, O₂, O₂ + N₂ (1:1), N₂, CO₂, N₂ + H₂ + CO₂ (8:1:1)). The best results were obtained when storing semen in an undiluted state at 4°C under O₂ (hatching rate after 15 days was 80.6%, controls were 98.2%). Good results were also obtained under air (after 9 days 94.7% vs 94.9% for the controls). Anaerobic conditions, dilution or an increase in temperature all rendered less favourable results.For the purpose of cryopreservation a diluent was developed on the basis of the composition of rainbow trout seminal plasma. The semen was mixed with the diluent immediately before freezing at a ratio of 1:1 or 1:3. The pellet-technique (Nagase, 1964) was found to be more convenient and successful than freezing in straws. The pellets were thawed in a 1% NaHCO₃-solution. The hatching results after storage periods of 1–4 months were very variable (2.6–80.3%).     

Influence of ionic composition on acid-base regulation in rainbow trout (Oncorhynchus mykiss) exposed to environmental hypercapnia

The influence of ambient calcium, bicarbonate and chloride levels on acid-base regulation was investigated in rainbow trout acclimated and exposed to hypercapnia in five different water types. In soft water (low [Ca⁺⁺] and [HCO₃ ⁻]), compensation of the respiratory acidosis was slow and incomplete within 72h. High ambient [HCO₃ ⁻] clearly improved extracellular HCO₃ ⁻ accumulation, and pH recovery was accomplished within 24h. This may result from stimulation of branchial HCO₃ ⁻ (influx)/Cl⁻ (outflux) exchange. Elevation of ambient [Cl⁻] had a small, positive effect on pH compensation. High ambient [Ca⁺⁺] improved the degree of pH compensation. Plasma [HCO₃ ⁻] and [Cl⁻] showed an inverse 1:1 relationship in all acclimation groups, revealing an ubiquitous chloride-mediated acid-base regulation. Ventilation activity was increased by hypercapnia and only returned to control values in hard water (high [HCO₃ ⁻]and [Ca⁺⁺]). During progressive hypercapnia (up to 3% CO₂), hard water acclimated fish obtained significantly higher plasma [HC0₃ ⁻] (51.2 mM) than fish acclimated to low [Ca⁺⁺]/high [HCO₃ ⁻] (44.7 mM). This suggests an additive effect of ambient Ca⁺⁺ on plasma HCO₃ ⁻ accumulation. At levels of CO₂ above 1%, some mortality was induced in low [Ca⁺⁺]/high [HCO₃ ⁻] water. Dying fish could be distinguished from surviving fish by an excessive Cl⁻loss and increasing extracellular anion gap.     

Effects of adrenaline on ionic equilibria in red blood cells of rainbow trout (Salmo gairdneri)

Effects of adrenaline on the equilibrium distributions of Na⁺ , K⁺ , H⁺ , Cl^– , and H₂O across the cell membrane of rainbow trout (Salmo gairdneri) erythrocytes were determinedin vitro, as a function of P CO₂ (1.76–7.77 torr). CO₂-carrying capacity of the blood was also examined. Plasma catecholamine concentrations inunanaesthetized, unrestrained trout were 3.1 nM adrenaline and 1.2 nM noradrenaline. Elevation of the plasma adrenaline concentrationin vitro to 4.6 × 10³ nM resulted in net gains of Na⁺ , Cl^– and H₂O by red cells, a net loss of H⁺ from red cells, and a pronounced red cell swelling. Adrenaline also reduced the CO₂-carrying capacity of trout bloodin vitro. The magnitudes of these effects increased with P_CO2 and, thus, were sensitive to blood HCO₃ ^– concentrations. The distribution of K⁺ between red cells and plasma was unaffected by adrenaline. Adrenergic-mediated ion movements and red cell swelling were sensitive to both propranolol and SITS. These results are consistent with the symport NaCl uptake model for adrenergic-mediated swelling of Baroinet al. (1984). The adrenergic response of fish erythrocytes may function to ameliorate the effects of blood acidoses on O₂-carrying capacity by maintaining red cell pH in the face of a decrease in plasma pH.     

