Choroid Gland Research Articles

Light and scanning electron microscopy of the eye of Siganus luridus (Rüppell, 1828).

The morphological characteristics of eyes in fishes are highly diverse and have evolved to meet the specific visual requirements as per their habitats. These morphological features of eyes are important for researchers and ecologists. The dusky spinefoot (Siganus luridus) is a tropical teleost fish with a laterally flattened body which lives in the Mediterranean Sea. Currently, there are no histological data relating to the Siganus luridus eye. In this study, the morphology of the Siganus luridus eye was examined to enhance our understanding of its structure and its relationship to fish ecology. Detailed gross and microscopic features were recorded using light and scanning microscopy. The key observations describe the main structural features of the eye of Siganus luridus, specifically, the diameter of the orbit, architecture of three tunics of eye and detailed lens description. The choroid was divided into four layers, and had a rete mirabile, consisting of numerous small blood vessels in the choroidal gland. The tapetum lucidum was observed, which is interesting since Siganus luridus is herbivore and herbivores typically lack a tapetum lucidum. These observations shed new light on the intricate eye structure of Siganus luridus and provide valuable insights into its visual abilities and adaptations to the aquatic environment and feeding behavior.

The eye of the tongue sole Cynoglossus bilineatus (Lacepède, 1802) (Teleostei: Pleuronectiformes)

We report the ocular features of the tongue sole, Cynoglossus bilineatus (Lacepède, 1802), a marine, bottom-dwelling flatfish. In this species, both eyes are located juxtaposed on the same side of the flat head. Histology revealed the sclera to be fibrous (collagenous) in nature. The choroid possesses the choriocapillaris, and adjacent to it, 3–4 rows of iridophores with stacks of cytoplasmic platelets. No choroidal gland is present. The retinal pigment epithelium (RPE) contains scanty melanin granules. Its vitread half is modified into a dense tapetum with lipid spheres (about 0.34 μm in diameter). In juveniles, the tapetal spheres arise by budding from the smooth endoplasmic reticulum of the RPE. There are blood vessels within the retina; the vitreal vessels penetrate the retina and ramify close to the level of the outer limiting membrane. The vessels are capillaries in nature. The photoreceptor layer contains abundant rods, and twin cones and single cones, being arranged into square mosaics. The optic disc is non-pleated and shows pan- cytokeratin immunopositivity, which is related to the bundled cytokeratin filaments detected in astrocytes by electron microscopy. The retinal tapetum and choroidal iridophores help the species to live in a muddy bottom having dim-light environment. The lack of a choroidal gland, hypoxic aquatic condition and presence of a dense retinal tapetum (that limits O2 transport to the photoreceptors) appear to have favored the proliferation of vitreal vessels within the retina in this species. The fibrous sclera has probably arisen to provide structural support to the eye in migration from the lateral to the dorsal aspect of the head during larval metamorphosis.

Structure and function of the retinal pigment epithelium, photoreceptors and cornea in the eye of Sardinella aurita (Clupeidae, Teleostei)

The structure of the pigment epithelium, photoreceptors and the cornea in the eye of a teleost, Sardinella aurita was examined by light and electron microscopy. The retinal pigment epithelium forms a single layer of cells joined laterally by cell junctions. Centrally in the retina these cells are columnar, while more peripherally they become cuboidal in shape. The basal (scleral) border of the pigment epithelial cells is not infolded but is relatively smooth. Phagosomes containing lysosome-like bodies are also common features of the retinal pigment epithelium. Numerous melanosomes (pigment granules) are abundant throughout the epithelial cells. These melanosomes probably absorb light which has passed through the photoreceptor layer. Four photoreceptor cells were identified; rods, long single cones, short single cones and double cones. The presence of these types suggests a diversity of photoreceptor function. Square mosaic pattern of cones and well-developed choroid gland are also main features of the eye. The inner segment of rods and cones were rich in organelles indicating much synthetic activity. Calycal processes projecting from cone outer segments are also observed. The cornea includes an epithelium with a complex pattern of surface microplicae, a basement membrane, dermal stroma, an iridescent layer, scleral stroma, Descemet’s membrane and endothelium. The autochthonous layer which is seen in some teleosts has not been observed in the cornea of this species. These and other observations were discussed in relation to the photic environment and habits of this fish.

