Evaluation of buoyancy dynamics in the early ontogenesis of climbing perch <Emphasis Type="Italic">Anabas testudineus</Emphasis> (Anabantidae)

The paper puts forward a new approach to estimation of buoyancy of hydrobionts using dispersion of various densities. The technique was applied to evaluate buoyancy variations in climbing perch Anabas testudineus at its early ontogeny. It was found that positive buoyancy characteristic of eggs and early stage larvae does not remain longer than the first eighty hours of development. Besides, this period is marked by significant fluctuations in buoyancy. The maximum buoyancy was recorded at the time of hatching of the embryos, which occurs at the age of approximately thirty hours. At ninety hours the buoyancy of larvae becomes negative. Later, it goes up somewhat, and the individual differences become more important in its dynamics pattern. Some individuals are neutrally buoyant, though no return to positive buoyancy was observed. The estimates obtained by the author create a foundation for further morphofunctional analysis of the hydrostatically significant structures in the early development of the climbing perch.     

The taxonomic status of some Atlanto‐Mediterranean species in the subgenus Holothuria (Echinodermata: Holothuroidea: Holothuriidae) based on molecular evidence

Molecular and morphological data were used to evaluate the taxonomic status of the species Holothuria tubulosa Gmelin, 1790 , Holothuria stellati Delle Chiaje, 1823 , Holothuria mammata Grube, 1840 , and Holothuria dakarensis Panning, 1939, belonging to the nominate subgenus Holothuria (Holothuria) (family Holothuriidae) from the Mediterranean Sea and Atlantic Ocean. A 16S rRNA marker distinguished three well‐supported clades with clear genetic differentiation amongst them. The morphometric characters, although they reflected the clades, showed great variability, and some specimens from different clades overlapped. The morphological data and the literature suggest that the clades correspond to H. dakarensis (from Cape Verde Islands), H. mammata (from the Atlanto‐Mediterranean area) and H. tubulosa (from the Mediterranean Sea). Holothuria stellati is considered here to be a junior subjective synonym of H. tubulosa. Great morphological intraspecific variation within H. tubulosa and H. mammata explains the confusion in the literature. Holothuria tubulosa includes specimens with distinctive ossicles, but others are similar to H. mammata. In these cases, the presence or absence of Cuvierian tubules proved a reliable indicator to the identity of these species; unfortunately this character is difficult to assess in preserved material. According to the results of discriminant analysis we propose a set of ossicle morphometric variables that permit the optimum assignation of individuals to the clades. Our results present a new perspective on the taxonomic status of species in Holothuria (Holothuria), and show how a molecular approach, combined with a morphological approach, can solve taxonomic problems.     

The effect of salinity on coelomic fluid osmolyte concentration and intracellular water content in Luidia clathrata (Say) (Echinodermata: Asteroidea)

• 1.1. The concentrations (mM) of osmolytes in the coelomic fluid of Luidia clathrata kept at 25‰S seawater (control individuals) were: 345, Na⁺; 10, K⁺; 10, Ca²⁺; 44, Mg²⁺; 387, Cl⁻; 0.67, amino acids; 0.09, NH₄⁺.
• 2.2. When individuals were transferred from 25‰S to 15‰S or 35‰S, the concentrations of inorganic ions in the coelomic fluid usually equilibrated within 24hr and became the same as those in the medium.
• 3.3. The intracellular water content (g intracellular H₂O/g solute-free dry tissue) of the pyloric caeca and tube feet of control individuals throughout the experiment was 2.13 and 5.40, respectively.
• 4.4. In tissues of individuals transferred to 15‰S, the intracellular water content increased by an average 50% in 12 hr but returned to 19% above control levels during 1 week.
• 5.5. In tissues of individuals transferred to 35‰S, the intracellular water content decreased by an average 17% in 12 hr and did not change during 1 week.
• 6.6. Luidia clathrata is an osmoconformer and partial cell volume regulator within the seasonal salinity range it encounters.