Role of salinity in the dissolution rates of CaCO3 and its implications for aquaculture liming

This work aimed at assessing the role of salinity in the dissolution rates of CaCO₃, discussing its implications for aquaculture liming. A simplified formula of artificial seawater without HCO₃^? was initially prepared. Four batches of 10 L of diluted artificial seawater (salinity = 3.3 g/L) without HCO₃^? were prepared. Sixteen Erlenmeyer flasks were filled up with 2 L each of the diluted artificial seawater without HCO₃^?. Besides, 16 other 2,000‐ml Erlenmeyer flasks were filled up with 2 L of distilled water (freshwater). The experimental treatments were formed by applying increasing amounts of analytical‐grade sodium bicarbonate (NaHCO₃) upon brackish water and freshwater. Accordingly, four initial levels of total alkalinity (TA) have been set up as follows: 4–6, 33–35, 62–63 and 120–122 mg/L. Next, approximately one gram of analytical‐grade calcium carbonate (CaCO₃) was applied onto each flask. Water's pH, TA and calcium concentration were determined weekly over a 7‐week period, by appropriate methods. For a same initial TA, TA increase over time after CaCO₃ application was lower in the brackish water flasks than in the freshwater ones. This was especially clear for moderate (63 mg/L) and high (120 mg/L) alkalinities. It was concluded that brackish and saline waters used for aquaculture would only benefit from CaCO₃ liming if their alkalinities were lower than 60–80 mg/L.     

Transport of juvenile dusky grouper Epinephelus marginatus under different packing densities: Metabolic and haematological responses

The aim of this study was to investigate a suitable packing density for the transport of juvenile dusky grouper, Epinephelus marginatus, based on the evaluation of stress responses in blood. After acclimation, fish were placed in plastic bags and transported for 8 hr on paved road at densities of 28, 45 and 64 g/L. Water quality was monitored before and after transport. Blood was collected before, upon arrival (0 hr), after 2 and 24 hr of transport. Plasma cortisol, blood glucose, partial pressures of O₂ (pO₂) and CO₂ (pCO₂), blood pH and HCO₃^? were evaluated. Blood smears were prepared for the verification of leucocyte profile and neutrophils:lymphocyte ratio (N:L). Blood pCO₂, pH and HCO₃^? increased significantly after transport for all treatments compared with pre‐transport. Glucose levels increased at the higher density whereas no effects were observed on plasma cortisol and pO₂ levels. Upon arrival, all treatments showed lymphopenia and neutrophilia which increased N:L ratio. Although lymphopenia was observed in higher densities until 2 hr after transport, haematological parameters were fully restored within 24 hr post transport. Furthermore, no mortalities were observed throughout the experimental period. Based on the transient physiological changes observed in this study, juvenile dusky grouper can be safely transported in plastic bags for 8 hr at a density of up to 64 g/L.     

The conversion of plasma HCO 3 − to CO2 by rainbow trout red blood cells in vitro: adrenergic inhibition and the influence of oxygenation status

This study employed a recently developed radioisotopic assay (Wood and Perry 1991) to examine the inhibition, induced by catecholamines, of the conversion of plasma HCO ₃ ^– to CO₂ in acidotic trout blood, and the influence of oxygenation status on the response. Blood was incubated in vitro at P_{CO 2}= 2 torr, and 10^–6 M noradrenaline was employed as the adrenergic stimulus. In particular we investigated whether the inhibition of plasma HCO ₃ ^– conversion could be explained by a limited supply of H⁺s for the intracellular HCO ₃ ^– dehydration reaction because of competition by the adrenergically activated Na /H⁺ exchanger. Hypoxia (P_{O 2}= 15 torr) was employed as a tool to intensify this competition. Hypoxia raised RBC pHi, pHe, and plasma total CO₂ concentration (C_{CO 2}) by the Haldane effect, and increased the magnitude of Na⁺/H⁺ activation, expressed as the change in the transmembrane pH gradient (pHe-pHi). However hypoxia did not alter the inhibition of the conversion of plasma HCO ₃ ^– to CO₂ caused by noradrenaline. Hypoxia itself stimulated the RBC-mediated conversion of plasma HCO ₃ ^– to CO₂ by about 20% in the presence or absence of noradrenaline. The conversion rate was strongly correlated with pHe, pHe-pHi, and plasma C_{CO 2} in these experiments, but not with pHi. We conclude that adrenergically mediated inhibition in the conversion of plasma HCO ₃ ^– to CO₂ by trout RBCs is not due to competitive limitation on intracellular H⁺s, but rather to changes in the electrochemical gradient for HCO ₃ ^– entry and/or to CO₂ recycling from plasma to RBC. The deoxygenated condition helps to promote CO₂ excretion at the level of the RBC.     

