Ultrastructural characterization of gills in juveniles of the Argentinian Silverside, Odontesthes bonariensis (Valenciennes, 1835) (Teleostei: Atheriniformes)

An ultrastructural study was performed on the gills of juvenile Argentinian silverside, Odontesthes bonariensis. The gills are composed of two sets of four holobranchs and, in turn, each holobranch consists of a gill arch and two rows of caudolaterally projecting branchial filaments. From the dorsal and ventral surfaces of each filament, branchial lamellae radiate out as foldings of the epithelial layer. Gill rakers are present on each of the gill arches, on the anteromedial side of the arch opposite to the filaments. Gill rakers, gill arches and branchial filaments are covered by a stratified epithelium, whereas branchial lamellae essentially consist of a thin epithelial envelope containing capillaries. In the stratified epithelium, mucous cells, rodlet cells, granular cells, pavement epithelial cells and mitochondria-rich cells are identified. The thin epithelium that lines the lamellae comprises two cell types, outer and inner epithelial cells, and the capillary walls on the inside of the epithelial envelope are defined by pillar cells. The ultrastructure of all these cell types is described and our findings are discussed in light of the existing data on fish gill morphology. In the gills of juvenile Argentinian silverside is of particular interest the characteristics showed by mitochondria-rich cells, such as their arrangement in clusters of 2-3 cells and their small and depressed surface in contact with the aquatic milieu, features which strongly resemble those of euryhaline species.     

Ultrastructure features of the surface of the gills and the lower pharyngeal jaw of the Tilapia Zilli,redbelly tilapia (Coptodon Zillii,Gervais, 1848)

The present investigation was designed to describe the surface ultrastructure of the gill system of tilapia Zilli. The gill system is formed from four gill arches and each gill arch carries a row of gill filaments on its convex border and two rows of the gill rakers on its concave border. The quadrilateral interbranchial septum has elevated part at the level of the third gill arch. By SEM observations, the gill arch was divided into three regions: rostral, middle and caudal region. The caudal region contained two characteristic structures: oval leaf‐like structure and rounded‐shaped structure. Each oval leaf‐like structure carried two lateral rows of the triangular pointed spines separated by a median groove. All surfaces of gill arches, rakers and filaments were covered with a mosaic of the polygonal pavement cells, in addition to the opening of chloride cells and mucous cells. The gill arch and gill raker had only one appearance of taste buds named type I. Meanwhile, the filaments contained two types of different appearance of the taste buds named: type I and type II. Type I was the main common and similar to that present in gill arch and raker and characterized by its blunt end, while type II had hair‐like structures that projected from the volcano‐shaped depression. The gill rakers were formed from central axis surrounded by two lateral lobulated regions which carry pointed spines, taste buds and the opening of chloride cells. The surface of triangular lower pharyngeal jaw carries numerous teeth‐like papillae which originated from the socket‐like depression.     

The histology and histochemical aspects of gills of the flower fish, <Emphasis Type="Italic">Pseudophoxinus antalyae</Emphasis>

Branchial epithelium of Pseudophoxinus antalyae was lined by both a thick stratified epithelium lining gill arches, gill rakers and primary filaments and a thin epithelium lining the lamellae. Mucous, chloride and rodlet cells, interspersed between pavement cells, were present in the branchial epithelium. With histochemical procedures for the characterization of glycoconjugates, mucous cells showed a strong positive reaction with Periodic acid-Shiff and Alcian Blue at pH 2.5, although with Alcian Blue at pH 0.5 and pH 1.0 the reaction was much weaker. When the combined Alcian Blue (pH 2.5) – Periodic acid-Shiff reaction was performed, most mucous cells were stained purple, whereas by the combined Aldehyde Fuchsin/Alcian Blue (pH 2.5), most cells showed a positive reaction only to Aldehyde Fuchsin. Methylation/ Alcian Blue (pH 2.5) and Methylation/ Saponification/ Alcian Blue (pH 2.5) methods showed the presence of sulphated and carboxylated glycoconjugates in mucous cells. Mucous cells were also detected to stain all metachromatically with Toluidine Blue.     

