Bass Gill Research Articles

Smooth muscle actin and myosin expression in gills of largemouth bass

In fish, the amplified surface area and narrow diffusion distances of the gill secondary lamellae contribute to vital physiological exchange processes. Local control of blood flow within the secondary lamellae has been speculated to also play a role in regulating various exchanges. However, secondary lamellae lack vascular smooth muscle cells; the intralamellar blood space is defined by a marginal endothelium and by buttressing pillar cells. Studies have suggested both the presence of smooth muscle filaments and contractile capacity in pillar cells. To further examine the possible role of secondary lamellar hemodynamic control in gill function, the expression of smooth muscle myofilaments was investigated in largemouth bass, Micropterus salmoides. Homogenates of gill epithelial scrapings, stomach and skeletal (trunk) muscle were analyzed by SDS PAGE and Western blot. Using a monoclonal anti-smooth muscle myosin antibody, positive signals were observed for bass gill and stomach, but not skeletal muscle. A monoclonal, smooth muscle anti-α-actin antibody also yielded tissue-specific signals for bass stomach and gill. Smooth muscle α-actin in bass gill and stomach also had slower elecrophoretic mobility, implying larger molecular mass, than α-actin from the control species (guinea pig). These antibodies are now being used in ongoing immunolocalization studies intended to test the hypothesis that smooth muscle myosin and α-actin are expressed in largemouth bass pillar cells.

The Na+/K+/2Cl- cotransporter in the sea bassDicentrarchus labraxduring ontogeny: involvement in osmoregulation

This study combines a cellular and molecular analysis of the Na(+)/K(+)/2Cl(-) cotransporter (NKCC) to determine the osmoregulatory role of this protein in different tissues during the ontogeny of the sea bass. We have characterized the complete sequence of the NKCC1 isoform isolated from the sea bass gills and have identified, by immunofluorescence, NKCC1, and other isoforms, within the epithelium of the major osmoregulatory organs. Different (absorptive and secretory) functions have been attributed to this protein according to the tissue and salinity. The effects of short- (1-4 days), medium- (7-21 days) and long (6 months)-term freshwater (FW) adaptations were investigated, in comparison with seawater (SW)-maintained sea bass. In adult sea bass after long-term adaptation to FW and SW, the gills had the highest expression of NKCC mRNA compared with the median/posterior kidney and to the posterior intestine. Expression of NKCC mRNA in the kidney was 95% (SW) and 63% (FW) lower, and in the intestine 98% (SW) and 77% (FW) lower. Compared to SW-maintained sea bass, long-term FW adaptation induced a significant 5.6-fold decrease in the branchial NKCC gene expression whereas the intestinal and renal expressions did not vary significantly. The cells of the intestine and collecting ducts as well as a part of the epithelium lining the urinary bladder expressed NKCC apically. Within the gill chloride cells, NKCC was found basolaterally in SW-acclimated fish; some apically stained cells were detected after 7 days of FW exposure and their relative number increased progressively following FW acclimation. The appearance of FW-type chloride cells induces a functional shift of the gills from a secretory to an absorptive epithelium, which was only completed after long-term exposure to FW. Short- and medium-term exposure to FW induced a progressive decrease in total NKCC content and an increase in functionally different branchial chloride cells. During development, the cotransporter was already expressed in tegumentary ionocytes and along the digestive tract of late embryos. NKCC was recorded in the branchial chamber and along the renal collecting ducts in prelarvae and also in the dorsal part of the urinary bladder in larvae. The expression of NKCC along the osmoregulatory epithelial cells and the presence of Na(+)/K(+)-ATPase within these cells contribute to the increase of the osmoregulatory capacity during sea bass ontogeny.