A critical analysis of gas transferin vivo and in a blood-perfused trout head preparation

Gas transfer and blood acid-base status in the blood-perfused trout head preparation (in vitro) were compared with intact trout (in vivo) fitted with oral membranes, dorsal aortic, ventral aortic, and opercular cannulae. Gas transfer rates were calculated from both arterial-venous blood differences and inspired-expired water differences using the Fick method. Oxygen uptake and carbon dioxide excretion were lower, while ammonia excretion was higher, in the blood-perfused head relative toin vivo rates. Gas transfer rates calculated from water were consistently greater than rates calculated from blood, the difference being greaterin vitro compared toin vivo. We conclude that the inadequacy of O₂ and CO₂ transfer in the blood-perfused head was not due to abnormal gill diffusive conductance, but was more likely related to the reduced magnitude of the blood-to-water O₂ and CO₂ diffusion gradients, low hematocrit, and decreased perfusion flow rate . Under the conditions of the present study, the blood-perfused trout head is not a suitable preparation for the study of oxygen transfer. We conclude this preparation is useful for evaluating branchial carbon dioxide or ammonia transfer only when comparable measurements or manipulations cannot be made on intact fish.     

Site of acid-base relevant ion transfer in the gills of rainbow trout (Oncorhynchus mykiss) exposed to environmental hypercapnia

In order to delineate the contribution of primary vs. secondary circulatory circuits in the gill for acid-base and ionic regulation, the flow and composition of the fluids in the central venous sinus (CVS) and the systemic circuit of rainbow trout were studied by application of a previously developed microcannulation technique during normocapnic and hypercapnic conditions. The average haematocrit (Hct) of blood from dorsal aorta (DA) and sinus venosus (SV) ranged from 20.1 to 26.7%, whereas average Hct in the fluid from the branchial vein (BV), representing drainage from the central venous sinus (CVS), was in the range of 4.2 to 7.0%. Under normocapnic conditions, the largest fraction of cardiac output, 92.9%, was directed through the systemic vascular circuit, whereas the CVS circuit was perfused with 7.1 % of cardiac output. Hypercapnia did not significantly affect the blood flow distribution between the two circuits. The pattern of acid-base regulation in dorsal aortic blood reflected the characteristic response of fish exposed to environmental hypercapnia. Upon initiation of environmental hypercapnia (2% CO₂), plasma P_{CO 2} was elevated in all three flow compartments (CVS, DA, SV), inducing an extracellular respiratory acidosis of about 0.4 pH units. pH and [HCO₃ ^-] values in the DA were consistently lower, than those for both CVS and SV sites throughout the hypercapnic period. During the 8h of exposure plasma bicarbonate concentration was elevated by about 12 mM, complemented by a fall in extracellular [Cl^-] of about 10 mM in all three compartments. The amount of HCO₃ ^- gained at the CVS site during 8h of hypercapnia (3.3 mmol · kg^-1) exceeds the amount accumulated in the extracellular space (2.1 mmol·kg^-1), suggesting the CVS as the main site of ionic acid-base regulation in trout.     

Cardiac,ventilatory and metabolic responses of two ecologically dissimilar species of fish to waterborne cyanide

Changes in heart rate, ventilatory activity and oxygen consumption were determined in trout (Salmo gairdneri) and brown bullhead catfish (Ictalurus nebulosus) during exposure to a steadily increasing concentration of waterborne cyanide selected to produce death in 8–9 hours for each species. The lethal cyanide concentration for the bullheads was an order of magnitude higher than for trout. Trout developed an immediate and gradually increasing bradycardia throughout the exposure period. Cyanide produced tachycardia in the bullhead followed by a gradual onset of bradycardia as the concentration of cyanide was raised. Pericardial injection of atropine (a muscarinic cholinergic antagonist) indicated that bradycardia in the trout was due initially to increased vagal tone but later due to the direct effect of cyanide on the heart. Hyperventilation in the trout persisted throughout the exposure period, although the rate and amplitude fluctuated and was variable between individual fish. During the last hour of exposure (highest cyanide concentration), ventilation was characterized by rapid, shallow breaths followed by a sudden respiratory arrest. The bullheads exhibited hyperventilation during the first 3 hours of exposure followed by a gradual, linear drop in ventilation rate and amplitude until death occurred. Cardiac and ventilatory responses in both species were attributed to stimulation of central and peripheral chemoreceptors by cyanide. Evidence is presented which suggests the initial response in the bullheads was due, at least in part, to gustatory stimulation by the cyanide. Oxygen consumption of the trout remained above pre-exposure levels for the majority of the test period. Oxygen consumption in the bullhead paralleled the changes in heart and ventilatory rates. Whole-body lactate levels of fingerlings of both species during cyanide exposure were measured to estimate the extent of anaerobiosis. Whole-body lactate levels were much greater in the bullheads than the trout, indicating a higher capacity for anaerobiosis, possibly due to a greater fuel supply. Overall, the trout responded to cyanide in a manner similar to that produced by environmental hypoxia whereas the bullheads experienced a gustatory stimulus which masked the hypoxia-like response.     

