Supplementation of potassium, magnesium and sodium chloride in practical diets for the Pacific white shrimp, Litopenaeus vannamei, reared in low salinity waters

The culture of Litopenaeus vannamei in inland low salinity waters is currently being practiced in various countries around the world. These environments are often deficient in key ions essential for normal physiological function, including potassium (K⁺) and magnesium (Mg²⁺). Farmers have sometimes been able to counteract ionic deficiencies in the water profile by adding mineral salts containing sources of K⁺ and Mg²⁺. The purpose of this study was to explore the possibility of correcting deficiencies of K⁺ and Mg²⁺ in the water profile with dietary supplementation of these minerals. Two separate 7‐week experiments were conducted in 4.0 g⁻¹ artificial low salinity water to evaluate the effects of mineral supplements (K⁺, Mg²⁺ and NaCl) to diets of L. vannamei reared in low salinity waters. In trial 1 seven diets were formulated (10 g NaCl kg⁻¹, 20 g NaCl kg⁻¹, 150 mg kg⁻¹ Mg²⁺, 300 mg kg⁻¹ Mg²⁺, 5 g K⁺ kg⁻¹, 10 g K⁺ kg⁻¹, and a basal diet to serve as a control). Minerals were added in the form of purified potassium chloride (KCl), magnesium chloride (MgCl₂·6H₂O) and NaCl. Trial 2 evaluated the use of a coating agent for the Mg²⁺ and NaCl treatments, while a K⁺ amino acid complex was utilized in the K⁺ treatments to reduce mineral leaching. Trial 2 was performed using similar treatment levels as trial 1. Shrimp survival and growth were assessed in both experiments. Results from trial 1 indicated no significant differences in survival, growth or percent weight gain. Results from trial 2 revealed no significant differences in survival and growth in the NaCl and Mg²⁺ treatments. However, significant differences in growth (P < 0.05) were observed when using the 10 g K⁺ kg⁻¹ treatment, suggesting that dietary supplementation of a K⁺ amino acid complex may help improve growth of the species in low salinity waters.     

Toxic effects of mercury chloride on silver catfish (Rhamdia quelen) spermatozoa

Heavy metals are highly toxic elements that are present in the environment, especially in water. Mercury chloride (HgCl₂) stands out among these compounds because of its strong ability to induce damage to any tissue with which it comes into contact. The gametes of spawning aquatic animals, such as fish, are susceptible to such damage. Thus, our objective was to evaluate the toxic potential of HgCl₂ in the capacitation and activation of Rhamdia quelen sperm. Semen was collected from seven males and activated in 58 mM sodium chloride (NaCl) containing 0 (control), 4^?10, 7^?10, 7^?9, and 7^?8 M HgCl₂. The evaluated variables included motility, vigor, motility time, morphology, membrane integrity, membrane fluidity, mitochondrial functionality, production of reactive oxygen species (ROS), and DNA fragmentation. All evaluated HgCl₂ concentrations increased primary pathologies and reduced motility, vigor and motility time. Damage to membrane integrity and fluidity began occurring at a concentration of 7^?10 M HgCl₂. These results indicate that HgCl₂ has a toxic effect on different sites of fish spermatozoa and that sperm motility decreases after exposure to HgCl₂, impairing sperm capacitation and activation.     

Effect of cryoprotectants, extenders and freezing rates on the fertilization rate of frozen striped catfish, Pangasius hypophthalmus (Sauvage), sperm

The effects of four cryoprotectants (methanol, MeOH; dimethyl sulphoxide, DMSO; dimethyl acetamide, DMA; and ethylene glycol, EG), three extenders (calcium‐free Hanks' balanced salt solution, C‐F HBSS, Hanks' balanced salt solution, HBSS and sodium chloride, NaCl) and two different freezing procedures (one‐ and two‐step) on the cryopreservation of striped catfish (Pangasius hypophthalmus (Sauvage)) sperm were investigated. Sperm were frozen using a controlled‐rate freezer in 250 μL straws and stored for 2 weeks in a liquid nitrogen (LN₂) container. They were then airthawed at room temperature, and fertilization, motility and viability were assessed. The highest fertilization rate of 41% (81% of control) was achieved with the combination of 12% DMSO and 0.9% NaCl using a one‐step freezing procedure (10°C min^?1). Also, DMA resulted in a higher fertilization rate (30% or 51% of the control) than MeOH (18% or 38% of the control) or EG (8% or 12% of the control). In addition, the three extenders used did not affect fertilization rates after cryopreservation with each cryoprotectant. There were no significant differences among the three cryoprotectant concentrations and between the one‐ and two‐step freezing procedures. However, fertilization rates of cryopreserved sperm were significantly lower than the controls (P<0.05). The results of this study indicate that high fertilization rates of striped catfish eggs can be achieved using cryopreserved sperm when frozen at 10°C min^?1 in DMSO or DMA with either 0.9% NaCl or C‐F HBSS.     

