Gills Of Salmon Research Articles

Glochidium morphology of the freshwater pearl mussel (Margaritifera margaritifera) and glochidiosis of Atlantic salmon (Salmo salar): a study by scanning electron microscopy

The morphology of glochidia of the freshwater pearl mussel Margaritifera margaritifera L. and the development of the cyst for 50 days after glochidial infection of wild and hatchery-reared Atlantic salmon (Salmo salar L.) parr were studied using scanning electron microscopy. The microvillar surface of the inner epithelium of the glochidium, which may function in nutrition, respiration, and osmoregulation, is described. Glochidia were found to have five sensory tufts as well as marginal ciliary bands which are believed to function in directing water currents. After artificial infection of salmon parr, cyst formation was the result of shape change and migration of gill epithelial cells, but not hyperplasia. The process of cyst formation lasted from 9 to 12 h. No mortality of salmon parr occurred during the experiment. Based on our study, glochidia appear to have a negligible effect on the gills of Atlantic salmon, its preferred fish host. These results are discussed in the context of the possibility of a mutually beneficial coexistence of Atlantic salmon and pearl mussels in northern European rivers such as the Varzuga River in Russia.

Aluminum dynamics on gills of Atlantic salmon fry in the presence of citrate and effects on integrity of gill structures

The effect of citrate as organic acid anions (A −) on the accumulation of aluminum (Al) on gills of Atlantic salmon ( Salmo salar) fry was examined in acidic media. Treatments with (Al−A −) = +10, 0, and −10 μeq/1([Al] = 0, 10, 20, 30, 40, 50, 60 μeq/1 and [citric acid] = 0, 10, 20, 50 μeq/1) were used. Depuration of gills loaded with Al (10 μeq/l) was also examined in the presence of citric acid (0, 10, 20, 40 μeq/l). Elimination of Al from gills was a much more rapid process (< 48 h) than net accumulation (still increasing after 15 d). The presence of citrate reduced net Al accumulation on gills during uptake but it did not accelerate elimination of Al during the rapid phase of depuration. The effect of citrate on uptake was probably a result of the competition between A − and negatively charged binding sites on the gill surface for inorganic Al, whereas short-term depuration of Al was considered to be primarily a physical phenomenon related to the efficiency of the sloughing process. The severity of gill lesions observed by scanning and transmission electron muscopy and supported by morphometrics was related to [Al] in solutions. Slight reductions in gill lesions occurred in the presence of citrate but protection of gills was not complete, indicating a greater bioavailability of Al than predicted. During depuration, the recovery of gill tissues from Al effects was slightly enhanced by increasing [citric acid]. Electron-dense particles on the gill epithelial surface and within chloride cell vesicles in fish exposed to high [Al] and after Al loading were possibly related to Al deposits. These particles were absent from the lamellar surfaces of gills after only 5 d depuration in Al-free media, indicating that removal of particles from the gill surface was rapid and effective. X-ray muanalysis revealed the presence of Al on the gills of fish exposed to Al and its absence after depuration. Probing on the gill surface detected small amounts of Al on epithelial cells and in chloride cell crypts, but most of the Al was in deposits or secretions on the lamellar surface, adding further support to the premise that the majority of Al accumulated on gills over a short time period can be readily sloughed off.

Thyroid Hormone Deiodination in Brain, Liver, Gill, Heart and Muscle of Atlantic Salmon (Salmo salar) during Photoperiodically-Induced Parr-Smolt Transformation. II. Outer- and Inner-Ring 3,5,3′-Triiodo-l-Thyronine and 3,3′,5′-Triiodo-l-Thyronine (Reverse T3) Deiodination