Effects of growth hormone on plasma ionic regulation,respiration and extracellular acid-base status in trout (Oncorhynchus mykiss) transferred to seawater

The effects of trout recombinant growth hormone (rtGH) treatment (0.25 g g^–1 by intraperitoneal implant) on plasma ionic regulation, extracellular acid-base status and respiration were investigated in freshwater rainbow trout and during a 4-day period after direct transfer into seawater (35 g 1^–1).In freshwater, rtGH treatment resulted in a significant increase in gill (Na⁺, K⁺) ATPase activity and in standard metabolism (MO₂). The latter would mainly result from a higher rate of protein synthesis. Direct transfer from freshwater to seawater induced a decrease in arterial blood pH, far more pronounced in controls than in treated fish. This effect could be regarded in both groups mainly as a metabolic acidosis resulting from extracellular ion composition changes (i.e., an increase higher in chloride than in sodium, more marked in controls than in treated fish). As the rise in PaCO₂, in spite of an increase in ventilatory activity, is more significant in controls than in treated fish, it can be assumed that rtGH treatment lightened the decrease in the gas diffusing capacity of gills induced by transfer to seawater. The initial increase in MO₂ in both controls and treated fish could be the consequence of an increase in energetic cost of ventilation and osmoregulation. Then, in treated fish, the persistent high level of M may indicate a stimulation of intermediary metabolism by rtGH. In addition, the absence in treated fish of an increase in plasma lactate concentration, as observed in controls, would indicate that rtGH attenuated the decrease in O₂ affinity of haemoglobin foreseeable from the metabolic acidosis.This article is dedicated to Professor Claude Peyraud, whose recent death has deeply saddened us. We respectfully pay a tribute to his memory.     

Long-term separate and combined effects of environmental hypercapnia and hyperoxia in Atlantic salmon (Salmo salar L.) smolts

Atlantic salmon (Salmo salar L.) parr (mean start weight 50 g) were reared in freshwater (FW) and exposed to three levels of oxygen saturation measured in effluent water; control group (93% O₂, LO₂), medium (111% O₂, MO₂) and high (123% O₂, HO₂). Further three groups were exposed to similar water oxygen levels in combination with elevated carbon dioxide levels (17–18 mg L^– 1 CO₂), named LO₂–CO₂, MO₂–CO₂ and HO₂–CO₂, respectively. The experiment was run in duplicate tanks for 42 days, and the fish were subsequently transferred to the same seawater (SW) regime for 45 days for an assessment of post-smolt growth. As a consequence of the CO₂ addition, tank pH levels in the FW period were reduced from 6.7 to 5.9 for the hypercapnia groups compared to for the normcapnia groups. Water temperature in FW ranged between 6.4 and 9.0 °C. Citrate was added to the water to complex labile aluminium.In the CO₂ groups observed ventilation frequencies were significantly increased compared to the control (p < 0.05). This difference declined towards the end of the FW period, suggesting acclimation to elevated CO₂. The degree of oxygenation appeared to contribute to the acclimation as the lowest mean ventilation frequency on day 36 was found in the HO₂–CO₂ group and the highest in the LO₂–CO₂ group. Lower plasma chloride and sodium levels were observed in the CO₂ groups relative to the respective oxygenation groups during the FW period, while plasma chloride and sodium levels were normalised to equal levels for all groups after 44 days in SW. No significant differences were found among treatments for blood concentrations of red blood cells, haemoglobin, potassium and glucose during the experiment.By termination of the FW period, the HO₂ group had significantly higher body weight than all other groups (p < 0.05), with specific growth rate significantly higher than the CO₂ groups (p < 0.05). Further, the condition factor was significantly lower in all the CO₂ groups at the end of the FW period compared to the control and normcapnia groups (p < 0.05). Although variable among replicates, occurrence of nephrocalcinosis was 10 times higher in the hypercapnia groups than in the control and normcapnia groups. Mortality was negligible (< 2.0%) during the trial, and most of the mortality occurred following SW transfer.     

