Carbonic anhydrase (acetazolamide-sensitive esterase) activity in the red blood cells of thermally-acclimated rainbow trout, salmo gairdneri

Haemato-immunological and growth response of mirror carp (Cyprinus carpio) fed a tropical earthworm meal in experimental diets

An investigation was conducted to evaluate the effect of feeding a tropical earthworm meal (Perionyx escavatus) on the haemato-immunological response and growth performance of mirror carp (Cyprinus carpio). Fish were fed diets for a total of 88 days, fishmeal served as the main protein source in the control diet. Two remaining diets consisted of fishmeal fixed at 33.65% provision of protein and the remaining 66.35% protein was provided by soybean meal (SBM diet) or P. excavatus meal (EW diet). Compared to control and SBM fed fish (7.69 ± 0.28 and 5.92 ± 0.31 g/dl, respectively), a significant increase in haemoglobin was measured in EW fed fish (9.57 ± 0.24 g/dl). Consequently significant elevations were also observed in mean corpuscular haemoglobin (MCH; 79.13 ± 4.59 pg) and mean corpuscular haemoglobin concentration (MCHC; 22.69 ± 0.54 pg) in EW fed fish. On the contrary, compared to control and SBM fed carp total leukocyte levels (2.72 ± 0.17 and 3.10 ± 0.17 × 10(4)/mm(3), respectively) were significantly decreased in the EW group (2.15 ± 0.14 × 10(4)/mm(3)). Moreover at day 14 and 21 post immunisation with bacterin isolated from Aeromonas hydrophila fish fed the EW diet displayed a significant reduction in respiratory burst activity (RBA) compared to control and SBM fed fish. After 60 days of feeding, fish fed EW diet showed a significant elevation in final body weight compared to fish fed a fishmeal based diet (control treatment) and fish fed a soybean meal based diet. Similar improvements were observed in feed utilisation efficiency. The present study shows that feeding P. excavatus meal to mirror carp decreases some aspects of the innate immune response, but at the same time gives rise to significant enhancement of growth and feed utilisation efficiency.

Interactive effects of salinity and elevated CO2 levels on juvenile eastern oysters, Crassostrea virginica

Rising levels of atmospheric CO2 lead to acidification of the ocean and alter seawater carbonate chemistry, which can negatively impact calcifying organisms, including mollusks. In estuaries, exposure to elevated CO2 levels often co-occurs with other stressors, such as reduced salinity, which enhances the acidification trend, affects ion and acid–base regulation of estuarine calcifiers and modifies their response to ocean acidification. We studied the interactive effects of salinity and partial pressure of CO2 (PCO2) on biomineralization and energy homeostasis in juveniles of the eastern oyster, Crassostrea virginica, a common estuarine bivalve. Juveniles were exposed for 11 weeks to one of two environmentally relevant salinities (30 or 15 PSU) either at current atmospheric PCO2 (∼400 μatm, normocapnia) or PCO2 projected by moderate IPCC scenarios for the year 2100 (∼700–800 μatm, hypercapnia). Exposure of the juvenile oysters to elevated PCO2 and/or low salinity led to a significant increase in mortality, reduction of tissue energy stores (glycogen and lipid) and negative soft tissue growth, indicating energy deficiency. Interestingly, tissue ATP levels were not affected by exposure to changing salinity and PCO2, suggesting that juvenile oysters maintain their cellular energy status at the expense of lipid and glycogen stores. At the same time, no compensatory upregulation of carbonic anhydrase activity was found under the conditions of low salinity and high PCO2. Metabolic profiling using magnetic resonance spectroscopy revealed altered metabolite status following low salinity exposure; specifically, acetate levels were lower in hypercapnic than in normocapnic individuals at low salinity. Combined exposure to hypercapnia and low salinity negatively affected mechanical properties of shells of the juveniles, resulting in reduced hardness and fracture resistance. Thus, our data suggest that the combined effects of elevated PCO2 and fluctuating salinity may jeopardize the survival of eastern oysters because of weakening of their shells and increased energy consumption.

Membrane-associated carbonic anhydrase in the respiratory system of the Pacific hagfish (Eptatretus stouti)