Ultrastructural and clinicopathological studies on the toxicity of cationic acrylamide-based flocculant to rainbow trout

Rainbow trout (Salmo gairdneri) of two age groups were exposed to a cationic acrylamide-based flocculant at various concentrations in static bioassay chambers. At lethal concentrations the flocculant produced severe gill alterations in all fish. The principal alterations were necrosis and separation of the respiratory epithelial cells covering secondary lamellae. Many necrotic chloride cells were also seen, their apical plasma membrane was destroyed, and mitochondria were swollen with separated cristae. An influx of a large amount of fluid into the interstitial spaces caused partial or complete separation of subepithelial spaces from the covering epithelial cells and basement membranes of underlying blood vessels. Clinicopathological alterations included marked decreases in blood pH, partial pressure of oxygen, bicarbonate and plasma sodium, and chloride concentrations. Hematocrit, total protein, and blood glucose were increased. Fish exposed to sublethal concentrations had gill alterations characterized by hypercellularity and thickening of the secondary lamellae. These were due to undifferentiated cell proliferation and macrophage and lymphocyte infiltration between the covering epithelial cells and the underlying blood vessels. Macrophages and undifferentiated cells had large phagolysosomes containing cytoplasmic organelles, an indication of cell injury and increased turnover.     

Observations on the Occurrence of Bacterial Gill Disease and Amoeba Gill Infestation in Rainbow Trout Cultured in a Water Recirculation System

Abstract

Spontaneous outbreaks of bacterial gill disease (BGD) occurred in 17-44-g rainbow trout Oncorhynchus mykiss after they were placed in a water recirculation system. In each of five groups stocked from September 1991 through July 1992, BGD occurred within 6–8 d after stocking. In each instance, BGD was followed by a secondary amoeba infestation. The spontaneous BGD outbreaks did not occur among previously stocked groups that had recovered from earlier BGD disease outbreaks. Examination of gill tissue by Gram stain and indirect fluorescent antibody technique showed increased numbers of filamentous bacteria associated with BGD after the rainbow trout were stocked into the system. Bacterial numbers decreased after a 1-h treatment with chloramine-T at concentrations of 9–15 mg/L but increased within 2 d after treatment. Although the chloramine-T treatments controlled mortality related to BGD, the amoeba infestation persisted. Histological examination of gills showed some focal hyperplasia before the rainbow trout were placed into the recirculation system, but hyperplasia became more extensive and lamellar fusion and mild telangiectasis developed within a week after placement in the system. The density at which the fingerling rainbow trout were stocked and the suspended solids present in tank water may have contributed to the BGD outbreaks. Exposure of juvenile rainbow trout to tank water from the recirculation system before they were placed into the system did not afford them protection against BGD after stocking.     

Gill epithelium of an angler catfish,Chaca chaca (Siluriformes,Chacidae): Enzyme and glycoprotein histochemistry

A series of histochemical techniques have been employed to localize alkaline phosphatase, acid phosphatase, non-specific esterase, catalase and peroxidase; and to visualize and characterize glycoprotein (GPs) moieties in the epithelium of gill arch, gill filaments and secondary lamellae of an angler catfish Chaca chaca. The epithelium of gill arch and gill filament shows strong alkaline phosphatase activity in the deeper layer epithelial cells; strong non-specific esterase activities in the outer layer epithelial cells; and weak acid phosphatase activity throughout the epithelium. The activity of these enzymes in the secondary lamellae is weak. The catalase and peroxidase show strong activities in the blood cells of the secondary lamellae. Various classes of GPs have been identified and characterized in the mucous secretions of the gill epithelium of C. chaca. These include—GPs with oxidizable vicinal diols, GPs with sialic acid residues without O-acyl substitution and GPs with O-sulphate esters. The functional significance of different enzymes in gill epithelium and the GPs in the mucus secreted on the surface has been discussed with the physiology of the gills in relation to the characteristic habit and habitat of the fish.     