Influence of Seaweed Aquaculture on Marine Inorganic Carbon Dynamics and Sea‐air CO2 Flux

On the basis of field data measured during four cruises from April 2011 to January 2012, spatial and seasonal variations of CO₂ dynamics and aqueous pCO₂ were investigated in the seaweed aquaculture area, Lidao town, China. Results showed that the mean annual concentrations of dissolved inorganic carbon (DIC), HCO₃^?, CO₃^2?, and CO₂ were 2024.79 ± 146.96, 1842.41 ± 132.13, 170.02 ± 42.82, and 12.35 ± 2.52 µmol/L, respectively. There were no significant differences between areas in concentrations of DIC and HCO₃^? (P > 0.05), while the differences for the concentration of CO₂ was very significant (P < 0.01). The mean annual values of aqueous pCO₂ and sea‐air CO₂ flux were 287.80 ± 37.90 µatm and ?32.71 ± 17.23 mmol/m²/d, respectively. There were very significant differences (P < 0.01) for aqueous pCO₂ and sea‐air CO₂ flux not only between different areas, but also between different seasons. The buffer factor β indicates that, inside the seaweed area, inorganic carbon dynamics are mainly influenced by photosynthesis and respiration process.     

Mortality of marine cultured rainbow trout, Oncorhynchus my kiss (Walbaum), during the summer in the Netherlands

Abstract. In northern Europe, rearing of rainbow trout, Oncorhynchus mykiss (Walbaum), in sea cages is a substantial part of fish culture. One of the major constraints for the development of this system in other parts of Europe is the unexplained mortality of fish during the summer. To investigate environmental aspects of this mortality, rainbow trout, cultured in cages in sea water, were monitored from May to October for three successive years. No evidence of bacterial involvement could be found, while water temperature and salinity strongly influence the mortality. This supports the suggestion that the mortality has been caused by patho-physiological changes due to higher metabolic requirements for osmoregulation at elevated water temperature in the saline environment which might result in a dissipation of O₂ by CO₂ on the hemoglobin.     

Changes in arterial PO₂, physiological blood parameters and intracellular antioxidants in free-swimming Atlantic cod (Gadus morhua) exposed to varying levels of hyperoxia

Free-swimming Atlantic cod (Gadus morhua) were exposed to water oxygen pressures (P _wO₂) ranging from 18.1 to 41.5 kPa and sampled for blood using an indwelling caudal artery cannula. Arterial blood oxygen pressure (P _aO₂) increased with increasing P _wO₂, from 12.0 kPa in normoxia (18.1 kPa) to 34.2 kPa in the highest hyperoxic level tested (41.5 kPa). Blood CO₂ pressure and plasma bicarbonate concentration increased with P _wO₂, indicating reduced ventilation with increased P _wO₂. Plasma glucose, sodium and potassium were not affected by water oxygen level. Blood oxidative stress biomarkers, reduced glutathione, oxidized glutathione and the oxidative stress index (ratio between oxidized and total glutathione) differed intermittently between normoxia and hyperoxia. The oxidative stress index was higher in the blood of exposed compared to unexposed control cod. Together with elevated P _aO₂, these findings suggest increased production of reactive oxygen species and increased oxidative stress in Atlantic cod exposed to hyperoxia.     

Assessment of hydrogeochemical characteristics of groundwater in shrimp farming areas in coastal Tamil Nadu, India

Brackishwater aquaculture is basically farming in coastal region, and it utilizes the saline water from either sea or estuary or creek. Assessment of hydrogeochemisty of groundwater resources in shrimp farming areas is very much required not only for monitoring the shrimp farming impacts, but also to suggest better management strategies for the long-term sustainability of shrimp farming and integrated water resources management in coastal regions. Watershed-based assessment is ideal as watershed is a geohydrological unit, and it will give the realistic and cumulative effects more precisely. With this background, the present investigation was carried out to evaluate the geochemical process regulating groundwater quality in shrimp farming areas of coastal miniwatersheds of Vellar and Coleroon river, Cuddalore district, Tamil Nadu, along the east coast of India. Representative groundwater (29) samples from shallow aquifer (hand pump and open well) were collected periodically (June 2008, January 2009, April 2009 and July 2009) using the simple random sampling method and analyzed for various water quality parameters viz. pH, TDS, total hardness, alkalinity, cations (Ca⁺, Mg⁺, Na⁺) and anions (Cl^?, SO₄ ^?, NO₃ ^?, HCO₃ ^?). The groundwater data indicated that the HCO₃ was the dominant ion in the study area with sodium (Na > Ca > Mg) and bicarbonate (HCO₃ > Cl > SO₄) as the predominant cation and anion, respectively. The large variations in mean and standard deviation of ionic concentration suggest that the water chemistry in the study region was not homogenous and may be influenced by complex sources for the hydrogeochemical processes. The piper trilinear diagram depicts the status of the groundwater quality and also suggests that the cation exchange and mineral dissolution was responsible for this elevated ionic composition at some locations in the study area. The multivariate statistical analysis viz., principal component analysis and cluster analysis clearly elucidated that the groundwater quality in the area is mainly due to natural process and the shrimp farming is not an influencing factor.     