Spermatozoon ultrastructure and sperm cryopreservation of the Brazilian dry season spawner fish pirapitinga,Brycon nattereri

The aims of this study were to describe the fresh spermatozoon ultrastructure using scanning and transmission electron microscopy and to improve the sperm cryopreservation methodology for the freshwater fish pirapitinga Brycon nattereri. Extenders (BTS^? and NaCl), straw volumes (0.5 and 4.0 mL), thawing temperatures (30 and 60 °C) and activating agents (0.29% NaCl and 1% NaHCO₃) were tested. Methylglycol was used as a cryoprotectant agent and sperm was frozen in nitrogen vapour (dry‐shipper). Post‐thawed sperm motility rate, motility quality (score 0=no movement; 5=rapidly swimming spermatozoa), duration of motility and spermatozoon morphology were evaluated. Fresh spermatozoon was 35.06 μm long, the head was ovoid (2.00 × 1.22 μm) with no acrosome, the midpiece was 2.15 μm long and the flagellum was 30.90 μm long with the typical 9+2 axoneme arrangement. Post‐thawed sperm motility rate (70–79% motile sperm), motility quality (score 3.1–3.7) and morphology (9.3–11.6% abnormal spermatozoa) were not affected by any of the parameters tested. The duration of sperm motility was longer when triggered in 1% NaHCO₃ (392–1031 s) compared with 0.29% NaCl (144–338 s). Brycon nattereri sperm cryopreserved under the conditions described above yields over 70% motility and should last long enough to fertilize oocytes, even after 2 years of freezing.     

Metabolic characteristics of the Japanese clam Ruditapes philippinarum (Adams & Reeve) during aerial exposure

Some metabolic end‐products in tissues and physiological parameters of haemolymph of the Japanese clam Ruditapes philippinarum (Adams & Reeve) were investigated under aerial exposure at 15 °C with low relative humidity (RH) (22%) or high RH (91%). Acclimated clams in water at 15 °C were used as a control and to supply the low or high RH experiment. The low RH experiment was conducted at air exposure for 50 h (LH₅₀), and the high RH experiment for 50 h (HH₅₀) and 100 h (HH₁₀₀). Accumulation of succinate and alanine in the tissues proved that the clam shifted its metabolism to anaerobiosis. Lactate accumulation did not occur. Glucose concentrations in tissues increased slightly during exposure except for HH₅₀. The total free amino acid contents (363–410 μmol g^?1) were higher than those of glucose (530–804 μmol 100 g^?1), suggesting that the free amino acids might play a more dominant role in the metabolism. Increase in the haemolymph pco ₂ did not influence the acid–base balance in the haemolymph during exposure at both humidity conditions. Increase in the haemolymph ammonia from 48.2 to 57.1 μmol 100 g^?1 and to 131.0 μmol 100 g^?1 at LH₅₀ and HH₁₀₀, respectively, suggested that ammonia might function as an important buffering factor during aerial exposure. Retention values of the haemolymph po ₂ even at the longest exposure time (16.30 mmHg at LH₅₀ and 14.69 mmHg at HH₁₀₀) indicated that the clams depend partially on some aerobic manner.     