     

Distributional success of the marine seaweedFucus vesiculosus L. in the brackish Baltic Sea correlates with osmotic capabilities of Baltic gametes

To understand the unique success of the marine seaweedFucus vesiculosus L. (PHaeophyceae) in the brackish Baltic Sea, the performance of gametes from Baltic [4.1–6.5S (Salinity)] and marine populations was studied. Sperm from BalticF. vesiculosus swam with a path velocity of c. 30–110 m/s and could fertilize eggs in waters of salinities from 4 to 33S. In their natural water, Baltic sperm were not negatively phototactic, unlike marine sperm in seawater; this should decrease the sperm:egg concentration at the seafloor and reduce the likelihood of polyspermy. Marine (Iceland, Sweden) sperm in seawater had a path velocity of c. 80–100 m/s, but performed poorly and could not fertilize eggs in natural or artificial Baltic water 6S; therefore, Baltic populations have adapted or acclimated to their brackish habitat. Baltic populations appear better adapted to their natural low salinities because, even after culturing Baltic and marine individuals in water from both the Baltic (6.5S) and the marine Skagerrak (21S), Baltic sperm were in both cases still able to swim and fertilize eggs at lower salinities (4S) than marine sperm; fertilization never occurred between marine gametes at 4–6S. However,F. vesiculosus acclimates to some salinities, since sperm from Baltic and marine males that had been cultured at 21S swam better (higher velocity, proportion that were motile and/or linearity) in marine salinities (21–33S) than when they were cultured at 6.5S. The effects of salinity on sperm motility and fertilization were osmolar rather than due to specific ionic requirements, over the tested range. The osmolalities (< c. 100 mmol/kg) at which fertilization success of Baltic gametes decreases nearly to zero correspond to the osmolality of Baltic water at the northernmost limit of distribution ofF. vesiculosus in the Baltic Sea. Therefore, the present range ofF. vesiculosus in the Baltic appears to correspond to the osmotic tolerance of the gametes. Very small natural or anthropogenic increases in ambient osmolality would be likely to cause a substantial expansion of this species into the inner Baltic.     

The sodium balance of the euryhaline marine loggerhead turtle,Caretta caretta

Summary The efflux of sodium ions from the loggerhead turtle,Caretta caretta, was investigated when animals were acclimated to seawater, freshwater, and during the acclimation period after transfer from seawater to freshwater. The rate of sodium loss in animals acclimated to seawater was found to be 3 M Na · g^–1 · hr^–1. Cannulation of the cloaca showed that only 5% of the gross efflux of sodium was via the cloaca and it was calculated that 60% of the gross efflux was via nasal gland secretion and 35 % via integumentary diffusional loss. Cannulation experiments indicated that a significant amount of sodium may enter the body via the cloaca. Transfer of animals from seawater to freshwater resulted in a decline of sodium efflux by 90–99 % within 6 hr, and a further decline to only approximately 0 01 M Na · g^–1· hr^–1 after 1–2 days in freshwater. Cannulation experiments of individuals acclimated to freshwater indicated that the role of the cloaca in sodium loss in freshwater was minimal. It was calculated that sodium loss in freshwater is so small that survival in freshwater for at least 20 days is possible without active extraction of sodium from the medium. No evidence could be found for active uptake of sodium ions from freshwater baths byCaretta.This research was supported by NSF grant GB 16839.     

Survival of Microorganisms under the Extreme Conditions of the Atacama Desert

Spores of Bacillus subtilis, conidia of Aspergillus niger, versicolor and ochraceus andcells of Deinococcus radiodurans have been exposed in the dark at two locations (at about 23°S and 24°S) in the Atacama Desert for up to 15 months. B. subtilis spores (survival 15%) and A. niger conidia (survival 30%) outlived the other species. The survival of the conidiaand spores species was only slightly poorer than that of thecorresponding laboratory controls. However, the Deinococcus radiodurans cells did not survive the desertexposure, because they are readily inactivated at relativehumidities between 40 and 80% which typically occurduring desert nights. Cellular monolayers of the dry sporesand conidia have in addition been exposed to the full sunlight for up to several hours. The solar fluences causing 63% loss in viability (F₃₇-values) have been determined.These F₃₇-values are compared with those determined atother global locations such as Punta Arenas (53°S), Key Largo (25°N) or Mainz (50°N) during the same season. Thesolar UVB radiation kills even the most resistantmicroorganisms within a few hours due to DNA damages. Thedata are also discussed with respect to possible similaritiesbetween the climatic conditions of the recent Atacama Desertand the deserts of early Mars.     