Bass Hepcidin Synthesis, Solution Structure, Antimicrobial Activities and Synergism, and in Vivo Hepatic Response to Bacterial Infections

Bass hepcidin was purified from the gill of hybrid striped bass (Morone chrysops x Morone saxatilis) based on antimicrobial activity against Escherichia coli. This 21-amino acid peptide has 8 cysteines engaged in 4 disulfide bonds and is very similar to human hepcidin, an antimicrobial peptide with iron regulatory properties. To gain insight into potential role(s) of bass hepcidin in innate immunity in fish, we synthesized the peptide, characterized its antimicrobial activities in vitro, determined its solution structure by NMR, and quantified hepatic gene expression in vivo following infection of bass with the fish pathogens, Streptococcus iniae or Aeromonas salmonicida. Its structure is very similar to that of human hepcidin, including the presence of an antiparallel beta-sheet, a conserved disulfide-bonding pattern, and a rare vicinal disulfide bond. Synthetic bass hepcidin was active in vitro against Gram-negative pathogens and fungi but showed no activity against key Gram-positive pathogens and a single yeast strain tested. Hepcidin was non-hemolytic at microbicidal concentrations and had lower specific activity than moronecidin, a broad spectrum, amphipathic, alpha-helical, antimicrobial peptide constitutively expressed in bass gill tissue. Good synergism between the bacterial killing activities of hepcidin and moronecidin was observed in vitro. Hepcidin gene expression in bass liver increased significantly within hours of infection with Gram-positive (S. iniae) or Gram-negative (A. salmonicida) pathogens and was 4-5 orders of magnitude above base-line 24-48 h post-infection. Our results suggest that hepcidin plays a key role in the antimicrobial defenses of bass and that its functions are potentially conserved between fish and human.

Oxygen availability causes morphological changes and a different VEGF/FIk‐1/HIF‐2 expression pattern in sea bass gills

The sea bass, Dicentrarchus labrax, is abundantly reared in intensive aquaculture and oxygen is one of the most important parameters. The gills of D. labrax exposed for three months to three different oxygen partial pressure conditions were investigated: normoxia, mild hyperoxia and mild hypoxia (respectively, 90–100%, 120–130% and 60–70% of the saturation value). Modifications to Po2 levels were studied with morphological and immuno‐histochemical techniques. In normoxia and mild hyperoxia conditions, the gills had the typical structure with rows of parallel filaments; nevertheless, hyperoxia treatment altered the pillar cell structure, leading to an enlargement of the vascular lumen. In hypoxia condition, gills were disorganized, the vascular lumen was reduced and the lamellae showed apical blebs and outer epithelial detachment. In vertebrates, the vascular endothelial growth factor and its main receptor Flk‐1 are two important oxygen dependent molecules whose expression can be regulated by the hypoxia inducible factor 2. In D. labrax, high expression of these factors was found in normoxia and mild hypoxia, while in mild hyperoxia they were very weak. Our data characterize the morphological changes occurring in D. labrax gills and the different expression pattern of the above‐mentioned factors after exposure to different oxygen partial pressure conditions.

Neurohypophysial hormone regulation of Cl- secretion: physiological evidence for V1-type receptors in sea bass gill respiratory cells in culture.