A comparative anatomical histological study of the Uvea in the eyes of two cyprinid fresh water teleost fishs living in a different light environment

The present study was designed to demonstrate the comparative anatomical, histological study of Uvea in the eyes of two cyprinid fresh water teleost fishs Garra rufa (first species) and Chondrostoma regius (second species). Which belong to family Cyprinidae Each species differ in light intensity, in that G. rufa bottom dwelling but C. regius approximately surface dwelling. The two species omnivorous in nutritional nature. The choroid in the two species, essentially similar in that it composed of connective tissue consist of fibers, melanocytes, sinusoid, blood vessels and nerves. On the other hand, variations appeared in the thickness and nature of these components, but the choroid was more developed in C. regius. The distinct structures in the choroids of the two species were tapetum lucidum and argenteum layer which were more developed in C. regius. On the other hand there were variations in chotoid components intraocularly for each species. The choroid gland appeared at both sides of optic nerve in the choroid, and more developed in C. regius. The most important result in this study was the appearance of choroid fissure and falciform process in the eye of G. ruffa only. The ciliary body disappear in both species, but its position called ciliary region which was distinct in the eye of both species. The ciliary region extended between the retina and iris which composed of two portions, the first one originated from the choroid and the other from the retina. The length of ciliary region differs between the two species as well as intraocularly. The iris showed a wide variations in the shape, thickness, length and nature of its components between the two species and intraocularly. The iris components have two origins. The first one from the choroid (iris stroma), the second from the retina which were the non pigmented ciliary cells and pigmented epithelium.We can conclude that the presence of tapetum lucidum ,argenteum layer,Choroid glands in the Choroid of both species indicate that they posses high visual acuity ,high resolution power and strong image contrast but G. ruffa have more visual power because the appearance of Chroid fissure and falciform process.

Histological study of middle layer of rabbit fish eye (siganus javus)

ObjectiveThis study investigates the histology of the middle layer of the eye in rabbit fish Siganus javus. MethodsThe eyes of twelve healthy fish were enucleated and histologic sections of 6μ were prepared. The sections were stained with Hematoxyline & Eosine (H&E) and Masson trichrom then were observed using light microscopy. ResultsThe middle or vascular layer consisted of the choroid and iris. The result revealed that the choroid coat was subdivided into five laminae: 1. Suprachoroid layer 2. Substina propria included choroidal gland or retemirabile, melanoid layers and connective tissue 3. Fibrouse layer 4. Choriocapillary layer 5. Separator layer. The extension of the choroid coat into the anterior compartment made the iris which mainly composed of connective tissue, blood vessels, melanocyte and a smooth muscle at the posterior part of the iris, adjacent to the pupil. The choroid coat did not continue rostrally adjacent to the cornea. Suspensory apparatus of the lens of the Siganus javus eye consisted of a dorsal suspensory ligament and a ventral retractor muscle. ConclusionsThe diversity and deviation in the detail of microscopic structures in the eye of teleosts is approved through this microscopic study in middle layer of rabbit fish eye however the five differentiated parts of choroid were distinguished as in many telelost species.

Feeding the vertebrate retina from the Cambrian to the Tertiary

AbstractThe retina of the vertebrate eye is metabolically active and requires nutritive support. During the last 540 million years it has evolved into forms as complicated and nutritionally demanding as those found in avian or primate eyes. Diffusion from the choroid is generally able to supply the metabolic needs of thin retinae. However, when the thickness exceeds the limits of diffusion, structures are needed to supplement the vascular supply from the choroid. These supplemental nutritive devices include the choroidal gland, the falciform process and preretinal vascular plexus of fish, the conus papillaris of lizards, the pecten oculi of birds, the intraretinal vessels of mammals and a few novel systems that remain difficult to classify. These vascular systems are among the most variable features of the vertebrate eye. Here, we review classical and recent findings regarding such retinal nutrition systems, propose a three category classification for them based on histologic origins and speculate on the evolutionary forces which drove their development.