Cell Response Associated to NaCI Effect in a Freshwater Telecost Epidermis

Sixteen adult fresh water teleosts ( Pimelodus maculatus) were used in an examination of the effect of salt water on the ultrastructure of the epidermis. Six animals were treated for 3 hours with 2% saline and six were treated with 1% saline for 8 hours. No diffrenences between treated groups were noted. Four animals served as untreated controls. Both transmission and freeze-facture electonmicroscopy was utilized in examining the epidermis.
The significant alterations in epidermis were observed within the superficial cell layer, in which a decreased density of micropolicae occurred, suggesting streching of the cell surface. An increased intercellular space was also observed in this layer. The cells demonstrated an increase in intracytoplasmic vesicles, and an enhancement of Golgi membranes in treated animals as compared to untreated animals.     

Evaluation of bithionol as a bath treatment for amoebic gill disease caused by Neoparamoeba spp

This study examined the toxicity of bithionol to Atlantic salmon Salmo salar and rainbow trout Oncorhynchus mykiss in fresh- and seawater and the efficacy of bithionol as a 1h seawater bath treatment for amoebic gill disease (AGD). To examine toxicity, fish were bathed for 1, 3 and 6h in bithionol, an anti-protozoal at 0, 1, 5, 10, 25 and 35mgL(-1) with toxicity determined by time to morbidity. Efficacy was examined by bathing AGD-affected Atlantic salmon and rainbow trout for 1h at bithionol concentrations of 1-25mgL(-1). Efficacy was determined by examining gill amoeba counts and identifying percent lesioned gill filaments at 1 and 24h after bath exposure to bithionol. For both species, bithionol was determined to be toxic at 25 and 35mgL(-1) exhibiting median lethal times (LT50s) ranging from 21 to 84min. Morbidity occurred in the 5 and 10mgL(-1) treatments, however, due to sampling regime there were not enough fish available to calculate LT50s. Only bithionol at 1mgL(-1) was considered non-toxic with no signs of morbidity. Bithionol was more toxic in seawater than freshwater and had no acute effects on gill Na+/K+ ATPase and succinic dehydrogenase, or plasma osmolality and chloride concentration. Bithionol at 1mgL(-1) reduced percent lesioned gill filaments in Atlantic salmon and rainbow trout by 33 and 27 per cent, respectively, compared to the seawater control. Similarly, numbers of amoeba were reduced by 33 and 43 per cent for Atlantic salmon and rainbow trout, respectively, when compared to the seawater control. Furthermore, bithionol reduced percent lesioned gill filaments as much as did the current industry standard of freshwater. This study demonstrated that a 1h seawater bath containing 1mgL(-1) bithionol could be an improvement to the current method of treatment for AGD-affected Atlantic salmon and rainbow trout.     

Detection of the hyaluronan receptor CD44 in the bovine oviductal epithelium

Hyaluronan is involved in fundamental reproductive events such as sperm storage in the female reproductive tract, fertilization, and early embryo development, these functions are presumably mediated by its major cell surface receptor, CD44. The present study was conducted to investigate the presence and localization of CD44 in the bovine oviductal epithelium, using immunohistochemical and Western blot methods on tissue sections and epithelial cell extracts collected from the uterotubal junction (UTJ), isthmus, and ampulla of animals in the oestrus or luteal phase of the oestrous cycle. While positive immunolabelling for CD44 was found on the ad-luminal surface and supra-nuclear region of epithelial cells in all tubal segments investigated, in the UTJ, there were epithelial cells in which the entire cytoplasm positively stained. We found no differences in terms of CD44-positive staining between the different stages of the oestrous cycle. Presence of CD44 was detected by Western blotting in the tubal epithelium as a single band at 200 kDa. Although it appeared in all tubal segments, the expression of CD44 protein was more accentuated in the sperm reservoir (UTJ) than in the other segments. This is the first time CD44 has been detected in the epithelium of the tubal sperm reservoir in cattle, suggesting a pathway for the action of hyaluronan in this segment.     