Outer-ring deiodinase (ORD) and inner-ring deiodinase (IRD) pathways for 3,5,3′-triiodo-l-thyronine (T3) and 3,3′,5′-T3 (reverse T3, rT3) were examined in microsomal fractions of liver, heart, gill, brain, and skeletal muscle of 20-month-old Atlantic salmon induced to undergo parr-smolt transformation (PST) in late February and March by imposing a 16-hr photoperiod. All tissues showed negligible T3ORD activity. T3IRD activity was detected in both the liver (Km = 0.65 nM; Vmax = 15.5 pmol T3 deiodinated · hr-1 · mg microsomal protein-1) and brain of smolts, but not in gill, heart, or skeletal muscle. rT3ORD was detected in liver, brain, and muscle, and at very low levels in gill and heart. rT3IRD activity occurred to some extent in all tissues except brain. T3IRD activity changed in brain during PST, and was low in brain and liver of post-smolts examined in late October. We conclude that (i) deiodination of T3 proceeds exclusively through an IRD pathway, which may permit regulation of T3 degradation independently of the ORD pathway responsible for T3 formation; (ii) deiodination of rT3 proceeds mainly through an ORD pathway but rT3IRD activity does occur in some tissues; and (iii) the altered brain T3IRD activity during PST suggests regulation of T3 turnover in the brain at this time.

Thyroid Hormone Deiodination in Brain, Liver, Gill, Heart and Muscle of Atlantic Salmon (Salmo salar) during Photoperiodically-Induced Parr-Smolt Transformation, I. Outer- and Inner-Ring Thyroxine Deiodination

Outer-ring deiodinase (ORD) and inner-ring deiodinase (IRD) pathways for l -thyroxine (T4) were examined in the microsomes of tissues of 20-month-old Atlantic salmon induced to undergo parr-smolt transformation (PST) in late February and March by imposing a 16-hr photoperiod. Smolt external characteristics, decline in condition factor, increases in brainsomatic index, cardiac-somatic index, gill-somatic index, gill Na+/K+ ATPase activity, and food consumption developed progressively during the 5-week study. Plasma T4 (4.1 ng/ml, Week 1) rose to 13.5 and 12.5 ng/ml (Weeks 3 and 4) and fell to 7.5 ng/ml (Week 5). Plasma T3 rose from 2.1 ng/ml (Week 1) to 3.8 ng/ml (Week 2) and fell to 2.4 ng/ml (Week 5). T4ORD activity occurred in liver, heart, gill, brain, and skeletal muscle, increasing in liver and heart between Weeks 1 and 2, and in brain between Weeks 4 and 5. Only liver T4ORD activity was correlated (r = + 0.946) with plasma T3 concentrations, suggesting that hepatic T4ORD may determine the plasma T3 concentration. For hepatic T4ORD the mean Km was 0.42 nM and the mean Vmax 1.2 pmols T4 converted · hr-1 · mg microsomal protein-1. HPLC analysis revealed 3,3′,5-T3(rT3) and 3.3′-diiodo-l-thyronine, as evidence of T4IRD activity, but only in liver and brain. The lower bound estimates of T4IRD activities to generate rT3 were 28% (liver) and 50% (brain) of the respective T4ORD activities. Brain T4IRD increased progressively during PST. In post-smolts in later October, plasma T3 concentrations and both hepatic and brain T4ORD and T4IRD activities were low, but some rT3 was produced. We conclude that during induced PST in Atlantic salmon (i) T4ORD activity increases in liver, heart, and brain, but not in gill or skeletal muscles; (ii) the hepatic T4ORD is highly correlated with plasma T3 and may therefore determine plasma T3; and (iii) there are changes in T4ORD and T4IRD in brain, which may reflect regulation of intracellular thyroid hormone metabolism in that tissue. However, it remains to be determined how changes in deiodinase activity relate to the surge in plasma T4 and the role of thyroid hormones daring PST.