Ionoregulatory responses to temperature change in two species of freshwater fish

We examined the ionoregulatory responses to temperature changes in two species of freshwater fish that differ in thermal preferences; the stenothermal, cold-water rainbow trout (Oncorhynchus mykiss) and the more eurythermal, warm-water common shiner (Notropis cornutus). We found that rainbow trout maintained constant plasma Na⁺ levels over the entire temperature regime (5–20 °C). Upon transfer from 15 °C (holding temperature) to 5 and 10 °C, rainbow trout experienced a significant drop in Na⁺ uptake (J_in ^Na), but after two weeks J_in ^Na had upregulated to warm temperature levels. Further, Na⁺ efflux (J_out ^Na) fell significantly at the colder temperatures. As a result, trout at the lowest temperatures were still in ion balance. When trout were exercised to exhaustion both O₂ consumption (MO₂) and J_out ^Na rose significantly at all temperatures, but while MO₂ continued to be dependent upon temperature, J_out ^Na was high and constant. In contrast to the trout, common shiners experienced a 20% drop in plasma Na⁺ at 5 °C. Upon exposure to cold temperatures they experienced a reduced J_in ^Na, and showed no signs of acclimation during the subsequent two weeks. Likewise J_out ^Na was constant at all temperatures. These findings raise questions regarding the degree to which fish employ homeostatic mechanisms designed to defend a set- point (i.e., steady-state) osmolarity and ionic composition.     

The effects of experimental anaemia on CO2 excretionin vitro in rainbow trout,Oncorhynchus mykiss

The effects of severe experimental anaemia on red blood cell HCO₃ ^– dehydrationin vitro were examined in rainbow trout,Oncorhynchus mykiss. After 5 days of anaemia (haematocrit=4.9±1.1%) induced by intraperitoneal injection of phenylhydrazine hydrochloride, fish displayed elevated arterial CO₂ tensions (anaemic PaCO₂=3.19±0.42 torrvs. control PaCO₂=1.35±0.17 torr) and a significant acidosis (anaemic pHa=7.73±0.04vs. control pHa=7.99±0.04). However, after 15–20 days of anaemia (hct=6.6±0.8%) induced by blood withdrawal, the arterial CO₂ tension was significantly lower than the control value, suggesting that physiological adjustments occurred within this time period to compensate for the lowered haematocrit. Compensation probably did not involve alterations in ventilation, which was unaffected by 5 days of anaemia (anaemic ;w=786±187 ml min^–1 kg^–1 vs. control ;w=945±175 min^–1 kg^–1), based on indirect Fick principle measurements.Potential adaptations to longer term anaemia at the level of the red blood cells were investigated using a radioisotopic HCO₃ ^– dehydration assay. Owing to the difference in haematocrits, the HCO₃ ^– dehydration rate for blood from anaemic fish was significantly lower than that for control fish following equilibration at the same CO₂ tension. This difference was eliminated when HCO₃ ^– dehydration rates were measured on blood samples adjusted to the same haematocrit, a result which implies that the intrinsic rate of CO₂ excretion at the level of the red blood cell was not up-regulated during anaemia. The difference was also eliminated by equilibrating the blood samples with CO₂ tensions appropriate for the group from which the sample was obtained,i.e., PCO₂=1.4 torr for control samples and PCO₂=3.2 torr for anaemic samples; each at the appropriate haematocrit. It is concluded that the elevated PaCO₂ helps to reset CO₂ excretion to the control level, but that some additional physiological adjustment occurs to lower the PaCO₂ after 15–20 days of anaemia.