Stable oxygen isotopes in<Emphasis Type="Italic"> Porites</Emphasis> corals monitor weekly temperature variations in the northern Gulf of Aqaba,Red Sea

In order to assess the ability of Porites corals to accurately record environmental variations, high-resolution (weekly/biweekly) coral ¹⁸O records were obtained from four coral colonies from the northern Gulf of Aqaba, which grew at depths of 7, 19, 29, and 42 m along one transect. Adjacent to each colony, hourly temperatures, biweekly salinities, and monthly ¹⁸O of seawater were continuously recorded over a period of 14 months (April 1999 to June 2000). Contrary to water temperature, which shows a regular and strong seasonal variation and change with depth, seawater ¹⁸O exhibits a weak seasonality and little change with depth. Positive correlations between seawater ¹⁸O and salinity were observed. The two parameters were related to each other by the equation ¹⁸O _Seawater (, VSMOW) = 0.281 × Salinity – 9.14. The high-resolution coral ¹⁸O records from this study show a regular pattern of seasonality and are able to capture fine details of the weekly average temperature records. They resolve more than 95% of the weekly average temperature range. On the other hand, attenuation and amplification of coral seasonal amplitudes were recorded in deep, slow-growing corals, which were not related to environmental effects (temperature and/or seawater ¹⁸O) or sampling resolution. We propose that these result from a combined effect of subannual variations in extension rate and variable rates of spine thickening of skeletal structures within the tissue layer. However, no smoothing or distortion of the isotopic signals was observed due to calcification within the tissue layer in shallow-water, fast-growing corals. The calculations from coral ¹⁸O calibrations against the in situ measurements show that temperature (T) is related to coral ¹⁸O ( _c ) and seawater ¹⁸O ( _w ) by the equation T (°C) = –5.38 ( _c – _w ) –1.08. Our results demonstrate that coral ¹⁸O from the northern Gulf of Aqaba is a reliable recorder of temperature variations, and that there is a minor contribution of seawater ¹⁸O to this proxy, which could be ignored.     

Age and growth of Lessepsian rabbitfish from the eastern Mediterranean

Rabbitfish are currently an important component of the eastern Mediterranean inshore fishery. This study estimates age and calculates growth of Siganus rivulatus and S. luridus from the Lebanese coastal waters based on otolith analysis and compares results with available data from different geographical locations. Annual periodicity of alternating zones was confirmed for S. rivulatus, in which one opaque and one translucent zone were observed to deposit each year, but not for S. luridus. Both species appear to have a maximum lifespan of 6 years. The von Bertalanffy growth functions were L_t = 318.9(1 ? e^{?0.225(t+1.307)}) for S. rivulatus and L_t = 274.9(1 ? e^{?0.330(t+1.039)}) for S. luridus and length–weight relationships were estimated as for S. rivulatus and for S. luridus. The rabbitfish catches of the Lebanese fishery consist mainly of individuals which have not reached their first maturity. Rabbitfish from the eastern Mediterranean coastal waters appear to grow rapidly most of the year and are thus able to maintain relatively important population size despite intensive fishing pressure.     

Microbial Diversity during Biodegradation of Crude Oil in Seawater from the North Sea

Microbial communities were characterized during biodegradation of immobilized oil in seawater from the Statfjord field and the German Bight in the North Sea. Seawater samples were collected at different distances from pollution sources at the two locations. A Statfjord oil was immobilized on hydrophobic synthetic Fluortex fabrics and submerged in closed flasks (no headspace) with natural or sterile seawater and incubated at 13°C for 56 days. Biodegradation of immobilized n-alkanes was measured by gas chromatography, total microbes were enumerated by epifluorescence microscopy, and culturable heterotrophic and oil-degrading microorganisms were quantified by most probable number (MPN) analysis. Polymerase chain reaction (PCR) amplification of bacterial 16S rDNA in water samples was conducted during biodegradation experiments. The amplified 16S rDNA fragments were characterized by denaturing gradient gel electrophoresis (DGGE), and by sequence analysis of cloned inserts. Biodegradation rates of alkanes in seawater collected at different distances from the pollution sources did not differ significantly (P > 0.05). Concentrations of oil-degrading microorganisms showed a temporary peak after 7 days of degradation, with a subsequent decline later in the period. DGGE analysis of 16S rRNA genes showed that community diversity decreased during the first 2–3 weeks of biodegradation, with the emergence of a few dominant bands. Cloning, restriction analysis, and sequence analysis of the 16S rDNA fragments revealed >30 different phylotypes. Abundant types during biodegradation belonged to the -Proteobacteria, in waters from both Statfjord and the German Bight. Cloning and sequencing studies indicated that the most abundant bacteria during biodegradation belonged to the family Rhodobacteraceae, with the closest relationship to the genera Sulfitobacter and Roseobacter.     