Effects of light, temperature and salinity on the growth rate of harmful marine diatoms, Chaetoceros convolutus and C. concavicornis that kill netpen salmon

Chaetoceros convolutus and C. concavicornis have been implicated in the death of salmon in netpens in the Pacific Northwest by damaging the salmon's gills. To better understand how environmental factors affect the distribution of these two species, the interacting effects of light, temperature and salinity on growth rate were examined by growing these species under a range of temperatures (4–18 °C), light (10–175 µmol photon m−2 s−1) and salinities (10–30‰). For C. convolutus, the growth rate showed a hyperbolic relationship with irradiance at 8, 14 and 18 °C and light saturation occurred at 9, 14 and 20 µmol photon mt s−1 respectively. At 4 °C for C. convolutus and 8 °C for C. concavicornis, cells grew at µmax, even at the lowest irradiances tested (10 µmol photon m−2 s−1). For C. convolutus, the amount of light required to saturate growth rate increased with temperature in an approximately linear fashion. The Q10 was 1.88, calculated by averaging over both species. C. concavicornis was the more euryhaline species growing at salinities as low as 17.5‰, while C. convolutus grew only at 25‰ and above.

Stress and cortisol treatment changed affinity and number of glucocorticoid receptors in leukocytes and gill of coho salmon

To determine whether glucocorticoid receptors were altered during observed changes in immune function after stress or cortisol treatment, we conducted a series of experiments in which juvenile coho salmon ( Oncorhynchus kisutch) were acutely or chronically stressed or fed a single meal containing cortisol. We then determined glucocorticoid receptor (GR) binding in cell-free gill preparations and whole leukocytes from spleen and anterior kidney using the synthetic hormone triamcinolone acetonide as radioligand. The affinities of GR were consistently lower in all tissues from chronically stressed fish than in tissues from controls; however, numbers of GR increased in whole leukocytes and decreased in gill. Acute stress had no affect on GR in gill and did not affect the affinity of GR in anterior kidney leukocytes, but did increase the number of GR in those leukocytes. Acute stress reduced affinity and increased numbers of GR in splenic leukocytes, suggesting heterogeneity of response to stress. Feeding cortisol to fish resulted in changes in GR from gill similar to those caused by chronic stress. Incubating leukocytes in cortisol for 3 or 24 h prior to assaying GR resulted in increased number and decreased affinity of GR in anterior kidney leukocytes, but had no effect on cells from spleen.

Morphometric Effects of Low pH and Limed Water on the Gills of Atlantic Salmon (Salmo salar)

Gills from adult Atlantic salmon held in water from an acid river (Westfield River, Queens County, Nova Scotia; mean pH 4.8) were compared to gills from fish held in the same water treated with limestone (mean pH 5.5) and gills from fish held in a nearby control river (Medway River; mean 5.4). Morphometric analysis showed that fish held in the acidic water had more gill chloride cells and mucous cells than those held in the limed water or the control river. The difference in chloride cell number was due to increased numbers of the cells on the primary lamellar epithelium; numbers of cells on the secondary lamellae did not increase with acid exposure. Male fish were found to have more chloride cells on their secondary lamellae than female fish. Chloride cells were larger and more nearly spherical in shape in the fish exposed to low pH water. The liming treatment was partially effective in preventing changes in gill histology. Changes in size, shape, and number of chloride cells probably represent a response of increasing ionic uptake to offset the losses of ions occurring during low pH stress.

Surface ultrastructural changes in the gills of sockeye salmon (teleostei: Oncorhynchus nerka) during seawater transfer: Comparison of successful and unsuccessful seawater adaptation.

Sockeye salmon were transferred rapidly from freshwater to seawater and the changes in gill morphology, in particular the distribution and sizes of chloride and mucous cells on the afferent filamental surface examined. Salmon that successfully adapted to seawater were compared with salmon that did not adapt to seawater and died as a consequence of osmoregulatory failure. The number of mucus cells (density), determined from scanning electron microscopy, increased significantly after seawater challenge. A greater increase in mucus cell density occurred in the salmon that failed to adapt to seawater. Light microscopy of transverse sections of gills detected no difference in mucus cell numbers after seawater challenge. It is proposed that mucus cells that lie just beneath the gill epithelium are activated in response to the seawater challenge, and migrate and open onto the epithelium. Freshwater-adapted salmon that had low densities of chloride cells prior to the seawater challenge failed to adapt, whereas salmon that had high densities of chloride cells adapted successfully to seawater. In the latter, the density of chloride cells on the afferent surface decreased after 30 days in seawater. The apical surface of the chloride cells of freshwater-adapted sockeye were either smooth or covered with microvilli. A greater proportion of microvilli-covered chloride cells occurred in the freshwater-adapted salmon that subsequently adapted to seawater.