The impact of elevated water nitrite concentration on physiology,growth and feed intake of African catfish Clarias gariepinus (Burchell 1822)

The nitrite threshold concentration in rearing water of African catfish (Clarias gariepinus) was assessed. African catfish with an initial mean (SD) weight of 219.7 (57.8) g were exposed to an increasing range of water nitrite from 6 (Control) to 928 μM nitrite for 28 days. Mean (SD) plasma nitrite concentrations increased from 5.0 (3.6) to 32.5 (12.6) μM at 928 μM ambient nitrite. The increase in nitrite was accompanied by gradual increase in plasma nitrate from 41.6 (28.4) μM to 420.2 (106.4) μM. Haematocrit, haemoglobin, methemoglobin, plasma concentrations of cortisol, glucose, lactate, osmolality, gill morphology and branchial Na⁺/K⁺‐ATPase activity were not affected. Feed intake, final weight, SGR, FCR and mortality were not affected. We advise not to exceed a water nitrite concentration of 43 μM (0.6 mg L^?1 NO₂^?‐N) to prevent the risk of reduced growth and feed intake in African catfish aquaculture.     

Functional partition of cells in the gill epithelium of the Japanese eel, Anguilla japonica, and the role of hormones

Viable chloride and pavement cells were isolated from the gill epithelium of Japanese eel, Anguilla japonica, by a 3-step percoll gradient centrifugation at low speed. Viability of the isolated cells were tested by the trypan blue exclusion test, rhodamine-123, or pre-labelling the cells with fluo-3 Ca²⁺ dye and examined by laser confocal microscopy. Isolated chloride cells responded to ionomycin with a rapid increase in Ca²⁺ fluorescence, which was abolished by chelating external Ca²⁺ with EGTA. Peptide hormones, including arginine vasotocin, isotocin, insulin-like growth factor I and II, and urotensin I increased Ca²⁺ entry, urotensin II had no effect, and eel corpuscles of Stannius extract reduced residual Ca²⁺ fluorescence. Isolated chloride cells and pavement cells from eels were analyzed for their enzymatic activities involved in intermediary and nitrogen metabolism. Chloride cells had high levels of glutaminase I, glutamate dehydrogenase, glutamate oxalacetate transaminase, HCO₃-ATPase and carbamoyl phosphate synthetase II. Pavement cells had highly active glucose-6-phosphate dehydrogenase and AMP deaminase. Both had high levels of lactate dehydrogenase compared with other tissues.     

Purification and characterization of chymotrypsin from viscera of vermiculated sailfin catfish, Pterygoplichthys disjunctivus, Weber, 1991

Pterygoplichthys disjunctivus viscera chymotrypsin was purified by fractionation with ammonium sulfate (30–70 % saturation), gel filtration, affinity, and ion exchange chromatography. Chymotrypsin molecular weight was approximately 29 kDa according to sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), shown a single band in zymogram. Electrofocusing study suggested being an anionic enzyme (pI ≈ 3.9), exhibiting maximal activity at pH 9 and 50 °C, using Suc-Ala-Ala-Pro-Phe-p-nitroanilide (SAAPNA) as substrate. Enzyme was effectively inhibited by phenyl methyl sulfonyl fluoride (PMSF) (99 %), and N-tosyl-l-phenylalanine chloromethyl ketone (TPCK) (94 %). Enzyme activity was affected by the following ions in decreasing order: Hg²⁺, Fe²⁺, Cu²⁺, Li¹⁺, Mg²⁺, K¹⁺, Mn²⁺, while Ca²⁺ had no effect. Chymotrypsin activity decreased continuously as NaCl concentration increased (from 0 to 30 %). K _m and V _max values were 0.72 ± 1.4 mM and 1.15 ± 0.06 μmol/min/mg of protein, respectively (SAAPNA as substrate). Results suggest the enzyme has a potential application where low processing temperatures are needed, such as in fish sauce production.     

Cobia Rachycentron canadum L. reared in low‐salinity water: does dietary sodium chloride affect growth and osmoregulation?

The effects of NaCl supplementation (0.0%, 2.5%, 5.0%, 7.5% and 10.0% dry weight of a basal diet) on growth, gill histological alterations and osmoregulation of juvenile cobia reared in low‐salinity water (5 g L^?1) were assessed. At the end of the experiment, gills were sampled for Na⁺, K⁺‐ATPase activity determination and histological evaluation. In all treatments, no mortality was observed. Results showed that dietary NaCl supplementation did not alter growth. At the highest supplementations (7.5% and 10.0%), juvenile cobia showed higher feed intake and feed conversion ratio. Na⁺, K⁺‐ATPase activity was higher in fish fed the diet without salt supplementation than in those fed with NaCl‐supplemented diets. The number of chloride cells significantly increased with increasing dietary salt level, being 2.5‐fold higher in fish fed with 10.0% NaCl supplementation (41 cells mm^?2) than in those from the non‐supplemented fed group (16 cells mm^?2). These findings indicate that dietary salt supplementation stimulated chloride cell proliferation paralleled with a reduction in the gill Na⁺, K⁺‐ATPase activity, suggesting a possible decrease in energy consumption associated with osmoregulation. However, the suggested energy sparing did not have a significant impact on juvenile cobia growth.     