Neurohypophysial hormone receptors were studied in primary cultures of sea bass (Dicentrarchus labrax) gill respiratory-like cells grown on permeable supports. This preparation was previously shown to provide a functional model for investigating the hormonal regulation of Cl- secretion. Under control conditions, the cultured monolayered epithelium had a short-circuit current (ISC) of 3.5+/-1.1 micro A x cm(-2). This current had previously been identified as an active Cl- secretion. The addition of increasing concentrations of the fish neurohypophysial hormones, arginine vasotocin (AVT) or isotocin (IT), elicited a concentration-dependent stimulation of the ISC. Maximal increases of 60.9+/-12.1% and 117.7+/-28.0% above the basal ISC value were obtained for 10(-7) M AVT and IT respectively. Half-maximal effects were obtained for 3.1 x 10(-9) M AVT and for 1.4 x 10(-9) M IT. Mucosal application of 1.0 mM diphenylalamine-2-carboxylic acid (a specific blocker of Cl- channels) after serosal addition of 5 x 10(-8) M AVT or IT inhibited not only the basal but also the stimulated current, revealing a correlation with a hormone-dependent Cl- transport. Specific V1 or V2 receptor analogues of vasopressin (mammalian hormone) were used to characterize the type of neurohypophysial hormone receptors pharmacologically. While the V1 agonist [Phe2,Orn8]-oxytocin stimulated the basal Cl- secretion with a similar profile to that of AVT or IT, the V2 agonist [Deamino1,Val4,d -Arg8]-vasopressin had no effect. The V1 antagonist [d(CH2)5 1,O-Me-Tyr2,Arg8]-vasopressin used at a concentration of 5 x 10(-7) M totally reversed the 10-8 M AVT-stimulated Cl- secretion, whereas the V2 antagonist [d(CH2)5 1,d -Ile2,Ile4,Arg8,Ala9]-vasopressin used at the same concentration had no significant effect. In contrast, similar experiments carried out in the presence of 10(-8) M IT showed that both antagonists significantly reduced the IT-stimulated Cl- secretion, with the efficiency of the V1 receptor antagonist being significantly greater than that of the V2. This study provides evidence for neurohypophysial hormone control of Cl- secretion in fish cultured gill respiratory cells. It suggests that on a physiological basis the hormonal effect is shared by the two peptides present in fish neurohypophysis (AVT and IT), acting by means of two distinct, although pharmacologically similar, V1-type receptors (according to the mammalian classification). These specific receptors are expected to play an important role in controlling ion homeostasis in seawater fish.

Morphometric adaptations of sea bass gills to different dissolved oxygen partial pressures

Morphometric adaptations of sea bass gills to different dissolved oxygen partial pressures

Morphometric adaptations of sea bass gills to different dissolved oxygen partial pressures

The total respiratory surface area (RSA) of sea bass Dicentrarchus labrax (initial mass 153 ± 27 g), reared in a brackish water recirculation system at 24° C for 3 months under three different oxygen partial pressures of 60, 90 and 140% saturation (87.0, 130.0 and 203.1 torr. respectively), was 351.98 (± 8.90), 264.86 (± 48.20) and 212.90 (± 57.22) mm2 g−1 body mass. RSA was negatively correlated with oxygen availability in the water. In the same experiment, no significant differences in the total length of filaments or frequency of lamellae were observed, although the total length of filaments was shorter in fish cultured under hyperoxia.

Histone-like proteins from fish are lethal to the parasitic dinoflagellate Amyloodinium ocellatum.

Antimicrobial proteins were purified from acid extracts of rainbow trout (Oncorhynchus mykiss) and sunshine bass (Morone saxatilis male x M. chrysops female) skin, gill and spleen by reverse-phase HPLC. Mass spectrometry and amino acid sequence data suggest that these proteins are closely related to histone H2B and histone H1 and thus they were designated histone-like proteins (HLPs). These proteins were lethal to Amyloodinium ocellatum, which is one of the most important parasitic agents affecting fish. Antibiotic concentrations as low as 12.5 microg/ml were inhibitory. Activity was directed against the trophont (feeding) stage of the parasite, while the disseminative (dinospore) stage was unaffected. Thus, HLPs act unlike typical drugs used to treat amyloodiniosis, which usually target the dinospore. Both the ability of the parasite to infect host cells, as well as the ability to grow and differentiate after infection were severely inhibited. This is in contrast to magainin 2, which was similarly toxic to both the dinospore and trophont stages. These findings provide further evidence that histone-like proteins may be important defensive molecules in fish.

Regulation of Cl- secretion in seawater fish (Dicentrarchus labrax) gill respiratory cells in primary culture.