Glucocorticoid receptors in leukocytes and gill of juvenile coho salmon ( Oncorhynchus kisutch)

We demonstrated that cytosol from the gill of coho salmon ( Oncorhynchas kisatch) had saturable, high affinity, low capacity binding to radiolabeled [ 3H]cortisol ( K d = 2.24 ± 0.28 n M, mean ± 1 SE; N max = 41.4 ± 7.4 fmol/mg protein) and radiolabeled [ 3H]triamcinolone acetonide (TA; K d = 0.38 ± 0.03 n M, N max = 37.8 ± 4.9 fmol/mg protein). Similarly, TA bound to cytosolic fractions of leukocytes harvested from spleen ( K d = 0.32 ± 0.03 n M, N max = 8.3 ± 2.0 fmol/mg protein) and anterior kidney ( K d = 0.37 ± 0.03 n M, N max = 30.2 ± 5.2 fmol/mg protein) and to whole leukocytes from spleen ( K d = 0.30 ± 0.04 n M, N max = 445 ± 57 sites/cell) and anterior kidney ( K d = 0.40 ± 0.04 n M, N max = 1198 ± 180 sites/cell). The competition hierarchies of steroid competitors were the same for both ligands and all tissues (TA > cortisol > 17α-hydroxyprogesterone > cortisone > aldosterone > testosterone). The differences in ligand binding in leukocytes from spleen and anterior kidney are consistent with previously reported organ-dependent sensitivity of leukocytes to cortisol.

スモルト期におけるサクラマスの鰓指質含量および指質組成

スモルト期におけるサクラマスの鰓指質含量および指質組成

Studies on cultured and gill‐attached Paramoeba sp. (Gymnamoebae: Paramoebidae) and the cytopathology of paramoebic gill disease in Atlantic salmon, Salmo salar L., from Tasmania

Abstract. The normally free‐living amoeba Paramoeba sp. is associated with epithelial hyperplasia on the gills of Atlantic salmon, Salmo salar L., in Tasmania. Gill‐attached paramoebae were significantly larger than cultured ones. Unlike cultured paramoebae, gill‐attached ones had small electron‐dense, cytoplasmic deposits and small surface projections at the host‐parasite interface. Examination of sequential samples of Tasmanian salmon gills from spring to summer indicated that pathological changes in the gill filaments were associated only with the presence of Paramoeba; the parasite was also associated with necrosis of surface epithelial cells, and cytoplasmic processes passed into and between surface cells of hyperplastic gill epithelium. The evidence points to the paramoebae as primary opportunistic pathogens causing mechanical and possibly chemical damage. Based on size and ultrastructure, the Paramoeba sp. most closely resembles P. pemaquidensis Page.

Influence of salinity on the energetics of gill and kidney of Atlantic salmon (Salmo salar)