Reduction of Salt in Haddock Mince: Effect of Different Salts on the Solubility of Proteins

ABSTRACT

Due to negative health effects of high sodium intake, it is recommended to reduce the daily salt intake by around 50%. To reduce the sodium content, sodium salts can be exchanged with potassium or magnesium salts. The effect of sodium, potassium, and magnesium chlorides on extractability of proteins from fresh and frozen haddock muscle and minces was studied. Salting with KCl and MgCl₂ instead of NaCl changed protein extractability. The highest solubility of the proteins was achieved using Na⁺. However, at low concentrations, extractability in K⁺ and Mg²⁺ is on the same level as Na⁺, showing that partial substitution of NaCl with KCl or MgCl₂ is possible. Freezing affected the structure of tissue and protein properties, resulting in decreased amount of salt soluble proteins.     

Effects of changes in plasma pH,CO2 and ammonia on ventilation in trout

We investigated ventillatory responses to a plasma alkaloids and hypocapnia,a nd the basis for the ventilatory response to sodium bicarbonate (NaHCO₃) infusion in rainbow trout. Plasma alkalosis and hypocapnia created by infusion of sodium hydroxide (NaOH) did not cause hypoventilation, whereas infusion of hydrochloric acid (HCl) caused vigorous hyperventilation, associated with an acidosis, a reduction in blood O₂ content (Ca_{O 2}) and a release of circulating catecholamines. Infusion of NaHCO₃ stimulated ventilation and caused an increase in plasma pH, total carbon dioxide content (Ca_{CO 2}) and catecholamine levels, and a reduction in oxygen tension (Pa_{O 2}). Infusion of ammonium bicarbonate (NH ₄HCO₃) caused hyperventilation and was associated with an increase in Ca_{CO 2} and plasma total ammonia (C_amm) and ammonia gas (NH₃) concentration. Infusion of sodium chloride (NaClI) and Cortland's saline had no effect on ventilation. The results indicate that trout do not exhibit the ventilatory sensitivity to pH seen in terrestrial vertebrates. Ventilatory responses to NaHCO₃ appear to have been a result of reductions in Pa_{O 2}, a release of catecholamines and an increase in Ca_{CO 2} whereas responses to NH₄HCO₃ appear to have been a result of increases in Ca_{CO 2} and C_amm.     

Geochemical changes in white seabream (Diplodus sargus) earth ponds during a production cycle

The knowledge of geochemical processes in fishponds is important in defining farming strategies and the carrying capacity of these systems, and is therefore essential for the management and sustainability of semi‐intensive aquaculture in earth ponds. The main purpose of the present work, developed in the Aquaculture Research Station located in Ria Formosa, was to study the geochemical changes in semi‐intensive earth ponds of white seabream Diplodus sargus L. during a production cycle, and relate it to farming conditions (fish biomass and feeding rate). Settled material and sediment samples were collected in a fish production pond and in a non‐fish production pond during 2 years. The results obtained showed that particle‐settling rates (S, g m⁻² day⁻¹) increased linearly with time (t, days): S=0.7t–34, in the fishpond. Increasing deposition of particulate material increased the organic matter content of bottom sediments, particularly during the second production year. Organic matter mineralization, during periods of high temperatures, led to high nutrient concentrations in porewater (NH₄⁺, 965 μM; NO₃⁻, 40 μM; HPO₄²⁻, 39 μM) and subsequently to an increase in benthic primary production in the fishpond. The geochemical similarities between fishpond sediments and shallow coastal system's sediments, along with the high fish survival rate (94%), suggest that for the assayed farming conditions there were no environmental constraints within the pond. However, some impact on bottom sediments, namely, an increase in settled material, organic matter deposition, nutrients in porewater and microphytobentos production, was evident above a fish biomass of 500 g m⁻³ and a feeding rate of 150 kg month⁻¹, indicating that pond environmental conditions should be carefully monitored from this point on.     