Beitrag zur vergleichenden Ophthalmo-Morphologie: Das Bachforellenauge

The aim of this study was to assess similarities and differences between the trout eye and the human eye. Gross and microscopic examinations of the formalin-fixed eyes of each five trout and human eyes (donor eyes not suitable for keratoplastic) were carried out. Compared to the human eye, the trout showed a flattening of the anterior-posterior axis, and cartilage-stabilized sclera. The peripheral cornea was much thicker than the central, had a multilayered thick epithelium, a distinct Bowman layer, and an implied Descement membrane. A ring-shaped ligament filled up the angle of the anterior chamber and linked the iris to the cornea. The lens showed a spherical aspect with a thick capsule and missing zonular fibres, however, a suspensory ligament of a superior part of the lens was present. Ventrally, at the end of the falciform process, a small, pigmented structure was in contact with the lens. The retina was similarly differentiated, but the choroid showed special structures like choroidal gland, falciform process and the argentea compared to the human eye. Great variations between the ocular anatomy of the trout and the human exist. However, the retina of the trout is fully differentiated and remarkably similar to that of human eyes.

Beyond buoyancy and vision: The potential for the Root effect to deliver oxygen to tissues other than the swim bladder and eye

Teleost fish possess a unique, pH-sensitive hemoglobin (Hb) that, in the presence of an acidosis, substantially reduces the affinity and carrying capacity for O₂ (Root effect). To date, this efficient O₂ delivery mechanism is only known for filling a swim bladder (SB) against huge pressure gradients (> 50 atm) associated with depth and for oxygenating the metabolically active, yet avascular retinal tissue of the eye. In spite of the clear benefits to O₂ delivery for buoyancy and vision, no study has been conducted to determine whether the Root effect may be important in optimizing O₂ delivery to other tissues such as muscle, which is the focus of this research.During environmental or exercise-induced stress, blood pH may fall; however, some fish regulate red blood cell (RBC) intracellular pH (pHi) by releasing catecholamines that activate the sodium/proton (Na⁺/H⁺) exchanger (βNHE) on the RBC membrane. The βNHE removes H⁺s from the RBC resulting in an intracellular alkalosis, an increase in Hb–O₂ affinity, and O₂ uptake at the respiratory surfaces is safeguarded, which is the ultimate goal of this mechanism. In our proposed model, when adrenergically stimulated blood encounters plasma-accessible carbonic anhydrase (CA), an enzyme found in the RBC but also membrane-bound and potentially plasma-accessible in select locations, it will catalyze H⁺s removed from the RBC to form CO₂. This CO₂ will back-diffuse into the RBC creating an intracellular acidosis (extracellular alkalosis), reducing Hb–O₂ affinity, and ultimately elevating PO₂ via the Root effect. We created an in vitro closed system using rainbow trout (Oncorhynchus mykiss) blood where we can (1) simulate an acid-induced Root effect, (2) adrenergically stimulate the RBCs, and finally (3) short-circuit the βNHE via CA (CA-mediated Root effect), all of which can be monitored in real-time ( Fig. 1). Data generated currently support our Hypothesis: adrenergic RBC pH regulation can be short-circuited in the presence of plasma-accessible CA, therefore generating a Root effect increase in PO₂. In fact, if this scenario also occurs in the tissues of O. mykiss, CA-mediated short-circuiting of adrenergic pH regulation can facilitate an increase in PO₂ over 30 times that which would be generated in vertebrates possessing only a Bohr shift! We are ready to test our model in vivo by implanting fiber-optic O₂ sensors in O. mykiss muscle while simulating environmental and exercise stress with and without CA blockers. Furthermore, even though CA is not found in general circulation, there are membrane-bound and potentially plasma-accessible isoforms in muscle endothelia, and research is underway to localize this enzyme to understand the relationship between location and function of the short-circuiting. Teleost fish, which are more numerous than all other vertebrates combined (terrestrial and aquatic), have evolved an extraordinary O₂ delivery mechanism, the Root effect, that allows O₂ delivery to the eye and to the SB, thus allowing efficient buoyancy regulation, which may be one of the most important factors responsible for the extensive adaptive radiation in teleost fishes. Therefore, it is particularly interesting that the Root effect has not yet been investigated for general O₂ delivery. If the Root effect can also facilitate general O₂ delivery in vivo, which our data currently support, this would help shed insight into how the Root effect was selected for prior to the evolution of the βNHE, choroid gland and retia of the eye, and the gas gland and rete mirabile associated with the SB.