The effect of seawater acclimation and adaptation to various salinities on the energetics of gill and kidney of Atlantic salmon (Salmo salar) was examined. Smolts and non-smolts previously reared in fresh water were exposed to a rapid increase in salinity to 30 ppt. Plasma osmolarity, [Na(+)], [Cl(-)], [K(+)] and [Mg(++)] increased in both groups but were significantly lower in smolts than non-smolts. Gill Na(+), K(+)-ATPase specific activity, initially higher in smolts, increased in both groups after 18 days in seawater. Kidney Na(+), K(+)-ATPase specific activity was not affected by salinity in either group. Gill and kidney citrate synthase specific activity was not affected by seawater exposure in smolts but decreased in non-smolts. In a second experiment, Atlantic salmon smolts reared in fresh water were acclimated to 0, 10 or 30 ppt seawater for 3 months at a temperature of 13-14°C. Gill Na(+), K(+)-ATPase was positively correlated with salinity, displaying 2.5- and 5-fold higher specific activity at 10 and 30 ppt, respectively, than at 0 ppt. Kidney Na(+), K(+)-ATPase specific activity was not significantly affected by environmental salinity. Citrate synthase and cytochrome c oxidase specific activities in gill were slightly (6-13%) lower at 10 ppt than at 0 and 30 ppt, whereas kidney activities were lowest at 30 ppt. Oxygen consumption of isolated gill filaments was significantly higher when incubated in isosmotic saline and at 30 ppt than at 0 ppt, but was not affected by the prior acclimation salinity. The results indicate that although high salinity induces increased gill Na(+), K(+)-ATPase activity, it does not induce substantial increases in metabolic capacity of gill or kidney.

In vitro stimulation of Na+-K+-ATPase activity and ouabain binding by cortisol in coho salmon gill

To investigate the hormonal control of gill Na+-K+-adenosinetriphosphatase (ATPase) (the sodium pump) in coho salmon, a technique for the culture of primary gill filaments for up to 4 days was developed. Trypan blue exclusion was greater than 99.9%, histological appearance of the cells was normal, and total [Na+], [K+], and protein content of gill filaments cultured for 2-4 days was unchanged from initial levels (measured immediately after isolation). In fish with initially low gill Na+-K+-ATPase activity (presmolts), cortisol (0.1, 1.0, and 10.0 micrograms/ml) caused a significant dose-dependent increase in gill Na+-K+-ATPase activity over initial (41%) and control levels (45%) after 4 days in culture. In fish with initially high gill Na+-K+-ATPase activity (postsmolts), cortisol partially prevented the decline in activity that occurred during 4 days of culture. The relative ability of steroids to increase gill Na+-K+-ATPase activity was dexamethasone greater than cortisol = 11-deoxycortisol greater than cortisone. Insulin (0.1, 1.0, and 10.0 micrograms/ml), alone or in combination with cortisol, had no significant effect on gill Na+-K+-ATPase activity. Cortisol treatment significantly increased maximum binding capacity of [3H]ouabain in gill tissue (from 2.92 to 5.22 pmol/mg dry wt) but had no significant effect on the dissociation constant. These results demonstrate that cortisol has direct effects on the osmoregulatory physiology of the teleost gill.

Ultrastructural features of chloride cells in the gill epithelium of the Atlantic salmon, Salmo salar, and their modifications during smoltification.

To elucidate the ultrastructural modifications of the gill epithelium during smoltification, gills of the Atlantic salmon (Salmo salar) were examined by electron microscopy at three stages of this process, which were defined as follows: "parrs" were freshwater fish that had not yet started their transformation; "freshwater smolts" were freshwater fish that were ready to enter seawater; and "seawater smolts" were smolts that had been transferred from fresh water and maintained for 4 days in seawater (35%). In the gill epithelium of parrs, there were two types of chloride cells. The large chloride cells contained deeply stained mitochondria and numerous apical, irregular, dense, membrane-bound bodies that formed 77% of the chloride cell population and were distinguished easily from small chloride cells that have distinctly paler mitochondria and no dense bodies in their apical cytoplasm. In freshwater smolts, the large chloride cells formed 95% of the chloride-cell population. In contrast to the small chloride cells that were not modified, they almost doubled in size. Their tubular system developed extensively to form a tight network with regular meshes significantly smaller than those observed in parr chloride cells. Forty percent of the large chloride cells were associated with a new type of cell, the accessory cell, to which they were bound by shallow apical junctions. Half of these accessory cells were not seen to be in contact with the external medium. In seawater smolts, 80% of the large chloride cells were associated with accessory cells. Most accessory cells reached the external medium and sent numerous cytoplasmic interdigitations within the apical portion of the adjacent chloride cells. As a result, a section through the apical portion of the chloride cells and their associated accessory cells revealed a mosaic of interlocked cell processes bound together by an extended, shallow apical junction. It was concluded that the Atlantic salmon develops in fresh water most of the ultrastructural modifications of the gill epithelium which in most euryhaline fish are triggered by exposure to seawater. The effective transfer into seawater would act only as a final stimulus to achieve some adequacy between the freshwater smolt and its new environment.