Gill morphology in two Mediterranean Sea fishes of similar feeding preferences: sea bream (Sparus aurata L) and sea bass (Dicentrarchus labrax)

The aim of the present study was to describe the gill morphology of the gilthead sea bream and sea bass fishes that showed the same feeding habits. Our study focused on the gross morphological, scanning and light microscopical features of the gills, where a many differences in the gill arches and gill rakers surface in both species were explained. Our results marked that; there was an interbranchial median elevation appeared in sea bream. The gill arches length and the gaps between decreased medial wards in both species. The gill rakers had similar arrangement and varied number in both species. The first lateral rakers row was the longest one in sea bass. However the gill filaments appeared in double rows. Gill filaments were long at middle and short at extremities of gill arch in both species. Scanning electron microscopy revealed the surfaces of gill arch covered by a mosaic of pavement cells, varied sized pores of chloride cells and many pointed spines on the rakers ventral border in both species. Two types of taste buds marked on the gill arches and rakers in sea bass. Many lamellae appeared on filaments in both species.     

Myxobolus cerebralis infection in rainbow trout (Oncorhynchus mykiss) and brown trout (Salmo trutta) exposed under natural stream conditions.

From early April into mid-June 1977, sequential groups of juvenile rainbow trout (Oncorhynchus mykiss) and brown trout (Salmo trutta) were each exposed for 10 days to the parasite Myxobolus cerebralis by immersion in a stream inhabited by infected wild trout. Following incubation in a M. cerebralis-free facility, trout were subsequently killed, and heads and gill arches were examined by routine histologic methods. A grading scale to quantify lesion severity was developed and applied. Percentage infected, lesion severity scores, effects of water temperature and flow rates on percentage infected and lesion severity scores, and resulting pathology were determined for each species at each exposure period. The percentage of rainbow trout infected with M. cerebralis was significantly higher than the percentage of brown trout infected for each exposure period. The percentages of rainbow trout infected in exposure periods later in the calendar year were significantly higher than those in earlier periods. The percentages of brown trout infected were not significantly different among exposure periods. Overall average lesion severity scores were significantly higher in rainbow than in brown trout. Lesion severity scores in rainbow trout increased over time (a positive correlation with exposure period). Lesion severity scores were not significantly different for brown trout among exposure periods. A significant correlation existed between water temperature and percentage of rainbow trout infected; a significant correlation also existed between water temperature and lesion severity scores in rainbow trout. Similar correlations did not exist for percentage of brown trout infected or accompanying lesion severity scores. In rainbow trout, ventral calvarium was the most common site of M. cerebralis replication, followed by gill arches. In brown trout, lesions were virtually confined to gill arches. Early lesions consisted of foci of cartilage necrosis with small numbers of M. cerebralis developmental stages. More advanced lesions consisted of multifocal areas of cartilage necrosis with numerous M. cerebralis developmental stages and/or mature myxospores bordered and/or infiltrated by mono- and multinuclear leukocytes. Lesions in brown trout were smaller and had fewer associated leukocytes and M. cerebralis developmental stages and/or mature myxospores. Higher infection rates, lesion severity scores, and differences in lesion location in rainbow versus brown trout explain in part why numbers of rainbow but not brown trout have fallen in western rivers inhabited with M. cerebralis-infected trout.     