Like other agnathans, the Pacific hagfish (Eptatretus stouti) lacks red blood cell (RBC) Cl(-)/HCO(3)(-) exchange. Despite this absence of anion exchange, the majority (86.7+/-1.4%) of the total CO(2) carried in the blood is found within the plasma as HCO(3)(-), and thus presumably is inaccessible to RBC carbonic anhydrase (CA). As such, a branchial plasma-accessible CA isozyme in hagfish would be beneficial for mobilizing the considerable plasma HCO(3)(-) stores for CO(2) excretion and blood acid-base balance. The current study used a combination of molecular and biochemical methods to identify two membrane-associated CA isozymes in the respiratory system of E. stouti. Using homology cloning methods, CA IV and XV-like isozymes were identified in the gill and RBC, respectively. Real-time PCR analysis of relative mRNA expression revealed that CA IV was specific to the gill, while CA XV was found in several tissues including the RBC, gill, liver, heart and muscle. Isolation of subcellular fractions of gill and RBC verified the presence of membrane-associated CA activity in each tissue that persisted after standard washing protocols. Unlike CA activity associated with the cytoplasmic fractions, the activity in gill membranes was not inhibited by sodium dodecyl sulphate, while RBC membrane activity was inhibited to a lesser degree than the cytoplasmic fraction. Additionally, incubation of gill membrane fractions with phosphatidylinositol-specific phospholipase C released significant CA activity into the supernatant indicating the presence of a glycophosphatidyl inositol-linkage to the membrane, as found with other CA IV and XV isozymes. These results demonstrate that Pacific hagfish possess gill and RBC plasma-accessible membrane-associated CA that may play important roles in respiratory gas exchange and acid-base balance.

Histochemical demonstration of carbonic anhydrase in gills and opercular epithelium of seawater- and freshwater-adapted killyfish (Fundulus heteroclitus)

Gills and operculum of seawater- and freshwater-adapted killyfish (Fundulus heteroclitus) were stained histochemically for carbonic anhydrase (CA). In the seawater-acclimatized specimens, CA was found predominantly in the chloride cells which were considerably larger than in the freshwater-adapted ones. Within these cells, the reaction products were concentrated in the apical parts of the cytoplasm. In contrast, chloride cells of freshwater-adapted fish were not, or only faintly, stained both in gills and opercular epithelium. Reaction products for CA were seen additionally in the cytoplasm of the outer respiratory cells lining the lamellae of gills both in seawater- and freshwater-adapted fish.

Environmentally-related changes in red cell levels of ionic modulators of hemoglobin-O2 affinity in rainbow trout, Salmo gairdneri

Hemoglobin content, plasma and red cell levels of chloride and magnesium and molar ion:hemoglobin ratios were examined in trout acclimatized to eight combinations of two treatment levels of temperature (5, 20 degrees C), O2 availability (less than or equal to 30%, greater than or equal to 75% saturation) and photoperiod (16L:8D, 8L:16D). Increases in hemoglobin content were associated with exposure to higher temperature, abbreviated daylength and hypoxia, with hypoxia greater than photoperiod greater than temperature. Under nominal "summer" conditions (20 degrees C, hypoxia, 16L:8D) photoperiodic influence was apparently masked by hypoxic and thermal effects. Temperature was the principal determinant of plasma and cellular chloride levels as well as [Cl:Hb]. O2 availability and photoperiod had little effect. Temperature was also the primary factor influencing magnesium, with hypoxia exerting a lesser influence. Photoperiod effects were negligible. With increased temperature and reduced O2 availability, plasma magnesium increased white cell magnesium levels and [Mg:Hb] declined. These observations suggest that with normal seasonal changes in environmental conditions, temperature-induced increases in the O2 requirements of summer trout are probably accompanied by increases in blood O2-carrying capacity and reductions in hemoglobin-O2 affinity with consequent increases in O2 delivery to tissues.

Lipoidal membranes stabilize isolated salmon and chicken carbonic anhydrase under conditions of increased temperature and pH

1. Solutions of purified carbonic anhydrase from chicken and salmon erythrocytes were incubated in buffer for 1 hr at 5 degrees or 22 degrees C, at pH 7.3, 7.6, 7.9 or 8.2. 2. At 22 degrees C the enzymes lost up to 25% of their ability to catalyze the CO2 hydration reaction when compared to control solutions maintained in the cold. 3. Loss of enzyme activity (approximately 50%) also occurred as pH was increased from 7.3 to 8.2. 4. The presence of lecithin vesicles or microsomes completely protected the enzymes from denaturation caused by pH changes and afforded partial protection from changes due to increased temperature.

In vitro effects of acephate on carbonic anhydrase activity in the blood and gills of rainbow trout, Salmo gairdneri

Acephate, a water-soluble organophosphate pesticide used to control terrestrial insect pests, may enter aquatic ecosystems in the course of its use and adversely affect fish populations. The in vitro effects of this insecticide on gill and red blood cell (RBC) carbonic anyhdrase (CA) activity in rainbow trout were investigated over a range of 100 mg/1 (0.55 mM) to 50,000 mg/l (273 mM) to assess the manner in which acephate might affect respiratory capacity in exposed fish. Concentrations required to produce 50% inhibition of CA activity in the gill and RBC preparations were 38,000 mg/l (207 mM) and 8,900 mg/l (48 mM) respectively. The toxic action of acephate may be related to inhibition of CA activity in the blood and gills with resultant disturbances of respiratory capacity and salt balance.