Tissue distribution of heavy metals in Dall's porpoise in the northwestern Pacific

Tissue distribution of heavy metals (iron, manganese, zinc, copper, lead, nickel, cadmium, and mercury) were investigated in the adult male, female, and foetal Dall's porpoises collected by salmon gill net in the north-western North Pacific. Determination of the metals was carried out by atomic absorption spectrophotometry. The heavy metal concentrations in the adults were generally high in liver, and low in blubber. Some metals showed organ- and metal-specific accumulations: zinc, nickel, and lead exhibited high concentrations in skin and bone; the cadmium concentration was relatively high in pancreas and adrenal and the highest concentration was observed in kidney. Similar tissue distribution patterns of metals were also found in the foetus, but the concentrations of manganese in bone, testis, and copper in liver, were relatively high compared with those in the adults. The concentration of cadmium in the foetus was very low, indicating that transplacental transfer of cadmium is negligible. The majority of the metal burdens in the body was in the muscle, liver and bone, whereas relatively high burden of cadmium was in the kidney. Based on these results, the suitability of tissues of a porpoise for ecological and physiological comparisons is discussed.

Egg development and control of the gill parasite, Salmincola salmoneus, on Atlantic salmon kelts ( Salmo salar) exposed to four different regimes of temperature and photoperiod

Atlantic salmon kelts ( Salmo salar) infected with copepod gill parasites ( Salmincola salmoneus) were kept in freshwater under four different regimes of temperature and photoperiod from January to October 1985. Egg development of S. salmoneus took over 3 months at 1–4°C with an ambient photoperiod. There were two peaks in egg production under this regime, one in May and another less distinct peak in August. At 7°C, with an advanced photoperiod, egg development took approximately 2 months and there were two peaks in egg production, one in March and the other in July. Egg development at 12°C with an ambient photoperiod took approximately 4–6 weeks and three peaks in egg production occurred: one in March, June and August. Since the same pattern of egg production was found at 12°C with an advanced photoperiod, temperature was determined to be the more important environmental variable affecting S. salmoneus egg production. Manual removal of S. salmoneus from the gills of salmon was found to be an effective control procedure if repeated regularly until no further adult copepods could be detected. Since copepod egg production was retarded and reinfection reduced in water temperatures of 2–3°C, it was suggested that manual removal efficiency would be enhanced by holding infected salmon at low temperatures until the copepods were removed.

Pyruvate kinase isozymes in farmed Atlantic salmon (Salmo salar): Pyruvate kinase and antioxidant parameters in pancreas disease

Pyruvate kinase (PK) isozyme electrophoretic patterns were obtained from extracts of Atlantic salmon liver, kidney, white muscle, red muscle, brain, heart, gill, spleen and caeca. PK isozymes were identified in the plasma of selenium-deficient and pancreas-diseased Atlantic salmon. The source of the PK in each case was shown from the isozyme pattern to be from skeletal muscle. By comparison with control fish plasma PK activity was increased and liver glutathione peroxidase activity decreased in Atlantic salmon with pancreas disease. Although plasma, liver and white muscle vitamin E levels were reduced in Atlantic salmon having pancreas disease, these levels were well in excess of those likely to be responsible for muscle damage.