Early development of eye and retina in lanternfish larvae

The morphological characteristics of the eyes and the retinae of lanternfish larvae of Lampanyctus crocodilus, Benthosema glaciale, and Myctophum punctatum were analyzed in pre-flexion, flexion, and post-flexion stages. Pre-flexion larvae of L. crocodilus, the species with the shallowest depth distribution, had spherical eyes located antero-laterally on a strongly laterally-compressed head, suggesting a forward binocular visual field. B. glaciale and M. punctatum larvae live deeper in the water column and had eyes elongated in the dorsal-ventral plane. The eyes of B. glaciale were prominent, projecting slightly outward from a laterally-compressed head, suggesting a strongly laterally-directed visual field. M. punctaum had stalked elongated eyes projecting from a dorso-ventrally flattened head. The eyes can be freely rotated allowing lateral, anterior and dorsally-directed vision. A prominent choroidal gland was situated beneath the ventral portion of the eye in M. punctatum and B. glaciale, while a smaller gland was present in the dorsal and ventral portions of the eye of L. crocodilus. In pre-flexion stage larvae, the retina of all three species was differentiated with numerous rod photoreceptors in the peripheral retinal areas and fewer cone photoreceptors mainly distributed in the central retina. This distribution suggests concomitant enhancement of scotopic sensitivity in the vertical visual plane and improved photopic acuity in the lateral and forward visual directions. The concurrent development of cones and rods, as observed in the pre-flexion stage of myctophid larvae, is consistent with meeting the special demands of visual planktivory in sub-surface waters. During larval development a gradual increase of ROS length was also accompanied by a progressive loss of cones that were almost totally absent in post-flexion larvae. This can be interpreted as an adaptive response to an impending deep mesopelagic adult life.

A Piscirickettsiosis‐like Syndrome in Cultured Nile Tilapia in Latin America with Francisella spp. as the Pathogenic Agent

In 2004, cultured Nile tilapia Oreochromis niloticus in several Latin America farms began to succumb to a disease similar to the piscirickettsiosis-like syndrome previously reported in tilapia in Taiwan and the United States. Mortality increased during 2005; reductions in tilapia biomass ranged from 5% to 80% in individual ponds and averaged 50% overall. All ages of fish have been involved. Clinical signs include lethargy, loss of appetite, petechia, exophthalmia, and abnormal swimming behavior. Gross lesions have included splenomegaly, renomegaly, and numerous white nodules observed in the spleen, kidney, testes, heart, ovaries, and occasionally the liver. A previously unreported black granulomatous lesion was reported in up to 30% of the fillets. Histologically, granulomatous infiltrates were observed in the kidney, spleen, liver, testes, ovary, and choroid gland, and rarely in the brain and heart. A small pleomorphic bacterium was observed in Giemsa-stained blood smears and spleen imprints. The bacterium did not grow on standard microbiological media and has not been isolated in cell culture. We obtained a near-complete 16S ribosomal DNA sequence with high similarity to Francisella spp. sequences previously identified in tilapias Oreochromis spp. (Taiwan), Atlantic cod Gadus morhua (Norway), and three-line grunts Parapristipoma trilineatum (Japan).

Vaccination induces major histocompatibility complex class II expression in the Atlantic salmon eye.

The aim of the study was to investigate the presence, distribution and density of major histocompatibility complex (MHC) class II+ cells in the ocular tissues of the Atlantic salmon, Salmo salar, prior to and following vaccination. Eyes were collected 14 days prior to and at 4, 11, 25 and 39 days and 4 months subsequent to vaccination with a commercial fish vaccine. A quantitative analysis was performed in sections on the number of immunopositive cells in the retinal layers. In all groups, MHC class II+ cells were detected in the area of the limbus but not in the central parts of the cornea. In the uvea, immunopositive cells were present in unvaccinated and vaccinated fish. Abundant immunopositive cells were identified in the choroid rete (or choroid gland) in all groups as well as in the ventral ciliary cleft, where macrophage-like MHC class II+ cells were seen. Quantitative histology of the retina revealed a significant increase in MHC class II+ cells in the outer plexiform layer (OPL) and the inner nuclear layer (INL) 4 days following vaccination. Positive cells were detected in all layers of the retina with the exception of the photoreceptor layer.