Susceptibility of channel catfish (Ictalurus punctatus) fed with dietary sodium chloride to nitrite toxicity

Juvenile channel catfish (Ictalurus punctatus) were fed with nutritionally complete, basal diets supplemented with NaCl at 0, 10, 20 or 40 g kg^?1 diet (0, 1, 2, or 4%) to apparent satiation twice daily for 10 weeks. Catfish were exposed to nitrite after six (7.70 mg L^?1 nitrite‐N) and ten (7.18 mg L^?1 nitrite‐N) weeks of feeding to determine the effect of dietary NaCl supplementation on resistance to nitrite toxicity. Fish were sampled before (baseline, pre‐exposure) and after 24‐h nitrite exposure to determine the effects of dietary NaCl on haematology (haematocrit, haemoglobin and methaemoglobin) and plasma electrolyte dynamics (nitrite, chloride, sodium and potassium). Mortality from nitrite toxicity was also determined. Mortality from nitrite exposure tended to decrease with increasing NaCl in the diet at 6 weeks and was significantly lower in the 40 g kg^?1 NaCl group (12.5%) compared to the control group (57.5%). A similar trend in mortality occurred at 10 weeks as well; however, the differences among dietary treatments were not significant. The improvements in blood MetHb (non‐significant), chloride and nitrite levels in catfish may at least in part be responsible for the improved survival after nitrite exposure, which trended in support of the prevailing hypotheses for the positive effects of NaCl on nitrite toxicity.     

Physical and Chemical Characteristics of Bottom Soil Profiles in Ponds at Auburn, Alabama, USA and a Proposed System for Describing Pond Soil Horizons

Soil cores were taken from each of three, 2-, 23-, and 52-yr-old research ponds (650–1,010 m² area) at Auburn, Alabama. Many physical and chemical variables changed in intensity with increasing depth in cores. Compared to original compacted pond soil, sediment contained more moisture; had lower bulk density (<1.4 g/cm³); possessed higher percentages of silt and clay; had greater porosity, specific surface area, and cation exchange capacity; and contained greater concentrations of organic matter and nutrients. Sediment organic matter was highly decomposed as evidenced by low proportions (5–15%) of carbon and nitrogen associated with the light fraction (soil retained on a 53-μm sieve). Sediment depth at 100-cm water depth increased with pond age (11.7 cm, 28.3 cm, and 48.3 cm in 2-, 23-, and 52-yr-old ponds, respectively), but sediment composition did not change greatly over time. Successive layers in cores were as follows: 1) water near the soil-water interface with a high concentration of solids; 2) high moisture content sediment with dry bulk density <0.3 g/cm³; 3) lower moisture content sediment with bulk density between 0.3 and 0.5–0.7 g/cm³; 4) rapid transition of bulk density from 0.5–0.7 g/cm³ to 1.4 g/cm³; 5) original compacted soil with bulk density of 1.4–1.7 g/cm³. We propose that these five layers be referred to as F (flocculent layer), S (stirred or mixed sediment), M (mature, bulk, un-mixed sediment), T (transitional layer), and P (original, undisturbed pond bottom) horizons, respectively. Superficial, oxidized sediment is termed an S_o horizon, and the reduced part of the S horizon is termed an S_r horizon. The upper part of the T horizon is an MT horizon when it is similar to the M horizon, or a FT horizon when it resembles the P horizon. A system for delineating horizons in pond soil profiles will be valuable in future attempts to classify pond soils.     

Effects of addition of a bird repellent to fish diets on their growth and bioaccumulation

The effects of adding the nonlethal bird repellent methyl anthranilate (MA), at levels of 100 and 1000 mg kg^?1, to fish feed on the bioaccumulation and growth of juvenile (10 g) hybrid striped bass (Morone chrysops×M. saxatilis) and juvenile (1 g) African cichlid fish Aulonocara jacobfreibergi were investigated under laboratory conditions. The bird repellent did not have any effect on the fish growth or survival over a period of 6 weeks. MA residues at low levels of 11.2±2.6 μg g^?1 were found in lipophilic tissues (liver) of MA‐fed fish. Control fish, which had no MA added to their diet, had a much lower level of 0.6±0.3 μg g^?1 MA in their liver. Fish muscle was found to contain negligible MA residues, while the outer body surface mucus did not contain any MA. Following a 6‐week depuration period, during which the previously MA‐fed hybrid striped bass were fed a feed to which no MA was added, the levels of MA residues detected were reduced by one order of magnitude.     