Observations on body proportions and egg production in the female parasitic copepod (Salmincola salmoneus) from the gills of Atlantic salmon (Salmo salar) kelts exposed to different temperatures and photoperiods

A total of 651 adult female Salmincola salmoneus were removed from the gills of Atlantic salmon kelts exposed to four temperature and photoperiod regimes. A comparative analysis of body proportions and egg production was undertaken on copepod samples. Mean trunk lengths were significantly different between regimes, but trunk widths were only significantly different between low temperature and 12 °C regimes. Mean egg sac lengths, widths, egg numbers, and egg diameters were significantly different between low temperature and 12 °C regimes, but not between 12 °C regimes with different photoperiods. Photoperiod may have had an effect on trunk length, but not on any other morphometric measurements. Cool water temperatures significantly reduced body size and numbers of eggs and this may account for some of the differences in body proportions observed by other investigators.

Osmoregulatory and endocrine relationships with chloride cell morphology and density during smoltification in coho salmon ( Oncorhynchus kisutch)

Chloride cell morphology and density in the gill and opercular membrane of coho salmon ( Oncorhynehus kisutch) were examined during the 1982 and 1983 smolt-seasons for structural correlates to smoltification-associated changes in hypoosmoregulatory ability and plasma hormone levels. Although not synchronous in the two years, plasma thyroxine levels displayed two peaks each year. In 1982, changes in gill Na +,K +-ATPase activity were preceded by elevations in plasma thyroxine. In 1983, the increase in enzyme activity corresponded with the April increases in plasma thyroxine and prolactin. Seawater (SW) acclimation experiments showed discrete increases in SW tolerance which coincided with changes in gill enzyme activity. Although these data suggest a relationship between SW tolerance and plasma thyroxine levels, the patterns in the two years were different. A significant peak in plasma prolactin levels in April suggests possible involvement in the parr-smolt transformation. Chloride cells were studied in the opercular membrane, a chloride cell-containing epithelium lining the branchial side of the operculum, and the gill epithelium. Opercular membrane chloride cells (1982), marked with a mitochondrion-specific fluorescent stain, increased nearly two-fold in late May, concurrent with the second increase in gill Na +,K +-ATPase activity and SW tolerance. Gill morphology was examined (1983) with scanning and transmission electron microscopy and light microscopy. Initially, the gill filament surface appeared rough but became smoother during smoltification and rough again toward the end of smoltification. Two mitochondrion-rich (chloride) cell types were present in the gill epithelium during smoltification. The electron-lucent type I cell contained large, circular mitochondria while the electron-dense type II cell contained thin, elongate mitochondria. Ultrastructurally, many type I cells appeared disrupted which may indicate cellular degeneration or a special response of type I cells to fixation. However, it was unusual to find either intact or disrupted type I cells after March. Chloride cell density (type I plus type II) remained constant during smoltification. The inability to distinguish between these cell types with the light microscope may have obscured changes in their individual densities. The data from both the opercular membrane and the gill epithelium and their relationship with gill Na +,K +-ATPase activity suggest that the development of SW tolerance during smoltification is partially due to changes in chloride cell enzyme activity and density. The presence of two mitochondrion-rich cell types is discussed with regard to their possible role in the hypoosmoregulatory changes which occur during smoltification.

The effect of acid water on the loss of divalent cations and primary amines from natural membranes

1. 1. Losses of Ca 2+, Mg 2+ and primary amines into waters between pH = 5 and 3 from eyed Chinook salmon eggs, Oncorhynchus tshawytscha, and gills excised from the freshwater, bivalve mollusc Anodonta californiensis were measured and compared to effluxes into distilled water. 2. 2. Sulfuric, nitric and hydrochloric acids were used. 3. 3. Even at pH = 5 losses of Ca 2+ and Mg 2+ from both biological systems occur at short times, minutes, and can exceed those found in water of higher pH (non-acid waters). 4. 4. Increasing acidity increases short term primary amine loss from both systems. 5. 5. For both divalent cation and amino acid losses gills of A. californiensis are more sensitive to acidity than eggs of O. tshawytscha.