Characterization of a piscirickettsiosis-like disease in Hawaiian tilapia.

In 1994, tilapia (Oreochromis mossambicus and Sarotherodon melanotheron) in wild and farmed populations on Oahu, Hawaii, USA, began to die of an unknown disease that was similar but not identical to piscirickettsiosis in salmonids. Only tilapia were affected. Diseased tilapia often swam erratically and had trouble staying at depth. Scattered cutaneous haemorrhage and exophthalmia were often noted. In many cases, fish were found dead with no clinical signs. Gills exhibited epithelial hyperplasia with severe multifocal consolidation of secondary lamellae. Multiple granulomas were observed in the gills, spleen, kidney, choroid gland and testes, but not in the liver. Tilapia mortalities occurred only during the cooler months (October to April) of the year and were not recorded during the warmer months (May to September). The mortalities declined with each successive year, after the 1994 outbreak, and currently losses are sporadic. Oxytetracycline-medicated feed reduced mortality. Cytologic examination of blood smears revealed moderate to large numbers of Gram-negative, pleomorphic, intracellular bacteria in rare circulating monocytes. Histologically, some predilection for nervous tissue and brain was observed. When viewed with transmission electron microscopy, pleomorphic coccoid bacteria, measuring 0.56 +/- 0.14 x 0.7 +/- 0.20 microm, occurred free in the cytoplasm and within phagolysosomes. The organisms had a double cell wall, no defined nucleus and variable electron-dense and -lucent areas. Unlike Piscirickettsia salmonis, the agent of piscirickettsiosis, the Hawaiian tilapia Piscirickettsia-like organism (HTPLO) does not form craterform lesions in the liver and is active above 20 degrees C. HTPLO can be transmitted horizontally by cohabitation, and cold stress induces the syndrome in juvenile tilapia from farms where the disease is endemic.

Morphogenesis of the eye of Siberian sturgeon

The most relevant changes in Acipenser baeri eye organization were detected between hatching and 5 days post hatch. At this age, the eye had an anterior chamber, lens, iris, choroid gland, scleral cartilage, cornea and a vitreous chamber lined by the retina (with two photoreceptors: rods and single cones).

An immunohistochemical study of Flexibacter psychrophilus infection in experimentally and naturally infected rainbow trout (Oncorhynchus mykiss) fry

DAO Diseases of Aquatic Organisms Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials DAO 25:53-61 (1996) - doi:10.3354/dao025053 An immunohistochemical study of Flexibacter psychrophilus infection in experimentally and naturally infected rainbow trout (Oncorhynchus mykiss) fry Evensen Ø, Lorenzen E An immunohistochemical method is described for the detection of Flexibacter psychrophilus in formalin-fixed, paraffin-wax-embedded fry of rainbow trout. Rabbit antiserum as well as rainbow trout hyperimmune serum were used in the study. The distribution and tissue localization of the bacterium was compared in naturally and experimentally (intraperitoneal injections) infected fry by use of immunohistochemistry. This study showed that F. psychrophilus could be detected in paraffin-wax-embedded tissue of rainbow trout fry by immunohistochemistry. The principal immunohistochemical findings in naturally and experimentally infected fry showed that there was a localization of bacteria in the monocyte-macrophage system, in skin lesions, and in the retina and the choroid gland of the eye. The dermal changes included superficial or deep ulcers extending to the subcutaneous tissue or the musculature accompanied by inflammatory cell infiltrates in which polymorphonuclear inflammatory cells were shown to contain the bacterium in the cytoplasm by immunostaining. The eye changes were likewise a common finding in chronic cases with severe inflammatory changes in the retina and with numerous bacteria in inflammatory (mainly polymorphonuclear) cells. F. psychrophilus infection in rainbow trout fry involves the monocyte-macrophage system extensively, and the concurrent localization of bacteria in the skin ulcers and retinal inflammation points to the probable involvement of the bacterium in the development of the lesions which are typically found during the chronic stage of the disease. Immunohistochemistry . Flexibacter psychrophilus . Rainbow trout . Fry Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in DAO Vol. 25, No. 1-2. Publication date: May 09, 1996 Print ISSN:0177-5103; Online ISSN:1616-1580 Copyright © 1996 Inter-Research.