Muscle co-contraction after anterior cruciate ligament reconstruction: Influence of functional level

Background

ACL reconstruction is recommended to improve function in subjects with ligament injuries. However, after surgery, some individuals are not able to return to their pre-injury functional level. The mechanisms related to this incapacity are not well understood.

Study design

Cross-sectional study.

Methods

Co-contraction levels were assessed in individuals who returned to their pre-injury functional level and in 10 individuals who were not able to return to full activity after unilateral ACL reconstruction. Electromyography of the vastus lateralis and biceps femoris muscles before and after sudden perturbations applied during the stance phase of walking was used to calculate co-contraction.

Results

The involved limb had lower co-contraction pre-perturbation than the non-involved limb in both groups (p = 0.049). The co-contraction level post-perturbation was significantly higher in the limited return group than in the full return group (p = 0.03).

Conclusion

Decreased co-contraction in the involved limb before perturbation may be caused by sensorial changes resulting from surgery or injury. Increased co-contraction levels observed in the limited return group after perturbation may be a compensatory mechanism to make up for possible decreased intrinsic stability of the knee joint.

Clinical relevance

Increased co-contraction after perturbation does not contribute to knee stability.     

Genetic variation in agronomically important species of Stylosanthes determined using random amplified polymorphic DNA markers

Summary Random amplified polymorphic DNA (RAPD) markers were generated from 20 cultivars and accessions representing four agronomically important species of Stylosanthes, S. scabra, S. hamata, S. guianensis, and S. humilis. Approximately 200 fragments generated by 22 primers of arbitrary sequence were used to assess the level of DNA variation. Relatively low levels of polymorphism (0–16% of total bands in pairwise comparisons) were found within each species, while polymorphisms between the species were much higher (up to 46%). Very few polymorphisms (0–2%) were detected between the individuals of the same cultivar or accession. A phenogram of relationships among the species was constructed based on band sharing. Four main clusters corresponding to each species were readily distinguished on this phenogram. The allotetraploid species S. hamata and its putative diploid progenitor, S. humilis, were more similar to each other than to S. scabra and S. guianensis. No variation in RAPD markers was found between the two commercial S. hamata cvs Verano and Amiga. Cultivar Oxley in S. guianensis was considerably different from the other cultivars and accessions of this species. The phylogenetic distinctions obtained with RAPDs were in agreement with other studies from morphology, cytology, and enzyme electrophoresis. The low level of polymorphisms observed within each species suggested that interspecific crosses may be a better vehicle for the construction of RAPD linkage maps in Stylosanthes.     

Phenotypic Variations and Molecular Identification of <Emphasis Type="Italic">Salmonella enterica</Emphasis> Serovar Typhimurium Cells Under Starvation in Seawater

In seawater, enteric bacteria evolve toward a stressed state that is difficult to identify because of major alterations of their phenotype. In this study, we incubated four reference strains of S. enterica serovar Typhimurium in seawater microcosms for 10 months and studied the modifications of their main phenotypic characters. All of the strains lost some key characters used for traditional identification of the Salmonella genus. They became able to produce acetoin, and tryptophane deaminase activity became positive, but they lost the capacity to use rhamnose. We were able to show some modifications of the level of enzymatic profile as well as in their antibiotic susceptibility. The atypical cells of S. enterica serovar Typhimurium were identified by polymerase chain reaction (PCR) methods using the internal transcribed spacer region, and they were confirmed by multiplex PCR after the simultaneous amplification of the phoP, Hin, and H-li genes.     

Morphological and physiological responses to increased salinity in marsh and dune ecotypes ofSporobolus virginicus (L.) Kunth

Summary Sporobolus virginicus (L.) Kunth is a halophytic grass native to tropical and warm temperate coasts throughout the world. A rhizomatous perennial with erect culms,S. virginicus occurs as two genetically distinct growth forms, which are designated by their characteristic habitats as marsh and dune. What accounts for the specific distribution and maintenance of two separate ecotypes ofS. virginicus is not known. The present study examined the effects of seawater salinity on several morphological and physiological responses of hydroponically cultivated marsh and dune plants to determine whether differential tolerance to substrate salinity might contribute to the observed pattern of habitation. Both marsh and dune form plants survived prolonged exposure to full-strength seawater and reproduced vegetatively via culms and rhizomes. Salinity-induced reductions in culm height, internode length, and leaf size led to a miniaturization of marsh and dune plants. Sodium ion levels were low (<1.0 mmol/g dry weight) in various organs of salinized plants irrespective of ecotype, and potassium ion content increased in all salt-challenged plants, as did quarternary ammonium compounds and proline. Significant differences, however, between marsh and dune plants with respect to the effects of salinity on resource allocation, flowering phenology, and protein composition suggested that external salt concentration has a role in determining ecotype distribution.     