1. Primary cultures of sea bass (Dicentrarchus labrax) gill cells grown on permeable membranes form a highly differentiated tight epithelium composed of respiratory-like cells. This preparation was also found to provide a functional model for investigating the hormonal regulation of Cl- secretion. 2. In control conditions, i.e. in the absence of hormones or other stimuli, the cultured epithelium showed a short-circuit current (Isc) of 8.8 +/- 0.4 microA cm-2, a transepithelial potential (Vt) of 28.6 +/- 0.6 mV (serosal side positive), and a transepithelial resistance (Rt) of 5026 +/- 127 Omega cm2. Addition of 50 nM PGE2 caused a stimulation of Isc, Vt and transepithelial conductance, Gt. The increase in Isc was probably due to the elevation in Cl- secretion, since it could be correlated with the stimulation of serosal to mucosal 36Cl- flux. Application of the neurohypophyseal peptide arginine vasotocin (AVT; 50 nM) or the beta-adrenergic agonist isoproterenol (isoprenaline; 0. 5 microM) evoked a stimulation in Cl- secretion, as was shown by the increases in Isc and Gt. The excitatory effect of isoproterenol followed by the inhibitory action of propranolol, a beta-adrenergic antagonist, suggested the presence of beta-adrenergic receptors. Noradrenaline (0.1 microM) elicited a reduction in Isc, Vt and Gt, which was counterbalanced by the addition of phentolamine, an alpha-adrenergic antagonist. This suggested an activation of alpha-adrenergic receptors. 3. This study provides evidence for hormonal control of the Cl- secretion in sea bass gill respiratory cells in culture, involving AVT, prostaglandin (PGE2), and beta- and alpha-adrenergic receptors.

Purification, Characterization and Activation of Fish Muscle Prokallikrein

Fish prokallikrein was isolated and characterized from skeletal muscle of the black sea bass, Centropristis striata. The prokallikrein was purified to apparent homogeneity by anion exchange perfusion chromatography and reversed phase high performance liquid chromatography. Initial identification was by its weak immunoreactivity with human tissue kallikrein antiserum. Two-dimensional gel electrophoresis and immunoblotting identified the protein as 36 kDa with a pI of 4.95–5.15. The prokallikrein was trypsin-activated to produce an approximately 36 kDa active enzyme as identified on an SDS-polyacrylamide gel overlayed with a membrane impregnated with the fluorogenic tripeptidyl substrate d-Val-Leu-Arg-7-amino-4-trifluoromethylcoumarin. A potential dimer at 72 kDa was also enzymatically active. Bass kallikrein cleaved low molecular weight dog kininogen to release kinin peptide as determined by radioimmunoassay. The enzyme's amidolytic activity, with a pH optimum at 9.0, was inhibited by aprotinin, benzamidine, and phenylmethanesulphonyl fluoride, but not by elastatinal, soybean trypsin inhibitor, or limabean trypsin inhibitor. Polyclonal antiserum raised against the purified bass muscle prokallikrein recognized 36 kDa and 72 kDa proteins in bass heart, skeletal muscle, spleen, swimbladder, gill, and kidney by Western blot analyses. The wide distribution of immunoreactive proteins in the tissues suggests a potential physiological role for fish kallikreins in muscle contraction and/or relaxation, the regulation of local blood flow, and in osmoregulation. The detection of fish prokallikrein and its activation leads the way for an evaluation of the impact of kallikreins in fish health and disease processes and for studying the evolution of kallikreins and related serine proteinases.

Chloride channels in primary cultures of seawater fish (Dicentrarchus labrax) gill.