Comparison of growth and differentiation of normal and neoplastic canine keratinocyte cultures

Neoplastic canine keratinocytes derived from a spontaneous oral squamous cell carcinoma were maintained in culture for more than 45 passages. The presence of desmosomes and keratin filaments was demonstrated by electron microscopy and immunohistochemistry. The keratinocytes were grown in two different culture conditions to induce variations in the stage of differentiation, i.e., in submerged cultures and at the air-liquid interface. For comparison, normal canine keratinocytes were grown under the same conditions. Anisocytosis was present in neoplastic cultures grown submerged in medium. Grown at the air-liquid interface, neoplastic keratinocytes differentiated into a well-organized, multilayered stratified squamous epithelium analogous to normal keratinocytes. Rare areas of irregular growth and formation of whorls were detected. Expression of lectin binding sites and specific cell surface antigens of neoplastic and normal keratinocytes demonstrated marked similarities between the two cell lines. Neoplastic cells lacked certain surface antigens that are present on normal cells. Squamous cell carcinoma cells grew faster than normal canine keratinocytes as demonstrated by growth curve evaluation. Neoplastic keratinocytes responded to growth stimulation by epidermal growth factor and cholera toxin as do normal keratinocytes. Neoplastic cells grown in medium lacking these factors proliferated faster than growth factor stimulated normal keratinocytes.     

MHC class II+ cells in the gills of Atlantic salmon (Salmo salar L.) affected by amoebic gill disease

Amoebic gill disease (AGD) is characterised by the association of Neoparamoeba sp. with hyperplastic gill tissue of affected fishes, however, the identity and role of host cells associated with AGD lesions are not known. Here, we investigated cells with an immunological role that were associated with AGD lesions by locating cellular MHC class II β chain. A tank housing Atlantic salmon (Salmo salar) was inoculated with Neoparamoeba sp., and MHC class II β chain expression in the gills was qualitatively assessed by immunohistochemistry. In AGD-naïve control fish, MHC class II⁺ cells were detected basolateral to the interlamellar epithelium as well as upon the interlamellar and secondary epithelium. In the gills of AGD affected fish MHC class II⁺ cells were observed in both affected and unaffected tissue. Within AGD lesions, numerous MHC class II⁺ cells were present and these cells exhibited variable levels of expression suggesting that like mammals, MHC class II expression is highly regulated. The presence of MHC class II⁺ cells within gill lesions is indicative of immune cell trafficking and these cells could contribute in an antigen presentation capacity to the development of an antibody response in fish chronically affected by AGD.     

Necrotic processes in the gill tissue of carp caused by changes in the aquatic environment

Histological findings show that various pathogenic processes are involved in the cases of clinically detected branchionecrosis. The changes in gills occurring at toxic branchionecrosis are a necrobiotic process in their nature; in gill lamellae this process manifests itself as a swelling of the respiratory epithelium and as dilation of lamellar sinuses, and in stratified epithelium of gill arch and filaments it takes on the form of the hypertrophy and hyperplasia of epithelial cells. In severe cases the swollen epithelium forms deposits filling up also the interlamellar space. Toxic branchionecrosis is a term referring to a disease when the pathological processes are caused by ammonia intoxication and autointoxication, the main role being played by pH value. At experimental ammonia intoxication the changes in gills are about the same as in toxic branchionecrosis but the symptoms are not so pronounced. Changes characteristic of spherosporosis involve severe necrotic processes in the respiratory epithelium as well as in the stratified epithelium of gills, and the epithelium harbours different developmental stages of spherospores. The spherospores are easily detected when stained with alcian blue at pH 2.5. The changes in the gills of carp naturally invaded by spherospores with additional ammonia intoxication correspond to findings characteristic of toxic branchionecrosis: degeneration of stratified and respiratory epithelium of gills combined with necrotic changes caused by the developmental stages of spherospores. When water is highly oxygenated with chlorinated lime, large cells with eosinophilic granules severely multiply mainly in the stratified epithelium of gills; this process is considered as an inflammatory process. Parasitic invasions by Trichodina and Chilodonella induce local inflammatory reactions with the swelling of the respiratory epithelium.     