Cephalic circulation in the air-breathing snakehead fish, Channa punctata, C. gachua, and C. marulius (Ophiocephalidae, Ophiocephaliformes).

The macrocirculation in the head of three air-breathing species of Channa was examined with the aid of vascular corrosion replicas and a scanning electron microscopic study was conducted on the pseudobranch, choroid gland and lentiform body. Two facultative air-breathing murrels, C. punctata and C. gachua, and one obligate air-breather, C. marulius were examined. In all three, the air-breathing organs (ABO) and systemic circulations were in-parallel, and both were in-series with the branchial circulation. Efferent branchial arteries from the first and second gill arches formed the arterial supply to the ABO, whereas the third and fourth arch efferents perfused systemic tissues. Postbranchial blood from the second gill arch also entered the systemic circulation directly via a shunt from the efferent branchial artery to the lateral aorta and via hypobranchial arteries. Vascular specialization to prevent mixing of oxygenated ABO venous and deoxygenated systemic venous blood was evident in arterial, but not venous circuits. Pseudobranchs of C. gachua and C. punctata are tri-lobed, in C. marulius they have numerous lobules. Pseudobranch lamellae are wider and shorter along the axis of blood flow than gill lamellae and folded perpendicular to this axis. Pseudobranch lamellae appear to be modified to minimize their epithelial surface while retaining an extensive vascular endothelial-pillar cell surface area, counter-current amplification is also possible. The choroid gland is an extensive planar counter-current capillary rete. The lentiform body of the eye is a globular capillary rete but there is no evidence of a counter-current circulation. The choroid and lentiform rete may have distinct physiological functions.

Optic cyst in a cyprinid teleost

Retinal herniation, leading to the formation of a small optic cyst in the choroid, is reported for the first time in a fish (Acrossocheilus hexagonolepis). The herniation resulted in the disorientation of photoreceptors and the displacement of the choroid gland towards the suprachoroid.

The visual system of the Florida garfish, Lepisosteus platyrhincus (Ginglymodi). III. Retinal ganglion cells.

The vitreal vascularization, optic nerve fiber layer and the retinal ganglion cells are examined in the Florida garfish, one of the two surviving genera of the ginglymode group of actinopterygian fishes. In the absence of a choroidal gland, a well developed system of hyaloid blood vessels overlie the inner retina. The optic nerve fiber and ganglion cell layers are integrated to form a series of alternating columns or fascicles emanating from an elongated optic nerve head. Horseradish peroxidase or cobaltous lysine infusion from the optic nerve reveals seven ganglion cell classes based on soma size and position, dendritic field size, retinal coverage and terminal stratification. Two discrete populations of giant ganglion cells with large somata and large dendritic fields stratify either within the sclerad region (type I cells) and/or within the middle region (type 2 cells) of the inner plexiform layer. Both giant ganglion cell populations (1% of total) form evenly distributed arrays with the dendritic arbor of each type covering the retina completely. Between seven and nine type 2 cells overlap the dendritic field of a single type 1 cell. Type 3 cells are small and located in the inner nuclear layer with a multistratified dendritic field terminating throughout the inner plexiform layer. Topographic analysis of the population of type 3 cells (4% of total) reveals a temporal area centralis (6.25 x 10(2) cells per mm2) and a ventral horizontal streak (6.25 x 10(2) cells per mm2). The large population of cells within the ganglion cell layer are classified as types 4, 5 and 6 based on soma size, dendritic field size and dendritic stratification and collectively these cells match the distribution of ganglion cells within the inner nuclear layer with 5.3 x 10(3) cells per mm2 in the temporal area centralis and 8.6 x 10(3) cells per mm2 in the horizontal streak. Type 7 cells possess small somata and send branches into both the inner and outer plexiform layers and have been termed biplexiform ganglion cells. Phylogenetic comparisons of several morphological features of the garfish retina reveals the polarity, conservation and the evolution of a number of visual characters.