Osmoregulation in two aquatic oligochaetes from habitats with different salinity and comparison to other annelids

The osmoregulatory capacity of two oligochaete species, Enchytraeus albidus Henle, 1837, and Heterochaeta costata (Claparède, 1863), was investigated by direct measurements of the osmolality of the coelomic fluid. Terrestrial and marine (28 S) populations of Enchytraeus albidus and a brackish water population (14 S) of H. costata were used in the study. The range of salinity acclimation investigated was 0–40. The response to osmotic stress was measured (a) after a long-term maintenance (>14 days) in various salinities (E. albidus only), and (b) after a hyperosmotic shock as a short-term time-course sequence. The rate of water loss following a hyperosmotic shock was measured for E. albidus. Long-term acclimation. E. albidus maintained a hyperosmotic coelomic fluid over all salinities tested. In low salinities the osmolality of the coelomic fluid of the marine population was significantly higher than that of the terrestrial population. Possible genetic discrepancies or long-term acclimation may account for this difference. The coelomic fluid of H. costata was hyperosmotic at 15%. S and isoosmotic at 30 S. Short-term acclimation (hyperosmotic shock). Both species investigated, kept at 15 S and then exposed to a salinity of 30, showed fast responses: within the first two hours the internal concentrations were adjusted to the new external condition with only small subsequent changes. Regulation of the body-water content after an exposure to a hyperosmotic shock was much slower: individuals of terrestrial E. albidus, acclimated for two weeks to either 0 or 15 S, had the same water content; hence, they showed a 100% regulation. However, after exposure to 30 S, a 100% regulation was still not attained 4 days after the hyperosmotic shock. Enchytraeus albidus is capable of actively reducing water loss following the hyperosmotic shock: the observed loss of water was only 40% of that expected for a passive osmotic flow. The observed reactions are compared with those in other annelids. It seems that an active transport of ions combined with a changeable permeability of the body wall play a major role in the regulation of body fluids.     

Sodium balance in the green turtle,Chelonia mydas, in seawater and freshwater

Summary Sodium balance in the green turtle,Chelonia mydas, has been investigated in both seawater and freshwater. In seawater the unidirectional Na efflux is 131 M · 100 g^–1 · h^–1, over 90% of which is via the head region and less than 5% each is via the cloaca and the integument. After 17 days in freshwater the efflux of Na has declined by 97% and the majority is via the cloaca. The integumental efflux in freshwater is less than that in seawater indicating that a change in skin permeability, trans-skin electrical potential or pattern of blood flow has taken place. Although there are indications that Na is actively extracted from freshwater by the green turtle, this species faces a net loss of Na of the medium and the blood Na concentration falls significantly. When transferred from seawater to freshwater the turtle's orbital salt gland is turned off within 25 h after transfer. The salt gland does not become functional until 400 h after transfer from freshwater to seawater.     

ISolation and rapid identification of yeasts from compromised hosts

In order to improve the isolation and identification of yeasts in a cancer research hospital, a protocol was developed utilizing an improved blood culture methodology and a four-test schema for rapid yeast identification. The blood culturing technique, based upon centrifugation, has shown a ten-fold increase in isolation of fungi from blood and has provided for: quantitation of organisms, unlimited selection of media and atmospheres for primary culturing, and a 1200 dilution of microorganisms away from serum antimicrobial factors and antibiotics. The four-test schema, which may be adapted for the identification of any unknown yeast in pure culture, consists of a dye pour plate auxanogram (DPPA), Tween 80-Oxgall-Caffeic acid (TOC), a rapid nitrate-reductase test (swab test) and Urea R Broth. Using this protocol, over 95% of the clinical isolates received were correctly identified within 24 hours and 100% by 48 hours. By using DPPA, a 14 sugar assimilation pattern for each isolate was determined within 12 to 16 hours; and in some cases, as little as 6 hours. Growth on TOC yielded one of the following results: (1) Candida albicans and Candida stellatoidea sequentially produced germ tubes and chlamydospores in 3 hours and 24 hours, respectively; (2) Cryptococcus neoformans produced a brown pigment specific for its identification in 12 hours or less. The swab test gave results on nitrate utilization in less than 15 minutes and urease was detected within 4 hours.     