Electrochemical ammonia removal and disinfection of aquaculture wastewater using batch and flow reactors incorporating PtRu/graphite anode and graphite cathode

Ammonia removal and disinfection are two major problems in aquaculture systems, which require clean and reliable water to support long-term growth and health of target animals. In this study, we report electrochemical ammonia removal and disinfection of wastewater from an aquaculture farm (Mari’s Gardens) in Hawaii. First, we attempted to reproduce the work of Zollig and co-authors, who reported that direct ammonia oxidation can occur between 1 V and 1.6 V vs SHE on a graphite electrode in a solution (pH = 9.0) containing 1 M NaClO₄, 0.25 M NH₄ClO₄, and 0.085 M NaCl. Our results, however, show that direct ammonia oxidation is unlikely to occur, at least at significant rates, on a graphite electrode in aqueous solutions (pH = 9.0) containing 0.7 M Na₂SO₄, 0.1 M (NH₄)₂SO₄, and 0.02 M NaCl. We tentatively attribute this discrepancy to the different physico-chemical characteristics of graphite electrodes made by different manufacturers. Second, PtRu/graphite electrodes were prepared using a pulsed electrodeposition method, and electrode activity towards ammonia removal and disinfection was examined in both synthetic and real aquaculture wastewater using batch and flow reactors. The PtRu catalyst was partially oxidized at the beginning of electrolysis, and a significant increase in the electrode activity towards indirect ammonia oxidation was observed. Ammonia removal was slow when NaCl concentration was 0.66 mM, but the addition of NaCl (up to 20 mM) led to a drastic increase in the ammonia removal rate, indicating that ammonia removal proceeds via indirect oxidation. The ammonia removal rate depends primarily on NaCl concentration and current density and is independent of the initial ammonia concentration and solution pH. The ammonia removal rates can be modeled by pseudo zero-order kinetics, and a linear correlation can be drawn between the ammonia removal rate (k, mg L⁻¹ min⁻¹) and the product of NaCl concentration ([Cl-], mM) and current density (j, mA/cm²): k = 0.0047 [Cl-] j (R² = 0.99). Free chlorine (Cl₂, HOCl, and OCl-) was not detected in the solution until the complete removal of ammonia. Combined chlorine (NH₂Cl, NHCl₂, and NCl₃) was measured at concentrations of 2–15 mg/L (as Cl₂) during the ammonia removal process but was eliminated as soon as ammonia was depleted and an excess of free chlorine was available. Our detailed findings on the formation of both free chlorine and combined chlorine are significant to the mechanistic study of indirect ammonia oxidation. Ammonia removal experiments in synthetic and real aquaculture wastewater showed similar results. However, ammonia removal in the flow reactor took about three times longer than that in the batch reactor under similar conditions, likely due to hydrodynamic mixing differences. In addition, it was found that E. coli bacteria can be completely inactivated (5-log reduction) within a short time (e.g., 5 min).     

Nitrate uptake by Enteromorpha spp. (Chlorophyceae): Applications to aquaculture systems

Enteromorpha linza and E. intestinalis thrive in aquatic systems rich in inorganic fixed nitrogen. At 15°C and ca. 1800 μW cm^?2 these algae showed a V_max for nitrate uptake of 129 μmol h^? g^?1 dry weight ( = ca. 22 μmol h^?1 g^?1 wet weight) and a K_s of 17 μM. At 20 μM rates averaged 70 ± 21 μmol h^?1 g^?1. They dropped to 19% of this value at 5°C, and at 0°C nitrate uptake ceased. In the first hour of darkness, nitrate uptake decreased to 35% and in the second hour to 10% of the rate in light. Enteromorpha spp. scavenged nitrate from the medium at concentrations < 0.5 μM, and no nitrate leaked out of the tissue into nitrate-free water. Information from this study may be useful in designing nutrient feeding strategies in aquaculture systems.     