Clinical and pathological features of common gill diseases of cultured salmonids in Ontario

We reviewed the clinical presentations and histopathology of 118 diagnostic submissions of trout with infectious gill diseases from commercial trout farms within Ontario. Bacterial gill disease (BGD) (56%) and nodular gill disease (NGD) (26.2%) together accounted for 82.2% of these submissions. Submissions of fish with BGD occurred in every month of the year, but were proportionally more frequent in late winter and spring than in late summer and fall. Chemotherapy of groups of fish with gill diseases was common prior to submission, but the success rate of such treatment was low (29% for BGD; 21% for NGD). Specific therapeutic protocols implemented following etiological diagnosis of BGD were successful in 80% of the previously unresponsive cases and in 88.8% of previously untreated cases. The gills of trout collected within 48-96 h of treatment and apparent clinical recovery lacked bacteria and necrotic epithelial cells, but features such as lamellar fusion and epithelial hyperplasia were similar between recovered and affected fish.     

Efficacy of a long-acting formulation of ceftiofur crystalline-free acid for the treatment of naturally occurring infectious bovine keratoconjunctivitis

OBJECTIVE: To evaluate the efficacy of ceftiofur crystalline-free acid (CCFA) administered into the posterior aspect of an ear for treatment of corneal ulceration associated with naturally occurring infectious bovine keratoconjunctivitis (IBK). ANIMALS: 78 beef calves located at Sierra Foothills Field Station (SFS) and 52 calves located at a commercial dairy (CD). All calves were from 3 to 9 months old. PROCEDURE: At each site, calves were randomly allocated to 1 of 2 treatment groups by use of a block design determined by corneal ulcer size. A single dose of CCFA (6.6 mg of ceftiofur equivalents/kg, s.c.) was administered into the posterior aspect of a pinna. A second group of calves received a single dose of vehicle (0.03 mL/kg, s.c.; controls). Corneal ulcers were photographed, and clinical signs were assessed in calves every 3 to 4 days for 21 days. RESULTS: A positive treatment effect was detected at SFS. Results at the CD were inconclusive because ulcer healing occurred rapidly in control and CCFA-treated calves. At SFS, treatment with CCFA resulted in shorter mean healing times, smaller corneal ulcer surface area measurements, amelioration of ocular discharge and photophobia, and a 50% increase in the percentage of calves healed by day 14. After adjustment for initial corneal ulcer size, treatment with CCFA resulted in a 4-fold increase in the odds of corneal ulcer healing by day 14, compared with controls. CONCLUSIONS AND CLINICAL RELEVANCE: A single dose of CCFA administered into the posterior aspect of a pinna had a positive treatment effect against naturally occurring IBK in calves with corneal ulcerations.     

Gill Infection Model for Columnaris Disease in Common Carp and Rainbow Trout

Challenge models generating gill lesions typical for columnaris disease were developed for the fry of both Common Carp Cyprinus carpio and Rainbow Trout Oncorhynchus mykiss by means of an immersion challenge and Flavobacterium columnare field isolates were characterized regarding virulence. Carp inoculated with highly virulent isolates revealed diffuse, whitish discoloration of the gills affecting all arches, while in trout mostly unilateral focal lesions, which were restricted to the first two gill arches, occurred. Light microscopic examination of the gills of carp exposed to highly virulent isolates revealed a diffuse loss of branchial structures and desquamation and necrosis of gill epithelium with fusion of filaments and lamellae. In severe cases, large parts of the filaments were replaced with necrotic debris entangled with massive clusters of F. columnare bacterial cells enwrapped in an eosinophilic matrix. In trout, histopathologic lesions were similar but less extensive and much more focal, and well delineated from apparently healthy tissue. Scanning and transmission electron microscopic observations of the affected gills showed long, slender bacterial cells contained in an extracellular matrix and in close contact with the destructed gill tissue.

This is the first study to reveal gill lesions typical for columnaris disease at macroscopic, light microscopic, and ultrastructural levels in both Common Carp and Rainbow Trout following a challenge with F. columnare. The results provide a basis for research opportunities to examine pathogen–gill interactions.