Patch-clamp experiments were undertaken on primary cultures of respiratory cells originating from sea bass (Dicentrarchus labrax) gills. A small-conductance Cl- channel of 8 pS was characterized in cell-attached configuration with 140 mM N-methyl-D-glucamine-Cl in the pipette and bath solutions. No activity was recorded below a membrane holding potential of +20 mV (-Vp, referenced to the pipette solution), and the channel showed an inward rectification. In the inside-out configuration the Cl- channel was active at all membrane holding potentials. Its open probability strongly increased with membrane depolarization. The channel activity could be increased by the application of protein kinase A+ATP. This channel was inhibited by 5-nitro-2-(3-phenylpropylamino)-benzoic acid, diphenylamino-2-carboxylic acid, and I- and was insensitive to 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid. The presence of Cl- channels in the apical membrane of respiratory cells provides additional evidence for an important role of this cell type in the control of ion homeostasis of seawater fish.

Fish gill respiratory cells in culture: a new model for Cl(-)-secreting epithelia.

Primary cultures of sea bass gill cells grown on permeable membranes form a confluent, polarized, functional tight epithelium as characterized by electron microscopy and electrophysiological and ion transport studies. Cultured with normal fetal bovine serum (FBS) and mounted in an Ussing chamber, the epithelium presents a small short-circuit current (Isc: 1.4 +/- 0.3 microA/cm2), a transepithelial voltage (Vt) of 12.7 +/- 2.7 mV (serosal positive) and a high transepithelial resistance (Rt: 12302 +/- 2477 omega x cm2). A higher degree of differentiation and increased ion transport capacities are observed with cells cultured with sea bass serum: numerous, organized microridges characteristic of respiratory cells are present on the apical cell surface and there are increased Isc (11.9 +/- 2.5 microA/cm2) and Vt (25.9 +/- 1.7 mV) and reduced Rt (4271 +/- 568 omega x cm2) as compared with FBS-treated cells. Apical amiloride addition (up to 100 microM) had no effect on Isc. The Isc, correlated with an active Cl- secretion measured as the difference between 36Cl- unidirectional fluxes, was partly blocked by serosal ouabain, bumetanide, DIDS or apical DPC or NPPB and stimulated by serosal dB-cAMP. It is concluded that the chloride secretion is mediated by a Na+/K+/2Cl- cotransport and a Cl-/HCO3- exchanger both responsible for Cl- entry through the basolateral membrane and by apical cAMP-sensitive Cl- channels. This study gives evidence of a functional, highly differentiated epithelium in cultures composed of fish gill respiratorylike cells, which could provide a useful preparation for studies on ion transport and their regulation. Furthermore, the chloride secretion through these cultures of respiratorylike cells makes it necessary to reconsider the previously accepted sea water model in which the chloride cells are given the unique role of ion transport through fish gills.

Environmental conditions at sea-cages, and ectoparasites on farmed European sea-bass, Dicentrarchus labrax (L.), and gilt-head sea-bream, Sparus aurata L., at two farms in Greece

Water quality in sea-cages, and metazoan ectoparasites on bass, Dicentrarchus labrax (L.), and bream, Sparus aurata L., were sampled at two fish farms in south-west Greece over 2 years. The seabed and marine life around the cages of one farm was surveyed using scuba. The most frequent and abundant parasites were the monogeans Sparicotyle chrysophrii and Furnestinia echeneis on the gills of bream, and Diplectanum aequans on the gills of bass. The copepod Caligus minimus occasionally occurred in the buccal cavity of bass, but only in low numbers. Prevalence and abundance of parasites increased with bass size but F echeneis levels decreased with bream size. There were no other clear relationships between water quality, parasite levels and fish size. Ammonia varied seasonally with sea temperature, and with oxygen levels below 6 mg 1-1 on many occasions, it is possible that fish suffered stress from a combination of high ammonia and low oxygen conditions. There was no accumulation of waste food or faeces below the cages at the one farm surveyed, but there were thousands of wild fish, including mullet (Mugilidae), Spicara sp. and Diplodus spp., present around the cages. Water quality may be improved by changes in farm management, such as reducing stocking densities below the present 16 kg nr-3. Oxygen should be monitored at the cages on site daily. How comparable environmental conditions and impacts, and parasitization are at other bass and bream sea cage farms is unknown.