Histopathology of vitamin C deficiency in a cichlid, Cichlasoma urophthalmus (Günther)

Abstract. This paper describes the histopathological changes observed in the Mexican native cichlid Cichlasoma urophthalmus (Günther) when try with an initial weight of between 160 and 170 mg were fed with diets deficient in vitamin C for 90 days. The epidermis showed an extensive inflammatory response, with spongiosis and also degenerative changes in the basal cells. Muscle showed a range of pathological changes including inflammation, changes in the number and position of the nuclei, vacuolation and necrosis, granular degeneration, and fibre loss. Gills showed thickening of the primary lamellae, oedema, hyperplasia, telangiectasis and atrophy of the bony supporting structures. Ganglia and neurones of nervous tissue were abnormal with changes which ranged from slight inflammation to central chromatolysis. The hepalopanereas was also affected and focal necrosis of the hepatocytes was frequently observed. The pancreas showed major changes with shrinkage of the acinar cells and reduction of zymogen granule content. Fish fed diets containing 0 and 40 mg vitamin C kg‐1 of diet were infected with Mycobacterium sp. and miliary tuberculosis was found affecting kidney, spleen, choroid gland, stomach, heart and muscle. The association between fish tuberculosis and vitamin C deficiency is discussed.

Disorders of the eye in finfish

As fish have been brought into confinement for display and culture, eye diseases have often caused difficulties, sometimes major. Types and possible etiological factors vary. All eyeball (orb) parts and attached organs and tissues (adnexa) are affected. Most common are exophthalmos (pop-eye), cataracts, keratopathy (several corneal lesions), various retinopathies, and uveitis (choroid and iris system lesions). Less frequent in cultured or feral fishes are: aphakia (no lens); choroid gland disease; cyclopia; edema of various tissues-including the lens; endophthalmos (sunken-eye); hyperemia of all parts; microphthalmos (small-eye); neoplasia of cornea, retina, and other parts; and others. These lesions may result from poor water quality, including gas imbalances (causing exophthalmos), toxicants (cataract, hyperemia, keratitis, and retinitis), low temperatures and osmotic imbalances (cataract); nutritional deficiencies (cataract, corneal, and retinal diseases); parasitemias (exophthalmos, cataract, keratitis, etc.); radiation damage (cataract, keratitis); trauma of careless handling; and injuries from unsafe culture systems. All conditions are exacerbated by stresses associated with culture, including overcrowding and aggressive behavior. Immunological deficiencies and genetic factors are also involved. In display aquaria, hatcheries, and nurseries, eye disease may not be fatal but often affects growth and is unsightly. Further, cataracts can indicate serious nutritional problems leading to other diseases. Exophthalmos, ocular hyperemia, cloudy corneas, cataracts, and granular and inflamed eye tissues may signal unfavorable water supply or parasitemia resulting from poor sanitation. Unthriftiness and deaths may result. Chances of survival or responsive behavior of released vision-impaired fish are markedly reduced and purposes of culture and release programs negated. Also, buyers, believing they reflect poor product quality, may reject animals with abnormal-appearing eyes. Whichever occurs, stock, biomass, time, and monetary losses can be significant. Eye diseases of fish, their possible causes, significance, and prevention or treatment, if any, are described and discussed.

Histopathology and ultrastructure of ocular lesions associated with gas bubble disease in salmonids

Ocular lesions associated with natural and experimental outbreaks of gas bubble disease (GBD) in commercial salmonids were assessed histologically and by scanning electron microscopy. Small gas emboli were first detected in the choroid gland of the posterior uvea. In subacute and chronic cases, bubble size increased markedly and localization in retrobulbar and periocular sites was favoured. During the acute phase of GBD, ocular lesions were limited to anatomical displacement of tissue and local degeneration of compressed tissues around the perimeter of bubbles. Subacute sequelae included the formation of anterior synechia, lens cataract, and suppurative panophthalmitis. During chronic stages, when large retrobulbar bubbles had caused severe exophthalmia, there was stretching of the optic nerve and of retinal blood vessels and severe distortion of the posterior aspects of the globe. The sequential development, pathogenesis and persistence of ocular lesions associated with GBD in fish are discussed.