Potassium flux in juvenile striped bass (Morone saxatilis): influence of external concentrations of sodium chloride and calcium

Whole-body influx and efflux of K⁺ were determined for 25-day-old striped bass,Morone saxatilis, in conditions that simulated harvesting fish from ponds. During the first 5h in fresh water with combined high NaCl (80 mM) and low Ca²⁺ (0.12 mM) concentrations, a combination that is acutely lethal to this age of striped bass, K⁺ influx for fish in 0.07 mM K⁺ was 21±1.7 (SEM) compared to 3.4±0.33 nmol g^–1 h^–1 for fish in water with low Na⁺ (0.25 mM) or high Ca²⁺ (2.5 mM) concentrations. Influx of K⁺ was inhibited during the first few hours after fish were placed in flux chambers. Potassium efflux as percentage of⁴²K lost per hour was two-fold higher from fish in the high Na-low Ca treatment compared to fish in low concentrations of Na⁺ or high concentrations of Ca²⁺. Potassium efflux was probably much greater than influx, but exact values for efflux could not be calculated from the data available. Survival of fish in water with high Na-low Ca was not increased by addition of KCl to the water, indicating that the net loss of K⁺ was probably not the cause of death.     

Effect of acid environments on cortisol and cortisol receptor activity in Atlantic salmon,Salmo salar

The cytosol and nuclear extract of gill tissue obtained from laboratory held Atlantic salmon,Salmo salar manifested saturable cortisol binding of high affinity and low capacity (cytosol: K_a = 0.198 ± 0.024 × 10⁹/M, N_max = 116.8 ± 20.8 fmol/mg protein; nuclear extract: K_a = 0.823 ± 0.057 × 10⁷/M, N_max = 1563 ± 330 fmol/mg protein; n = 4). The cytosol receptor activity displayed high steroid and tissue specificity and a single binding peak at 191,000 Da following gel permeation chromatography. Atlantic salmon exposed for 3 or 8 months to waters from the Medway River (pH about 5.1), the Westfield River (pH about 4.8) and calcium carbonate treated Westfield River (pH about 5.6) showed no gill cytosol receptor activity. Cortisol receptor activity in the gill nuclear extracts from fish in limed Westfield River water in December (3 months) was less than half the activity in the fish treated with Medway River water (p < 0.05) although the plasma cortisol values were not different. In May (8 months), the plasma cortisol of fish in limed water was almost twice that of the fish held in acid Westfield River water (p = 0.058).     

Effects of selenium dietary enhancement on hatchery-reared coho salmon, Oncorhynchus kisutch (Walbaum), when compared with wild coho: hepatic enzymes and seawater adaptation evaluated

Hatchery-reared coho salmon, Oncorhynchus kisutch (Walbaum), were fed elevated levels of selenium (as Na₂SeO₃) to raise eviscerated body burdens to the level measured in wild counterparts. The goal was to find a dietary concentration that would achieve the desired effect without causing damage to growth and normal development. To measure some indices of health, the detoxifying enzymes chosen were hepatic glutathione peroxidase (GSH-Px) and hepatic superoxide dismutase (SOD). Eviscerated body selenium (Se) concentration, GSH-Px and SOD levels were measured during and at the end of the 9 month freshwater feeding trial. Selenium retention and enzyme activity were also measured during 6 months’residence in sea water (SW). Selenium supplements were added to a commercial ration to give final concentrations of 1.1, 8.6, 11.1, 13.6 μg g^-1 Se in the four respective diets. The results indicated that a dietary concentration of 8.6 μg g^-1 selenium was capable of inducing eviscerated body burdens similar to those found in wild fish. The elevated selenium levels persisted throughout the freshwater (FW) rearing phase, but declined when the fish were fed an unsupplemented ration upon SW entry. Superoxide dismutase levels did not increase above control levels. Glutathione peroxidase levels increased in fish fed the supplemented diets. GSH-Px activity declined in the higher supplemented dietary groups when all groups were reduced to the control group level of 1.1 μg g^-1. Cumulative mortality in SW was 20% in fish fed either the 1.1 or the 8.6 μg g^-1 Se diets. The 8.6 μg g^-1 Se supplemented diets did produce healthy coho, comparable to their wild counterparts.