Competition between two annual herbs,Atriplex gmelini C.A. Mey and Chenopodium album L., in mixed cultures irrigated with seawater of various concentrations

Summary Atriplex gmelini and Chenopodium album were grown in mixed stands with various combinations of plant density and mixing ratio, and irrigated with seawater of different concentrations (f) to formulate the effect of changing concentration on the competitive relationship between the species.In single-species stands, the mean plant weight (w)plant density () relation for each level of seawater concentration could well be described by Shinozaki-Kira's reciprocal equation of crowding effect. On the other hand, the response of w to f followed Hozumi-Shinozaki's formulation for an optimum growth factor at respective levels of .By introducing the density conversion factor (q) that enabled the conversion of the density of one species to that of the other species on the basis of their effects on growth of respective species, the results of mixed culture experiments could be successfully formulated by similar reciprocal equations. The dependence of q and coefficient values of the equations on seawater concentration was also formulated in a way similar to the case of pure stands.Based on all these quantitative relations, a comprehensive formulation was developed to describe the effects of plant density and seawater concentration on the growth of two species in mixed stands. The behavior of species biomass in mixed stands was then examined by means of the formulation.It was thereby demonstrated that the relative dominance of two species in a mixed stand was strongly affected not only by total plant density and density ratio between the two species but also by concentration of irrigated seawater. Even the optimum seawater concentration that resulted in the maximum species biomass differed between pure and mixed cultures.     

Comparison ofin Situ andin Vitro survival ofCandida albicans in seawater

The survival in seawater of several laboratory and field isolates ofCandida albicans was investigated. Initial studies were madein vitro (flasks) to confirm previous reports. Frequent sampling of viable cells showed that flask experiments, even repeated, produced varied patterns of survival in this closed system. As an alternative, multiple experiments were run in untreated seawater in dialysis bags and plexiglas chambers at ambient temperature (17 to 22C) in flowing seawater. Die-off rates of all cultures tested in dialysis bags were very rapid in the first day and may have been related to high levels of dissolved organic carbon in the tubing. Distilled water-or acid-washed bags did not yield significantly higher survival rates in all cases. When plexiglas chambers closed with Nuclepore membranes were used, survival rates decreased to 5% to 15% of the original population after 6 days. Chamber data were more uniform and represented approximately a twofold increase in survival over that shown previously inin vitro (flask) studies. Some evidence was obtained in all three test systems for the greater survival rate of a field isolate ofC. albicans compared with that noted for a laboratory (ATCC) strain. The results are considered to more accurately depict the survival ofC. albicans in summer temperate recreational waters.     

Effects of salinity on chloride cells in the euryhaline cyprinodontid fish Rivulus marmoratus

Summary The ultrastructure and density of chloride cells in the gill, opercular epithelium, and opercular skin of the euryhaline self-fertilizing fish Rivulus marmoratus (Cyprinodontidae) were studied with electron and fluorescence microscopy. R. marmoratus raised from birth in 1, 50, 100, and 200% seawater were compared. Chloride cells from fish raised in each of the four salinities exhibited an invaginated pit structure at the apical crypt. Multicellular complexes were present in the 1% seawater group and in those fish raised in higher salinities where elaborate interdigitations were seen between cells. Chloride cells from gills of fish raised in 200% seawater had a significantly higher percentage of their cytoplasmic volume composed of mitochondria than did those from fish raised in 1% seawater (69.9% vs 37.4%). The opercular skin and opercular epithelium had the same density of chloride cells (4.2×10⁴-4.5×10⁴ chloride cells/cm²), and this number did not vary significantly with increased salinity. The opercular skin thus appears far more responsive to environmental salinity than the opercular epithelium. Chloride cells from the opercular epithelium of fish raised in 200% seawater were found to be 39% larger than those from fish raised in 1% seawater, whereas the chloride cells from the opercular skin of the 200% seawater group were 107% larger than those from the 1% seawater group.