Received January 10, 2014; accepted July 27, 2014     

IgA and secretory component (SC) in the third eyelid of domestic animals: a comparative study

Objective The third eyelid of domestic animals is important for the production and distribution of tears, in removing ocular debris and in protection of the globe, and has significant immunologic functions. Although it is known that tears contain antibodies of the immunoglobulin A (IgA) isotype which are produced mainly by plasma cells of the lacrimal gland, very little is known about the antibody repertoires in the third eyelid of domestic animals. To assess whether IgA is derived from local synthesis, we analyzed the location of IgA‐producing cells and the cellular distribution of secretory component (SC) in the third eyelid of domestic animals in a comparative study. Animal studied A total of 83 third eyelids of dogs, cats, pigs, cows, sheep, goats and horses were investigated in the course of this study. Procedures Third eyelids were obtained immediately after death, cut length‐wise, fixed overnight and processed for immunohistochemical detection of IgA and SC by the ABC technique. Results The results show that IgA‐producing plasma cells are densely populated in subepithelial spaces of the surface epithelium as well as in the nictitating gland in a species‐specific manner. In contrast, the SC could be demonstrated exclusively in glandular acinar and ductal epithelial cells and in different cell types of the surface epithelium, preferentially located on the bulbar side of the nictitating membrane. Conclusion It is suggested that most of the SC is locally produced by resident plasma cells and subsequently transferred through the surface epithelium and glandular duct cells by transcytosis. This indicates that the third eyelid is an important member of the secretory immune system in domestic animals.     

Histomorphometric and Progesterone Receptor Immunohistochemical Analysis in the Oviduct of Newly Hatched Chicks Treated with Follicle-Stimulating Hormone during Embryonic Development

In this study we evaluated the histomorphology and ultra-structure of the oviduct of newly hatched chicks, as well as the immunohistochemical expression of progesterone receptor (PR) in this tissue after follicle-stimulating hormone (FSH) treatment on days 13, 15 and 17 of embryonic development. Results indicated a marked difference in the histology of the oviduct of newly hatched chicks treated with FSH. Magnum mucosa from these animals presented a pseudostratified epithelium with evaginations from the lumen into the epithelium and from the latter into the stroma beneath where tubular glands are formed. In contrast magnum mucosa from control animals presented columnar epithelium with no evaginations. In magnum epithelium FSH also induced the formation of cilia and microvilli projections into the lumen as well as an increase in the wall and lumen areas and in the density of nuclei per unit-area. PR immunoreactivity was only observed in the oviduct of FSH treated animals. PR was located in the nucleus of epithelial luminal cells, mucosal stromal cells and smooth muscle cells. These findings suggest that FSH induces an adequate hormonal milieu for the cytodifferentiation and PR gene expression in the chick oviduct.     

Clinical and pathological observations on Streptococcus sp. infection on South African trout farms with gas supersaturated water supplies

Infection with a faecal Streptococcus species belonging to Lancefield group D has been a major cause of mortalities on certain trout farms on the escarpment of the Mpumalanga Province in the Republic of South Africa. Evidence is given of a connection between subclinical gas bubble disease and infection with this organism in rainbow trout, Oncorhynchus mykiss. The condition causes serious losses during the summer months when water temperatures rise above 18 degrees C. The larger table-size fish are affected first and present with exophthalmos before developing signs of a typical bacterial septicaemia. The design of the water supply to the fish ponds on these farms allowed supersaturation of the water with atmospheric gas. Vortex formation at water extraction points appears to have been the main cause of air entrainment into the water supply leading to the ponds. By correcting the faults responsible for the development of hyperbaric gas pressure in the water, it was possible to control this disease on two badly affected farms. The overlapping similarities in the clinical signs and pathology of gas bubble disease and that seen in fish suffering from Streptococcus D infection are discussed, as well as the diagnostically significant changes in the gill tissues that are specific to subclinical exposure to gas supersaturation in the water. An explanation is given for the increased susceptibility to infection with this organism.