Surface complexation of aluminum on isolated fish gill cells

Cells from the gills of largemouth bass (Micropterus salmoides) were isolated and exposed to dilute solutions of Al, Al in the presence of fluoride, or Al plus dissolved organic matter (DOM) to determine the cells` metal binding potential in an acidic medium. Microelectrophoresis was employed to monitor the extent of aluminum sorption to cells in the presence of added ligand. In the absence of Al, the gill cells exhibit an appreciable negative charge; Al binding to the cell surface increases the electric potential at the shear plane and leads to a reduction in the cell`s (negative) electrophoretic mobility. In the presence of both Al and F, aluminum complexation at the gill surface is only marginally reduced; the formation of a mixed ligand complex, [F-Al-L-cell], is proposed to account for the observed results. The presence of such ternary complexes was subsequently verified by {sup 19}F nuclear magnetic resonance spectroscopy and by potentiometry. Addition of DOM increased the negative electrophoretic mobility of the isolated gill cells both in the presence and absence of aluminum (7.4 {mu}M). 45 refs., 7 figs., 1 tab.

Effects of tributyltin compounds on ionic regulation and gill ATPase activity in estuarine fish

1. Striped bass ( Morone saxatilis) were exposed to 0, 0.10, 0.34, or 1.09 μg/l tributyltin (TBT) for 14 days. Gill Mg 2+ ATPase and serum Na +, K +, Ca + and Mg + were not altered. Na +K +ATPase was significantly ( P < 0.05) increased (+ 48%) at 0.10 μg/l. 2. In striped bass gill homogenates exposed to TBT in vitro, there was significant inhibition of Na +K +ATPase at 106.0 μg/l (17.2%) and Mg 2+ATPase at 53.0 and 106.0 μg/l (16.0% and 24.3%, respectively). 3. In mummichog ( Fundulus heteroclitus) gill homogenates, there was significant inhibition of Na +K +ATPase at 25.3 and 50.5 μg/l (10.9% and 16.1%) and Mg 2+ATPase at 5.1, 25.3, and 50.5 μg/l (26.7%, 32.2%, and 36.2%).

Na +-like effect of monovalent cations in the stimulation of sea bass gill Mg 2+-dependent Na +-stimulated ATPase

1. 1. The Mg 2+-dependent ouabain insensitive-ATPase activity present in gill microsomal preparations from Dicentrarchus labrax is stimulated not only by Na + but also by K +, NH 4 + or Li +. 2. 2. These cations at 50–100 mM concentrations are similarly efficient to Na + in stimulating the enzyme activity with similar K m values. 3. 3. Whatever cation stimulates the activity, the enzyme is poorly sensitive to ouabain and 100% inhibited by 1.5–2.5 mM ethacrynic acid. 4. 4. All activity vs cation concentration curves show a biphasic profile with activation following the Michaelis-Menten kinetics ( Hill coefficient h ≅ 1) and, at greater-than-optimal concentrations, cooperative inhibition (h ≅ −2). 5. 5. The absence of additivity when the enzyme is activated by binary mixtures of cations, each of which may act as competitive inhibitor of the other confirms the involvement of the same binding site for the monovalent cations.

Ouabain-insensitive Na + stimulation of a microsomal Mg +-ATPase in gills of sea bass ( Dicentrarchus labrax L.)

1. 1. Bass gill microsomal preparations contain a Mg 2+-dependent Na +-stimulated ATPase activity in the absence of K +, whose characteristics are compared with those of the (Na + + K +)-ATPase of the same preparations. The activity at 30°C is 11.3 μmol Pi-mg −1protein-hr −1 under optimal conditions (5mM MgATP, 75 mM Na + 75 mM HEPES, pH 6.0) and exhibits a lower pH optimum than the (Na + + K +-ATPase. 2. 2. The Na + stimulation of ATPase is only 17% inhibited by 10 −3M ouabain and completely abolished by 2.5mM ethacrinic acid which on the contrary cause, respectively, 100% and 34% inhibition of the (Na + + K +)-ATPase. 3. 3. Both Na +- and (Na + + K +) stimulated activities can hydrolyze nucleotides other than ATP in the efficiency order ATP > CTP > UTP > GTP and ATP > CTP > GPT > UTP, respectively. 4. 4. In the presence of 10 −3M ouabain millimolar concentrations of K + ion lower the Na + activation (90% inhibition at 40 mM K +). 5. 5. The Na +-ATPase is less sensitive than (Na + + K +)-ATPase to the Ca 2+ induced inhibition as the former is only 57.5% inhibited by a concentration of 1 × 10 −2M which completely suppresses the latter. 6. 6. The thermosensitivity follows the order Mg 2+- > (Na + + K +)- > Na +-ATPase. A similar break of the Arrhenius plot of the three enzymes is found. 7. 7. Only some of these characteristics do coincide with those of a Na +-ATPase described elsewhere. A presumptive physiological role of Na +-ATPase activity in seawater adapted teleost gills is suggested.

Distribution and development of rodlet cells in the gills and pseudobranch of the bass, Dicentrachus labrax (L)

Rodlet cells in various stages of development were found in large numbers in the bass gill and pseudobranch. In the gill, rodlet cells were found in the epithelium at the base of the secondary lamellae and on the filament between adjacent lamellae, whilst in the pseudobranch they were found over the whole area of the secondary lamellae as well as in the filament epithelium.During early development, rodlet cells are characterised by their amorphous cell inclusions, prominent supranuclear Golgi complex and network of granular endoplasmic reticulum. Later, with formation of a fibrous border the arrangement of the cell organelles undergoes reorganisation; the endoplasmic reticulum becomes distended, numerous vesicles appear and the mitochondria aggregate in the apical region of the cell. One of the most striking features is the development of club‐shaped sacs containing electron dense cores, which are orientated towards the open apex of the cell.Various staining properties of rodlet cells for light and electron microscopy were compared with those of mucous cells found in the same tissues. Possible functions of the cell are discussed.

Studies on Ergasilus labracis Krøyer (Cyclopidea: Ergasilidae) parasitic on striped bass, Morone saxatilis, from the lower Chesapeake Bay. I. Distribution, life cycle, and seasonal abundance.

Information on the distribution, life cycle, and seasonal abundance of the copepod Ergasilus labracis Krøyer, parasitic on the gills of lower Chesapeake Bay striped bass, Morone saxatilis (Walbaum), is presented after a 12-month survey. The overall prevalence of E. labracis was 90% in all localities sampled and it was found to be as euryhaline as its host; it has been found in salinities from 0.l‰ to 32.0‰. E. labracis was present and reproductively active throughout the year, suffering only a temporary slowdown in egg production at the beginning of the winter. Peak invasion of striped bass gills by infective larvae occurred during April and May; minor peaks were also recorded during July and October. The free-living stage was estimated to last as long as 6 weeks during early spring. Duration of other developmental stages was also extrapolated. Attempts to rear larvae in the laboratory past the metanauplius stage failed. Larvae could be kept for a maximum of 23 days after hatching if fed nannoplankton and kept at 20 °C in river water of 16–18‰.

Gill ATPase activities in the smallmouth bass ( Micropterus dolomieui)

1. 1. MgATPase activity in bass gill microsomes was relatively stable to preincubation at 37°C but activity decreased after preincubation at 45°C. 2. 2. At an assay temperature of 13°C, Na-ATPase activity could not be demonstrated after 37°C preincubation but was evident after preincubation at 45°C. 3. 3. At an assay temperature of 37°C, addition of Na + resulted in a decrease in ATPase activity. 4. 4. Ouabain-sensitive NaK-ATPase activity could be demonstrated at both assay temperatures.